Merge pull request #20834 from ChayimFriedman2/hir-ns

Migrate `hir` types to next solver
diff --git a/crates/hir-ty/src/autoderef.rs b/crates/hir-ty/src/autoderef.rs
index 0be00af..abd1b8b 100644
--- a/crates/hir-ty/src/autoderef.rs
+++ b/crates/hir-ty/src/autoderef.rs
@@ -5,23 +5,21 @@
 
 use std::fmt;
 
-use hir_def::TraitId;
-use hir_def::{TypeAliasId, lang_item::LangItem};
+use hir_def::{TraitId, TypeAliasId, lang_item::LangItem};
 use rustc_type_ir::inherent::{IntoKind, Ty as _};
 use tracing::debug;
 use triomphe::Arc;
 
-use crate::next_solver::TraitRef;
-use crate::next_solver::infer::InferOk;
-use crate::next_solver::infer::traits::Obligation;
 use crate::{
     TraitEnvironment,
     db::HirDatabase,
     infer::unify::InferenceTable,
     next_solver::{
-        Ty, TyKind,
-        infer::traits::{ObligationCause, PredicateObligations},
-        mapping::{ChalkToNextSolver, NextSolverToChalk},
+        Canonical, TraitRef, Ty, TyKind,
+        infer::{
+            InferOk,
+            traits::{Obligation, ObligationCause, PredicateObligations},
+        },
         obligation_ctxt::ObligationCtxt,
     },
 };
@@ -38,17 +36,16 @@
 pub fn autoderef<'db>(
     db: &'db dyn HirDatabase,
     env: Arc<TraitEnvironment<'db>>,
-    ty: crate::Canonical<crate::Ty>,
-) -> impl Iterator<Item = crate::Ty> + use<> {
+    ty: Canonical<'db, Ty<'db>>,
+) -> impl Iterator<Item = Ty<'db>> + use<'db> {
     let mut table = InferenceTable::new(db, env);
-    let interner = table.interner();
-    let ty = table.instantiate_canonical(ty.to_nextsolver(interner));
+    let ty = table.instantiate_canonical(ty);
     let mut autoderef = Autoderef::new_no_tracking(&mut table, ty);
     let mut v = Vec::new();
     while let Some((ty, _steps)) = autoderef.next() {
         // `ty` may contain unresolved inference variables. Since there's no chance they would be
         // resolved, just replace with fallback type.
-        let resolved = autoderef.table.resolve_completely(ty).to_chalk(interner);
+        let resolved = autoderef.table.resolve_completely(ty);
 
         // If the deref chain contains a cycle (e.g. `A` derefs to `B` and `B` derefs to `A`), we
         // would revisit some already visited types. Stop here to avoid duplication.
diff --git a/crates/hir-ty/src/chalk_ext.rs b/crates/hir-ty/src/chalk_ext.rs
index 6956a0a..e996037 100644
--- a/crates/hir-ty/src/chalk_ext.rs
+++ b/crates/hir-ty/src/chalk_ext.rs
@@ -1,66 +1,32 @@
 //! Various extensions traits for Chalk types.
 
-use chalk_ir::{
-    FloatTy, IntTy, Mutability, Scalar, TyVariableKind, TypeOutlives, UintTy, cast::Cast,
-};
-use hir_def::{
-    DefWithBodyId, FunctionId, GenericDefId, HasModule, ItemContainerId, Lookup, TraitId,
-    builtin_type::{BuiltinFloat, BuiltinInt, BuiltinType, BuiltinUint},
-    hir::generics::{TypeOrConstParamData, TypeParamProvenance},
-    lang_item::LangItem,
-    type_ref::Rawness,
-};
+use chalk_ir::Mutability;
+use hir_def::{FunctionId, ItemContainerId, Lookup, TraitId};
 
 use crate::{
-    AdtId, AliasEq, AliasTy, Binders, CallableDefId, CallableSig, Canonical, CanonicalVarKinds,
-    ClosureId, DynTy, FnPointer, ImplTraitId, InEnvironment, Interner, Lifetime, ProjectionTy,
-    QuantifiedWhereClause, Substitution, ToChalk, TraitRef, Ty, TyBuilder, TyKind, TypeFlags,
-    WhereClause,
-    db::HirDatabase,
-    from_assoc_type_id, from_chalk_trait_id, from_foreign_def_id, from_placeholder_idx,
-    generics::generics,
-    next_solver::{DbInterner, mapping::NextSolverToChalk},
-    to_chalk_trait_id,
+    AdtId, Binders, CallableDefId, CallableSig, DynTy, Interner, Lifetime, ProjectionTy,
+    Substitution, ToChalk, TraitRef, Ty, TyKind, TypeFlags, WhereClause, db::HirDatabase,
+    from_assoc_type_id, from_chalk_trait_id, generics::generics, to_chalk_trait_id,
     utils::ClosureSubst,
 };
 
-pub trait TyExt {
+pub(crate) trait TyExt {
     fn is_unit(&self) -> bool;
-    fn is_integral(&self) -> bool;
-    fn is_scalar(&self) -> bool;
-    fn is_floating_point(&self) -> bool;
-    fn is_never(&self) -> bool;
-    fn is_str(&self) -> bool;
     fn is_unknown(&self) -> bool;
     fn contains_unknown(&self) -> bool;
-    fn is_ty_var(&self) -> bool;
-    fn is_union(&self) -> bool;
 
     fn as_adt(&self) -> Option<(hir_def::AdtId, &Substitution)>;
-    fn as_builtin(&self) -> Option<BuiltinType>;
     fn as_tuple(&self) -> Option<&Substitution>;
-    fn as_closure(&self) -> Option<ClosureId>;
     fn as_fn_def(&self, db: &dyn HirDatabase) -> Option<FunctionId>;
     fn as_reference(&self) -> Option<(&Ty, Lifetime, Mutability)>;
-    fn as_raw_ptr(&self) -> Option<(&Ty, Mutability)>;
-    fn as_reference_or_ptr(&self) -> Option<(&Ty, Rawness, Mutability)>;
-    fn as_generic_def(&self, db: &dyn HirDatabase) -> Option<GenericDefId>;
 
     fn callable_def(&self, db: &dyn HirDatabase) -> Option<CallableDefId>;
     fn callable_sig(&self, db: &dyn HirDatabase) -> Option<CallableSig>;
 
     fn strip_references(&self) -> &Ty;
-    fn strip_reference(&self) -> &Ty;
 
     /// If this is a `dyn Trait`, returns that trait.
     fn dyn_trait(&self) -> Option<TraitId>;
-
-    fn impl_trait_bounds(&self, db: &dyn HirDatabase) -> Option<Vec<QuantifiedWhereClause>>;
-    fn associated_type_parent_trait(&self, db: &dyn HirDatabase) -> Option<TraitId>;
-    fn is_copy(self, db: &dyn HirDatabase, owner: DefWithBodyId) -> bool;
-
-    /// FIXME: Get rid of this, it's not a good abstraction
-    fn equals_ctor(&self, other: &Ty) -> bool;
 }
 
 impl TyExt for Ty {
@@ -68,33 +34,6 @@
         matches!(self.kind(Interner), TyKind::Tuple(0, _))
     }
 
-    fn is_integral(&self) -> bool {
-        matches!(
-            self.kind(Interner),
-            TyKind::Scalar(Scalar::Int(_) | Scalar::Uint(_))
-                | TyKind::InferenceVar(_, TyVariableKind::Integer)
-        )
-    }
-
-    fn is_scalar(&self) -> bool {
-        matches!(self.kind(Interner), TyKind::Scalar(_))
-    }
-
-    fn is_floating_point(&self) -> bool {
-        matches!(
-            self.kind(Interner),
-            TyKind::Scalar(Scalar::Float(_)) | TyKind::InferenceVar(_, TyVariableKind::Float)
-        )
-    }
-
-    fn is_never(&self) -> bool {
-        matches!(self.kind(Interner), TyKind::Never)
-    }
-
-    fn is_str(&self) -> bool {
-        matches!(self.kind(Interner), TyKind::Str)
-    }
-
     fn is_unknown(&self) -> bool {
         matches!(self.kind(Interner), TyKind::Error)
     }
@@ -103,14 +42,6 @@
         self.data(Interner).flags.contains(TypeFlags::HAS_ERROR)
     }
 
-    fn is_ty_var(&self) -> bool {
-        matches!(self.kind(Interner), TyKind::InferenceVar(_, _))
-    }
-
-    fn is_union(&self) -> bool {
-        matches!(self.adt_id(Interner), Some(AdtId(hir_def::AdtId::UnionId(_))))
-    }
-
     fn as_adt(&self) -> Option<(hir_def::AdtId, &Substitution)> {
         match self.kind(Interner) {
             TyKind::Adt(AdtId(adt), parameters) => Some((*adt, parameters)),
@@ -118,37 +49,6 @@
         }
     }
 
-    fn as_builtin(&self) -> Option<BuiltinType> {
-        match self.kind(Interner) {
-            TyKind::Str => Some(BuiltinType::Str),
-            TyKind::Scalar(Scalar::Bool) => Some(BuiltinType::Bool),
-            TyKind::Scalar(Scalar::Char) => Some(BuiltinType::Char),
-            TyKind::Scalar(Scalar::Float(fty)) => Some(BuiltinType::Float(match fty {
-                FloatTy::F128 => BuiltinFloat::F128,
-                FloatTy::F64 => BuiltinFloat::F64,
-                FloatTy::F32 => BuiltinFloat::F32,
-                FloatTy::F16 => BuiltinFloat::F16,
-            })),
-            TyKind::Scalar(Scalar::Int(ity)) => Some(BuiltinType::Int(match ity {
-                IntTy::Isize => BuiltinInt::Isize,
-                IntTy::I8 => BuiltinInt::I8,
-                IntTy::I16 => BuiltinInt::I16,
-                IntTy::I32 => BuiltinInt::I32,
-                IntTy::I64 => BuiltinInt::I64,
-                IntTy::I128 => BuiltinInt::I128,
-            })),
-            TyKind::Scalar(Scalar::Uint(ity)) => Some(BuiltinType::Uint(match ity {
-                UintTy::Usize => BuiltinUint::Usize,
-                UintTy::U8 => BuiltinUint::U8,
-                UintTy::U16 => BuiltinUint::U16,
-                UintTy::U32 => BuiltinUint::U32,
-                UintTy::U64 => BuiltinUint::U64,
-                UintTy::U128 => BuiltinUint::U128,
-            })),
-            _ => None,
-        }
-    }
-
     fn as_tuple(&self) -> Option<&Substitution> {
         match self.kind(Interner) {
             TyKind::Tuple(_, substs) => Some(substs),
@@ -156,13 +56,6 @@
         }
     }
 
-    fn as_closure(&self) -> Option<ClosureId> {
-        match self.kind(Interner) {
-            TyKind::Closure(id, _) => Some(*id),
-            _ => None,
-        }
-    }
-
     fn as_fn_def(&self, db: &dyn HirDatabase) -> Option<FunctionId> {
         match self.callable_def(db) {
             Some(CallableDefId::FunctionId(func)) => Some(func),
@@ -177,33 +70,6 @@
         }
     }
 
-    fn as_raw_ptr(&self) -> Option<(&Ty, Mutability)> {
-        match self.kind(Interner) {
-            TyKind::Raw(mutability, ty) => Some((ty, *mutability)),
-            _ => None,
-        }
-    }
-
-    fn as_reference_or_ptr(&self) -> Option<(&Ty, Rawness, Mutability)> {
-        match self.kind(Interner) {
-            TyKind::Ref(mutability, _, ty) => Some((ty, Rawness::Ref, *mutability)),
-            TyKind::Raw(mutability, ty) => Some((ty, Rawness::RawPtr, *mutability)),
-            _ => None,
-        }
-    }
-
-    fn as_generic_def(&self, db: &dyn HirDatabase) -> Option<GenericDefId> {
-        match *self.kind(Interner) {
-            TyKind::Adt(AdtId(adt), ..) => Some(adt.into()),
-            TyKind::FnDef(callable, ..) => {
-                Some(GenericDefId::from_callable(db, ToChalk::from_chalk(db, callable)))
-            }
-            TyKind::AssociatedType(type_alias, ..) => Some(from_assoc_type_id(type_alias).into()),
-            TyKind::Foreign(type_alias, ..) => Some(from_foreign_def_id(type_alias).into()),
-            _ => None,
-        }
-    }
-
     fn callable_def(&self, db: &dyn HirDatabase) -> Option<CallableDefId> {
         match self.kind(Interner) {
             &TyKind::FnDef(def, ..) => Some(ToChalk::from_chalk(db, def)),
@@ -244,177 +110,6 @@
         }
         t
     }
-
-    fn strip_reference(&self) -> &Ty {
-        self.as_reference().map_or(self, |(ty, _, _)| ty)
-    }
-
-    fn impl_trait_bounds(&self, db: &dyn HirDatabase) -> Option<Vec<QuantifiedWhereClause>> {
-        let handle_async_block_type_impl_trait = |def: DefWithBodyId| {
-            let krate = def.module(db).krate();
-            if let Some(future_trait) = LangItem::Future.resolve_trait(db, krate) {
-                // This is only used by type walking.
-                // Parameters will be walked outside, and projection predicate is not used.
-                // So just provide the Future trait.
-                let impl_bound = Binders::empty(
-                    Interner,
-                    WhereClause::Implemented(TraitRef {
-                        trait_id: to_chalk_trait_id(future_trait),
-                        substitution: Substitution::empty(Interner),
-                    }),
-                );
-                Some(vec![impl_bound])
-            } else {
-                None
-            }
-        };
-
-        match self.kind(Interner) {
-            TyKind::OpaqueType(opaque_ty_id, subst) => {
-                match db.lookup_intern_impl_trait_id((*opaque_ty_id).into()) {
-                    ImplTraitId::AsyncBlockTypeImplTrait(def, _expr) => {
-                        handle_async_block_type_impl_trait(def)
-                    }
-                    ImplTraitId::ReturnTypeImplTrait(func, idx) => {
-                        db.return_type_impl_traits(func).map(|it| {
-                            let data =
-                                (*it).as_ref().map(|rpit| rpit.impl_traits[idx].bounds.clone());
-                            data.substitute(Interner, &subst).into_value_and_skipped_binders().0
-                        })
-                    }
-                    ImplTraitId::TypeAliasImplTrait(alias, idx) => {
-                        db.type_alias_impl_traits(alias).map(|it| {
-                            let data =
-                                (*it).as_ref().map(|rpit| rpit.impl_traits[idx].bounds.clone());
-                            data.substitute(Interner, &subst).into_value_and_skipped_binders().0
-                        })
-                    }
-                }
-            }
-            TyKind::Alias(AliasTy::Opaque(opaque_ty)) => {
-                let predicates = match db.lookup_intern_impl_trait_id(opaque_ty.opaque_ty_id.into())
-                {
-                    ImplTraitId::ReturnTypeImplTrait(func, idx) => {
-                        db.return_type_impl_traits(func).map(|it| {
-                            let data =
-                                (*it).as_ref().map(|rpit| rpit.impl_traits[idx].bounds.clone());
-                            data.substitute(Interner, &opaque_ty.substitution)
-                        })
-                    }
-                    ImplTraitId::TypeAliasImplTrait(alias, idx) => {
-                        db.type_alias_impl_traits(alias).map(|it| {
-                            let data =
-                                (*it).as_ref().map(|rpit| rpit.impl_traits[idx].bounds.clone());
-                            data.substitute(Interner, &opaque_ty.substitution)
-                        })
-                    }
-                    ImplTraitId::AsyncBlockTypeImplTrait(def, _) => {
-                        return handle_async_block_type_impl_trait(def);
-                    }
-                };
-
-                predicates.map(|it| it.into_value_and_skipped_binders().0)
-            }
-            TyKind::Placeholder(idx) => {
-                let id = from_placeholder_idx(db, *idx).0;
-                let generic_params = db.generic_params(id.parent);
-                let param_data = &generic_params[id.local_id];
-                match param_data {
-                    TypeOrConstParamData::TypeParamData(p) => match p.provenance {
-                        TypeParamProvenance::ArgumentImplTrait => {
-                            let substs = TyBuilder::placeholder_subst(db, id.parent);
-                            let predicates = db
-                                .generic_predicates(id.parent)
-                                .iter()
-                                .map(|pred| pred.clone().substitute(Interner, &substs))
-                                .filter(|wc| match wc.skip_binders() {
-                                    WhereClause::Implemented(tr) => {
-                                        &tr.self_type_parameter(Interner) == self
-                                    }
-                                    WhereClause::AliasEq(AliasEq {
-                                        alias: AliasTy::Projection(proj),
-                                        ty: _,
-                                    }) => &proj.self_type_parameter(db) == self,
-                                    WhereClause::TypeOutlives(TypeOutlives { ty, lifetime: _ }) => {
-                                        ty == self
-                                    }
-                                    _ => false,
-                                })
-                                .collect::<Vec<_>>();
-
-                            Some(predicates)
-                        }
-                        _ => None,
-                    },
-                    _ => None,
-                }
-            }
-            _ => None,
-        }
-    }
-
-    fn associated_type_parent_trait(&self, db: &dyn HirDatabase) -> Option<TraitId> {
-        match self.kind(Interner) {
-            TyKind::AssociatedType(id, ..) => match from_assoc_type_id(*id).lookup(db).container {
-                ItemContainerId::TraitId(trait_id) => Some(trait_id),
-                _ => None,
-            },
-            TyKind::Alias(AliasTy::Projection(projection_ty)) => {
-                match from_assoc_type_id(projection_ty.associated_ty_id).lookup(db).container {
-                    ItemContainerId::TraitId(trait_id) => Some(trait_id),
-                    _ => None,
-                }
-            }
-            _ => None,
-        }
-    }
-
-    fn is_copy(self, db: &dyn HirDatabase, owner: DefWithBodyId) -> bool {
-        let crate_id = owner.module(db).krate();
-        let Some(copy_trait) = LangItem::Copy.resolve_trait(db, crate_id) else {
-            return false;
-        };
-        let trait_ref = TyBuilder::trait_ref(db, copy_trait).push(self).build();
-        let env = db.trait_environment_for_body(owner);
-        let goal = Canonical {
-            value: InEnvironment::new(
-                &env.env.to_chalk(DbInterner::new_with(db, Some(env.krate), env.block)),
-                trait_ref.cast(Interner),
-            ),
-            binders: CanonicalVarKinds::empty(Interner),
-        };
-        !db.trait_solve(crate_id, None, goal).no_solution()
-    }
-
-    fn equals_ctor(&self, other: &Ty) -> bool {
-        match (self.kind(Interner), other.kind(Interner)) {
-            (TyKind::Adt(adt, ..), TyKind::Adt(adt2, ..)) => adt == adt2,
-            (TyKind::Slice(_), TyKind::Slice(_)) | (TyKind::Array(_, _), TyKind::Array(_, _)) => {
-                true
-            }
-            (TyKind::FnDef(def_id, ..), TyKind::FnDef(def_id2, ..)) => def_id == def_id2,
-            (TyKind::OpaqueType(ty_id, ..), TyKind::OpaqueType(ty_id2, ..)) => ty_id == ty_id2,
-            (TyKind::AssociatedType(ty_id, ..), TyKind::AssociatedType(ty_id2, ..)) => {
-                ty_id == ty_id2
-            }
-            (TyKind::Foreign(ty_id, ..), TyKind::Foreign(ty_id2, ..)) => ty_id == ty_id2,
-            (TyKind::Closure(id1, _), TyKind::Closure(id2, _)) => id1 == id2,
-            (TyKind::Ref(mutability, ..), TyKind::Ref(mutability2, ..))
-            | (TyKind::Raw(mutability, ..), TyKind::Raw(mutability2, ..)) => {
-                mutability == mutability2
-            }
-            (
-                TyKind::Function(FnPointer { num_binders, sig, .. }),
-                TyKind::Function(FnPointer { num_binders: num_binders2, sig: sig2, .. }),
-            ) => num_binders == num_binders2 && sig == sig2,
-            (TyKind::Tuple(cardinality, _), TyKind::Tuple(cardinality2, _)) => {
-                cardinality == cardinality2
-            }
-            (TyKind::Str, TyKind::Str) | (TyKind::Never, TyKind::Never) => true,
-            (TyKind::Scalar(scalar), TyKind::Scalar(scalar2)) => scalar == scalar2,
-            _ => false,
-        }
-    }
 }
 
 pub trait ProjectionTyExt {
@@ -445,9 +140,8 @@
     }
 }
 
-pub trait DynTyExt {
+pub(crate) trait DynTyExt {
     fn principal(&self) -> Option<Binders<Binders<&TraitRef>>>;
-    fn principal_id(&self) -> Option<chalk_ir::TraitId<Interner>>;
 }
 
 impl DynTyExt for DynTy {
@@ -461,13 +155,6 @@
             })
         })
     }
-
-    fn principal_id(&self) -> Option<chalk_ir::TraitId<Interner>> {
-        self.bounds.skip_binders().interned().first().and_then(|b| match b.skip_binders() {
-            crate::WhereClause::Implemented(trait_ref) => Some(trait_ref.trait_id),
-            _ => None,
-        })
-    }
 }
 
 pub trait TraitRefExt {
diff --git a/crates/hir-ty/src/consteval_chalk.rs b/crates/hir-ty/src/consteval_chalk.rs
index 4589743..07b783e 100644
--- a/crates/hir-ty/src/consteval_chalk.rs
+++ b/crates/hir-ty/src/consteval_chalk.rs
@@ -11,48 +11,15 @@
 
 use crate::{
     Const, ConstData, ConstScalar, ConstValue, GenericArg, Interner, MemoryMap, Substitution,
-    TraitEnvironment, Ty, TyBuilder,
+    TraitEnvironment, Ty,
     db::HirDatabase,
     generics::Generics,
     lower::ParamLoweringMode,
-    next_solver::{
-        DbInterner,
-        mapping::{ChalkToNextSolver, NextSolverToChalk},
-    },
+    next_solver::{DbInterner, mapping::ChalkToNextSolver},
     to_placeholder_idx,
 };
 
-use super::mir::pad16;
-
-/// Extension trait for [`Const`]
-pub trait ConstExt {
-    /// Is a [`Const`] unknown?
-    fn is_unknown(&self) -> bool;
-}
-
-impl ConstExt for Const {
-    fn is_unknown(&self) -> bool {
-        match self.data(Interner).value {
-            // interned Unknown
-            chalk_ir::ConstValue::Concrete(chalk_ir::ConcreteConst {
-                interned: ConstScalar::Unknown,
-            }) => true,
-
-            // interned concrete anything else
-            chalk_ir::ConstValue::Concrete(..) => false,
-
-            _ => {
-                tracing::error!(
-                    "is_unknown was called on a non-concrete constant value! {:?}",
-                    self
-                );
-                true
-            }
-        }
-    }
-}
-
-pub fn path_to_const<'g>(
+pub(crate) fn path_to_const<'g>(
     db: &dyn HirDatabase,
     resolver: &Resolver<'_>,
     path: &Path,
@@ -94,7 +61,7 @@
     }
 }
 
-pub fn unknown_const(ty: Ty) -> Const {
+pub(crate) fn unknown_const(ty: Ty) -> Const {
     ConstData {
         ty,
         value: ConstValue::Concrete(chalk_ir::ConcreteConst { interned: ConstScalar::Unknown }),
@@ -102,18 +69,18 @@
     .intern(Interner)
 }
 
-pub fn unknown_const_as_generic(ty: Ty) -> GenericArg {
+pub(crate) fn unknown_const_as_generic(ty: Ty) -> GenericArg {
     unknown_const(ty).cast(Interner)
 }
 
 /// Interns a constant scalar with the given type
-pub fn intern_const_scalar(value: ConstScalar, ty: Ty) -> Const {
+pub(crate) fn intern_const_scalar(value: ConstScalar, ty: Ty) -> Const {
     ConstData { ty, value: ConstValue::Concrete(chalk_ir::ConcreteConst { interned: value }) }
         .intern(Interner)
 }
 
 /// Interns a constant scalar with the given type
-pub fn intern_const_ref(
+pub(crate) fn intern_const_ref(
     db: &dyn HirDatabase,
     value: &LiteralConstRef,
     ty: Ty,
@@ -139,47 +106,3 @@
     };
     intern_const_scalar(bytes, ty)
 }
-
-/// Interns a possibly-unknown target usize
-pub fn usize_const(db: &dyn HirDatabase, value: Option<u128>, krate: Crate) -> Const {
-    intern_const_ref(
-        db,
-        &value.map_or(LiteralConstRef::Unknown, LiteralConstRef::UInt),
-        TyBuilder::usize(),
-        krate,
-    )
-}
-
-pub fn try_const_usize(db: &dyn HirDatabase, c: &Const) -> Option<u128> {
-    let interner = DbInterner::new_with(db, None, None);
-    match &c.data(Interner).value {
-        chalk_ir::ConstValue::BoundVar(_) => None,
-        chalk_ir::ConstValue::InferenceVar(_) => None,
-        chalk_ir::ConstValue::Placeholder(_) => None,
-        chalk_ir::ConstValue::Concrete(c) => match &c.interned {
-            ConstScalar::Bytes(it, _) => Some(u128::from_le_bytes(pad16(it, false))),
-            ConstScalar::UnevaluatedConst(c, subst) => {
-                let ec = db.const_eval(*c, subst.to_nextsolver(interner), None).ok()?;
-                try_const_usize(db, &ec.to_chalk(interner))
-            }
-            _ => None,
-        },
-    }
-}
-
-pub fn try_const_isize(db: &dyn HirDatabase, c: &Const) -> Option<i128> {
-    let interner = DbInterner::new_with(db, None, None);
-    match &c.data(Interner).value {
-        chalk_ir::ConstValue::BoundVar(_) => None,
-        chalk_ir::ConstValue::InferenceVar(_) => None,
-        chalk_ir::ConstValue::Placeholder(_) => None,
-        chalk_ir::ConstValue::Concrete(c) => match &c.interned {
-            ConstScalar::Bytes(it, _) => Some(i128::from_le_bytes(pad16(it, true))),
-            ConstScalar::UnevaluatedConst(c, subst) => {
-                let ec = db.const_eval(*c, subst.to_nextsolver(interner), None).ok()?;
-                try_const_isize(db, &ec.to_chalk(interner))
-            }
-            _ => None,
-        },
-    }
-}
diff --git a/crates/hir-ty/src/infer/coerce.rs b/crates/hir-ty/src/infer/coerce.rs
index 10c1f9c..ce5c989 100644
--- a/crates/hir-ty/src/infer/coerce.rs
+++ b/crates/hir-ty/src/infer/coerce.rs
@@ -46,7 +46,7 @@
 use rustc_type_ir::{
     BoundVar, TypeAndMut,
     error::TypeError,
-    inherent::{Const as _, GenericArg as _, IntoKind, Region as _, Safety, SliceLike, Ty as _},
+    inherent::{Const as _, GenericArg as _, IntoKind, Safety, SliceLike, Ty as _},
 };
 use smallvec::{SmallVec, smallvec};
 use tracing::{debug, instrument};
@@ -59,15 +59,15 @@
     infer::{AllowTwoPhase, InferenceContext, TypeMismatch, unify::InferenceTable},
     next_solver::{
         Binder, BoundConst, BoundRegion, BoundRegionKind, BoundTy, BoundTyKind, CallableIdWrapper,
-        ClauseKind, CoercePredicate, Const, ConstKind, DbInterner, ErrorGuaranteed, GenericArgs,
-        PolyFnSig, PredicateKind, Region, RegionKind, SolverDefId, TraitRef, Ty, TyKind,
+        Canonical, ClauseKind, CoercePredicate, Const, ConstKind, DbInterner, ErrorGuaranteed,
+        GenericArgs, PolyFnSig, PredicateKind, Region, RegionKind, SolverDefId, TraitRef, Ty,
+        TyKind,
         infer::{
             DefineOpaqueTypes, InferCtxt, InferOk, InferResult,
             relate::RelateResult,
             select::{ImplSource, SelectionError},
             traits::{Obligation, ObligationCause, PredicateObligation, PredicateObligations},
         },
-        mapping::{ChalkToNextSolver, NextSolverToChalk},
         obligation_ctxt::ObligationCtxt,
     },
     utils::TargetFeatureIsSafeInTarget,
@@ -1525,7 +1525,7 @@
 pub fn could_coerce<'db>(
     db: &'db dyn HirDatabase,
     env: Arc<TraitEnvironment<'db>>,
-    tys: &crate::Canonical<(crate::Ty, crate::Ty)>,
+    tys: &Canonical<'db, (Ty<'db>, Ty<'db>)>,
 ) -> bool {
     coerce(db, env, tys).is_ok()
 }
@@ -1533,12 +1533,11 @@
 fn coerce<'db>(
     db: &'db dyn HirDatabase,
     env: Arc<TraitEnvironment<'db>>,
-    tys: &crate::Canonical<(crate::Ty, crate::Ty)>,
-) -> Result<(Vec<Adjustment<'db>>, crate::Ty), TypeError<DbInterner<'db>>> {
+    tys: &Canonical<'db, (Ty<'db>, Ty<'db>)>,
+) -> Result<(Vec<Adjustment<'db>>, Ty<'db>), TypeError<DbInterner<'db>>> {
     let mut table = InferenceTable::new(db, env);
     let interner = table.interner();
-    let tys = tys.to_nextsolver(interner);
-    let ((ty1_with_vars, ty2_with_vars), vars) = table.infer_ctxt.instantiate_canonical(&tys);
+    let ((ty1_with_vars, ty2_with_vars), vars) = table.infer_ctxt.instantiate_canonical(tys);
 
     let cause = ObligationCause::new();
     // FIXME: Target features.
@@ -1614,5 +1613,5 @@
         &mut fallback_const,
         &mut fallback_region,
     );
-    Ok((adjustments, ty.to_chalk(interner)))
+    Ok((adjustments, ty))
 }
diff --git a/crates/hir-ty/src/infer/path.rs b/crates/hir-ty/src/infer/path.rs
index 110f767..f70ed90 100644
--- a/crates/hir-ty/src/infer/path.rs
+++ b/crates/hir-ty/src/infer/path.rs
@@ -1,7 +1,7 @@
 //! Path expression resolution.
 
 use hir_def::{
-    AdtId, AssocItemId, GenericDefId, GenericParamId, ItemContainerId, Lookup,
+    AdtId, AssocItemId, GenericDefId, ItemContainerId, Lookup,
     expr_store::path::{Path, PathSegment},
     resolver::{ResolveValueResult, TypeNs, ValueNs},
 };
@@ -10,7 +10,7 @@
 use stdx::never;
 
 use crate::{
-    InferenceDiagnostic, ValueTyDefId, consteval,
+    InferenceDiagnostic, ValueTyDefId,
     generics::generics,
     infer::diagnostics::InferenceTyLoweringContext as TyLoweringContext,
     lower_nextsolver::LifetimeElisionKind,
@@ -118,22 +118,12 @@
             self.interner(),
             generic_def.into(),
             self_subst.iter().flat_map(|it| it.iter()).chain(substs.iter().skip(parent_substs_len)),
-            |_, _, id, _| self.error_param(id),
+            |_, _, id, _| GenericArg::error_from_id(self.interner(), id),
         );
 
         Some(ValuePathResolution::GenericDef(value_def, generic_def, substs))
     }
 
-    fn error_param(&mut self, id: GenericParamId) -> GenericArg<'db> {
-        match id {
-            GenericParamId::TypeParamId(_) => self.types.error.into(),
-            GenericParamId::ConstParamId(id) => {
-                consteval::unknown_const_as_generic(self.db.const_param_ty_ns(id))
-            }
-            GenericParamId::LifetimeParamId(_) => self.types.re_error.into(),
-        }
-    }
-
     pub(super) fn resolve_value_path_inner(
         &mut self,
         path: &Path,
diff --git a/crates/hir-ty/src/infer/unify.rs b/crates/hir-ty/src/infer/unify.rs
index 89bab4e..114c90c 100644
--- a/crates/hir-ty/src/infer/unify.rs
+++ b/crates/hir-ty/src/infer/unify.rs
@@ -2,29 +2,27 @@
 
 use std::fmt;
 
-use chalk_ir::cast::Cast;
-use hir_def::GenericParamId;
-use hir_def::{AdtId, lang_item::LangItem};
+use hir_def::{AdtId, GenericParamId, lang_item::LangItem};
 use hir_expand::name::Name;
 use intern::sym;
 use rustc_hash::{FxHashMap, FxHashSet};
-use rustc_type_ir::{DebruijnIndex, InferConst, InferTy, RegionVid};
 use rustc_type_ir::{
-    TyVid, TypeFoldable, TypeFolder, TypeSuperFoldable, TypeVisitableExt, UpcastFrom,
+    DebruijnIndex, InferConst, InferTy, RegionVid, TyVid, TypeFoldable, TypeFolder,
+    TypeSuperFoldable, TypeVisitableExt, UpcastFrom,
     inherent::{Const as _, IntoKind, Ty as _},
     solve::{Certainty, GoalSource},
 };
 use smallvec::SmallVec;
 use triomphe::Arc;
 
-use crate::next_solver::{Binder, ConstKind, GenericArgs, RegionKind, SolverDefId};
 use crate::{
-    Interner, TraitEnvironment,
+    TraitEnvironment,
     db::{HirDatabase, InternedOpaqueTyId},
     infer::InferenceContext,
     next_solver::{
-        self, AliasTy, ClauseKind, Const, DbInterner, ErrorGuaranteed, GenericArg, Predicate,
-        PredicateKind, Region, SolverDefIds, TraitRef, Ty, TyKind, TypingMode,
+        self, AliasTy, Binder, Canonical, ClauseKind, Const, ConstKind, DbInterner,
+        ErrorGuaranteed, GenericArg, GenericArgs, Predicate, PredicateKind, Region, RegionKind,
+        SolverDefId, SolverDefIds, TraitRef, Ty, TyKind, TypingMode,
         fulfill::{FulfillmentCtxt, NextSolverError},
         infer::{
             DbInternerInferExt, DefineOpaqueTypes, InferCtxt, InferOk, InferResult,
@@ -33,7 +31,6 @@
             traits::{Obligation, ObligationCause, PredicateObligation},
         },
         inspect::{InspectConfig, InspectGoal, ProofTreeVisitor},
-        mapping::{ChalkToNextSolver, NextSolverToChalk},
         obligation_ctxt::ObligationCtxt,
     },
     traits::{
@@ -115,10 +112,10 @@
 /// This means that there may be some unresolved goals that actually set bounds for the placeholder
 /// type for the types to unify. For example `Option<T>` and `Option<U>` unify although there is
 /// unresolved goal `T = U`.
-pub fn could_unify(
-    db: &dyn HirDatabase,
-    env: Arc<TraitEnvironment<'_>>,
-    tys: &crate::Canonical<(crate::Ty, crate::Ty)>,
+pub fn could_unify<'db>(
+    db: &'db dyn HirDatabase,
+    env: Arc<TraitEnvironment<'db>>,
+    tys: &Canonical<'db, (Ty<'db>, Ty<'db>)>,
 ) -> bool {
     could_unify_impl(db, env, tys, |ctxt| ctxt.select_where_possible())
 }
@@ -127,32 +124,28 @@
 ///
 /// This means that placeholder types are not considered to unify if there are any bounds set on
 /// them. For example `Option<T>` and `Option<U>` do not unify as we cannot show that `T = U`
-pub fn could_unify_deeply(
-    db: &dyn HirDatabase,
-    env: Arc<TraitEnvironment<'_>>,
-    tys: &crate::Canonical<(crate::Ty, crate::Ty)>,
+pub fn could_unify_deeply<'db>(
+    db: &'db dyn HirDatabase,
+    env: Arc<TraitEnvironment<'db>>,
+    tys: &Canonical<'db, (Ty<'db>, Ty<'db>)>,
 ) -> bool {
     could_unify_impl(db, env, tys, |ctxt| ctxt.select_all_or_error())
 }
 
-fn could_unify_impl(
-    db: &dyn HirDatabase,
-    env: Arc<TraitEnvironment<'_>>,
-    tys: &crate::Canonical<(crate::Ty, crate::Ty)>,
-    select: for<'a, 'db> fn(&mut ObligationCtxt<'a, 'db>) -> Vec<NextSolverError<'db>>,
+fn could_unify_impl<'db>(
+    db: &'db dyn HirDatabase,
+    env: Arc<TraitEnvironment<'db>>,
+    tys: &Canonical<'db, (Ty<'db>, Ty<'db>)>,
+    select: for<'a> fn(&mut ObligationCtxt<'a, 'db>) -> Vec<NextSolverError<'db>>,
 ) -> bool {
     let interner = DbInterner::new_with(db, Some(env.krate), env.block);
     // FIXME(next-solver): I believe this should use `PostAnalysis` (this is only used for IDE things),
     // but this causes some bug because of our incorrect impl of `type_of_opaque_hir_typeck()` for TAIT
     // and async blocks.
-    let infcx = interner.infer_ctxt().build(TypingMode::Analysis {
-        defining_opaque_types_and_generators: SolverDefIds::new_from_iter(interner, []),
-    });
+    let infcx = interner.infer_ctxt().build(TypingMode::non_body_analysis());
     let cause = ObligationCause::dummy();
     let at = infcx.at(&cause, env.env);
-    let vars = make_substitutions(tys, &infcx);
-    let ty1_with_vars = vars.apply(tys.value.0.clone(), Interner).to_nextsolver(interner);
-    let ty2_with_vars = vars.apply(tys.value.1.clone(), Interner).to_nextsolver(interner);
+    let ((ty1_with_vars, ty2_with_vars), _) = infcx.instantiate_canonical(tys);
     let mut ctxt = ObligationCtxt::new(&infcx);
     let can_unify = at
         .eq(DefineOpaqueTypes::No, ty1_with_vars, ty2_with_vars)
@@ -161,26 +154,6 @@
     can_unify && select(&mut ctxt).is_empty()
 }
 
-fn make_substitutions(
-    tys: &crate::Canonical<(crate::Ty, crate::Ty)>,
-    infcx: &InferCtxt<'_>,
-) -> crate::Substitution {
-    let interner = infcx.interner;
-    crate::Substitution::from_iter(
-        Interner,
-        tys.binders.iter(Interner).map(|it| match &it.kind {
-            chalk_ir::VariableKind::Ty(_) => infcx.next_ty_var().to_chalk(interner).cast(Interner),
-            // FIXME: maybe wrong?
-            chalk_ir::VariableKind::Lifetime => {
-                infcx.next_ty_var().to_chalk(interner).cast(Interner)
-            }
-            chalk_ir::VariableKind::Const(_ty) => {
-                infcx.next_const_var().to_chalk(interner).cast(Interner)
-            }
-        }),
-    )
-}
-
 #[derive(Clone)]
 pub(crate) struct InferenceTable<'db> {
     pub(crate) db: &'db dyn HirDatabase,
diff --git a/crates/hir-ty/src/lib.rs b/crates/hir-ty/src/lib.rs
index 76cc652..734483a 100644
--- a/crates/hir-ty/src/lib.rs
+++ b/crates/hir-ty/src/lib.rs
@@ -39,7 +39,7 @@
 
 pub mod autoderef;
 pub mod consteval;
-pub mod consteval_chalk;
+mod consteval_chalk;
 pub mod db;
 pub mod diagnostics;
 pub mod display;
@@ -62,7 +62,7 @@
 use std::hash::Hash;
 
 use chalk_ir::{
-    NoSolution, VariableKinds,
+    VariableKinds,
     fold::{Shift, TypeFoldable},
     interner::HasInterner,
 };
@@ -74,15 +74,16 @@
 use mir::{MirEvalError, VTableMap};
 use rustc_hash::{FxBuildHasher, FxHashMap, FxHashSet};
 use rustc_type_ir::{
-    UpcastFrom,
-    inherent::{SliceLike, Ty as _},
+    TypeSuperVisitable, TypeVisitableExt, UpcastFrom,
+    inherent::{IntoKind, SliceLike, Ty as _},
 };
 use syntax::ast::{ConstArg, make};
 use traits::FnTrait;
 use triomphe::Arc;
 
+#[cfg(not(debug_assertions))]
+use crate::next_solver::ErrorGuaranteed;
 use crate::{
-    consteval::unknown_const,
     db::HirDatabase,
     display::{DisplayTarget, HirDisplay},
     generics::Generics,
@@ -104,11 +105,10 @@
     could_coerce, could_unify, could_unify_deeply,
 };
 pub use interner::Interner;
-pub use lower::{
-    ImplTraitLoweringMode, LifetimeElisionKind, ParamLoweringMode, TyDefId, TyLoweringContext,
-    ValueTyDefId, diagnostics::*,
+pub use lower::{ImplTraitLoweringMode, ParamLoweringMode, TyDefId, ValueTyDefId, diagnostics::*};
+pub use lower_nextsolver::{
+    LifetimeElisionKind, TyLoweringContext, associated_type_shorthand_candidates,
 };
-pub use lower_nextsolver::associated_type_shorthand_candidates;
 pub use mapping::{
     ToChalk, from_assoc_type_id, from_chalk_trait_id, from_foreign_def_id, from_placeholder_idx,
     lt_from_placeholder_idx, lt_to_placeholder_idx, to_assoc_type_id, to_chalk_trait_id,
@@ -124,20 +124,16 @@
 };
 pub use variance::Variance;
 
-pub use chalk_ir::{
-    AdtId, BoundVar, DebruijnIndex, Mutability, Safety, Scalar, TyVariableKind,
-    cast::Cast,
-    visit::{TypeSuperVisitable, TypeVisitable, TypeVisitor},
-};
+use chalk_ir::{AdtId, BoundVar, DebruijnIndex, Safety, Scalar};
 
-pub type ForeignDefId = chalk_ir::ForeignDefId<Interner>;
-pub type AssocTypeId = chalk_ir::AssocTypeId<Interner>;
-pub type FnDefId = chalk_ir::FnDefId<Interner>;
-pub type ClosureId = chalk_ir::ClosureId<Interner>;
-pub type OpaqueTyId = chalk_ir::OpaqueTyId<Interner>;
-pub type PlaceholderIndex = chalk_ir::PlaceholderIndex;
+pub(crate) type ForeignDefId = chalk_ir::ForeignDefId<Interner>;
+pub(crate) type AssocTypeId = chalk_ir::AssocTypeId<Interner>;
+pub(crate) type FnDefId = chalk_ir::FnDefId<Interner>;
+pub(crate) type ClosureId = chalk_ir::ClosureId<Interner>;
+pub(crate) type OpaqueTyId = chalk_ir::OpaqueTyId<Interner>;
+pub(crate) type PlaceholderIndex = chalk_ir::PlaceholderIndex;
 
-pub type CanonicalVarKinds = chalk_ir::CanonicalVarKinds<Interner>;
+pub(crate) type CanonicalVarKinds = chalk_ir::CanonicalVarKinds<Interner>;
 
 pub(crate) type VariableKind = chalk_ir::VariableKind<Interner>;
 /// Represents generic parameters and an item bound by them. When the item has parent, the binders
@@ -148,49 +144,48 @@
 /// parameters/arguments for an item MUST come before those for its parent. This is to facilitate
 /// the integration with chalk-solve, which mildly puts constraints as such. See #13335 for its
 /// motivation in detail.
-pub type Binders<T> = chalk_ir::Binders<T>;
+pub(crate) type Binders<T> = chalk_ir::Binders<T>;
 /// Interned list of generic arguments for an item. When an item has parent, the `Substitution` for
 /// it contains generic arguments for both its parent and itself. See chalk's documentation for
 /// details.
 ///
 /// See `Binders` for the constraint on the ordering.
-pub type Substitution = chalk_ir::Substitution<Interner>;
-pub type GenericArg = chalk_ir::GenericArg<Interner>;
-pub type GenericArgData = chalk_ir::GenericArgData<Interner>;
+pub(crate) type Substitution = chalk_ir::Substitution<Interner>;
+pub(crate) type GenericArg = chalk_ir::GenericArg<Interner>;
+pub(crate) type GenericArgData = chalk_ir::GenericArgData<Interner>;
 
-pub type Ty = chalk_ir::Ty<Interner>;
+pub(crate) type Ty = chalk_ir::Ty<Interner>;
 pub type TyKind = chalk_ir::TyKind<Interner>;
-pub type TypeFlags = chalk_ir::TypeFlags;
+pub(crate) type TypeFlags = chalk_ir::TypeFlags;
 pub(crate) type DynTy = chalk_ir::DynTy<Interner>;
-pub type FnPointer = chalk_ir::FnPointer<Interner>;
+pub(crate) type FnPointer = chalk_ir::FnPointer<Interner>;
 pub(crate) use chalk_ir::FnSubst; // a re-export so we don't lose the tuple constructor
 
 pub type AliasTy = chalk_ir::AliasTy<Interner>;
 
-pub type ProjectionTy = chalk_ir::ProjectionTy<Interner>;
+pub(crate) type ProjectionTy = chalk_ir::ProjectionTy<Interner>;
 pub(crate) type OpaqueTy = chalk_ir::OpaqueTy<Interner>;
-pub(crate) type InferenceVar = chalk_ir::InferenceVar;
 
 pub(crate) type Lifetime = chalk_ir::Lifetime<Interner>;
 pub(crate) type LifetimeData = chalk_ir::LifetimeData<Interner>;
 pub(crate) type LifetimeOutlives = chalk_ir::LifetimeOutlives<Interner>;
 
-pub type ConstValue = chalk_ir::ConstValue<Interner>;
+pub(crate) type ConstValue = chalk_ir::ConstValue<Interner>;
 
-pub type Const = chalk_ir::Const<Interner>;
+pub(crate) type Const = chalk_ir::Const<Interner>;
 pub(crate) type ConstData = chalk_ir::ConstData<Interner>;
 pub(crate) type ConcreteConst = chalk_ir::ConcreteConst<Interner>;
 
-pub type TraitRef = chalk_ir::TraitRef<Interner>;
-pub type QuantifiedWhereClause = Binders<WhereClause>;
-pub type Canonical<T> = chalk_ir::Canonical<T>;
+pub(crate) type TraitRef = chalk_ir::TraitRef<Interner>;
+pub(crate) type QuantifiedWhereClause = Binders<WhereClause>;
+pub(crate) type Canonical<T> = chalk_ir::Canonical<T>;
 
 pub(crate) type ChalkTraitId = chalk_ir::TraitId<Interner>;
 pub(crate) type QuantifiedWhereClauses = chalk_ir::QuantifiedWhereClauses<Interner>;
 
 pub(crate) type FnSig = chalk_ir::FnSig<Interner>;
 
-pub type InEnvironment<T> = chalk_ir::InEnvironment<T>;
+pub(crate) type InEnvironment<T> = chalk_ir::InEnvironment<T>;
 pub type AliasEq = chalk_ir::AliasEq<Interner>;
 pub type WhereClause = chalk_ir::WhereClause<Interner>;
 
@@ -717,130 +712,167 @@
 /// 'Canonicalizes' the `t` by replacing any errors with new variables. Also
 /// ensures there are no unbound variables or inference variables anywhere in
 /// the `t`.
-pub fn replace_errors_with_variables<T>(t: &T) -> Canonical<T>
+pub fn replace_errors_with_variables<'db, T>(
+    interner: DbInterner<'db>,
+    t: &T,
+) -> crate::next_solver::Canonical<'db, T>
 where
-    T: HasInterner<Interner = Interner> + TypeFoldable<Interner> + Clone,
+    T: rustc_type_ir::TypeFoldable<DbInterner<'db>> + Clone,
 {
-    use chalk_ir::{
-        Fallible,
-        fold::{FallibleTypeFolder, TypeSuperFoldable},
-    };
-    struct ErrorReplacer {
-        vars: usize,
+    use rustc_type_ir::{FallibleTypeFolder, TypeSuperFoldable};
+    struct ErrorReplacer<'db> {
+        interner: DbInterner<'db>,
+        vars: Vec<crate::next_solver::CanonicalVarKind<'db>>,
+        binder: rustc_type_ir::DebruijnIndex,
     }
-    impl FallibleTypeFolder<Interner> for ErrorReplacer {
-        type Error = NoSolution;
+    impl<'db> FallibleTypeFolder<DbInterner<'db>> for ErrorReplacer<'db> {
+        #[cfg(debug_assertions)]
+        type Error = ();
+        #[cfg(not(debug_assertions))]
+        type Error = std::convert::Infallible;
 
-        fn as_dyn(&mut self) -> &mut dyn FallibleTypeFolder<Interner, Error = Self::Error> {
-            self
+        fn cx(&self) -> DbInterner<'db> {
+            self.interner
         }
 
-        fn interner(&self) -> Interner {
-            Interner
+        fn try_fold_binder<T>(
+            &mut self,
+            t: crate::next_solver::Binder<'db, T>,
+        ) -> Result<crate::next_solver::Binder<'db, T>, Self::Error>
+        where
+            T: rustc_type_ir::TypeFoldable<DbInterner<'db>>,
+        {
+            self.binder.shift_in(1);
+            let result = t.try_super_fold_with(self);
+            self.binder.shift_out(1);
+            result
         }
 
-        fn try_fold_ty(&mut self, ty: Ty, outer_binder: DebruijnIndex) -> Fallible<Ty> {
-            if let TyKind::Error = ty.kind(Interner) {
-                let index = self.vars;
-                self.vars += 1;
-                Ok(TyKind::BoundVar(BoundVar::new(outer_binder, index)).intern(Interner))
-            } else {
-                ty.try_super_fold_with(self.as_dyn(), outer_binder)
+        fn try_fold_ty(
+            &mut self,
+            t: crate::next_solver::Ty<'db>,
+        ) -> Result<crate::next_solver::Ty<'db>, Self::Error> {
+            if !t.has_type_flags(
+                rustc_type_ir::TypeFlags::HAS_ERROR
+                    | rustc_type_ir::TypeFlags::HAS_TY_INFER
+                    | rustc_type_ir::TypeFlags::HAS_CT_INFER
+                    | rustc_type_ir::TypeFlags::HAS_RE_INFER,
+            ) {
+                return Ok(t);
+            }
+
+            #[cfg(debug_assertions)]
+            let error = || Err(());
+            #[cfg(not(debug_assertions))]
+            let error = || Ok(crate::next_solver::Ty::new_error(self.interner, ErrorGuaranteed));
+
+            match t.kind() {
+                crate::next_solver::TyKind::Error(_) => {
+                    let var = rustc_type_ir::BoundVar::from_usize(self.vars.len());
+                    self.vars.push(crate::next_solver::CanonicalVarKind::Ty {
+                        ui: rustc_type_ir::UniverseIndex::ZERO,
+                        sub_root: var,
+                    });
+                    Ok(crate::next_solver::Ty::new_bound(
+                        self.interner,
+                        self.binder,
+                        crate::next_solver::BoundTy {
+                            var,
+                            kind: crate::next_solver::BoundTyKind::Anon,
+                        },
+                    ))
+                }
+                crate::next_solver::TyKind::Infer(_) => error(),
+                crate::next_solver::TyKind::Bound(index, _) if index > self.binder => error(),
+                _ => t.try_super_fold_with(self),
             }
         }
 
-        fn try_fold_inference_ty(
+        fn try_fold_const(
             &mut self,
-            _var: InferenceVar,
-            _kind: TyVariableKind,
-            _outer_binder: DebruijnIndex,
-        ) -> Fallible<Ty> {
-            if cfg!(debug_assertions) {
-                // we don't want to just panic here, because then the error message
-                // won't contain the whole thing, which would not be very helpful
-                Err(NoSolution)
-            } else {
-                Ok(TyKind::Error.intern(Interner))
+            ct: crate::next_solver::Const<'db>,
+        ) -> Result<crate::next_solver::Const<'db>, Self::Error> {
+            if !ct.has_type_flags(
+                rustc_type_ir::TypeFlags::HAS_ERROR
+                    | rustc_type_ir::TypeFlags::HAS_TY_INFER
+                    | rustc_type_ir::TypeFlags::HAS_CT_INFER
+                    | rustc_type_ir::TypeFlags::HAS_RE_INFER,
+            ) {
+                return Ok(ct);
+            }
+
+            #[cfg(debug_assertions)]
+            let error = || Err(());
+            #[cfg(not(debug_assertions))]
+            let error = || Ok(crate::next_solver::Const::error(self.interner));
+
+            match ct.kind() {
+                crate::next_solver::ConstKind::Error(_) => {
+                    let var = rustc_type_ir::BoundVar::from_usize(self.vars.len());
+                    self.vars.push(crate::next_solver::CanonicalVarKind::Const(
+                        rustc_type_ir::UniverseIndex::ZERO,
+                    ));
+                    Ok(crate::next_solver::Const::new_bound(
+                        self.interner,
+                        self.binder,
+                        crate::next_solver::BoundConst { var },
+                    ))
+                }
+                crate::next_solver::ConstKind::Infer(_) => error(),
+                crate::next_solver::ConstKind::Bound(index, _) if index > self.binder => error(),
+                _ => ct.try_super_fold_with(self),
             }
         }
 
-        fn try_fold_free_var_ty(
+        fn try_fold_region(
             &mut self,
-            _bound_var: BoundVar,
-            _outer_binder: DebruijnIndex,
-        ) -> Fallible<Ty> {
-            if cfg!(debug_assertions) {
-                // we don't want to just panic here, because then the error message
-                // won't contain the whole thing, which would not be very helpful
-                Err(NoSolution)
-            } else {
-                Ok(TyKind::Error.intern(Interner))
+            region: crate::next_solver::Region<'db>,
+        ) -> Result<crate::next_solver::Region<'db>, Self::Error> {
+            #[cfg(debug_assertions)]
+            let error = || Err(());
+            #[cfg(not(debug_assertions))]
+            let error = || Ok(crate::next_solver::Region::error(self.interner));
+
+            match region.kind() {
+                crate::next_solver::RegionKind::ReError(_) => {
+                    let var = rustc_type_ir::BoundVar::from_usize(self.vars.len());
+                    self.vars.push(crate::next_solver::CanonicalVarKind::Region(
+                        rustc_type_ir::UniverseIndex::ZERO,
+                    ));
+                    Ok(crate::next_solver::Region::new_bound(
+                        self.interner,
+                        self.binder,
+                        crate::next_solver::BoundRegion {
+                            var,
+                            kind: crate::next_solver::BoundRegionKind::Anon,
+                        },
+                    ))
+                }
+                crate::next_solver::RegionKind::ReVar(_) => error(),
+                crate::next_solver::RegionKind::ReBound(index, _) if index > self.binder => error(),
+                _ => Ok(region),
             }
         }
-
-        fn try_fold_inference_const(
-            &mut self,
-            ty: Ty,
-            _var: InferenceVar,
-            _outer_binder: DebruijnIndex,
-        ) -> Fallible<Const> {
-            if cfg!(debug_assertions) {
-                Err(NoSolution)
-            } else {
-                let interner = DbInterner::conjure();
-                Ok(unknown_const(ty.to_nextsolver(interner)).to_chalk(interner))
-            }
-        }
-
-        fn try_fold_free_var_const(
-            &mut self,
-            ty: Ty,
-            _bound_var: BoundVar,
-            _outer_binder: DebruijnIndex,
-        ) -> Fallible<Const> {
-            if cfg!(debug_assertions) {
-                Err(NoSolution)
-            } else {
-                let interner = DbInterner::conjure();
-                Ok(unknown_const(ty.to_nextsolver(interner)).to_chalk(interner))
-            }
-        }
-
-        fn try_fold_inference_lifetime(
-            &mut self,
-            _var: InferenceVar,
-            _outer_binder: DebruijnIndex,
-        ) -> Fallible<Lifetime> {
-            if cfg!(debug_assertions) { Err(NoSolution) } else { Ok(error_lifetime()) }
-        }
-
-        fn try_fold_free_var_lifetime(
-            &mut self,
-            _bound_var: BoundVar,
-            _outer_binder: DebruijnIndex,
-        ) -> Fallible<Lifetime> {
-            if cfg!(debug_assertions) { Err(NoSolution) } else { Ok(error_lifetime()) }
-        }
     }
-    let mut error_replacer = ErrorReplacer { vars: 0 };
-    let value = match t.clone().try_fold_with(&mut error_replacer, DebruijnIndex::INNERMOST) {
+
+    let mut error_replacer =
+        ErrorReplacer { vars: Vec::new(), binder: rustc_type_ir::DebruijnIndex::ZERO, interner };
+    let value = match t.clone().try_fold_with(&mut error_replacer) {
         Ok(t) => t,
         Err(_) => panic!("Encountered unbound or inference vars in {t:?}"),
     };
-    let kinds = (0..error_replacer.vars).map(|_| {
-        chalk_ir::CanonicalVarKind::new(
-            chalk_ir::VariableKind::Ty(TyVariableKind::General),
-            chalk_ir::UniverseIndex::ROOT,
-        )
-    });
-    Canonical { value, binders: chalk_ir::CanonicalVarKinds::from_iter(Interner, kinds) }
+    crate::next_solver::Canonical {
+        value,
+        max_universe: rustc_type_ir::UniverseIndex::ZERO,
+        variables: crate::next_solver::CanonicalVars::new_from_iter(interner, error_replacer.vars),
+    }
 }
 
 pub fn callable_sig_from_fn_trait<'db>(
-    self_ty: &Ty,
+    self_ty: crate::next_solver::Ty<'db>,
     trait_env: Arc<TraitEnvironment<'db>>,
     db: &'db dyn HirDatabase,
-) -> Option<(FnTrait, CallableSig)> {
+) -> Option<(FnTrait, crate::next_solver::PolyFnSig<'db>)> {
     let krate = trait_env.krate;
     let fn_once_trait = FnTrait::FnOnce.get_id(db, krate)?;
     let output_assoc_type = fn_once_trait
@@ -857,7 +889,7 @@
     // - Self: FnOnce<?args_ty>
     // - <Self as FnOnce<?args_ty>>::Output == ?ret_ty
     let args_ty = table.next_ty_var();
-    let args = [self_ty.to_nextsolver(table.interner()), args_ty];
+    let args = [self_ty, args_ty];
     let trait_ref = crate::next_solver::TraitRef::new(table.interner(), fn_once_trait.into(), args);
     let projection = crate::next_solver::Ty::new_alias(
         table.interner(),
@@ -880,23 +912,24 @@
                 ))
                 .no_solution()
             {
-                let ret_ty = table.resolve_completely(return_ty).to_chalk(table.interner());
-                let args_ty = table.resolve_completely(args_ty).to_chalk(table.interner());
-                let params = args_ty
-                    .as_tuple()?
-                    .iter(Interner)
-                    .map(|it| it.assert_ty_ref(Interner))
-                    .cloned();
+                let ret_ty = table.resolve_completely(return_ty);
+                let args_ty = table.resolve_completely(args_ty);
+                let crate::next_solver::TyKind::Tuple(params) = args_ty.kind() else {
+                    return None;
+                };
+                let inputs_and_output = crate::next_solver::Tys::new_from_iter(
+                    table.interner(),
+                    params.iter().chain(std::iter::once(ret_ty)),
+                );
 
                 return Some((
                     fn_x,
-                    CallableSig::from_params_and_return(
-                        params,
-                        ret_ty,
-                        false,
-                        Safety::Safe,
-                        FnAbi::RustCall,
-                    ),
+                    crate::next_solver::Binder::dummy(crate::next_solver::FnSig {
+                        inputs_and_output,
+                        c_variadic: false,
+                        safety: crate::next_solver::abi::Safety::Safe,
+                        abi: FnAbi::RustCall,
+                    }),
                 ));
             }
         }
@@ -906,74 +939,43 @@
     }
 }
 
-struct PlaceholderCollector<'db> {
-    db: &'db dyn HirDatabase,
-    placeholders: FxHashSet<TypeOrConstParamId>,
+struct ParamCollector {
+    params: FxHashSet<TypeOrConstParamId>,
 }
 
-impl PlaceholderCollector<'_> {
-    fn collect(&mut self, idx: PlaceholderIndex) {
-        let id = from_placeholder_idx(self.db, idx).0;
-        self.placeholders.insert(id);
-    }
-}
+impl<'db> rustc_type_ir::TypeVisitor<DbInterner<'db>> for ParamCollector {
+    type Result = ();
 
-impl TypeVisitor<Interner> for PlaceholderCollector<'_> {
-    type BreakTy = ();
-
-    fn as_dyn(&mut self) -> &mut dyn TypeVisitor<Interner, BreakTy = Self::BreakTy> {
-        self
-    }
-
-    fn interner(&self) -> Interner {
-        Interner
-    }
-
-    fn visit_ty(
-        &mut self,
-        ty: &Ty,
-        outer_binder: DebruijnIndex,
-    ) -> std::ops::ControlFlow<Self::BreakTy> {
-        let has_placeholder_bits = TypeFlags::HAS_TY_PLACEHOLDER | TypeFlags::HAS_CT_PLACEHOLDER;
-        let chalk_ir::TyData { kind, flags } = ty.data(Interner);
-
-        if let TyKind::Placeholder(idx) = kind {
-            self.collect(*idx);
-        } else if flags.intersects(has_placeholder_bits) {
-            return ty.super_visit_with(self, outer_binder);
-        } else {
-            // Fast path: don't visit inner types (e.g. generic arguments) when `flags` indicate
-            // that there are no placeholders.
+    fn visit_ty(&mut self, ty: crate::next_solver::Ty<'db>) -> Self::Result {
+        if let crate::next_solver::TyKind::Param(param) = ty.kind() {
+            self.params.insert(param.id.into());
         }
 
-        std::ops::ControlFlow::Continue(())
+        ty.super_visit_with(self);
     }
 
-    fn visit_const(
-        &mut self,
-        constant: &chalk_ir::Const<Interner>,
-        _outer_binder: DebruijnIndex,
-    ) -> std::ops::ControlFlow<Self::BreakTy> {
-        if let chalk_ir::ConstValue::Placeholder(idx) = constant.data(Interner).value {
-            self.collect(idx);
+    fn visit_const(&mut self, konst: crate::next_solver::Const<'db>) -> Self::Result {
+        if let crate::next_solver::ConstKind::Param(param) = konst.kind() {
+            self.params.insert(param.id.into());
         }
-        std::ops::ControlFlow::Continue(())
+
+        konst.super_visit_with(self);
     }
 }
 
-/// Returns unique placeholders for types and consts contained in `value`.
-pub fn collect_placeholders<T>(value: &T, db: &dyn HirDatabase) -> Vec<TypeOrConstParamId>
+/// Returns unique params for types and consts contained in `value`.
+pub fn collect_params<'db, T>(value: &T) -> Vec<TypeOrConstParamId>
 where
-    T: ?Sized + TypeVisitable<Interner>,
+    T: ?Sized + rustc_type_ir::TypeVisitable<DbInterner<'db>>,
 {
-    let mut collector = PlaceholderCollector { db, placeholders: FxHashSet::default() };
-    _ = value.visit_with(&mut collector, DebruijnIndex::INNERMOST);
-    collector.placeholders.into_iter().collect()
+    let mut collector = ParamCollector { params: FxHashSet::default() };
+    value.visit_with(&mut collector);
+    Vec::from_iter(collector.params)
 }
 
-pub fn known_const_to_ast(
-    konst: &Const,
-    db: &dyn HirDatabase,
+pub fn known_const_to_ast<'db>(
+    konst: crate::next_solver::Const<'db>,
+    db: &'db dyn HirDatabase,
     display_target: DisplayTarget,
 ) -> Option<ConstArg> {
     Some(make::expr_const_value(konst.display(db, display_target).to_string().as_str()))
diff --git a/crates/hir-ty/src/lower.rs b/crates/hir-ty/src/lower.rs
index ee7b0cd..b18d713 100644
--- a/crates/hir-ty/src/lower.rs
+++ b/crates/hir-ty/src/lower.rs
@@ -86,7 +86,7 @@
 pub(crate) struct PathDiagnosticCallbackData(pub(crate) TypeRefId);
 
 #[derive(Debug, Clone)]
-pub enum LifetimeElisionKind {
+pub(crate) enum LifetimeElisionKind {
     /// Create a new anonymous lifetime parameter and reference it.
     ///
     /// If `report_in_path`, report an error when encountering lifetime elision in a path:
@@ -111,14 +111,6 @@
     /// error on default object bounds (e.g., `Box<dyn Foo>`).
     AnonymousReportError,
 
-    /// Resolves elided lifetimes to `'static` if there are no other lifetimes in scope,
-    /// otherwise give a warning that the previous behavior of introducing a new early-bound
-    /// lifetime is a bug and will be removed (if `only_lint` is enabled).
-    StaticIfNoLifetimeInScope { only_lint: bool },
-
-    /// Signal we cannot find which should be the anonymous lifetime.
-    ElisionFailure,
-
     /// Infer all elided lifetimes.
     Infer,
 }
@@ -132,7 +124,7 @@
 }
 
 #[derive(Debug)]
-pub struct TyLoweringContext<'db> {
+pub(crate) struct TyLoweringContext<'db> {
     pub db: &'db dyn HirDatabase,
     resolver: &'db Resolver<'db>,
     store: &'db ExpressionStore,
@@ -152,7 +144,7 @@
 }
 
 impl<'db> TyLoweringContext<'db> {
-    pub fn new(
+    pub(crate) fn new(
         db: &'db dyn HirDatabase,
         resolver: &'db Resolver<'db>,
         store: &'db ExpressionStore,
@@ -177,7 +169,7 @@
         }
     }
 
-    pub fn with_debruijn<T>(
+    pub(crate) fn with_debruijn<T>(
         &mut self,
         debruijn: DebruijnIndex,
         f: impl FnOnce(&mut TyLoweringContext<'_>) -> T,
@@ -188,7 +180,7 @@
         result
     }
 
-    pub fn with_shifted_in<T>(
+    pub(crate) fn with_shifted_in<T>(
         &mut self,
         debruijn: DebruijnIndex,
         f: impl FnOnce(&mut TyLoweringContext<'_>) -> T,
@@ -207,25 +199,15 @@
         result
     }
 
-    pub fn with_impl_trait_mode(self, impl_trait_mode: ImplTraitLoweringMode) -> Self {
+    pub(crate) fn with_impl_trait_mode(self, impl_trait_mode: ImplTraitLoweringMode) -> Self {
         Self { impl_trait_mode: ImplTraitLoweringState::new(impl_trait_mode), ..self }
     }
 
-    pub fn with_type_param_mode(self, type_param_mode: ParamLoweringMode) -> Self {
+    pub(crate) fn with_type_param_mode(self, type_param_mode: ParamLoweringMode) -> Self {
         Self { type_param_mode, ..self }
     }
 
-    pub fn impl_trait_mode(&mut self, impl_trait_mode: ImplTraitLoweringMode) -> &mut Self {
-        self.impl_trait_mode = ImplTraitLoweringState::new(impl_trait_mode);
-        self
-    }
-
-    pub fn type_param_mode(&mut self, type_param_mode: ParamLoweringMode) -> &mut Self {
-        self.type_param_mode = type_param_mode;
-        self
-    }
-
-    pub fn push_diagnostic(&mut self, type_ref: TypeRefId, kind: TyLoweringDiagnosticKind) {
+    pub(crate) fn push_diagnostic(&mut self, type_ref: TypeRefId, kind: TyLoweringDiagnosticKind) {
         self.diagnostics.push(TyLoweringDiagnostic { source: type_ref, kind });
     }
 }
@@ -249,11 +231,11 @@
 }
 
 impl<'db> TyLoweringContext<'db> {
-    pub fn lower_ty(&mut self, type_ref: TypeRefId) -> Ty {
+    pub(crate) fn lower_ty(&mut self, type_ref: TypeRefId) -> Ty {
         self.lower_ty_ext(type_ref).0
     }
 
-    pub fn lower_const(&mut self, const_ref: &ConstRef, const_type: Ty) -> Const {
+    pub(crate) fn lower_const(&mut self, const_ref: &ConstRef, const_type: Ty) -> Const {
         let const_ref = &self.store[const_ref.expr];
         match const_ref {
             hir_def::hir::Expr::Path(path) => path_to_const(
@@ -308,7 +290,7 @@
         }
     }
 
-    pub fn lower_path_as_const(&mut self, path: &Path, const_type: Ty) -> Const {
+    pub(crate) fn lower_path_as_const(&mut self, path: &Path, const_type: Ty) -> Const {
         path_to_const(
             self.db,
             self.resolver,
@@ -325,7 +307,7 @@
         self.generics.get_or_init(|| generics(self.db, self.def))
     }
 
-    pub fn lower_ty_ext(&mut self, type_ref_id: TypeRefId) -> (Ty, Option<TypeNs>) {
+    pub(crate) fn lower_ty_ext(&mut self, type_ref_id: TypeRefId) -> (Ty, Option<TypeNs>) {
         let mut res = None;
         let type_ref = &self.store[type_ref_id];
         let ty = match type_ref {
@@ -774,7 +756,7 @@
         ImplTrait { bounds: crate::make_single_type_binders(predicates) }
     }
 
-    pub fn lower_lifetime(&self, lifetime: LifetimeRefId) -> Lifetime {
+    pub(crate) fn lower_lifetime(&self, lifetime: LifetimeRefId) -> Lifetime {
         match self.resolver.resolve_lifetime(&self.store[lifetime]) {
             Some(resolution) => match resolution {
                 LifetimeNs::Static => static_lifetime(),
diff --git a/crates/hir-ty/src/lower/path.rs b/crates/hir-ty/src/lower/path.rs
index f988b616..09a256a 100644
--- a/crates/hir-ty/src/lower/path.rs
+++ b/crates/hir-ty/src/lower/path.rs
@@ -21,18 +21,17 @@
 use crate::{
     AliasEq, AliasTy, GenericArgsProhibitedReason, ImplTraitLoweringMode, IncorrectGenericsLenKind,
     Interner, ParamLoweringMode, PathGenericsSource, PathLoweringDiagnostic, ProjectionTy,
-    QuantifiedWhereClause, Substitution, TraitRef, Ty, TyBuilder, TyDefId, TyKind,
-    TyLoweringContext, WhereClause,
+    QuantifiedWhereClause, Substitution, TraitRef, Ty, TyBuilder, TyDefId, TyKind, WhereClause,
     consteval_chalk::{unknown_const, unknown_const_as_generic},
     db::HirDatabase,
     error_lifetime,
     generics::{Generics, generics},
-    lower::{LifetimeElisionKind, named_associated_type_shorthand_candidates},
+    lower::{LifetimeElisionKind, TyLoweringContext, named_associated_type_shorthand_candidates},
     next_solver::{
         DbInterner,
         mapping::{ChalkToNextSolver, NextSolverToChalk},
     },
-    static_lifetime, to_assoc_type_id, to_chalk_trait_id, to_placeholder_idx,
+    to_assoc_type_id, to_chalk_trait_id, to_placeholder_idx,
     utils::associated_type_by_name_including_super_traits,
 };
 
@@ -650,14 +649,6 @@
                 });
             }
 
-            fn report_elision_failure(&mut self, def: GenericDefId, expected_count: u32) {
-                self.ctx.on_diagnostic(PathLoweringDiagnostic::ElisionFailure {
-                    generics_source: self.generics_source,
-                    def,
-                    expected_count,
-                });
-            }
-
             fn report_missing_lifetime(&mut self, def: GenericDefId, expected_count: u32) {
                 self.ctx.on_diagnostic(PathLoweringDiagnostic::MissingLifetime {
                     generics_source: self.generics_source,
@@ -810,8 +801,6 @@
         hard_error: bool,
     );
 
-    fn report_elision_failure(&mut self, def: GenericDefId, expected_count: u32);
-
     fn report_missing_lifetime(&mut self, def: GenericDefId, expected_count: u32);
 
     fn report_len_mismatch(
@@ -884,13 +873,6 @@
                 ctx.report_missing_lifetime(def, lifetime_args_len as u32);
                 had_error = true
             }
-            LifetimeElisionKind::ElisionFailure => {
-                ctx.report_elision_failure(def, lifetime_args_len as u32);
-                had_error = true;
-            }
-            LifetimeElisionKind::StaticIfNoLifetimeInScope { only_lint: _ } => {
-                // FIXME: Check there are other lifetimes in scope, and error/lint.
-            }
             LifetimeElisionKind::Elided(_) => {
                 ctx.report_elided_lifetimes_in_path(def, lifetime_args_len as u32, false);
             }
@@ -1099,15 +1081,11 @@
                 // If there are fewer arguments than parameters, it means we're inferring the remaining arguments.
                 let param = if let GenericParamId::LifetimeParamId(_) = param_id {
                     match &lifetime_elision {
-                        LifetimeElisionKind::ElisionFailure
-                        | LifetimeElisionKind::AnonymousCreateParameter { report_in_path: true }
+                        LifetimeElisionKind::AnonymousCreateParameter { report_in_path: true }
                         | LifetimeElisionKind::AnonymousReportError => {
                             assert!(had_count_error);
                             ctx.inferred_kind(def, param_id, param, infer_args, &substs)
                         }
-                        LifetimeElisionKind::StaticIfNoLifetimeInScope { only_lint: _ } => {
-                            static_lifetime().cast(Interner)
-                        }
                         LifetimeElisionKind::Elided(lifetime) => lifetime.clone().cast(Interner),
                         LifetimeElisionKind::AnonymousCreateParameter { report_in_path: false }
                         | LifetimeElisionKind::Infer => {
diff --git a/crates/hir-ty/src/lower_nextsolver.rs b/crates/hir-ty/src/lower_nextsolver.rs
index 5a0bcce..abca6b6 100644
--- a/crates/hir-ty/src/lower_nextsolver.rs
+++ b/crates/hir-ty/src/lower_nextsolver.rs
@@ -40,7 +40,7 @@
 use hir_expand::name::Name;
 use intern::{Symbol, sym};
 use la_arena::{Arena, ArenaMap, Idx};
-use path::{PathDiagnosticCallback, PathLoweringContext, builtin};
+use path::{PathDiagnosticCallback, PathLoweringContext};
 use rustc_ast_ir::Mutability;
 use rustc_hash::FxHashSet;
 use rustc_pattern_analysis::Captures;
@@ -105,7 +105,7 @@
 }
 
 #[derive(Debug, Clone)]
-pub(crate) enum LifetimeElisionKind<'db> {
+pub enum LifetimeElisionKind<'db> {
     /// Create a new anonymous lifetime parameter and reference it.
     ///
     /// If `report_in_path`, report an error when encountering lifetime elision in a path:
@@ -174,7 +174,7 @@
 }
 
 #[derive(Debug)]
-pub(crate) struct TyLoweringContext<'db, 'a> {
+pub struct TyLoweringContext<'db, 'a> {
     pub db: &'db dyn HirDatabase,
     interner: DbInterner<'db>,
     resolver: &'a Resolver<'db>,
@@ -192,7 +192,7 @@
 }
 
 impl<'db, 'a> TyLoweringContext<'db, 'a> {
-    pub(crate) fn new(
+    pub fn new(
         db: &'db dyn HirDatabase,
         resolver: &'a Resolver<'db>,
         store: &'a ExpressionStore,
@@ -271,7 +271,7 @@
 }
 
 impl<'db, 'a> TyLoweringContext<'db, 'a> {
-    pub(crate) fn lower_ty(&mut self, type_ref: TypeRefId) -> Ty<'db> {
+    pub fn lower_ty(&mut self, type_ref: TypeRefId) -> Ty<'db> {
         self.lower_ty_ext(type_ref).0
     }
 
@@ -361,7 +361,7 @@
     }
 
     #[tracing::instrument(skip(self), ret)]
-    pub(crate) fn lower_ty_ext(&mut self, type_ref_id: TypeRefId) -> (Ty<'db>, Option<TypeNs>) {
+    pub fn lower_ty_ext(&mut self, type_ref_id: TypeRefId) -> (Ty<'db>, Option<TypeNs>) {
         let interner = self.interner;
         let mut res = None;
         let type_ref = &self.store[type_ref_id];
@@ -1013,7 +1013,7 @@
 pub(crate) fn ty_query<'db>(db: &'db dyn HirDatabase, def: TyDefId) -> EarlyBinder<'db, Ty<'db>> {
     let interner = DbInterner::new_with(db, None, None);
     match def {
-        TyDefId::BuiltinType(it) => EarlyBinder::bind(builtin(interner, it)),
+        TyDefId::BuiltinType(it) => EarlyBinder::bind(Ty::from_builtin_type(interner, it)),
         TyDefId::AdtId(it) => EarlyBinder::bind(Ty::new_adt(
             interner,
             it,
@@ -1401,6 +1401,7 @@
 pub struct GenericPredicates<'db>(Option<Arc<[Clause<'db>]>>);
 
 impl<'db> GenericPredicates<'db> {
+    #[inline]
     pub fn instantiate(
         &self,
         interner: DbInterner<'db>,
@@ -1410,6 +1411,11 @@
             .as_ref()
             .map(|it| EarlyBinder::bind(it.iter().copied()).iter_instantiated(interner, args))
     }
+
+    #[inline]
+    pub fn instantiate_identity(&self) -> Option<impl Iterator<Item = Clause<'db>>> {
+        self.0.as_ref().map(|it| it.iter().copied())
+    }
 }
 
 impl<'db> ops::Deref for GenericPredicates<'db> {
@@ -1458,8 +1464,7 @@
         for pred in maybe_parent_generics.where_predicates() {
             for pred in ctx.lower_where_predicate(pred, false, &generics, PredicateFilter::All) {
                 if let rustc_type_ir::ClauseKind::Trait(tr) = pred.kind().skip_binder() {
-                    traits_in_scope
-                        .push((convert_ty_for_result(interner, tr.self_ty()), tr.def_id().0));
+                    traits_in_scope.push((tr.self_ty(), tr.def_id().0));
                 }
                 clauses.push(pred);
             }
diff --git a/crates/hir-ty/src/lower_nextsolver/path.rs b/crates/hir-ty/src/lower_nextsolver/path.rs
index b003cc5..ef2c392 100644
--- a/crates/hir-ty/src/lower_nextsolver/path.rs
+++ b/crates/hir-ty/src/lower_nextsolver/path.rs
@@ -550,7 +550,9 @@
 
     fn lower_path_inner(&mut self, typeable: TyDefId, infer_args: bool) -> Ty<'db> {
         let generic_def = match typeable {
-            TyDefId::BuiltinType(builtinty) => return builtin(self.ctx.interner, builtinty),
+            TyDefId::BuiltinType(builtinty) => {
+                return Ty::from_builtin_type(self.ctx.interner, builtinty);
+            }
             TyDefId::AdtId(it) => it.into(),
             TyDefId::TypeAliasId(it) => it.into(),
         };
@@ -1350,42 +1352,3 @@
         }),
     )
 }
-
-pub(crate) fn builtin<'db>(interner: DbInterner<'db>, builtin: BuiltinType) -> Ty<'db> {
-    match builtin {
-        BuiltinType::Char => Ty::new(interner, rustc_type_ir::TyKind::Char),
-        BuiltinType::Bool => Ty::new_bool(interner),
-        BuiltinType::Str => Ty::new(interner, rustc_type_ir::TyKind::Str),
-        BuiltinType::Int(t) => {
-            let int_ty = match primitive::int_ty_from_builtin(t) {
-                chalk_ir::IntTy::Isize => rustc_type_ir::IntTy::Isize,
-                chalk_ir::IntTy::I8 => rustc_type_ir::IntTy::I8,
-                chalk_ir::IntTy::I16 => rustc_type_ir::IntTy::I16,
-                chalk_ir::IntTy::I32 => rustc_type_ir::IntTy::I32,
-                chalk_ir::IntTy::I64 => rustc_type_ir::IntTy::I64,
-                chalk_ir::IntTy::I128 => rustc_type_ir::IntTy::I128,
-            };
-            Ty::new_int(interner, int_ty)
-        }
-        BuiltinType::Uint(t) => {
-            let uint_ty = match primitive::uint_ty_from_builtin(t) {
-                chalk_ir::UintTy::Usize => rustc_type_ir::UintTy::Usize,
-                chalk_ir::UintTy::U8 => rustc_type_ir::UintTy::U8,
-                chalk_ir::UintTy::U16 => rustc_type_ir::UintTy::U16,
-                chalk_ir::UintTy::U32 => rustc_type_ir::UintTy::U32,
-                chalk_ir::UintTy::U64 => rustc_type_ir::UintTy::U64,
-                chalk_ir::UintTy::U128 => rustc_type_ir::UintTy::U128,
-            };
-            Ty::new_uint(interner, uint_ty)
-        }
-        BuiltinType::Float(t) => {
-            let float_ty = match primitive::float_ty_from_builtin(t) {
-                chalk_ir::FloatTy::F16 => rustc_type_ir::FloatTy::F16,
-                chalk_ir::FloatTy::F32 => rustc_type_ir::FloatTy::F32,
-                chalk_ir::FloatTy::F64 => rustc_type_ir::FloatTy::F64,
-                chalk_ir::FloatTy::F128 => rustc_type_ir::FloatTy::F128,
-            };
-            Ty::new_float(interner, float_ty)
-        }
-    }
-}
diff --git a/crates/hir-ty/src/method_resolution.rs b/crates/hir-ty/src/method_resolution.rs
index 110fee8..98c8f3e 100644
--- a/crates/hir-ty/src/method_resolution.rs
+++ b/crates/hir-ty/src/method_resolution.rs
@@ -5,7 +5,6 @@
 use std::ops::ControlFlow;
 
 use base_db::Crate;
-use chalk_ir::{UniverseIndex, WithKind, cast::Cast};
 use hir_def::{
     AdtId, AssocItemId, BlockId, ConstId, FunctionId, HasModule, ImplId, ItemContainerId, Lookup,
     ModuleId, TraitId, TypeAliasId,
@@ -29,8 +28,7 @@
 use crate::next_solver::infer::InferCtxt;
 use crate::next_solver::infer::select::ImplSource;
 use crate::{
-    CanonicalVarKinds, DebruijnIndex, GenericArgData, InEnvironment, Interner, TraitEnvironment,
-    TyBuilder, VariableKind,
+    TraitEnvironment, TyBuilder,
     autoderef::{self, AutoderefKind},
     db::HirDatabase,
     infer::{Adjust, Adjustment, OverloadedDeref, PointerCast, unify::InferenceTable},
@@ -42,7 +40,6 @@
             DbInternerInferExt, DefineOpaqueTypes,
             traits::{Obligation, ObligationCause, PredicateObligation},
         },
-        mapping::NextSolverToChalk,
         obligation_ctxt::ObligationCtxt,
     },
     traits::next_trait_solve_canonical_in_ctxt,
@@ -1390,9 +1387,8 @@
     match self_ty.kind() {
         TyKind::Param(_) => {
             let env = table.trait_env.clone();
-            let traits = env
-                .traits_in_scope_from_clauses(self_ty.to_chalk(table.interner()))
-                .flat_map(|t| all_super_traits(db, t));
+            let traits =
+                env.traits_in_scope_from_clauses(self_ty).flat_map(|t| all_super_traits(db, t));
             iterate_inherent_trait_methods(
                 self_ty,
                 table,
@@ -1755,50 +1751,6 @@
     })
 }
 
-pub fn implements_trait_unique<'db>(
-    ty: &crate::Canonical<crate::Ty>,
-    db: &'db dyn HirDatabase,
-    env: &TraitEnvironment<'db>,
-    trait_: TraitId,
-) -> bool {
-    let goal = generic_implements_goal(db, env, trait_, ty);
-    db.trait_solve(env.krate, env.block, goal.cast(Interner)).certain()
-}
-
-/// This creates Substs for a trait with the given Self type and type variables
-/// for all other parameters, to query next solver with it.
-#[tracing::instrument(skip_all)]
-fn generic_implements_goal<'db>(
-    db: &'db dyn HirDatabase,
-    env: &TraitEnvironment<'db>,
-    trait_: TraitId,
-    self_ty: &crate::Canonical<crate::Ty>,
-) -> crate::Canonical<crate::InEnvironment<crate::DomainGoal>> {
-    let binders = self_ty.binders.interned();
-    let trait_ref = TyBuilder::trait_ref(db, trait_)
-        .push(self_ty.value.clone())
-        .fill_with_bound_vars(DebruijnIndex::INNERMOST, binders.len())
-        .build();
-
-    let kinds =
-        binders.iter().cloned().chain(trait_ref.substitution.iter(Interner).skip(1).map(|it| {
-            let vk = match it.data(Interner) {
-                GenericArgData::Ty(_) => VariableKind::Ty(chalk_ir::TyVariableKind::General),
-                GenericArgData::Lifetime(_) => VariableKind::Lifetime,
-                GenericArgData::Const(c) => VariableKind::Const(c.data(Interner).ty.clone()),
-            };
-            WithKind::new(vk, UniverseIndex::ROOT)
-        }));
-    let binders = CanonicalVarKinds::from_iter(Interner, kinds);
-
-    let obligation = trait_ref.cast(Interner);
-    let value = InEnvironment::new(
-        &env.env.to_chalk(DbInterner::new_with(db, Some(env.krate), env.block)),
-        obligation,
-    );
-    crate::Canonical { binders, value }
-}
-
 /// This creates Substs for a trait with the given Self type and type variables
 /// for all other parameters, to query the trait solver with it.
 #[tracing::instrument(skip_all)]
diff --git a/crates/hir-ty/src/next_solver/consts.rs b/crates/hir-ty/src/next_solver/consts.rs
index da86fa3..2fc1fc4 100644
--- a/crates/hir-ty/src/next_solver/consts.rs
+++ b/crates/hir-ty/src/next_solver/consts.rs
@@ -7,8 +7,8 @@
 use macros::{TypeFoldable, TypeVisitable};
 use rustc_ast_ir::{try_visit, visit::VisitorResult};
 use rustc_type_ir::{
-    BoundVar, FlagComputation, Flags, TypeFoldable, TypeSuperFoldable, TypeSuperVisitable,
-    TypeVisitable, TypeVisitableExt, WithCachedTypeInfo,
+    BoundVar, DebruijnIndex, FlagComputation, Flags, TypeFoldable, TypeSuperFoldable,
+    TypeSuperVisitable, TypeVisitable, TypeVisitableExt, WithCachedTypeInfo,
     inherent::{IntoKind, ParamEnv as _, PlaceholderLike, SliceLike},
     relate::Relate,
 };
@@ -62,6 +62,10 @@
         Const::new(interner, ConstKind::Placeholder(placeholder))
     }
 
+    pub fn new_bound(interner: DbInterner<'db>, index: DebruijnIndex, bound: BoundConst) -> Self {
+        Const::new(interner, ConstKind::Bound(index, bound))
+    }
+
     pub fn new_valtree(
         interner: DbInterner<'db>,
         ty: Ty<'db>,
@@ -159,11 +163,11 @@
 /// Represents a typed, fully evaluated constant.
 #[derive(Debug, Copy, Clone, Eq, PartialEq, Hash, TypeFoldable, TypeVisitable)]
 pub struct ValueConst<'db> {
-    pub(crate) ty: Ty<'db>,
+    pub ty: Ty<'db>,
     // FIXME: Should we ignore this for TypeVisitable, TypeFoldable?
     #[type_visitable(ignore)]
     #[type_foldable(identity)]
-    pub(crate) value: Valtree<'db>,
+    pub value: Valtree<'db>,
 }
 
 impl<'db> ValueConst<'db> {
diff --git a/crates/hir-ty/src/next_solver/def_id.rs b/crates/hir-ty/src/next_solver/def_id.rs
index 3e4c417..789be3b 100644
--- a/crates/hir-ty/src/next_solver/def_id.rs
+++ b/crates/hir-ty/src/next_solver/def_id.rs
@@ -158,6 +158,15 @@
             _ => panic!("expected opaque type, found {self:?}"),
         }
     }
+
+    #[inline]
+    #[track_caller]
+    pub fn expect_type_alias(self) -> TypeAliasId {
+        match self {
+            SolverDefId::TypeAliasId(it) => it,
+            _ => panic!("expected type alias, found {self:?}"),
+        }
+    }
 }
 
 impl<'db> inherent::DefId<DbInterner<'db>> for SolverDefId {
diff --git a/crates/hir-ty/src/next_solver/generic_arg.rs b/crates/hir-ty/src/next_solver/generic_arg.rs
index 79527da..38293c4 100644
--- a/crates/hir-ty/src/next_solver/generic_arg.rs
+++ b/crates/hir-ty/src/next_solver/generic_arg.rs
@@ -69,6 +69,14 @@
             _ => None,
         }
     }
+
+    pub fn error_from_id(interner: DbInterner<'db>, id: GenericParamId) -> GenericArg<'db> {
+        match id {
+            GenericParamId::TypeParamId(_) => Ty::new_error(interner, ErrorGuaranteed).into(),
+            GenericParamId::ConstParamId(_) => Const::error(interner).into(),
+            GenericParamId::LifetimeParamId(_) => Region::error(interner).into(),
+        }
+    }
 }
 
 impl<'db> From<Term<'db>> for GenericArg<'db> {
@@ -192,6 +200,13 @@
         interner.mk_args(&args)
     }
 
+    /// Creates an all-error `GenericArgs`.
+    pub fn error_for_item(interner: DbInterner<'db>, def_id: SolverDefId) -> GenericArgs<'db> {
+        GenericArgs::for_item(interner, def_id, |_, _, id, _| {
+            GenericArg::error_from_id(interner, id)
+        })
+    }
+
     /// Like `for_item`, but prefers the default of a parameter if it has any.
     pub fn for_item_with_defaults<F>(
         interner: DbInterner<'db>,
diff --git a/crates/hir-ty/src/next_solver/interner.rs b/crates/hir-ty/src/next_solver/interner.rs
index cd16675..3fd8e7b 100644
--- a/crates/hir-ty/src/next_solver/interner.rs
+++ b/crates/hir-ty/src/next_solver/interner.rs
@@ -304,6 +304,7 @@
         DbInterner { db, krate, block }
     }
 
+    #[inline]
     pub fn db(&self) -> &'db dyn HirDatabase {
         self.db
     }
@@ -1952,7 +1953,6 @@
         false
     }
 
-    // FIXME(next-solver): Make this a query? Can this make cycles?
     fn impl_specializes(
         self,
         specializing_impl_def_id: Self::ImplId,
diff --git a/crates/hir-ty/src/next_solver/region.rs b/crates/hir-ty/src/next_solver/region.rs
index 13c333b..5e7eb75 100644
--- a/crates/hir-ty/src/next_solver/region.rs
+++ b/crates/hir-ty/src/next_solver/region.rs
@@ -3,7 +3,8 @@
 use hir_def::LifetimeParamId;
 use intern::{Interned, Symbol};
 use rustc_type_ir::{
-    BoundVar, Flags, INNERMOST, RegionVid, TypeFlags, TypeFoldable, TypeVisitable, VisitorResult,
+    BoundVar, DebruijnIndex, Flags, INNERMOST, RegionVid, TypeFlags, TypeFoldable, TypeVisitable,
+    VisitorResult,
     inherent::{IntoKind, PlaceholderLike, SliceLike},
     relate::Relate,
 };
@@ -62,6 +63,14 @@
         Region::new(interner, RegionKind::ReErased)
     }
 
+    pub fn new_bound(
+        interner: DbInterner<'db>,
+        index: DebruijnIndex,
+        bound: BoundRegion,
+    ) -> Region<'db> {
+        Region::new(interner, RegionKind::ReBound(index, bound))
+    }
+
     pub fn is_placeholder(&self) -> bool {
         matches!(self.inner(), RegionKind::RePlaceholder(..))
     }
diff --git a/crates/hir-ty/src/next_solver/ty.rs b/crates/hir-ty/src/next_solver/ty.rs
index c596912..44b85ab 100644
--- a/crates/hir-ty/src/next_solver/ty.rs
+++ b/crates/hir-ty/src/next_solver/ty.rs
@@ -3,18 +3,22 @@
 use std::iter;
 use std::ops::ControlFlow;
 
-use hir_def::type_ref::Rawness;
-use hir_def::{AdtId, GenericDefId, TypeOrConstParamId, TypeParamId};
+use hir_def::{
+    AdtId, DefWithBodyId, GenericDefId, HasModule, TypeOrConstParamId, TypeParamId,
+    hir::generics::{TypeOrConstParamData, TypeParamProvenance},
+    lang_item::LangItem,
+};
+use hir_def::{TraitId, type_ref::Rawness};
 use intern::{Interned, Symbol, sym};
 use rustc_abi::{Float, Integer, Size};
 use rustc_ast_ir::{Mutability, try_visit, visit::VisitorResult};
 use rustc_type_ir::{
-    BoundVar, ClosureKind, CollectAndApply, FlagComputation, Flags, FloatTy, FloatVid, InferTy,
-    IntTy, IntVid, Interner, TyVid, TypeFoldable, TypeSuperFoldable, TypeSuperVisitable,
-    TypeVisitable, TypeVisitableExt, TypeVisitor, UintTy, WithCachedTypeInfo,
+    AliasTyKind, BoundVar, ClosureKind, CollectAndApply, FlagComputation, Flags, FloatTy, FloatVid,
+    InferTy, IntTy, IntVid, Interner, TyVid, TypeFoldable, TypeSuperFoldable, TypeSuperVisitable,
+    TypeVisitable, TypeVisitableExt, TypeVisitor, UintTy, Upcast, WithCachedTypeInfo,
     inherent::{
-        Abi, AdtDef as _, BoundVarLike, Const as _, GenericArgs as _, IntoKind, ParamLike,
-        PlaceholderLike, Safety as _, SliceLike, Ty as _,
+        Abi, AdtDef as _, BoundExistentialPredicates, BoundVarLike, Const as _, GenericArgs as _,
+        IntoKind, ParamLike, PlaceholderLike, Safety as _, SliceLike, Ty as _,
     },
     relate::Relate,
     solve::SizedTraitKind,
@@ -24,13 +28,14 @@
 use smallvec::SmallVec;
 
 use crate::{
-    FnAbi,
+    FnAbi, ImplTraitId,
     db::HirDatabase,
     interner::InternedWrapperNoDebug,
     next_solver::{
-        AdtDef, Binder, CallableIdWrapper, ClosureIdWrapper, Const, CoroutineIdWrapper, FnSig,
-        GenericArg, PolyFnSig, Region, TypeAliasIdWrapper,
+        AdtDef, Binder, CallableIdWrapper, Clause, ClauseKind, ClosureIdWrapper, Const,
+        CoroutineIdWrapper, FnSig, GenericArg, PolyFnSig, Region, TraitRef, TypeAliasIdWrapper,
         abi::Safety,
+        mapping::ChalkToNextSolver,
         util::{CoroutineArgsExt, IntegerTypeExt},
     },
 };
@@ -409,7 +414,7 @@
 
     pub fn as_reference(self) -> Option<(Ty<'db>, Region<'db>, Mutability)> {
         match self.kind() {
-            TyKind::Ref(lifetime, ty, mutability) => Some((ty, lifetime, mutability)),
+            TyKind::Ref(region, ty, mutability) => Some((ty, region, mutability)),
             _ => None,
         }
     }
@@ -422,6 +427,18 @@
         }
     }
 
+    pub fn as_tuple(self) -> Option<Tys<'db>> {
+        match self.kind() {
+            TyKind::Tuple(tys) => Some(tys),
+            _ => None,
+        }
+    }
+
+    pub fn dyn_trait(self) -> Option<TraitId> {
+        let TyKind::Dynamic(bounds, _) = self.kind() else { return None };
+        Some(bounds.principal_def_id()?.0)
+    }
+
     pub fn strip_references(self) -> Ty<'db> {
         let mut t = self;
         while let TyKind::Ref(_lifetime, ty, _mutability) = t.kind() {
@@ -443,6 +460,176 @@
             interner,
         ))
     }
+
+    pub fn from_builtin_type(
+        interner: DbInterner<'db>,
+        ty: hir_def::builtin_type::BuiltinType,
+    ) -> Ty<'db> {
+        let kind = match ty {
+            hir_def::builtin_type::BuiltinType::Char => TyKind::Char,
+            hir_def::builtin_type::BuiltinType::Bool => TyKind::Bool,
+            hir_def::builtin_type::BuiltinType::Str => TyKind::Str,
+            hir_def::builtin_type::BuiltinType::Int(int) => TyKind::Int(match int {
+                hir_def::builtin_type::BuiltinInt::Isize => rustc_type_ir::IntTy::Isize,
+                hir_def::builtin_type::BuiltinInt::I8 => rustc_type_ir::IntTy::I8,
+                hir_def::builtin_type::BuiltinInt::I16 => rustc_type_ir::IntTy::I16,
+                hir_def::builtin_type::BuiltinInt::I32 => rustc_type_ir::IntTy::I32,
+                hir_def::builtin_type::BuiltinInt::I64 => rustc_type_ir::IntTy::I64,
+                hir_def::builtin_type::BuiltinInt::I128 => rustc_type_ir::IntTy::I128,
+            }),
+            hir_def::builtin_type::BuiltinType::Uint(uint) => TyKind::Uint(match uint {
+                hir_def::builtin_type::BuiltinUint::Usize => rustc_type_ir::UintTy::Usize,
+                hir_def::builtin_type::BuiltinUint::U8 => rustc_type_ir::UintTy::U8,
+                hir_def::builtin_type::BuiltinUint::U16 => rustc_type_ir::UintTy::U16,
+                hir_def::builtin_type::BuiltinUint::U32 => rustc_type_ir::UintTy::U32,
+                hir_def::builtin_type::BuiltinUint::U64 => rustc_type_ir::UintTy::U64,
+                hir_def::builtin_type::BuiltinUint::U128 => rustc_type_ir::UintTy::U128,
+            }),
+            hir_def::builtin_type::BuiltinType::Float(float) => TyKind::Float(match float {
+                hir_def::builtin_type::BuiltinFloat::F16 => rustc_type_ir::FloatTy::F16,
+                hir_def::builtin_type::BuiltinFloat::F32 => rustc_type_ir::FloatTy::F32,
+                hir_def::builtin_type::BuiltinFloat::F64 => rustc_type_ir::FloatTy::F64,
+                hir_def::builtin_type::BuiltinFloat::F128 => rustc_type_ir::FloatTy::F128,
+            }),
+        };
+        Ty::new(interner, kind)
+    }
+
+    pub fn as_builtin(self) -> Option<hir_def::builtin_type::BuiltinType> {
+        let builtin = match self.kind() {
+            TyKind::Char => hir_def::builtin_type::BuiltinType::Char,
+            TyKind::Bool => hir_def::builtin_type::BuiltinType::Bool,
+            TyKind::Str => hir_def::builtin_type::BuiltinType::Str,
+            TyKind::Int(int) => hir_def::builtin_type::BuiltinType::Int(match int {
+                rustc_type_ir::IntTy::Isize => hir_def::builtin_type::BuiltinInt::Isize,
+                rustc_type_ir::IntTy::I8 => hir_def::builtin_type::BuiltinInt::I8,
+                rustc_type_ir::IntTy::I16 => hir_def::builtin_type::BuiltinInt::I16,
+                rustc_type_ir::IntTy::I32 => hir_def::builtin_type::BuiltinInt::I32,
+                rustc_type_ir::IntTy::I64 => hir_def::builtin_type::BuiltinInt::I64,
+                rustc_type_ir::IntTy::I128 => hir_def::builtin_type::BuiltinInt::I128,
+            }),
+            TyKind::Uint(uint) => hir_def::builtin_type::BuiltinType::Uint(match uint {
+                rustc_type_ir::UintTy::Usize => hir_def::builtin_type::BuiltinUint::Usize,
+                rustc_type_ir::UintTy::U8 => hir_def::builtin_type::BuiltinUint::U8,
+                rustc_type_ir::UintTy::U16 => hir_def::builtin_type::BuiltinUint::U16,
+                rustc_type_ir::UintTy::U32 => hir_def::builtin_type::BuiltinUint::U32,
+                rustc_type_ir::UintTy::U64 => hir_def::builtin_type::BuiltinUint::U64,
+                rustc_type_ir::UintTy::U128 => hir_def::builtin_type::BuiltinUint::U128,
+            }),
+            TyKind::Float(float) => hir_def::builtin_type::BuiltinType::Float(match float {
+                rustc_type_ir::FloatTy::F16 => hir_def::builtin_type::BuiltinFloat::F16,
+                rustc_type_ir::FloatTy::F32 => hir_def::builtin_type::BuiltinFloat::F32,
+                rustc_type_ir::FloatTy::F64 => hir_def::builtin_type::BuiltinFloat::F64,
+                rustc_type_ir::FloatTy::F128 => hir_def::builtin_type::BuiltinFloat::F128,
+            }),
+            _ => return None,
+        };
+        Some(builtin)
+    }
+
+    // FIXME: Should this be here?
+    pub fn impl_trait_bounds(self, db: &'db dyn HirDatabase) -> Option<Vec<Clause<'db>>> {
+        let interner = DbInterner::new_with(db, None, None);
+
+        match self.kind() {
+            TyKind::Alias(AliasTyKind::Opaque, opaque_ty) => {
+                match db.lookup_intern_impl_trait_id(opaque_ty.def_id.expect_opaque_ty()) {
+                    ImplTraitId::ReturnTypeImplTrait(func, idx) => {
+                        db.return_type_impl_traits_ns(func).map(|it| {
+                            let data = (*it).as_ref().map_bound(|rpit| {
+                                &rpit.impl_traits[idx.to_nextsolver(interner)].predicates
+                            });
+                            data.iter_instantiated_copied(interner, opaque_ty.args.as_slice())
+                                .collect()
+                        })
+                    }
+                    ImplTraitId::TypeAliasImplTrait(alias, idx) => {
+                        db.type_alias_impl_traits_ns(alias).map(|it| {
+                            let data = (*it).as_ref().map_bound(|rpit| {
+                                &rpit.impl_traits[idx.to_nextsolver(interner)].predicates
+                            });
+                            data.iter_instantiated_copied(interner, opaque_ty.args.as_slice())
+                                .collect()
+                        })
+                    }
+                    ImplTraitId::AsyncBlockTypeImplTrait(def, _) => {
+                        let krate = def.module(db).krate();
+                        if let Some(future_trait) = LangItem::Future.resolve_trait(db, krate) {
+                            // This is only used by type walking.
+                            // Parameters will be walked outside, and projection predicate is not used.
+                            // So just provide the Future trait.
+                            let impl_bound = TraitRef::new(
+                                interner,
+                                future_trait.into(),
+                                GenericArgs::new_from_iter(interner, []),
+                            )
+                            .upcast(interner);
+                            Some(vec![impl_bound])
+                        } else {
+                            None
+                        }
+                    }
+                }
+            }
+            TyKind::Param(param) => {
+                // FIXME: We shouldn't use `param.id` here.
+                let generic_params = db.generic_params(param.id.parent());
+                let param_data = &generic_params[param.id.local_id()];
+                match param_data {
+                    TypeOrConstParamData::TypeParamData(p) => match p.provenance {
+                        TypeParamProvenance::ArgumentImplTrait => {
+                            let predicates = db
+                                .generic_predicates_ns(param.id.parent())
+                                .instantiate_identity()
+                                .into_iter()
+                                .flatten()
+                                .filter(|wc| match wc.kind().skip_binder() {
+                                    ClauseKind::Trait(tr) => tr.self_ty() == self,
+                                    ClauseKind::Projection(pred) => pred.self_ty() == self,
+                                    ClauseKind::TypeOutlives(pred) => pred.0 == self,
+                                    _ => false,
+                                })
+                                .collect::<Vec<_>>();
+
+                            Some(predicates)
+                        }
+                        _ => None,
+                    },
+                    _ => None,
+                }
+            }
+            _ => None,
+        }
+    }
+
+    /// FIXME: Get rid of this, it's not a good abstraction
+    pub fn equals_ctor(self, other: Ty<'db>) -> bool {
+        match (self.kind(), other.kind()) {
+            (TyKind::Adt(adt, ..), TyKind::Adt(adt2, ..)) => adt.def_id() == adt2.def_id(),
+            (TyKind::Slice(_), TyKind::Slice(_)) | (TyKind::Array(_, _), TyKind::Array(_, _)) => {
+                true
+            }
+            (TyKind::FnDef(def_id, ..), TyKind::FnDef(def_id2, ..)) => def_id == def_id2,
+            (TyKind::Alias(_, alias, ..), TyKind::Alias(_, alias2)) => {
+                alias.def_id == alias2.def_id
+            }
+            (TyKind::Foreign(ty_id, ..), TyKind::Foreign(ty_id2, ..)) => ty_id == ty_id2,
+            (TyKind::Closure(id1, _), TyKind::Closure(id2, _)) => id1 == id2,
+            (TyKind::Ref(.., mutability), TyKind::Ref(.., mutability2))
+            | (TyKind::RawPtr(.., mutability), TyKind::RawPtr(.., mutability2)) => {
+                mutability == mutability2
+            }
+            (TyKind::FnPtr(sig, hdr), TyKind::FnPtr(sig2, hdr2)) => sig == sig2 && hdr == hdr2,
+            (TyKind::Tuple(tys), TyKind::Tuple(tys2)) => tys.len() == tys2.len(),
+            (TyKind::Str, TyKind::Str)
+            | (TyKind::Never, TyKind::Never)
+            | (TyKind::Char, TyKind::Char)
+            | (TyKind::Bool, TyKind::Bool) => true,
+            (TyKind::Int(int), TyKind::Int(int2)) => int == int2,
+            (TyKind::Float(float), TyKind::Float(float2)) => float == float2,
+            _ => false,
+        }
+    }
 }
 
 pub fn references_non_lt_error<'db, T: TypeVisitableExt<DbInterner<'db>>>(t: &T) -> bool {
diff --git a/crates/hir-ty/src/traits.rs b/crates/hir-ty/src/traits.rs
index 16ad54a..cd125f3 100644
--- a/crates/hir-ty/src/traits.rs
+++ b/crates/hir-ty/src/traits.rs
@@ -12,7 +12,7 @@
 use rustc_next_trait_solver::solve::{HasChanged, SolverDelegateEvalExt};
 use rustc_type_ir::{
     InferCtxtLike, TypingMode,
-    inherent::{SliceLike, Span as _, Ty as _},
+    inherent::{IntoKind, SliceLike, Span as _, Ty as _},
     solve::Certainty,
 };
 use span::Edition;
@@ -28,6 +28,7 @@
         DbInterner, GenericArg, ParamEnv, Predicate, SolverContext, Span,
         infer::{DbInternerInferExt, InferCtxt, traits::ObligationCause},
         mapping::{ChalkToNextSolver, NextSolverToChalk, convert_canonical_args_for_result},
+        obligation_ctxt::ObligationCtxt,
         util::mini_canonicalize,
     },
     utils::UnevaluatedConstEvaluatorFolder,
@@ -43,7 +44,7 @@
     pub krate: Crate,
     pub block: Option<BlockId>,
     // FIXME make this a BTreeMap
-    traits_from_clauses: Box<[(Ty, TraitId)]>,
+    traits_from_clauses: Box<[(crate::next_solver::Ty<'db>, TraitId)]>,
     pub env: ParamEnv<'db>,
 }
 
@@ -60,7 +61,7 @@
     pub fn new(
         krate: Crate,
         block: Option<BlockId>,
-        traits_from_clauses: Box<[(Ty, TraitId)]>,
+        traits_from_clauses: Box<[(crate::next_solver::Ty<'db>, TraitId)]>,
         env: ParamEnv<'db>,
     ) -> Arc<Self> {
         Arc::new(TraitEnvironment { krate, block, traits_from_clauses, env })
@@ -71,13 +72,28 @@
         Arc::make_mut(this).block = Some(block);
     }
 
-    pub fn traits_in_scope_from_clauses(&self, ty: Ty) -> impl Iterator<Item = TraitId> + '_ {
+    pub fn traits_in_scope_from_clauses(
+        &self,
+        ty: crate::next_solver::Ty<'db>,
+    ) -> impl Iterator<Item = TraitId> + '_ {
         self.traits_from_clauses
             .iter()
             .filter_map(move |(self_ty, trait_id)| (*self_ty == ty).then_some(*trait_id))
     }
 }
 
+/// This should be used in `hir` only.
+pub fn structurally_normalize_ty<'db>(
+    infcx: &InferCtxt<'db>,
+    ty: crate::next_solver::Ty<'db>,
+    env: Arc<TraitEnvironment<'db>>,
+) -> crate::next_solver::Ty<'db> {
+    let crate::next_solver::TyKind::Alias(..) = ty.kind() else { return ty };
+    let mut ocx = ObligationCtxt::new(infcx);
+    let ty = ocx.structurally_normalize_ty(&ObligationCause::dummy(), env.env, ty).unwrap_or(ty);
+    ty.replace_infer_with_error(infcx.interner)
+}
+
 pub(crate) fn normalize_projection_query<'db>(
     db: &'db dyn HirDatabase,
     projection: ProjectionTy,
@@ -440,3 +456,43 @@
         self.lang_item().resolve_trait(db, krate)
     }
 }
+
+/// This should not be used in `hir-ty`, only in `hir`.
+pub fn implements_trait_unique<'db>(
+    ty: crate::next_solver::Ty<'db>,
+    db: &'db dyn HirDatabase,
+    env: Arc<TraitEnvironment<'db>>,
+    trait_: TraitId,
+) -> bool {
+    implements_trait_unique_impl(db, env, trait_, &mut |infcx| {
+        infcx.fill_rest_fresh_args(trait_.into(), [ty.into()])
+    })
+}
+
+/// This should not be used in `hir-ty`, only in `hir`.
+pub fn implements_trait_unique_with_args<'db>(
+    db: &'db dyn HirDatabase,
+    env: Arc<TraitEnvironment<'db>>,
+    trait_: TraitId,
+    args: crate::next_solver::GenericArgs<'db>,
+) -> bool {
+    implements_trait_unique_impl(db, env, trait_, &mut |_| args)
+}
+
+fn implements_trait_unique_impl<'db>(
+    db: &'db dyn HirDatabase,
+    env: Arc<TraitEnvironment<'db>>,
+    trait_: TraitId,
+    create_args: &mut dyn FnMut(&InferCtxt<'db>) -> crate::next_solver::GenericArgs<'db>,
+) -> bool {
+    let interner = DbInterner::new_with(db, Some(env.krate), env.block);
+    // FIXME(next-solver): I believe this should be `PostAnalysis`.
+    let infcx = interner.infer_ctxt().build(TypingMode::non_body_analysis());
+
+    let args = create_args(&infcx);
+    let trait_ref = rustc_type_ir::TraitRef::new_from_args(interner, trait_.into(), args);
+    let goal = crate::next_solver::Goal::new(interner, env.env, trait_ref);
+
+    let result = crate::traits::next_trait_solve_in_ctxt(&infcx, goal);
+    matches!(result, Ok((_, Certainty::Yes)))
+}
diff --git a/crates/hir/src/attrs.rs b/crates/hir/src/attrs.rs
index c230bba..147f1b8 100644
--- a/crates/hir/src/attrs.rs
+++ b/crates/hir/src/attrs.rs
@@ -14,11 +14,7 @@
     mod_path::{ModPath, PathKind},
     name::Name,
 };
-use hir_ty::{
-    db::HirDatabase,
-    method_resolution,
-    next_solver::{DbInterner, mapping::ChalkToNextSolver},
-};
+use hir_ty::{db::HirDatabase, method_resolution};
 
 use crate::{
     Adt, AsAssocItem, AssocItem, BuiltinType, Const, ConstParam, DocLinkDef, Enum, ExternCrateDecl,
@@ -261,7 +257,7 @@
     name: &Name,
     ns: Option<Namespace>,
 ) -> Option<DocLinkDef> {
-    let canonical = ty.canonical();
+    let canonical = ty.canonical(db);
     let krate = ty.krate(db);
     let environment = resolver
         .generic_def()
@@ -275,11 +271,7 @@
     //
     // FIXME: resolve type aliases (which are not yielded by iterate_path_candidates)
     _ = method_resolution::iterate_path_candidates(
-        &canonical.to_nextsolver(DbInterner::new_with(
-            db,
-            Some(environment.krate),
-            environment.block,
-        )),
+        &canonical,
         db,
         environment,
         &traits_in_scope,
diff --git a/crates/hir/src/diagnostics.rs b/crates/hir/src/diagnostics.rs
index c094487..a6d67e8 100644
--- a/crates/hir/src/diagnostics.rs
+++ b/crates/hir/src/diagnostics.rs
@@ -19,7 +19,6 @@
     PathLoweringDiagnostic, TyLoweringDiagnostic, TyLoweringDiagnosticKind,
     db::HirDatabase,
     diagnostics::{BodyValidationDiagnostic, UnsafetyReason},
-    next_solver::{DbInterner, mapping::NextSolverToChalk},
 };
 use syntax::{
     AstNode, AstPtr, SyntaxError, SyntaxNodePtr, TextRange,
@@ -641,7 +640,6 @@
             ExprOrPatId::ExprId(expr) => expr_syntax(expr),
             ExprOrPatId::PatId(pat) => pat_syntax(pat),
         };
-        let interner = DbInterner::new_with(db, None, None);
         Some(match d {
             &InferenceDiagnostic::NoSuchField { field: expr, private, variant } => {
                 let expr_or_pat = match expr {
@@ -668,11 +666,7 @@
             }
             InferenceDiagnostic::ExpectedFunction { call_expr, found } => {
                 let call_expr = expr_syntax(*call_expr)?;
-                ExpectedFunction {
-                    call: call_expr,
-                    found: Type::new(db, def, found.to_chalk(interner)),
-                }
-                .into()
+                ExpectedFunction { call: call_expr, found: Type::new(db, def, *found) }.into()
             }
             InferenceDiagnostic::UnresolvedField {
                 expr,
@@ -684,7 +678,7 @@
                 UnresolvedField {
                     expr,
                     name: name.clone(),
-                    receiver: Type::new(db, def, receiver.to_chalk(interner)),
+                    receiver: Type::new(db, def, *receiver),
                     method_with_same_name_exists: *method_with_same_name_exists,
                 }
                 .into()
@@ -700,9 +694,8 @@
                 UnresolvedMethodCall {
                     expr,
                     name: name.clone(),
-                    receiver: Type::new(db, def, receiver.to_chalk(interner)),
-                    field_with_same_name: (*field_with_same_name)
-                        .map(|ty| Type::new(db, def, ty.to_chalk(interner))),
+                    receiver: Type::new(db, def, *receiver),
+                    field_with_same_name: (*field_with_same_name).map(|ty| Type::new(db, def, ty)),
                     assoc_func_with_same_name: assoc_func_with_same_name.map(Into::into),
                 }
                 .into()
@@ -729,7 +722,7 @@
             }
             InferenceDiagnostic::TypedHole { expr, expected } => {
                 let expr = expr_syntax(*expr)?;
-                TypedHole { expr, expected: Type::new(db, def, expected.to_chalk(interner)) }.into()
+                TypedHole { expr, expected: Type::new(db, def, *expected) }.into()
             }
             &InferenceDiagnostic::MismatchedTupleStructPatArgCount { pat, expected, found } => {
                 let expr_or_pat = match pat {
@@ -746,13 +739,12 @@
             }
             InferenceDiagnostic::CastToUnsized { expr, cast_ty } => {
                 let expr = expr_syntax(*expr)?;
-                CastToUnsized { expr, cast_ty: Type::new(db, def, cast_ty.to_chalk(interner)) }
-                    .into()
+                CastToUnsized { expr, cast_ty: Type::new(db, def, *cast_ty) }.into()
             }
             InferenceDiagnostic::InvalidCast { expr, error, expr_ty, cast_ty } => {
                 let expr = expr_syntax(*expr)?;
-                let expr_ty = Type::new(db, def, expr_ty.to_chalk(interner));
-                let cast_ty = Type::new(db, def, cast_ty.to_chalk(interner));
+                let expr_ty = Type::new(db, def, *expr_ty);
+                let cast_ty = Type::new(db, def, *cast_ty);
                 InvalidCast { expr, error: *error, expr_ty, cast_ty }.into()
             }
             InferenceDiagnostic::TyDiagnostic { source, diag } => {
diff --git a/crates/hir/src/display.rs b/crates/hir/src/display.rs
index 2bf9bb8..49bf843 100644
--- a/crates/hir/src/display.rs
+++ b/crates/hir/src/display.rs
@@ -11,7 +11,7 @@
     type_ref::{TypeBound, TypeRef, TypeRefId},
 };
 use hir_ty::{
-    AliasEq, AliasTy, Interner, ProjectionTyExt, TraitRefExt, TyKind, WhereClause,
+    AliasEq, AliasTy, Interner, ProjectionTyExt, TraitRefExt, TyBuilder, TyKind, WhereClause,
     db::HirDatabase,
     display::{
         HirDisplay, HirDisplayError, HirDisplayWithExpressionStore, HirFormatter, SizedByDefault,
@@ -23,8 +23,8 @@
 use crate::{
     Adt, AsAssocItem, AssocItem, AssocItemContainer, Const, ConstParam, Crate, Enum,
     ExternCrateDecl, Field, Function, GenericParam, HasCrate, HasVisibility, Impl, LifetimeParam,
-    Macro, Module, SelfParam, Static, Struct, StructKind, Trait, TraitRef, TupleField, TyBuilder,
-    Type, TypeAlias, TypeNs, TypeOrConstParam, TypeParam, Union, Variant,
+    Macro, Module, SelfParam, Static, Struct, StructKind, Trait, TraitRef, TupleField, Type,
+    TypeAlias, TypeNs, TypeOrConstParam, TypeParam, Union, Variant,
 };
 
 impl HirDisplay for Function {
diff --git a/crates/hir/src/has_source.rs b/crates/hir/src/has_source.rs
index ae82275..6f427d7 100644
--- a/crates/hir/src/has_source.rs
+++ b/crates/hir/src/has_source.rs
@@ -238,7 +238,7 @@
                 .map(|value| InFile { file_id, value })
             }
             Callee::Closure(closure, _) => {
-                let InternedClosure(owner, expr_id) = db.lookup_intern_closure(closure.into());
+                let InternedClosure(owner, expr_id) = db.lookup_intern_closure(closure);
                 let (_, source_map) = db.body_with_source_map(owner);
                 let ast @ InFile { file_id, value } = source_map.expr_syntax(expr_id).ok()?;
                 let root = db.parse_or_expand(file_id);
diff --git a/crates/hir/src/lib.rs b/crates/hir/src/lib.rs
index 59038c2..55da277 100644
--- a/crates/hir/src/lib.rs
+++ b/crates/hir/src/lib.rs
@@ -71,29 +71,31 @@
     proc_macro::ProcMacroKind,
 };
 use hir_ty::{
-    AliasTy, CallableSig, Canonical, CanonicalVarKinds, Cast, ClosureId, GenericArg,
-    GenericArgData, Interner, ParamKind, ProjectionTy, QuantifiedWhereClause, Scalar, Substitution,
-    TraitEnvironment, TraitRefExt, Ty, TyBuilder, TyDefId, TyExt, TyKind, TyLoweringDiagnostic,
-    ValueTyDefId, WhereClause, all_super_traits, autoderef, check_orphan_rules,
-    consteval_chalk::{ConstExt, try_const_usize, unknown_const_as_generic},
+    TraitEnvironment, TyDefId, TyLoweringDiagnostic, ValueTyDefId, all_super_traits, autoderef,
+    check_orphan_rules,
+    consteval::try_const_usize,
+    db::InternedClosureId,
     diagnostics::BodyValidationDiagnostic,
-    direct_super_traits, error_lifetime, known_const_to_ast,
+    direct_super_traits, known_const_to_ast,
     layout::{Layout as TyLayout, RustcEnumVariantIdx, RustcFieldIdx, TagEncoding},
     method_resolution,
     mir::{MutBorrowKind, interpret_mir},
     next_solver::{
-        ClauseKind, DbInterner, GenericArgs, TypingMode,
+        AliasTy, Canonical, ClauseKind, ConstKind, DbInterner, ErrorGuaranteed, GenericArg,
+        GenericArgs, PolyFnSig, Region, SolverDefId, Ty, TyKind, TypingMode,
         infer::{DbInternerInferExt, InferCtxt},
-        mapping::{ChalkToNextSolver, NextSolverToChalk, convert_ty_for_result},
     },
-    primitive::UintTy,
-    traits::FnTrait,
+    traits::{self, FnTrait, structurally_normalize_ty},
 };
 use itertools::Itertools;
 use rustc_hash::FxHashSet;
+use rustc_type_ir::{
+    AliasTyKind, TypeSuperVisitable, TypeVisitable, TypeVisitor,
+    inherent::{AdtDef, IntoKind, SliceLike, Term as _, Ty as _},
+};
 use smallvec::SmallVec;
 use span::{AstIdNode, Edition, FileId};
-use stdx::{format_to, impl_from, never, variance::PhantomCovariantLifetime};
+use stdx::{format_to, impl_from, never};
 use syntax::{
     AstNode, AstPtr, SmolStr, SyntaxNode, SyntaxNodePtr, T, TextRange, ToSmolStr,
     ast::{self, HasAttrs as _, HasName, HasVisibility as _},
@@ -112,7 +114,6 @@
         VisibleTraits,
     },
 };
-use rustc_type_ir::inherent::{IntoKind, SliceLike};
 
 // Be careful with these re-exports.
 //
@@ -156,6 +157,8 @@
         proc_macro::{ProcMacros, ProcMacrosBuilder},
         tt,
     },
+    // FIXME: Properly encapsulate mir
+    hir_ty::mir,
     hir_ty::{
         CastError, FnAbi, PointerCast, Variance, attach_db, attach_db_allow_change,
         consteval::ConstEvalError,
@@ -168,8 +171,6 @@
         mir::{MirEvalError, MirLowerError},
         next_solver::abi::Safety,
     },
-    // FIXME: Properly encapsulate mir
-    hir_ty::{Interner as ChalkTyInterner, mir},
     intern::{Symbol, sym},
 };
 
@@ -750,6 +751,9 @@
 
         let inherent_impls = db.inherent_impls_in_crate(self.id.krate());
 
+        let interner = DbInterner::new_with(db, Some(self.id.krate()), self.id.containing_block());
+        let infcx = interner.infer_ctxt().build(TypingMode::non_body_analysis());
+
         let mut impl_assoc_items_scratch = vec![];
         for impl_def in self.impl_defs(db) {
             GenericDef::Impl(impl_def).diagnostics(db, acc);
@@ -874,26 +878,15 @@
                     .collect();
 
                 if !missing.is_empty() {
-                    let interner = DbInterner::new_with(db, None, None);
-                    let args: crate::next_solver::GenericArgs<'_> =
-                        hir_ty::generics::generics(db, impl_def.id.into())
-                            .placeholder_subst(db)
-                            .to_nextsolver(interner);
-                    let self_ty =
-                        db.impl_self_ty(impl_def.id).instantiate(interner, args).to_chalk(interner);
-                    let self_ty = if let TyKind::Alias(AliasTy::Projection(projection)) =
-                        self_ty.kind(Interner)
-                    {
-                        db.normalize_projection(
-                            projection.clone(),
-                            db.trait_environment(impl_def.id.into()),
-                        )
-                    } else {
-                        self_ty
-                    };
+                    let self_ty = db.impl_self_ty(impl_def.id).instantiate_identity();
+                    let self_ty = structurally_normalize_ty(
+                        &infcx,
+                        self_ty,
+                        db.trait_environment(impl_def.id.into()),
+                    );
                     let self_ty_is_guaranteed_unsized = matches!(
-                        self_ty.kind(Interner),
-                        TyKind::Dyn(..) | TyKind::Slice(..) | TyKind::Str
+                        self_ty.kind(),
+                        TyKind::Dynamic(..) | TyKind::Slice(..) | TyKind::Str
                     );
                     if self_ty_is_guaranteed_unsized {
                         missing.retain(|(_, assoc_item)| {
@@ -1300,17 +1293,11 @@
         let ty = db
             .infer(self.owner)
             .tuple_field_access_type(self.tuple)
-            .to_chalk(interner)
-            .as_slice(Interner)
+            .as_slice()
             .get(self.index as usize)
-            .and_then(|arg| arg.ty(Interner))
-            .cloned()
-            .unwrap_or_else(|| TyKind::Error.intern(Interner));
-        Type {
-            env: db.trait_environment_for_body(self.owner),
-            ty,
-            _pd: PhantomCovariantLifetime::new(),
-        }
+            .copied()
+            .unwrap_or_else(|| Ty::new_error(interner, ErrorGuaranteed));
+        Type { env: db.trait_environment_for_body(self.owner), ty }
     }
 }
 
@@ -1378,17 +1365,9 @@
             VariantDef::Union(it) => it.id.into(),
             VariantDef::Variant(it) => it.parent_enum(db).id.into(),
         };
-        let mut generics = generics.map(|it| it.ty);
-        let substs = TyBuilder::subst_for_def(db, def_id, None)
-            .fill(|x| match x {
-                ParamKind::Type => {
-                    generics.next().unwrap_or_else(|| TyKind::Error.intern(Interner)).cast(Interner)
-                }
-                ParamKind::Const(ty) => unknown_const_as_generic(ty.clone()),
-                ParamKind::Lifetime => error_lifetime().cast(Interner),
-            })
-            .build();
-        let ty = db.field_types(var_id)[self.id].clone().substitute(Interner, &substs);
+        let interner = DbInterner::new_with(db, None, None);
+        let args = generic_args_from_tys(interner, def_id.into(), generics.map(|ty| ty.ty));
+        let ty = db.field_types_ns(var_id)[self.id].instantiate(interner, args);
         Type::new(db, var_id, ty)
     }
 
@@ -1448,8 +1427,8 @@
         Type::from_def(db, self.id)
     }
 
-    pub fn ty_placeholders(self, db: &dyn HirDatabase) -> Type<'_> {
-        Type::from_def_placeholders(db, self.id)
+    pub fn ty_params(self, db: &dyn HirDatabase) -> Type<'_> {
+        Type::from_def_params(db, self.id)
     }
 
     pub fn constructor_ty(self, db: &dyn HirDatabase) -> Type<'_> {
@@ -1537,8 +1516,8 @@
         Type::from_def(db, self.id)
     }
 
-    pub fn ty_placeholders(self, db: &dyn HirDatabase) -> Type<'_> {
-        Type::from_def_placeholders(db, self.id)
+    pub fn ty_params(self, db: &dyn HirDatabase) -> Type<'_> {
+        Type::from_def_params(db, self.id)
     }
 
     pub fn constructor_ty(self, db: &dyn HirDatabase) -> Type<'_> {
@@ -1604,40 +1583,43 @@
         Type::from_def(db, self.id)
     }
 
-    pub fn ty_placeholders<'db>(self, db: &'db dyn HirDatabase) -> Type<'db> {
-        Type::from_def_placeholders(db, self.id)
+    pub fn ty_params<'db>(self, db: &'db dyn HirDatabase) -> Type<'db> {
+        Type::from_def_params(db, self.id)
     }
 
     /// The type of the enum variant bodies.
     pub fn variant_body_ty<'db>(self, db: &'db dyn HirDatabase) -> Type<'db> {
+        let interner = DbInterner::new_with(db, None, None);
         Type::new_for_crate(
             self.id.lookup(db).container.krate(),
-            TyBuilder::builtin(match db.enum_signature(self.id).variant_body_type() {
+            match db.enum_signature(self.id).variant_body_type() {
                 layout::IntegerType::Pointer(sign) => match sign {
-                    true => hir_def::builtin_type::BuiltinType::Int(
-                        hir_def::builtin_type::BuiltinInt::Isize,
-                    ),
-                    false => hir_def::builtin_type::BuiltinType::Uint(
-                        hir_def::builtin_type::BuiltinUint::Usize,
-                    ),
+                    true => Ty::new_int(interner, rustc_type_ir::IntTy::Isize),
+                    false => Ty::new_uint(interner, rustc_type_ir::UintTy::Usize),
                 },
                 layout::IntegerType::Fixed(i, sign) => match sign {
-                    true => hir_def::builtin_type::BuiltinType::Int(match i {
-                        layout::Integer::I8 => hir_def::builtin_type::BuiltinInt::I8,
-                        layout::Integer::I16 => hir_def::builtin_type::BuiltinInt::I16,
-                        layout::Integer::I32 => hir_def::builtin_type::BuiltinInt::I32,
-                        layout::Integer::I64 => hir_def::builtin_type::BuiltinInt::I64,
-                        layout::Integer::I128 => hir_def::builtin_type::BuiltinInt::I128,
-                    }),
-                    false => hir_def::builtin_type::BuiltinType::Uint(match i {
-                        layout::Integer::I8 => hir_def::builtin_type::BuiltinUint::U8,
-                        layout::Integer::I16 => hir_def::builtin_type::BuiltinUint::U16,
-                        layout::Integer::I32 => hir_def::builtin_type::BuiltinUint::U32,
-                        layout::Integer::I64 => hir_def::builtin_type::BuiltinUint::U64,
-                        layout::Integer::I128 => hir_def::builtin_type::BuiltinUint::U128,
-                    }),
+                    true => Ty::new_int(
+                        interner,
+                        match i {
+                            layout::Integer::I8 => rustc_type_ir::IntTy::I8,
+                            layout::Integer::I16 => rustc_type_ir::IntTy::I16,
+                            layout::Integer::I32 => rustc_type_ir::IntTy::I32,
+                            layout::Integer::I64 => rustc_type_ir::IntTy::I64,
+                            layout::Integer::I128 => rustc_type_ir::IntTy::I128,
+                        },
+                    ),
+                    false => Ty::new_uint(
+                        interner,
+                        match i {
+                            layout::Integer::I8 => rustc_type_ir::UintTy::U8,
+                            layout::Integer::I16 => rustc_type_ir::UintTy::U16,
+                            layout::Integer::I32 => rustc_type_ir::UintTy::U32,
+                            layout::Integer::I64 => rustc_type_ir::UintTy::U64,
+                            layout::Integer::I128 => rustc_type_ir::UintTy::U128,
+                        },
+                    ),
                 },
-            }),
+            },
         )
     }
 
@@ -1813,26 +1795,18 @@
 
 impl Adt {
     pub fn has_non_default_type_params(self, db: &dyn HirDatabase) -> bool {
-        let subst = db.generic_defaults(self.into());
-        (subst.is_empty() && db.generic_params(self.into()).len_type_or_consts() != 0)
-            || subst.iter().any(|ty| match ty.skip_binders().data(Interner) {
-                GenericArgData::Ty(it) => it.is_unknown(),
-                _ => false,
-            })
+        has_non_default_type_params(db, self.into())
     }
 
     pub fn layout(self, db: &dyn HirDatabase) -> Result<Layout, LayoutError> {
         let env = db.trait_environment(self.into());
         let interner = DbInterner::new_with(db, Some(env.krate), env.block);
-        db.layout_of_adt(
-            self.into(),
-            TyBuilder::adt(db, self.into())
-                .fill_with_defaults(db, || TyKind::Error.intern(Interner))
-                .build_into_subst()
-                .to_nextsolver(interner),
-            env,
-        )
-        .map(|layout| Layout(layout, db.target_data_layout(self.krate(db).id).unwrap()))
+        let adt_id = AdtId::from(self);
+        let args = GenericArgs::for_item_with_defaults(interner, adt_id.into(), |_, _, id, _| {
+            GenericArg::error_from_id(interner, id)
+        });
+        db.layout_of_adt(adt_id, args, env)
+            .map(|layout| Layout(layout, db.target_data_layout(self.krate(db).id).unwrap()))
     }
 
     /// Turns this ADT into a type. Any type parameters of the ADT will be
@@ -1851,18 +1825,12 @@
         args: impl IntoIterator<Item = Type<'db>>,
     ) -> Type<'db> {
         let id = AdtId::from(self);
-        let mut it = args.into_iter().map(|t| t.ty);
-        let ty = TyBuilder::def_ty(db, id.into(), None)
-            .fill(|x| {
-                let r = it.next().unwrap_or_else(|| TyKind::Error.intern(Interner));
-                match x {
-                    ParamKind::Type => r.cast(Interner),
-                    ParamKind::Const(ty) => unknown_const_as_generic(ty.clone()),
-                    ParamKind::Lifetime => error_lifetime().cast(Interner),
-                }
-            })
-            .build(DbInterner::conjure())
-            .to_chalk(DbInterner::conjure());
+        let interner = DbInterner::new_with(db, None, None);
+        let ty = Ty::new_adt(
+            interner,
+            id,
+            generic_args_from_tys(interner, id.into(), args.into_iter().map(|ty| ty.ty)),
+        );
         Type::new(db, id, ty)
     }
 
@@ -2023,7 +1991,6 @@
         style_lints: bool,
     ) {
         let krate = self.module(db).id.krate();
-        let interner = DbInterner::new_with(db, Some(krate), None);
 
         let (body, source_map) = db.body_with_source_map(self.into());
         let sig_source_map = match self {
@@ -2073,16 +2040,8 @@
             acc.push(
                 TypeMismatch {
                     expr_or_pat,
-                    expected: Type::new(
-                        db,
-                        DefWithBodyId::from(self),
-                        mismatch.expected.to_chalk(interner),
-                    ),
-                    actual: Type::new(
-                        db,
-                        DefWithBodyId::from(self),
-                        mismatch.actual.to_chalk(interner),
-                    ),
+                    expected: Type::new(db, DefWithBodyId::from(self), mismatch.expected),
+                    actual: Type::new(db, DefWithBodyId::from(self), mismatch.actual),
                 }
                 .into(),
             );
@@ -2152,13 +2111,7 @@
                         }
                         mir::MirSpan::Unknown => continue,
                     };
-                    acc.push(
-                        MovedOutOfRef {
-                            ty: Type::new_for_crate(krate, moof.ty.to_chalk(interner)),
-                            span,
-                        }
-                        .into(),
-                    )
+                    acc.push(MovedOutOfRef { ty: Type::new_for_crate(krate, moof.ty), span }.into())
                 }
                 let mol = &borrowck_result.mutability_of_locals;
                 for (binding_id, binding_data) in body.bindings() {
@@ -2308,30 +2261,24 @@
 
     pub fn fn_ptr_type(self, db: &dyn HirDatabase) -> Type<'_> {
         let resolver = self.id.resolver(db);
-        let substs = TyBuilder::placeholder_subst(db, self.id);
         let interner = DbInterner::new_with(db, None, None);
-        let args: crate::next_solver::GenericArgs<'_> = substs.to_nextsolver(interner);
-        let callable_sig = db
-            .callable_item_signature(self.id.into())
-            .instantiate(interner, args)
-            .skip_binder()
-            .to_chalk(interner);
-        let ty = TyKind::Function(callable_sig.to_fn_ptr()).intern(Interner);
+        // FIXME: This shouldn't be `instantiate_identity()`, we shouldn't leak `TyKind::Param`s.
+        let callable_sig = db.callable_item_signature(self.id.into()).instantiate_identity();
+        let ty = Ty::new_fn_ptr(interner, callable_sig);
         Type::new_with_resolver_inner(db, &resolver, ty)
     }
 
+    // FIXME: Find a better API to express all combinations here, perhaps we should have `PreInstantiationType`?
+
     /// Get this function's return type
     pub fn ret_type(self, db: &dyn HirDatabase) -> Type<'_> {
         let resolver = self.id.resolver(db);
-        let substs = TyBuilder::placeholder_subst(db, self.id);
-        let interner = DbInterner::new_with(db, None, None);
-        let args: crate::next_solver::GenericArgs<'_> = substs.to_nextsolver(interner);
+        // FIXME: This shouldn't be `instantiate_identity()`, we shouldn't leak `TyKind::Param`s.
         let ty = db
             .callable_item_signature(self.id.into())
-            .instantiate(interner, args)
+            .instantiate_identity()
             .skip_binder()
-            .output()
-            .to_chalk(interner);
+            .output();
         Type::new_with_resolver_inner(db, &resolver, ty)
     }
 
@@ -2342,32 +2289,15 @@
         generics: impl Iterator<Item = Type<'db>>,
     ) -> Type<'db> {
         let resolver = self.id.resolver(db);
-        let parent_id: Option<GenericDefId> = match self.id.lookup(db).container {
-            ItemContainerId::ImplId(it) => Some(it.into()),
-            ItemContainerId::TraitId(it) => Some(it.into()),
-            ItemContainerId::ModuleId(_) | ItemContainerId::ExternBlockId(_) => None,
-        };
-        let mut generics = generics.map(|it| it.ty);
-        let mut filler = |x: &_| match x {
-            ParamKind::Type => {
-                generics.next().unwrap_or_else(|| TyKind::Error.intern(Interner)).cast(Interner)
-            }
-            ParamKind::Const(ty) => unknown_const_as_generic(ty.clone()),
-            ParamKind::Lifetime => error_lifetime().cast(Interner),
-        };
-
-        let parent_substs =
-            parent_id.map(|id| TyBuilder::subst_for_def(db, id, None).fill(&mut filler).build());
-        let substs = TyBuilder::subst_for_def(db, self.id, parent_substs).fill(&mut filler).build();
+        let interner = DbInterner::new_with(db, None, None);
+        let args = generic_args_from_tys(interner, self.id.into(), generics.map(|ty| ty.ty));
 
         let interner = DbInterner::new_with(db, None, None);
-        let args: crate::next_solver::GenericArgs<'_> = substs.to_nextsolver(interner);
         let ty = db
             .callable_item_signature(self.id.into())
             .instantiate(interner, args)
             .skip_binder()
-            .output()
-            .to_chalk(interner);
+            .output();
         Type::new_with_resolver_inner(db, &resolver, ty)
     }
 
@@ -2376,18 +2306,17 @@
             return None;
         }
         let resolver = self.id.resolver(db);
-        let substs = TyBuilder::placeholder_subst(db, self.id);
-        let interner = DbInterner::new_with(db, None, None);
-        let args: crate::next_solver::GenericArgs<'_> = substs.to_nextsolver(interner);
+        // FIXME: This shouldn't be `instantiate_identity()`, we shouldn't leak `TyKind::Param`s.
         let ret_ty = db
             .callable_item_signature(self.id.into())
-            .instantiate(interner, args)
+            .instantiate_identity()
             .skip_binder()
-            .output()
-            .to_chalk(interner);
+            .output();
         for pred in ret_ty.impl_trait_bounds(db).into_iter().flatten() {
-            if let WhereClause::AliasEq(output_eq) = pred.into_value_and_skipped_binders().0 {
-                return Type::new_with_resolver_inner(db, &resolver, output_eq.ty).into();
+            if let ClauseKind::Projection(projection) = pred.kind().skip_binder()
+                && let Some(output_ty) = projection.term.as_type()
+            {
+                return Type::new_with_resolver_inner(db, &resolver, output_ty).into();
             }
         }
         None
@@ -2403,24 +2332,15 @@
 
     pub fn assoc_fn_params(self, db: &dyn HirDatabase) -> Vec<Param<'_>> {
         let environment = db.trait_environment(self.id.into());
-        let substs = TyBuilder::placeholder_subst(db, self.id);
-        let interner = DbInterner::new_with(db, None, None);
-        let args: crate::next_solver::GenericArgs<'_> = substs.to_nextsolver(interner);
-        let callable_sig = db
-            .callable_item_signature(self.id.into())
-            .instantiate(interner, args)
-            .skip_binder()
-            .to_chalk(interner);
+        // FIXME: This shouldn't be `instantiate_identity()`, we shouldn't leak `TyKind::Param`s.
+        let callable_sig =
+            db.callable_item_signature(self.id.into()).instantiate_identity().skip_binder();
         callable_sig
-            .params()
+            .inputs()
             .iter()
             .enumerate()
             .map(|(idx, ty)| {
-                let ty = Type {
-                    env: environment.clone(),
-                    ty: ty.clone(),
-                    _pd: PhantomCovariantLifetime::new(),
-                };
+                let ty = Type { env: environment.clone(), ty };
                 Param { func: Callee::Def(CallableDefId::FunctionId(self.id)), ty, idx }
             })
             .collect()
@@ -2437,26 +2357,17 @@
 
     pub fn params_without_self(self, db: &dyn HirDatabase) -> Vec<Param<'_>> {
         let environment = db.trait_environment(self.id.into());
-        let substs = TyBuilder::placeholder_subst(db, self.id);
-        let interner = DbInterner::new_with(db, None, None);
-        let args: crate::next_solver::GenericArgs<'_> = substs.to_nextsolver(interner);
-        let callable_sig = db
-            .callable_item_signature(self.id.into())
-            .instantiate(interner, args)
-            .skip_binder()
-            .to_chalk(interner);
+        // FIXME: This shouldn't be `instantiate_identity()`, we shouldn't leak `TyKind::Param`s.
+        let callable_sig =
+            db.callable_item_signature(self.id.into()).instantiate_identity().skip_binder();
         let skip = if db.function_signature(self.id).has_self_param() { 1 } else { 0 };
         callable_sig
-            .params()
+            .inputs()
             .iter()
             .enumerate()
             .skip(skip)
             .map(|(idx, ty)| {
-                let ty = Type {
-                    env: environment.clone(),
-                    ty: ty.clone(),
-                    _pd: PhantomCovariantLifetime::new(),
-                };
+                let ty = Type { env: environment.clone(), ty };
                 Param { func: Callee::Def(CallableDefId::FunctionId(self.id)), ty, idx }
             })
             .collect()
@@ -2469,50 +2380,18 @@
         generics: impl Iterator<Item = Type<'db>>,
     ) -> Vec<Param<'db>> {
         let environment = db.trait_environment(self.id.into());
-        let parent_id: Option<GenericDefId> = match self.id.lookup(db).container {
-            ItemContainerId::ImplId(it) => Some(it.into()),
-            ItemContainerId::TraitId(it) => Some(it.into()),
-            ItemContainerId::ModuleId(_) | ItemContainerId::ExternBlockId(_) => None,
-        };
-        let mut generics = generics.map(|it| it.ty);
-        let parent_substs = parent_id.map(|id| {
-            TyBuilder::subst_for_def(db, id, None)
-                .fill(|x| match x {
-                    ParamKind::Type => generics
-                        .next()
-                        .unwrap_or_else(|| TyKind::Error.intern(Interner))
-                        .cast(Interner),
-                    ParamKind::Const(ty) => unknown_const_as_generic(ty.clone()),
-                    ParamKind::Lifetime => error_lifetime().cast(Interner),
-                })
-                .build()
-        });
-
-        let substs = TyBuilder::subst_for_def(db, self.id, parent_substs)
-            .fill(|_| {
-                let ty = generics.next().unwrap_or_else(|| TyKind::Error.intern(Interner));
-                GenericArg::new(Interner, GenericArgData::Ty(ty))
-            })
-            .build();
         let interner = DbInterner::new_with(db, None, None);
-        let args: crate::next_solver::GenericArgs<'_> = substs.to_nextsolver(interner);
-        let callable_sig = db
-            .callable_item_signature(self.id.into())
-            .instantiate(interner, args)
-            .skip_binder()
-            .to_chalk(interner);
+        let args = generic_args_from_tys(interner, self.id.into(), generics.map(|ty| ty.ty));
+        let callable_sig =
+            db.callable_item_signature(self.id.into()).instantiate(interner, args).skip_binder();
         let skip = if db.function_signature(self.id).has_self_param() { 1 } else { 0 };
         callable_sig
-            .params()
+            .inputs()
             .iter()
             .enumerate()
             .skip(skip)
             .map(|(idx, ty)| {
-                let ty = Type {
-                    env: environment.clone(),
-                    ty: ty.clone(),
-                    _pd: PhantomCovariantLifetime::new(),
-                };
+                let ty = Type { env: environment.clone(), ty };
                 Param { func: Callee::Def(CallableDefId::FunctionId(self.id)), ty, idx }
             })
             .collect()
@@ -2694,18 +2573,18 @@
     Owned,
 }
 
-impl From<hir_ty::Mutability> for Access {
-    fn from(mutability: hir_ty::Mutability) -> Access {
+impl From<hir_ty::next_solver::Mutability> for Access {
+    fn from(mutability: hir_ty::next_solver::Mutability) -> Access {
         match mutability {
-            hir_ty::Mutability::Not => Access::Shared,
-            hir_ty::Mutability::Mut => Access::Exclusive,
+            hir_ty::next_solver::Mutability::Not => Access::Shared,
+            hir_ty::next_solver::Mutability::Mut => Access::Exclusive,
         }
     }
 }
 
 #[derive(Clone, PartialEq, Eq, Hash, Debug)]
 pub struct Param<'db> {
-    func: Callee,
+    func: Callee<'db>,
     /// The index in parameter list, including self parameter.
     idx: usize,
     ty: Type<'db>,
@@ -2751,7 +2630,7 @@
                 }
             }
             Callee::Closure(closure, _) => {
-                let c = db.lookup_intern_closure(closure.into());
+                let c = db.lookup_intern_closure(closure);
                 let body = db.body(c.0);
                 if let Expr::Closure { args, .. } = &body[c.1]
                     && let Pat::Bind { id, .. } = &body[args[self.idx]]
@@ -2795,17 +2674,12 @@
     }
 
     pub fn ty<'db>(&self, db: &'db dyn HirDatabase) -> Type<'db> {
-        let substs = TyBuilder::placeholder_subst(db, self.func);
-        let interner = DbInterner::new_with(db, None, None);
-        let args: crate::next_solver::GenericArgs<'_> = substs.to_nextsolver(interner);
-        let callable_sig = db
-            .callable_item_signature(self.func.into())
-            .instantiate(interner, args)
-            .skip_binder()
-            .to_chalk(interner);
+        // FIXME: This shouldn't be `instantiate_identity()`, we shouldn't leak `TyKind::Param`s.
+        let callable_sig =
+            db.callable_item_signature(self.func.into()).instantiate_identity().skip_binder();
         let environment = db.trait_environment(self.func.into());
-        let ty = callable_sig.params()[0].clone();
-        Type { env: environment, ty, _pd: PhantomCovariantLifetime::new() }
+        let ty = callable_sig.inputs().as_slice()[0];
+        Type { env: environment, ty }
     }
 
     // FIXME: Find better API to also handle const generics
@@ -2814,36 +2688,13 @@
         db: &'db dyn HirDatabase,
         generics: impl Iterator<Item = Type<'db>>,
     ) -> Type<'db> {
-        let parent_id: GenericDefId = match self.func.lookup(db).container {
-            ItemContainerId::ImplId(it) => it.into(),
-            ItemContainerId::TraitId(it) => it.into(),
-            ItemContainerId::ModuleId(_) | ItemContainerId::ExternBlockId(_) => {
-                panic!("Never get here")
-            }
-        };
-
-        let mut generics = generics.map(|it| it.ty);
-        let mut filler = |x: &_| match x {
-            ParamKind::Type => {
-                generics.next().unwrap_or_else(|| TyKind::Error.intern(Interner)).cast(Interner)
-            }
-            ParamKind::Const(ty) => unknown_const_as_generic(ty.clone()),
-            ParamKind::Lifetime => error_lifetime().cast(Interner),
-        };
-
-        let parent_substs = TyBuilder::subst_for_def(db, parent_id, None).fill(&mut filler).build();
-        let substs =
-            TyBuilder::subst_for_def(db, self.func, Some(parent_substs)).fill(&mut filler).build();
         let interner = DbInterner::new_with(db, None, None);
-        let args: crate::next_solver::GenericArgs<'_> = substs.to_nextsolver(interner);
-        let callable_sig = db
-            .callable_item_signature(self.func.into())
-            .instantiate(interner, args)
-            .skip_binder()
-            .to_chalk(interner);
+        let args = generic_args_from_tys(interner, self.func.into(), generics.map(|ty| ty.ty));
+        let callable_sig =
+            db.callable_item_signature(self.func.into()).instantiate(interner, args).skip_binder();
         let environment = db.trait_environment(self.func.into());
-        let ty = callable_sig.params()[0].clone();
-        Type { env: environment, ty, _pd: PhantomCovariantLifetime::new() }
+        let ty = callable_sig.inputs().as_slice()[0];
+        Type { env: environment, ty }
     }
 }
 
@@ -2936,11 +2787,11 @@
     }
 
     /// Evaluate the constant.
-    pub fn eval(self, db: &dyn HirDatabase) -> Result<EvaluatedConst, ConstEvalError<'_>> {
+    pub fn eval(self, db: &dyn HirDatabase) -> Result<EvaluatedConst<'_>, ConstEvalError<'_>> {
         let interner = DbInterner::new_with(db, None, None);
-        let ty = db.value_ty(self.id.into()).unwrap().instantiate_identity().to_chalk(interner);
+        let ty = db.value_ty(self.id.into()).unwrap().instantiate_identity();
         db.const_eval(self.id.into(), GenericArgs::new_from_iter(interner, []), None)
-            .map(|it| EvaluatedConst { const_: it.to_chalk(interner), def: self.id.into(), ty })
+            .map(|it| EvaluatedConst { const_: it, def: self.id.into(), ty })
     }
 }
 
@@ -2950,29 +2801,28 @@
     }
 }
 
-pub struct EvaluatedConst {
+pub struct EvaluatedConst<'db> {
     def: DefWithBodyId,
-    const_: hir_ty::Const,
-    ty: hir_ty::Ty,
+    const_: hir_ty::next_solver::Const<'db>,
+    ty: Ty<'db>,
 }
 
-impl EvaluatedConst {
+impl<'db> EvaluatedConst<'db> {
     pub fn render(&self, db: &dyn HirDatabase, display_target: DisplayTarget) -> String {
         format!("{}", self.const_.display(db, display_target))
     }
 
-    pub fn render_debug<'db>(&self, db: &'db dyn HirDatabase) -> Result<String, MirEvalError<'db>> {
-        let interner = DbInterner::new_with(db, None, None);
-        let data = self.const_.data(Interner);
-        if let TyKind::Scalar(s) = data.ty.kind(Interner)
-            && matches!(s, Scalar::Int(_) | Scalar::Uint(_))
-            && let hir_ty::ConstValue::Concrete(c) = &data.value
-            && let hir_ty::ConstScalar::Bytes(b, _) = &c.interned
+    pub fn render_debug(&self, db: &'db dyn HirDatabase) -> Result<String, MirEvalError<'db>> {
+        let kind = self.const_.kind();
+        if let ConstKind::Value(c) = kind
+            && let ty = c.ty.kind()
+            && let TyKind::Int(_) | TyKind::Uint(_) = ty
         {
+            let b = &c.value.inner().memory;
             let value = u128::from_le_bytes(mir::pad16(b, false));
-            let value_signed = i128::from_le_bytes(mir::pad16(b, matches!(s, Scalar::Int(_))));
+            let value_signed = i128::from_le_bytes(mir::pad16(b, matches!(ty, TyKind::Int(_))));
             let mut result =
-                if let Scalar::Int(_) = s { value_signed.to_string() } else { value.to_string() };
+                if let TyKind::Int(_) = ty { value_signed.to_string() } else { value.to_string() };
             if value >= 10 {
                 format_to!(result, " ({value:#X})");
                 return Ok(result);
@@ -2980,12 +2830,7 @@
                 return Ok(result);
             }
         }
-        mir::render_const_using_debug_impl(
-            db,
-            self.def,
-            self.const_.to_nextsolver(interner),
-            self.ty.to_nextsolver(interner),
-        )
+        mir::render_const_using_debug_impl(db, self.def, self.const_, self.ty)
     }
 }
 
@@ -3023,11 +2868,11 @@
     }
 
     /// Evaluate the static initializer.
-    pub fn eval(self, db: &dyn HirDatabase) -> Result<EvaluatedConst, ConstEvalError<'_>> {
+    pub fn eval(self, db: &dyn HirDatabase) -> Result<EvaluatedConst<'_>, ConstEvalError<'_>> {
         let interner = DbInterner::new_with(db, None, None);
-        let ty = db.value_ty(self.id.into()).unwrap().instantiate_identity().to_chalk(interner);
+        let ty = db.value_ty(self.id.into()).unwrap().instantiate_identity();
         db.const_eval(self.id.into(), GenericArgs::new_from_iter(interner, []), None)
-            .map(|it| EvaluatedConst { const_: it.to_chalk(interner), def: self.id.into(), ty })
+            .map(|it| EvaluatedConst { const_: it, def: self.id.into(), ty })
     }
 }
 
@@ -3148,12 +2993,7 @@
 
 impl TypeAlias {
     pub fn has_non_default_type_params(self, db: &dyn HirDatabase) -> bool {
-        let subst = db.generic_defaults(self.id.into());
-        (subst.is_empty() && db.generic_params(self.id.into()).len_type_or_consts() != 0)
-            || subst.iter().any(|ty| match ty.skip_binders().data(Interner) {
-                GenericArgData::Ty(it) => it.is_unknown(),
-                _ => false,
-            })
+        has_non_default_type_params(db, self.id.into())
     }
 
     pub fn module(self, db: &dyn HirDatabase) -> Module {
@@ -3164,8 +3004,8 @@
         Type::from_def(db, self.id)
     }
 
-    pub fn ty_placeholders(self, db: &dyn HirDatabase) -> Type<'_> {
-        Type::from_def_placeholders(db, self.id)
+    pub fn ty_params(self, db: &dyn HirDatabase) -> Type<'_> {
+        Type::from_def_params(db, self.id)
     }
 
     pub fn name(self, db: &dyn HirDatabase) -> Name {
@@ -3218,7 +3058,8 @@
 
     pub fn ty<'db>(self, db: &'db dyn HirDatabase) -> Type<'db> {
         let core = Crate::core(db).map(|core| core.id).unwrap_or_else(|| db.all_crates()[0]);
-        Type::new_for_crate(core, TyBuilder::builtin(self.inner))
+        let interner = DbInterner::new_with(db, None, None);
+        Type::new_for_crate(core, Ty::from_builtin_type(interner, self.inner))
     }
 
     pub fn name(self) -> Name {
@@ -3894,14 +3735,13 @@
 #[derive(Debug)]
 pub struct GenericSubstitution<'db> {
     def: GenericDefId,
-    subst: Substitution,
+    subst: GenericArgs<'db>,
     env: Arc<TraitEnvironment<'db>>,
-    _pd: PhantomCovariantLifetime<'db>,
 }
 
 impl<'db> GenericSubstitution<'db> {
-    fn new(def: GenericDefId, subst: Substitution, env: Arc<TraitEnvironment<'db>>) -> Self {
-        Self { def, subst, env, _pd: PhantomCovariantLifetime::new() }
+    fn new(def: GenericDefId, subst: GenericArgs<'db>, env: Arc<TraitEnvironment<'db>>) -> Self {
+        Self { def, subst, env }
     }
 
     pub fn types(&self, db: &'db dyn HirDatabase) -> Vec<(Symbol, Type<'db>)> {
@@ -3931,26 +3771,23 @@
             TypeOrConstParamData::TypeParamData(param) => Some(param.name.clone()),
             TypeOrConstParamData::ConstParamData(_) => None,
         });
-        let parent_len = self.subst.len(Interner)
+        let parent_len = self.subst.len()
             - generics
                 .iter_type_or_consts()
                 .filter(|g| matches!(g.1, TypeOrConstParamData::TypeParamData(..)))
                 .count();
-        let container_params = self.subst.as_slice(Interner)[..parent_len]
+        let container_params = self.subst.as_slice()[..parent_len]
             .iter()
-            .filter_map(|param| param.ty(Interner).cloned())
+            .filter_map(|param| param.ty())
             .zip(container_type_params.into_iter().flatten());
-        let self_params = self.subst.as_slice(Interner)[parent_len..]
+        let self_params = self.subst.as_slice()[parent_len..]
             .iter()
-            .filter_map(|param| param.ty(Interner).cloned())
+            .filter_map(|param| param.ty())
             .zip(type_params);
         container_params
             .chain(self_params)
             .filter_map(|(ty, name)| {
-                Some((
-                    name?.symbol().clone(),
-                    Type { ty, env: self.env.clone(), _pd: PhantomCovariantLifetime::new() },
-                ))
+                Some((name?.symbol().clone(), Type { ty, env: self.env.clone() }))
             })
             .collect()
     }
@@ -4057,8 +3894,7 @@
         let def = self.parent;
         let infer = db.infer(def);
         let ty = infer[self.binding_id];
-        let interner = DbInterner::new_with(db, None, None);
-        Type::new(db, def, ty.to_chalk(interner))
+        Type::new(db, def, ty)
     }
 
     /// All definitions for this local. Example: `let (a$0, _) | (_, a$0) = it;`
@@ -4313,8 +4149,10 @@
 
     pub fn ty(self, db: &dyn HirDatabase) -> Type<'_> {
         let resolver = self.id.parent().resolver(db);
-        let ty = TyKind::Placeholder(hir_ty::to_placeholder_idx_no_index(db, self.id.into()))
-            .intern(Interner);
+        let interner = DbInterner::new_with(db, None, None);
+        let index = hir_ty::param_idx(db, self.id.into()).unwrap();
+        let name = self.name(db).symbol().clone();
+        let ty = Ty::new_param(interner, self.id, index as u32, name);
         Type::new_with_resolver_inner(db, &resolver, ty)
     }
 
@@ -4334,9 +4172,9 @@
     pub fn default(self, db: &dyn HirDatabase) -> Option<Type<'_>> {
         let ty = generic_arg_from_param(db, self.id.into())?;
         let resolver = self.id.parent().resolver(db);
-        match ty.data(Interner) {
-            GenericArgData::Ty(it) if *it.kind(Interner) != TyKind::Error => {
-                Some(Type::new_with_resolver_inner(db, &resolver, it.clone()))
+        match ty {
+            GenericArg::Ty(it) if !it.is_ty_error() => {
+                Some(Type::new_with_resolver_inner(db, &resolver, it))
             }
             _ => None,
         }
@@ -4397,7 +4235,7 @@
     }
 
     pub fn ty(self, db: &dyn HirDatabase) -> Type<'_> {
-        Type::new(db, self.id.parent(), db.const_param_ty(self.id))
+        Type::new(db, self.id.parent(), db.const_param_ty_ns(self.id))
     }
 
     pub fn default(
@@ -4406,17 +4244,16 @@
         display_target: DisplayTarget,
     ) -> Option<ast::ConstArg> {
         let arg = generic_arg_from_param(db, self.id.into())?;
-        known_const_to_ast(arg.constant(Interner)?, db, display_target)
+        known_const_to_ast(arg.konst()?, db, display_target)
     }
 }
 
-fn generic_arg_from_param(db: &dyn HirDatabase, id: TypeOrConstParamId) -> Option<GenericArg> {
+fn generic_arg_from_param(db: &dyn HirDatabase, id: TypeOrConstParamId) -> Option<GenericArg<'_>> {
     let local_idx = hir_ty::param_idx(db, id)?;
-    let defaults = db.generic_defaults(id.parent);
-    let ty = defaults.get(local_idx)?.clone();
-    let full_subst = TyBuilder::placeholder_subst(db, id.parent);
-    let subst = &full_subst.as_slice(Interner)[..local_idx];
-    Some(ty.substitute(Interner, &subst))
+    let defaults = db.generic_defaults_ns(id.parent);
+    let ty = defaults.get(local_idx)?;
+    // FIXME: This shouldn't be `instantiate_identity()`, we shouldn't leak `TyKind::Param`s.
+    Some(ty.instantiate_identity())
 }
 
 #[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
@@ -4498,13 +4335,8 @@
         module.id.def_map(db)[module.id.local_id].scope.impls().map(Into::into).collect()
     }
 
-    pub fn all_for_type<'db>(
-        db: &'db dyn HirDatabase,
-        Type { ty, env, _pd: _ }: Type<'db>,
-    ) -> Vec<Impl> {
-        let interner = DbInterner::new_with(db, None, None);
-        let ty_ns = ty.to_nextsolver(interner);
-        let def_crates = match method_resolution::def_crates(db, ty_ns, env.krate) {
+    pub fn all_for_type<'db>(db: &'db dyn HirDatabase, Type { ty, env }: Type<'db>) -> Vec<Impl> {
+        let def_crates = match method_resolution::def_crates(db, ty, env.krate) {
             Some(def_crates) => def_crates,
             None => return Vec::new(),
         };
@@ -4512,10 +4344,10 @@
         let filter = |impl_def: &Impl| {
             let self_ty = impl_def.self_ty(db);
             let rref = self_ty.remove_ref();
-            ty.equals_ctor(rref.as_ref().map_or(&self_ty.ty, |it| &it.ty))
+            ty.equals_ctor(rref.as_ref().map_or(self_ty.ty, |it| it.ty))
         };
 
-        let fp = TyFingerprint::for_inherent_impl(ty_ns);
+        let fp = TyFingerprint::for_inherent_impl(ty);
         let fp = match fp {
             Some(fp) => fp,
             None => return Vec::new(),
@@ -4525,7 +4357,7 @@
         def_crates.iter().for_each(|&id| {
             all.extend(
                 db.inherent_impls_in_crate(id)
-                    .for_self_ty(ty_ns)
+                    .for_self_ty(ty)
                     .iter()
                     .cloned()
                     .map(Self::from)
@@ -4546,16 +4378,10 @@
             );
         }
 
-        if let Some(block) = ty.adt_id(Interner).and_then(|def| def.0.module(db).containing_block())
-        {
+        if let Some(block) = ty.as_adt().and_then(|(def, _)| def.module(db).containing_block()) {
             if let Some(inherent_impls) = db.inherent_impls_in_block(block) {
                 all.extend(
-                    inherent_impls
-                        .for_self_ty(ty_ns)
-                        .iter()
-                        .cloned()
-                        .map(Self::from)
-                        .filter(filter),
+                    inherent_impls.for_self_ty(ty).iter().cloned().map(Self::from).filter(filter),
                 );
             }
             if let Some(trait_impls) = db.trait_impls_in_block(block) {
@@ -4601,10 +4427,8 @@
 
     pub fn self_ty(self, db: &dyn HirDatabase) -> Type<'_> {
         let resolver = self.id.resolver(db);
-        let interner = DbInterner::new_with(db, Some(resolver.krate()), None);
-        let substs = TyBuilder::placeholder_subst(db, self.id);
-        let args: crate::next_solver::GenericArgs<'_> = substs.to_nextsolver(interner);
-        let ty = db.impl_self_ty(self.id).instantiate(interner, args).to_chalk(interner);
+        // FIXME: This shouldn't be `instantiate_identity()`, we shouldn't leak `TyKind::Param`s.
+        let ty = db.impl_self_ty(self.id).instantiate_identity();
         Type::new_with_resolver_inner(db, &resolver, ty)
     }
 
@@ -4666,7 +4490,6 @@
 pub struct TraitRef<'db> {
     env: Arc<TraitEnvironment<'db>>,
     trait_ref: hir_ty::next_solver::TraitRef<'db>,
-    _pd: PhantomCovariantLifetime<'db>,
 }
 
 impl<'db> TraitRef<'db> {
@@ -4678,7 +4501,7 @@
         let env = resolver
             .generic_def()
             .map_or_else(|| TraitEnvironment::empty(resolver.krate()), |d| db.trait_environment(d));
-        TraitRef { env, trait_ref, _pd: PhantomCovariantLifetime::new() }
+        TraitRef { env, trait_ref }
     }
 
     pub fn trait_(&self) -> Trait {
@@ -4687,57 +4510,51 @@
 
     pub fn self_ty(&self) -> TypeNs<'_> {
         let ty = self.trait_ref.self_ty();
-        TypeNs { env: self.env.clone(), ty, _pd: PhantomCovariantLifetime::new() }
+        TypeNs { env: self.env.clone(), ty }
     }
 
     /// Returns `idx`-th argument of this trait reference if it is a type argument. Note that the
     /// first argument is the `Self` type.
     pub fn get_type_argument(&self, idx: usize) -> Option<TypeNs<'db>> {
-        self.trait_ref.args.as_slice().get(idx).and_then(|arg| arg.ty()).map(|ty| TypeNs {
-            env: self.env.clone(),
-            ty,
-            _pd: PhantomCovariantLifetime::new(),
-        })
+        self.trait_ref
+            .args
+            .as_slice()
+            .get(idx)
+            .and_then(|arg| arg.ty())
+            .map(|ty| TypeNs { env: self.env.clone(), ty })
     }
 }
 
 #[derive(Clone, Debug, PartialEq, Eq, Hash)]
-pub struct Closure {
-    id: ClosureId,
-    subst: Substitution,
+pub struct Closure<'db> {
+    id: InternedClosureId,
+    subst: GenericArgs<'db>,
 }
 
-impl From<Closure> for ClosureId {
-    fn from(value: Closure) -> Self {
-        value.id
-    }
-}
-
-impl Closure {
-    fn as_ty(self) -> Ty {
-        TyKind::Closure(self.id, self.subst).intern(Interner)
+impl<'db> Closure<'db> {
+    fn as_ty(&self, db: &'db dyn HirDatabase) -> Ty<'db> {
+        let interner = DbInterner::new_with(db, None, None);
+        Ty::new_closure(interner, self.id.into(), self.subst)
     }
 
     pub fn display_with_id(&self, db: &dyn HirDatabase, display_target: DisplayTarget) -> String {
-        self.clone()
-            .as_ty()
+        self.as_ty(db)
             .display(db, display_target)
             .with_closure_style(ClosureStyle::ClosureWithId)
             .to_string()
     }
 
     pub fn display_with_impl(&self, db: &dyn HirDatabase, display_target: DisplayTarget) -> String {
-        self.clone()
-            .as_ty()
+        self.as_ty(db)
             .display(db, display_target)
             .with_closure_style(ClosureStyle::ImplFn)
             .to_string()
     }
 
-    pub fn captured_items<'db>(&self, db: &'db dyn HirDatabase) -> Vec<ClosureCapture<'db>> {
-        let owner = db.lookup_intern_closure((self.id).into()).0;
-        let infer = &db.infer(owner);
-        let info = infer.closure_info(self.id.into());
+    pub fn captured_items(&self, db: &'db dyn HirDatabase) -> Vec<ClosureCapture<'db>> {
+        let owner = db.lookup_intern_closure(self.id).0;
+        let infer = db.infer(owner);
+        let info = infer.closure_info(self.id);
         info.0
             .iter()
             .cloned()
@@ -4745,25 +4562,21 @@
             .collect()
     }
 
-    pub fn capture_types<'db>(&self, db: &'db dyn HirDatabase) -> Vec<Type<'db>> {
-        let owner = db.lookup_intern_closure((self.id).into()).0;
-        let infer = &db.infer(owner);
-        let (captures, _) = infer.closure_info(self.id.into());
-        let interner = DbInterner::new_with(db, None, None);
+    pub fn capture_types(&self, db: &'db dyn HirDatabase) -> Vec<Type<'db>> {
+        let owner = db.lookup_intern_closure(self.id).0;
+        let infer = db.infer(owner);
+        let (captures, _) = infer.closure_info(self.id);
+        let env = db.trait_environment_for_body(owner);
         captures
             .iter()
-            .map(|capture| Type {
-                env: db.trait_environment_for_body(owner),
-                ty: capture.ty(db, self.subst.to_nextsolver(interner)).to_chalk(interner),
-                _pd: PhantomCovariantLifetime::new(),
-            })
+            .map(|capture| Type { env: env.clone(), ty: capture.ty(db, self.subst) })
             .collect()
     }
 
     pub fn fn_trait(&self, db: &dyn HirDatabase) -> FnTrait {
-        let owner = db.lookup_intern_closure((self.id).into()).0;
-        let infer = &db.infer(owner);
-        let info = infer.closure_info(self.id.into());
+        let owner = db.lookup_intern_closure(self.id).0;
+        let infer = db.infer(owner);
+        let info = infer.closure_info(self.id);
         info.1
     }
 }
@@ -4771,7 +4584,7 @@
 #[derive(Clone, Debug, PartialEq, Eq)]
 pub struct ClosureCapture<'db> {
     owner: DefWithBodyId,
-    closure: ClosureId,
+    closure: InternedClosureId,
     capture: hir_ty::CapturedItem<'db>,
 }
 
@@ -4889,15 +4702,14 @@
 #[derive(Clone, PartialEq, Eq, Debug, Hash)]
 pub struct Type<'db> {
     env: Arc<TraitEnvironment<'db>>,
-    ty: Ty,
-    _pd: PhantomCovariantLifetime<'db>,
+    ty: Ty<'db>,
 }
 
 impl<'db> Type<'db> {
     pub(crate) fn new_with_resolver(
         db: &'db dyn HirDatabase,
         resolver: &Resolver<'_>,
-        ty: Ty,
+        ty: Ty<'db>,
     ) -> Self {
         Type::new_with_resolver_inner(db, resolver, ty)
     }
@@ -4905,275 +4717,252 @@
     pub(crate) fn new_with_resolver_inner(
         db: &'db dyn HirDatabase,
         resolver: &Resolver<'_>,
-        ty: Ty,
+        ty: Ty<'db>,
     ) -> Self {
         let environment = resolver
             .generic_def()
             .map_or_else(|| TraitEnvironment::empty(resolver.krate()), |d| db.trait_environment(d));
-        Type { env: environment, ty, _pd: PhantomCovariantLifetime::new() }
+        Type { env: environment, ty }
     }
 
-    pub(crate) fn new_for_crate(krate: base_db::Crate, ty: Ty) -> Self {
-        Type { env: TraitEnvironment::empty(krate), ty, _pd: PhantomCovariantLifetime::new() }
+    pub(crate) fn new_for_crate(krate: base_db::Crate, ty: Ty<'db>) -> Self {
+        Type { env: TraitEnvironment::empty(krate), ty }
     }
 
-    fn new(db: &'db dyn HirDatabase, lexical_env: impl HasResolver, ty: Ty) -> Self {
+    fn new(db: &'db dyn HirDatabase, lexical_env: impl HasResolver, ty: Ty<'db>) -> Self {
         let resolver = lexical_env.resolver(db);
         let environment = resolver
             .generic_def()
             .map_or_else(|| TraitEnvironment::empty(resolver.krate()), |d| db.trait_environment(d));
-        Type { env: environment, ty, _pd: PhantomCovariantLifetime::new() }
+        Type { env: environment, ty }
     }
 
     fn from_def(db: &'db dyn HirDatabase, def: impl Into<TyDefId> + HasResolver) -> Self {
         let interner = DbInterner::new_with(db, None, None);
         let ty = db.ty(def.into());
-        let substs = TyBuilder::unknown_subst(
-            db,
-            match def.into() {
-                TyDefId::AdtId(it) => GenericDefId::AdtId(it),
-                TyDefId::TypeAliasId(it) => GenericDefId::TypeAliasId(it),
-                TyDefId::BuiltinType(_) => {
-                    return Type::new(db, def, ty.skip_binder().to_chalk(interner));
-                }
-            },
-        );
-        let args: hir_ty::next_solver::GenericArgs<'_> = substs.to_nextsolver(interner);
-        Type::new(db, def, ty.instantiate(interner, args).to_chalk(interner))
+        let def = match def.into() {
+            TyDefId::AdtId(it) => GenericDefId::AdtId(it),
+            TyDefId::TypeAliasId(it) => GenericDefId::TypeAliasId(it),
+            TyDefId::BuiltinType(_) => {
+                return Type::new(db, def, ty.skip_binder());
+            }
+        };
+        let args = GenericArgs::error_for_item(interner, def.into());
+        Type::new(db, def, ty.instantiate(interner, args))
     }
 
-    fn from_def_placeholders(
-        db: &'db dyn HirDatabase,
-        def: impl Into<TyDefId> + HasResolver,
-    ) -> Self {
-        let interner = DbInterner::new_with(db, None, None);
+    // FIXME: We shouldn't leak `TyKind::Param`s.
+    fn from_def_params(db: &'db dyn HirDatabase, def: impl Into<TyDefId> + HasResolver) -> Self {
         let ty = db.ty(def.into());
-        let substs = TyBuilder::placeholder_subst(
-            db,
-            match def.into() {
-                TyDefId::AdtId(it) => GenericDefId::AdtId(it),
-                TyDefId::TypeAliasId(it) => GenericDefId::TypeAliasId(it),
-                TyDefId::BuiltinType(_) => {
-                    return Type::new(db, def, ty.skip_binder().to_chalk(interner));
-                }
-            },
-        );
-        let args: hir_ty::next_solver::GenericArgs<'_> = substs.to_nextsolver(interner);
-        Type::new(db, def, ty.instantiate(interner, args).to_chalk(interner))
+        Type::new(db, def, ty.instantiate_identity())
     }
 
     fn from_value_def(
         db: &'db dyn HirDatabase,
         def: impl Into<ValueTyDefId> + HasResolver,
     ) -> Self {
-        let Some(ty) = db.value_ty(def.into()) else {
-            return Type::new(db, def, TyKind::Error.intern(Interner));
-        };
         let interner = DbInterner::new_with(db, None, None);
-        let substs = TyBuilder::unknown_subst(
-            db,
-            match def.into() {
-                ValueTyDefId::ConstId(it) => GenericDefId::ConstId(it),
-                ValueTyDefId::FunctionId(it) => GenericDefId::FunctionId(it),
-                ValueTyDefId::StructId(it) => GenericDefId::AdtId(AdtId::StructId(it)),
-                ValueTyDefId::UnionId(it) => GenericDefId::AdtId(AdtId::UnionId(it)),
-                ValueTyDefId::EnumVariantId(it) => {
-                    GenericDefId::AdtId(AdtId::EnumId(it.lookup(db).parent))
-                }
-                ValueTyDefId::StaticId(_) => {
-                    return Type::new(db, def, ty.skip_binder().to_chalk(interner));
-                }
-            },
-        );
-        let args: crate::next_solver::GenericArgs<'_> = substs.to_nextsolver(interner);
-        Type::new(db, def, ty.instantiate(interner, args).to_chalk(interner))
+        let Some(ty) = db.value_ty(def.into()) else {
+            return Type::new(db, def, Ty::new_error(interner, ErrorGuaranteed));
+        };
+        let def = match def.into() {
+            ValueTyDefId::ConstId(it) => GenericDefId::ConstId(it),
+            ValueTyDefId::FunctionId(it) => GenericDefId::FunctionId(it),
+            ValueTyDefId::StructId(it) => GenericDefId::AdtId(AdtId::StructId(it)),
+            ValueTyDefId::UnionId(it) => GenericDefId::AdtId(AdtId::UnionId(it)),
+            ValueTyDefId::EnumVariantId(it) => {
+                GenericDefId::AdtId(AdtId::EnumId(it.lookup(db).parent))
+            }
+            ValueTyDefId::StaticId(_) => {
+                return Type::new(db, def, ty.skip_binder());
+            }
+        };
+        let args = GenericArgs::error_for_item(interner, def.into());
+        Type::new(db, def, ty.instantiate(interner, args))
     }
 
     pub fn new_slice(ty: Self) -> Self {
-        Type { env: ty.env, ty: TyBuilder::slice(ty.ty), _pd: PhantomCovariantLifetime::new() }
+        let interner = DbInterner::conjure();
+        Type { env: ty.env, ty: Ty::new_slice(interner, ty.ty) }
     }
 
     pub fn new_tuple(krate: base_db::Crate, tys: &[Self]) -> Self {
-        let tys = tys.iter().map(|it| it.ty.clone());
-        Type {
-            env: TraitEnvironment::empty(krate),
-            ty: TyBuilder::tuple_with(tys),
-            _pd: PhantomCovariantLifetime::new(),
-        }
+        let tys = tys.iter().map(|it| it.ty);
+        let interner = DbInterner::conjure();
+        Type { env: TraitEnvironment::empty(krate), ty: Ty::new_tup_from_iter(interner, tys) }
     }
 
     pub fn is_unit(&self) -> bool {
-        matches!(self.ty.kind(Interner), TyKind::Tuple(0, ..))
+        self.ty.is_unit()
     }
 
     pub fn is_bool(&self) -> bool {
-        matches!(self.ty.kind(Interner), TyKind::Scalar(Scalar::Bool))
+        matches!(self.ty.kind(), TyKind::Bool)
     }
 
     pub fn is_str(&self) -> bool {
-        matches!(self.ty.kind(Interner), TyKind::Str)
+        matches!(self.ty.kind(), TyKind::Str)
     }
 
     pub fn is_never(&self) -> bool {
-        matches!(self.ty.kind(Interner), TyKind::Never)
+        matches!(self.ty.kind(), TyKind::Never)
     }
 
     pub fn is_mutable_reference(&self) -> bool {
-        matches!(self.ty.kind(Interner), TyKind::Ref(hir_ty::Mutability::Mut, ..))
+        matches!(self.ty.kind(), TyKind::Ref(.., hir_ty::next_solver::Mutability::Mut))
     }
 
     pub fn is_reference(&self) -> bool {
-        matches!(self.ty.kind(Interner), TyKind::Ref(..))
+        matches!(self.ty.kind(), TyKind::Ref(..))
     }
 
     pub fn contains_reference(&self, db: &'db dyn HirDatabase) -> bool {
-        return go(db, &self.ty);
+        let interner = DbInterner::new_with(db, None, None);
+        return self.ty.visit_with(&mut Visitor { interner }).is_break();
 
         fn is_phantom_data(db: &dyn HirDatabase, adt_id: AdtId) -> bool {
             match adt_id {
-                hir_def::AdtId::StructId(s) => {
+                AdtId::StructId(s) => {
                     let flags = db.struct_signature(s).flags;
                     flags.contains(StructFlags::IS_PHANTOM_DATA)
                 }
-                hir_def::AdtId::UnionId(_) => false,
-                hir_def::AdtId::EnumId(_) => false,
+                AdtId::UnionId(_) | AdtId::EnumId(_) => false,
             }
         }
 
-        fn go(db: &dyn HirDatabase, ty: &Ty) -> bool {
-            match ty.kind(Interner) {
-                // Reference itself
-                TyKind::Ref(_, _, _) => true,
+        struct Visitor<'db> {
+            interner: DbInterner<'db>,
+        }
 
-                // For non-phantom_data adts we check variants/fields as well as generic parameters
-                TyKind::Adt(adt_id, substitution) if !is_phantom_data(db, adt_id.0) => {
-                    let _variant_id_to_fields = |id: VariantId| {
-                        let variant_data = &id.fields(db);
-                        if variant_data.fields().is_empty() {
-                            vec![]
-                        } else {
-                            let field_types = db.field_types(id);
-                            variant_data
-                                .fields()
+        impl<'db> TypeVisitor<DbInterner<'db>> for Visitor<'db> {
+            type Result = ControlFlow<()>;
+
+            fn visit_ty(&mut self, ty: Ty<'db>) -> Self::Result {
+                match ty.kind() {
+                    // Reference itself
+                    TyKind::Ref(..) => ControlFlow::Break(()),
+
+                    // For non-phantom_data adts we check variants/fields as well as generic parameters
+                    TyKind::Adt(adt_def, args)
+                        if !is_phantom_data(self.interner.db(), adt_def.def_id().0) =>
+                    {
+                        let _variant_id_to_fields = |id: VariantId| {
+                            let variant_data = &id.fields(self.interner.db());
+                            if variant_data.fields().is_empty() {
+                                vec![]
+                            } else {
+                                let field_types = self.interner.db().field_types_ns(id);
+                                variant_data
+                                    .fields()
+                                    .iter()
+                                    .map(|(idx, _)| {
+                                        field_types[idx].instantiate(self.interner, args)
+                                    })
+                                    .filter(|it| !it.references_non_lt_error())
+                                    .collect()
+                            }
+                        };
+                        let variant_id_to_fields = |_: VariantId| vec![];
+
+                        let variants: Vec<Vec<Ty<'db>>> = match adt_def.def_id().0 {
+                            AdtId::StructId(id) => {
+                                vec![variant_id_to_fields(id.into())]
+                            }
+                            AdtId::EnumId(id) => id
+                                .enum_variants(self.interner.db())
+                                .variants
                                 .iter()
-                                .map(|(idx, _)| {
-                                    field_types[idx].clone().substitute(Interner, substitution)
-                                })
-                                .filter(|it| !it.contains_unknown())
-                                .collect()
-                        }
-                    };
-                    let variant_id_to_fields = |_: VariantId| vec![];
+                                .map(|&(variant_id, _, _)| variant_id_to_fields(variant_id.into()))
+                                .collect(),
+                            AdtId::UnionId(id) => {
+                                vec![variant_id_to_fields(id.into())]
+                            }
+                        };
 
-                    let variants = match adt_id.0 {
-                        hir_def::AdtId::StructId(id) => {
-                            vec![variant_id_to_fields(id.into())]
-                        }
-                        hir_def::AdtId::EnumId(id) => id
-                            .enum_variants(db)
-                            .variants
-                            .iter()
-                            .map(|&(variant_id, _, _)| variant_id_to_fields(variant_id.into()))
-                            .collect(),
-                        hir_def::AdtId::UnionId(id) => {
-                            vec![variant_id_to_fields(id.into())]
-                        }
-                    };
-
-                    variants
-                        .into_iter()
-                        .flat_map(|variant| variant.into_iter())
-                        .any(|ty| go(db, &ty))
-                        || substitution
-                            .iter(Interner)
-                            .filter_map(|x| x.ty(Interner))
-                            .any(|ty| go(db, ty))
+                        variants
+                            .into_iter()
+                            .flat_map(|variant| variant.into_iter())
+                            .try_for_each(|ty| ty.visit_with(self))?;
+                        args.visit_with(self)
+                    }
+                    // And for `PhantomData<T>`, we check `T`.
+                    _ => ty.super_visit_with(self),
                 }
-                // And for `PhantomData<T>`, we check `T`.
-                TyKind::Adt(_, substitution)
-                | TyKind::Tuple(_, substitution)
-                | TyKind::OpaqueType(_, substitution)
-                | TyKind::AssociatedType(_, substitution)
-                | TyKind::Alias(AliasTy::Projection(ProjectionTy { substitution, .. }))
-                | TyKind::FnDef(_, substitution) => {
-                    substitution.iter(Interner).filter_map(|x| x.ty(Interner)).any(|ty| go(db, ty))
-                }
-
-                // For `[T]` or `*T` we check `T`
-                TyKind::Array(ty, _) | TyKind::Slice(ty) | TyKind::Raw(_, ty) => go(db, ty),
-
-                // Consider everything else as not reference
-                _ => false,
             }
         }
     }
 
     pub fn as_reference(&self) -> Option<(Type<'db>, Mutability)> {
-        let (ty, _lt, m) = self.ty.as_reference()?;
-        let m = Mutability::from_mutable(matches!(m, hir_ty::Mutability::Mut));
-        Some((self.derived(ty.clone()), m))
+        let TyKind::Ref(_lt, ty, m) = self.ty.kind() else { return None };
+        let m = Mutability::from_mutable(matches!(m, hir_ty::next_solver::Mutability::Mut));
+        Some((self.derived(ty), m))
     }
 
     pub fn add_reference(&self, mutability: Mutability) -> Self {
+        let interner = DbInterner::conjure();
         let ty_mutability = match mutability {
-            Mutability::Shared => hir_ty::Mutability::Not,
-            Mutability::Mut => hir_ty::Mutability::Mut,
+            Mutability::Shared => hir_ty::next_solver::Mutability::Not,
+            Mutability::Mut => hir_ty::next_solver::Mutability::Mut,
         };
-        self.derived(TyKind::Ref(ty_mutability, error_lifetime(), self.ty.clone()).intern(Interner))
+        self.derived(Ty::new_ref(interner, Region::error(interner), self.ty, ty_mutability))
     }
 
     pub fn is_slice(&self) -> bool {
-        matches!(self.ty.kind(Interner), TyKind::Slice(..))
+        matches!(self.ty.kind(), TyKind::Slice(..))
     }
 
     pub fn is_usize(&self) -> bool {
-        matches!(self.ty.kind(Interner), TyKind::Scalar(Scalar::Uint(UintTy::Usize)))
+        matches!(self.ty.kind(), TyKind::Uint(rustc_type_ir::UintTy::Usize))
     }
 
     pub fn is_float(&self) -> bool {
-        matches!(self.ty.kind(Interner), TyKind::Scalar(Scalar::Float(_)))
+        matches!(self.ty.kind(), TyKind::Float(_))
     }
 
     pub fn is_char(&self) -> bool {
-        matches!(self.ty.kind(Interner), TyKind::Scalar(Scalar::Char))
+        matches!(self.ty.kind(), TyKind::Char)
     }
 
     pub fn is_int_or_uint(&self) -> bool {
-        matches!(self.ty.kind(Interner), TyKind::Scalar(Scalar::Int(_) | Scalar::Uint(_)))
+        matches!(self.ty.kind(), TyKind::Int(_) | TyKind::Uint(_))
     }
 
     pub fn is_scalar(&self) -> bool {
-        matches!(self.ty.kind(Interner), TyKind::Scalar(_))
+        matches!(
+            self.ty.kind(),
+            TyKind::Bool | TyKind::Char | TyKind::Int(_) | TyKind::Uint(_) | TyKind::Float(_)
+        )
     }
 
     pub fn is_tuple(&self) -> bool {
-        matches!(self.ty.kind(Interner), TyKind::Tuple(..))
+        matches!(self.ty.kind(), TyKind::Tuple(..))
     }
 
     pub fn remove_ref(&self) -> Option<Type<'db>> {
-        match &self.ty.kind(Interner) {
-            TyKind::Ref(.., ty) => Some(self.derived(ty.clone())),
+        match self.ty.kind() {
+            TyKind::Ref(_, ty, _) => Some(self.derived(ty)),
             _ => None,
         }
     }
 
     pub fn as_slice(&self) -> Option<Type<'db>> {
-        match &self.ty.kind(Interner) {
-            TyKind::Slice(ty) => Some(self.derived(ty.clone())),
+        match self.ty.kind() {
+            TyKind::Slice(ty) => Some(self.derived(ty)),
             _ => None,
         }
     }
 
     pub fn strip_references(&self) -> Self {
-        self.derived(self.ty.strip_references().clone())
+        self.derived(self.ty.strip_references())
     }
 
+    // FIXME: This is the same as `remove_ref()`, remove one of these methods.
     pub fn strip_reference(&self) -> Self {
-        self.derived(self.ty.strip_reference().clone())
+        self.derived(self.ty.strip_reference())
     }
 
     pub fn is_unknown(&self) -> bool {
-        self.ty.is_unknown()
+        self.ty.is_ty_error()
     }
 
     /// Checks that particular type `ty` implements `std::future::IntoFuture` or
@@ -5189,9 +4978,7 @@
             })
             .or_else(|| LangItem::Future.resolve_trait(db, self.env.krate))?;
 
-        let canonical_ty =
-            Canonical { value: self.ty.clone(), binders: CanonicalVarKinds::empty(Interner) };
-        if !method_resolution::implements_trait_unique(&canonical_ty, db, &self.env, trait_) {
+        if !traits::implements_trait_unique(self.ty, db, self.env.clone(), trait_) {
             return None;
         }
 
@@ -5219,9 +5006,7 @@
         let Some(iterator_trait) = LangItem::Iterator.resolve_trait(db, self.env.krate) else {
             return false;
         };
-        let canonical_ty =
-            Canonical { value: self.ty.clone(), binders: CanonicalVarKinds::empty(Interner) };
-        method_resolution::implements_trait_unique(&canonical_ty, db, &self.env, iterator_trait)
+        traits::implements_trait_unique(self.ty, db, self.env.clone(), iterator_trait)
     }
 
     /// Resolves the projection `<Self as IntoIterator>::IntoIter` and returns the resulting type
@@ -5234,9 +5019,7 @@
             },
         )?;
 
-        let canonical_ty =
-            Canonical { value: self.ty.clone(), binders: CanonicalVarKinds::empty(Interner) };
-        if !method_resolution::implements_trait_unique(&canonical_ty, db, &self.env, trait_) {
+        if !traits::implements_trait_unique(self.ty, db, self.env.clone(), trait_) {
             return None;
         }
 
@@ -5256,43 +5039,18 @@
             None => return false,
         };
 
-        let canonical_ty =
-            Canonical { value: self.ty.clone(), binders: CanonicalVarKinds::empty(Interner) };
-        method_resolution::implements_trait_unique(&canonical_ty, db, &self.env, fnonce_trait)
+        traits::implements_trait_unique(self.ty, db, self.env.clone(), fnonce_trait)
     }
 
     // FIXME: Find better API that also handles const generics
     pub fn impls_trait(&self, db: &'db dyn HirDatabase, trait_: Trait, args: &[Type<'db>]) -> bool {
-        let mut it = args.iter().map(|t| t.ty.clone());
-        let trait_ref = TyBuilder::trait_ref(db, trait_.id)
-            .push(self.ty.clone())
-            .fill(|x| {
-                match x {
-                    ParamKind::Type => {
-                        it.next().unwrap_or_else(|| TyKind::Error.intern(Interner)).cast(Interner)
-                    }
-                    ParamKind::Const(ty) => {
-                        // FIXME: this code is not covered in tests.
-                        unknown_const_as_generic(ty.clone())
-                    }
-                    ParamKind::Lifetime => error_lifetime().cast(Interner),
-                }
-            })
-            .build();
-
-        let goal = Canonical {
-            value: hir_ty::InEnvironment::new(
-                &self.env.env.to_chalk(DbInterner::new_with(
-                    db,
-                    Some(self.env.krate),
-                    self.env.block,
-                )),
-                trait_ref.cast(Interner),
-            ),
-            binders: CanonicalVarKinds::empty(Interner),
-        };
-
-        !db.trait_solve(self.env.krate, self.env.block, goal).no_solution()
+        let interner = DbInterner::new_with(db, None, None);
+        let args = generic_args_from_tys(
+            interner,
+            trait_.id.into(),
+            std::iter::once(self.ty).chain(args.iter().map(|ty| ty.ty)),
+        );
+        traits::implements_trait_unique_with_args(db, self.env.clone(), trait_.id, args)
     }
 
     pub fn normalize_trait_assoc_type(
@@ -5301,27 +5059,25 @@
         args: &[Type<'db>],
         alias: TypeAlias,
     ) -> Option<Type<'db>> {
-        let mut args = args.iter();
-        let trait_id = match alias.id.lookup(db).container {
-            ItemContainerId::TraitId(id) => id,
-            _ => unreachable!("non assoc type alias reached in normalize_trait_assoc_type()"),
-        };
-        let parent_subst = TyBuilder::subst_for_def(db, trait_id, None)
-            .push(self.ty.clone())
-            .fill(|it| {
-                // FIXME: this code is not covered in tests.
-                match it {
-                    ParamKind::Type => args.next().unwrap().ty.clone().cast(Interner),
-                    ParamKind::Const(ty) => unknown_const_as_generic(ty.clone()),
-                    ParamKind::Lifetime => error_lifetime().cast(Interner),
-                }
-            })
-            .build();
+        let interner = DbInterner::new_with(db, Some(self.env.krate), self.env.block);
+        let args = generic_args_from_tys(
+            interner,
+            alias.id.into(),
+            std::iter::once(self.ty).chain(args.iter().map(|ty| ty.ty)),
+        );
         // FIXME: We don't handle GATs yet.
-        let projection = TyBuilder::assoc_type_projection(db, alias.id, Some(parent_subst)).build();
+        let projection = Ty::new_alias(
+            interner,
+            AliasTyKind::Projection,
+            AliasTy::new(interner, alias.id.into(), args),
+        );
 
-        let ty = db.normalize_projection(projection, self.env.clone());
-        if ty.is_unknown() { None } else { Some(self.derived(ty)) }
+        // FIXME(next-solver): This needs to be `PostAnalysis`, but this currently causes errors due to our incorrect
+        // handling of opaques. `non_body_analysis()` will also cause errors (from not revealing opaques inside their
+        // defining places), so we choose between two bad options.
+        let infcx = interner.infer_ctxt().build(TypingMode::non_body_analysis());
+        let ty = structurally_normalize_ty(&infcx, projection, self.env.clone());
+        if ty.is_ty_error() { None } else { Some(self.derived(ty)) }
     }
 
     pub fn is_copy(&self, db: &'db dyn HirDatabase) -> bool {
@@ -5332,23 +5088,27 @@
     }
 
     pub fn as_callable(&self, db: &'db dyn HirDatabase) -> Option<Callable<'db>> {
-        let callee = match self.ty.kind(Interner) {
-            TyKind::Closure(id, subst) => Callee::Closure(*id, subst.clone()),
-            TyKind::Function(_) => Callee::FnPtr,
-            TyKind::FnDef(..) => Callee::Def(self.ty.callable_def(db)?),
+        let interner = DbInterner::new_with(db, None, None);
+        let callee = match self.ty.kind() {
+            TyKind::Closure(id, subst) => Callee::Closure(id.0, subst),
+            TyKind::FnPtr(..) => Callee::FnPtr,
+            TyKind::FnDef(id, _) => Callee::Def(id.0),
             kind => {
                 // This will happen when it implements fn or fn mut, since we add an autoborrow adjustment
-                let (ty, kind) = if let TyKind::Ref(_, _, ty) = kind {
-                    (ty, ty.kind(Interner))
+                let (ty, kind) = if let TyKind::Ref(_, ty, _) = kind {
+                    (ty, ty.kind())
                 } else {
-                    (&self.ty, kind)
+                    (self.ty, kind)
                 };
                 if let TyKind::Closure(closure, subst) = kind {
-                    let sig = ty.callable_sig(db)?;
+                    let sig = subst
+                        .split_closure_args_untupled()
+                        .closure_sig_as_fn_ptr_ty
+                        .callable_sig(interner)?;
                     return Some(Callable {
                         ty: self.clone(),
                         sig,
-                        callee: Callee::Closure(*closure, subst.clone()),
+                        callee: Callee::Closure(closure.0, subst),
                         is_bound_method: false,
                     });
                 }
@@ -5362,32 +5122,32 @@
             }
         };
 
-        let sig = self.ty.callable_sig(db)?;
+        let sig = self.ty.callable_sig(interner)?;
         Some(Callable { ty: self.clone(), sig, callee, is_bound_method: false })
     }
 
     pub fn is_closure(&self) -> bool {
-        matches!(self.ty.kind(Interner), TyKind::Closure { .. })
+        matches!(self.ty.kind(), TyKind::Closure { .. })
     }
 
-    pub fn as_closure(&self) -> Option<Closure> {
-        match self.ty.kind(Interner) {
-            TyKind::Closure(id, subst) => Some(Closure { id: *id, subst: subst.clone() }),
+    pub fn as_closure(&self) -> Option<Closure<'db>> {
+        match self.ty.kind() {
+            TyKind::Closure(id, subst) => Some(Closure { id: id.0, subst }),
             _ => None,
         }
     }
 
     pub fn is_fn(&self) -> bool {
-        matches!(self.ty.kind(Interner), TyKind::FnDef(..) | TyKind::Function { .. })
+        matches!(self.ty.kind(), TyKind::FnDef(..) | TyKind::FnPtr { .. })
     }
 
     pub fn is_array(&self) -> bool {
-        matches!(self.ty.kind(Interner), TyKind::Array(..))
+        matches!(self.ty.kind(), TyKind::Array(..))
     }
 
     pub fn is_packed(&self, db: &'db dyn HirDatabase) -> bool {
-        let adt_id = match *self.ty.kind(Interner) {
-            TyKind::Adt(hir_ty::AdtId(adt_id), ..) => adt_id,
+        let adt_id = match self.ty.kind() {
+            TyKind::Adt(adt_def, ..) => adt_def.def_id().0,
             _ => return false,
         };
 
@@ -5399,100 +5159,64 @@
     }
 
     pub fn is_raw_ptr(&self) -> bool {
-        matches!(self.ty.kind(Interner), TyKind::Raw(..))
+        matches!(self.ty.kind(), TyKind::RawPtr(..))
     }
 
     pub fn remove_raw_ptr(&self) -> Option<Type<'db>> {
-        if let TyKind::Raw(_, ty) = self.ty.kind(Interner) {
-            Some(self.derived(ty.clone()))
-        } else {
-            None
-        }
+        if let TyKind::RawPtr(ty, _) = self.ty.kind() { Some(self.derived(ty)) } else { None }
     }
 
     pub fn contains_unknown(&self) -> bool {
-        // FIXME: When we get rid of `ConstScalar::Unknown`, we can just look at precomputed
-        // `TypeFlags` in `TyData`.
-        return go(&self.ty);
-
-        fn go(ty: &Ty) -> bool {
-            match ty.kind(Interner) {
-                TyKind::Error => true,
-
-                TyKind::Adt(_, substs)
-                | TyKind::AssociatedType(_, substs)
-                | TyKind::Tuple(_, substs)
-                | TyKind::OpaqueType(_, substs)
-                | TyKind::FnDef(_, substs)
-                | TyKind::Closure(_, substs) => {
-                    substs.iter(Interner).filter_map(|a| a.ty(Interner)).any(go)
-                }
-
-                TyKind::Array(_ty, len) if len.is_unknown() => true,
-                TyKind::Array(ty, _)
-                | TyKind::Slice(ty)
-                | TyKind::Raw(_, ty)
-                | TyKind::Ref(_, _, ty) => go(ty),
-
-                TyKind::Scalar(_)
-                | TyKind::Str
-                | TyKind::Never
-                | TyKind::Placeholder(_)
-                | TyKind::BoundVar(_)
-                | TyKind::InferenceVar(_, _)
-                | TyKind::Dyn(_)
-                | TyKind::Function(_)
-                | TyKind::Alias(_)
-                | TyKind::Foreign(_)
-                | TyKind::Coroutine(..)
-                | TyKind::CoroutineWitness(..) => false,
-            }
-        }
+        self.ty.references_non_lt_error()
     }
 
     pub fn fields(&self, db: &'db dyn HirDatabase) -> Vec<(Field, Self)> {
-        let (variant_id, substs) = match self.ty.kind(Interner) {
-            TyKind::Adt(hir_ty::AdtId(AdtId::StructId(s)), substs) => ((*s).into(), substs),
-            TyKind::Adt(hir_ty::AdtId(AdtId::UnionId(u)), substs) => ((*u).into(), substs),
+        let interner = DbInterner::new_with(db, None, None);
+        let (variant_id, substs) = match self.ty.kind() {
+            TyKind::Adt(adt_def, substs) => {
+                let id = match adt_def.def_id().0 {
+                    AdtId::StructId(id) => id.into(),
+                    AdtId::UnionId(id) => id.into(),
+                    AdtId::EnumId(_) => return Vec::new(),
+                };
+                (id, substs)
+            }
             _ => return Vec::new(),
         };
 
-        db.field_types(variant_id)
+        db.field_types_ns(variant_id)
             .iter()
             .map(|(local_id, ty)| {
                 let def = Field { parent: variant_id.into(), id: local_id };
-                let ty = ty.clone().substitute(Interner, substs);
+                let ty = ty.instantiate(interner, substs);
                 (def, self.derived(ty))
             })
             .collect()
     }
 
     pub fn tuple_fields(&self, _db: &'db dyn HirDatabase) -> Vec<Self> {
-        if let TyKind::Tuple(_, substs) = &self.ty.kind(Interner) {
-            substs
-                .iter(Interner)
-                .map(|ty| self.derived(ty.assert_ty_ref(Interner).clone()))
-                .collect()
+        if let TyKind::Tuple(substs) = self.ty.kind() {
+            substs.iter().map(|ty| self.derived(ty)).collect()
         } else {
             Vec::new()
         }
     }
 
     pub fn as_array(&self, db: &'db dyn HirDatabase) -> Option<(Self, usize)> {
-        if let TyKind::Array(ty, len) = &self.ty.kind(Interner) {
-            try_const_usize(db, len).map(|it| (self.derived(ty.clone()), it as usize))
+        if let TyKind::Array(ty, len) = self.ty.kind() {
+            try_const_usize(db, len).map(|it| (self.derived(ty), it as usize))
         } else {
             None
         }
     }
 
     pub fn fingerprint_for_trait_impl(&self) -> Option<TyFingerprint> {
-        let interner = DbInterner::conjure();
-        TyFingerprint::for_trait_impl(self.ty.to_nextsolver(interner))
+        TyFingerprint::for_trait_impl(self.ty)
     }
 
-    pub(crate) fn canonical(&self) -> Canonical<Ty> {
-        hir_ty::replace_errors_with_variables(&self.ty)
+    pub(crate) fn canonical(&self, db: &'db dyn HirDatabase) -> Canonical<'db, Ty<'db>> {
+        let interner = DbInterner::new_with(db, None, None);
+        hir_ty::replace_errors_with_variables(interner, &self.ty)
     }
 
     /// Returns types that this type dereferences to (including this type itself). The returned
@@ -5504,9 +5228,10 @@
         self.autoderef_(db).map(move |ty| self.derived(ty))
     }
 
-    fn autoderef_(&self, db: &'db dyn HirDatabase) -> impl Iterator<Item = Ty> {
+    fn autoderef_(&self, db: &'db dyn HirDatabase) -> impl Iterator<Item = Ty<'db>> {
+        let interner = DbInterner::new_with(db, None, None);
         // There should be no inference vars in types passed here
-        let canonical = hir_ty::replace_errors_with_variables(&self.ty);
+        let canonical = hir_ty::replace_errors_with_variables(interner, &self.ty);
         autoderef(db, self.env.clone(), canonical)
     }
 
@@ -5532,8 +5257,7 @@
         krate: Crate,
         callback: &mut dyn FnMut(AssocItemId) -> bool,
     ) {
-        let interner = DbInterner::new_with(db, None, None);
-        let ty_ns = self.ty.to_nextsolver(interner);
+        let ty_ns = self.ty;
         let def_crates = match method_resolution::def_crates(db, ty_ns, krate.id) {
             Some(it) => it,
             None => return,
@@ -5570,15 +5294,13 @@
     /// - "U"
     /// ```
     pub fn type_arguments(&self) -> impl Iterator<Item = Type<'db>> + '_ {
-        self.ty
-            .strip_references()
-            .as_adt()
-            .map(|(_, substs)| substs)
-            .or_else(|| self.ty.strip_references().as_tuple())
-            .into_iter()
-            .flat_map(|substs| substs.iter(Interner))
-            .filter_map(|arg| arg.ty(Interner).cloned())
-            .map(move |ty| self.derived(ty))
+        match self.ty.strip_references().kind() {
+            TyKind::Adt(_, substs) => Either::Left(substs.types().map(move |ty| self.derived(ty))),
+            TyKind::Tuple(substs) => {
+                Either::Right(Either::Left(substs.iter().map(move |ty| self.derived(ty))))
+            }
+            _ => Either::Right(Either::Right(std::iter::empty())),
+        }
     }
 
     /// Iterates its type and const arguments
@@ -5608,15 +5330,13 @@
             .strip_references()
             .as_adt()
             .into_iter()
-            .flat_map(|(_, substs)| substs.iter(Interner))
-            .filter_map(move |arg| {
-                // arg can be either a `Ty` or `constant`
-                if let Some(ty) = arg.ty(Interner) {
-                    Some(format_smolstr!("{}", ty.display(db, display_target)))
-                } else {
-                    arg.constant(Interner)
-                        .map(|const_| format_smolstr!("{}", const_.display(db, display_target)))
+            .flat_map(|(_, substs)| substs.iter())
+            .filter_map(move |arg| match arg {
+                GenericArg::Ty(ty) => Some(format_smolstr!("{}", ty.display(db, display_target))),
+                GenericArg::Const(const_) => {
+                    Some(format_smolstr!("{}", const_.display(db, display_target)))
                 }
+                GenericArg::Lifetime(_) => None,
             })
     }
 
@@ -5733,8 +5453,9 @@
             ?name,
         )
         .entered();
+        let interner = DbInterner::new_with(db, None, None);
         // There should be no inference vars in types passed here
-        let canonical = hir_ty::replace_errors_with_variables(&self.ty);
+        let canonical = hir_ty::replace_errors_with_variables(interner, &self.ty);
 
         let krate = scope.krate();
         let environment = scope
@@ -5743,11 +5464,7 @@
             .map_or_else(|| TraitEnvironment::empty(krate.id), |d| db.trait_environment(d));
 
         _ = method_resolution::iterate_method_candidates_dyn(
-            &canonical.to_nextsolver(DbInterner::new_with(
-                db,
-                Some(environment.krate),
-                environment.block,
-            )),
+            &canonical,
             db,
             environment,
             traits_in_scope,
@@ -5825,7 +5542,8 @@
             }
         }
 
-        let canonical = hir_ty::replace_errors_with_variables(&self.ty);
+        let interner = DbInterner::new_with(db, None, None);
+        let canonical = hir_ty::replace_errors_with_variables(interner, &self.ty);
 
         let krate = scope.krate();
         let environment = scope
@@ -5834,11 +5552,7 @@
             .map_or_else(|| TraitEnvironment::empty(krate.id), |d| db.trait_environment(d));
 
         _ = method_resolution::iterate_path_candidates(
-            &canonical.to_nextsolver(DbInterner::new_with(
-                db,
-                Some(environment.krate),
-                environment.block,
-            )),
+            &canonical,
             db,
             environment,
             traits_in_scope,
@@ -5877,7 +5591,7 @@
     pub fn env_traits(&self, db: &'db dyn HirDatabase) -> impl Iterator<Item = Trait> {
         let _p = tracing::info_span!("env_traits").entered();
         self.autoderef_(db)
-            .filter(|ty| matches!(ty.kind(Interner), TyKind::Placeholder(_)))
+            .filter(|ty| matches!(ty.kind(), TyKind::Param(_)))
             .flat_map(|ty| {
                 self.env
                     .traits_in_scope_from_clauses(ty)
@@ -5888,136 +5602,66 @@
 
     pub fn as_impl_traits(&self, db: &'db dyn HirDatabase) -> Option<impl Iterator<Item = Trait>> {
         self.ty.impl_trait_bounds(db).map(|it| {
-            it.into_iter().filter_map(|pred| match pred.skip_binders() {
-                hir_ty::WhereClause::Implemented(trait_ref) => {
-                    Some(Trait::from(trait_ref.hir_trait_id()))
-                }
+            it.into_iter().filter_map(|pred| match pred.kind().skip_binder() {
+                ClauseKind::Trait(trait_ref) => Some(Trait::from(trait_ref.def_id().0)),
                 _ => None,
             })
         })
     }
 
     pub fn as_associated_type_parent_trait(&self, db: &'db dyn HirDatabase) -> Option<Trait> {
-        self.ty.associated_type_parent_trait(db).map(Into::into)
+        let TyKind::Alias(AliasTyKind::Projection, alias) = self.ty.kind() else { return None };
+        match alias.def_id.expect_type_alias().loc(db).container {
+            ItemContainerId::TraitId(id) => Some(Trait { id }),
+            _ => None,
+        }
     }
 
-    fn derived(&self, ty: Ty) -> Self {
-        Type { env: self.env.clone(), ty, _pd: PhantomCovariantLifetime::new() }
+    fn derived(&self, ty: Ty<'db>) -> Self {
+        Type { env: self.env.clone(), ty }
     }
 
-    /// Visits every type, including generic arguments, in this type. `cb` is called with type
+    /// Visits every type, including generic arguments, in this type. `callback` is called with type
     /// itself first, and then with its generic arguments.
-    pub fn walk(&self, db: &'db dyn HirDatabase, mut cb: impl FnMut(Type<'db>)) {
-        fn walk_substs<'db>(
+    pub fn walk(&self, db: &'db dyn HirDatabase, callback: impl FnMut(Type<'db>)) {
+        struct Visitor<'db, F> {
             db: &'db dyn HirDatabase,
-            type_: &Type<'db>,
-            substs: &Substitution,
-            cb: &mut impl FnMut(Type<'db>),
-        ) {
-            for ty in substs.iter(Interner).filter_map(|a| a.ty(Interner)) {
-                walk_type(db, &type_.derived(ty.clone()), cb);
+            env: Arc<TraitEnvironment<'db>>,
+            callback: F,
+            visited: FxHashSet<Ty<'db>>,
+        }
+        impl<'db, F> TypeVisitor<DbInterner<'db>> for Visitor<'db, F>
+        where
+            F: FnMut(Type<'db>),
+        {
+            type Result = ();
+
+            fn visit_ty(&mut self, ty: Ty<'db>) -> Self::Result {
+                if !self.visited.insert(ty) {
+                    return;
+                }
+
+                (self.callback)(Type { env: self.env.clone(), ty });
+
+                if let Some(bounds) = ty.impl_trait_bounds(self.db) {
+                    bounds.visit_with(self);
+                }
+
+                ty.super_visit_with(self);
             }
         }
 
-        fn walk_bounds<'db>(
-            db: &'db dyn HirDatabase,
-            type_: &Type<'db>,
-            bounds: &[QuantifiedWhereClause],
-            cb: &mut impl FnMut(Type<'db>),
-        ) {
-            for pred in bounds {
-                if let WhereClause::Implemented(trait_ref) = pred.skip_binders() {
-                    cb(type_.clone());
-                    // skip the self type. it's likely the type we just got the bounds from
-                    if let [self_ty, params @ ..] = trait_ref.substitution.as_slice(Interner) {
-                        for ty in
-                            params.iter().filter(|&ty| ty != self_ty).filter_map(|a| a.ty(Interner))
-                        {
-                            walk_type(db, &type_.derived(ty.clone()), cb);
-                        }
-                    }
-                }
-            }
-        }
-
-        fn walk_type<'db>(
-            db: &'db dyn HirDatabase,
-            type_: &Type<'db>,
-            cb: &mut impl FnMut(Type<'db>),
-        ) {
-            let ty = type_.ty.strip_references();
-            match ty.kind(Interner) {
-                TyKind::Adt(_, substs) => {
-                    cb(type_.derived(ty.clone()));
-                    walk_substs(db, type_, substs, cb);
-                }
-                TyKind::AssociatedType(_, substs)
-                | TyKind::Alias(AliasTy::Projection(hir_ty::ProjectionTy {
-                    substitution: substs,
-                    ..
-                })) => {
-                    if ty.associated_type_parent_trait(db).is_some() {
-                        cb(type_.derived(ty.clone()));
-                    }
-                    walk_substs(db, type_, substs, cb);
-                }
-                TyKind::OpaqueType(_, subst) => {
-                    if let Some(bounds) = ty.impl_trait_bounds(db) {
-                        walk_bounds(db, &type_.derived(ty.clone()), &bounds, cb);
-                    }
-
-                    walk_substs(db, type_, subst, cb);
-                }
-                TyKind::Alias(AliasTy::Opaque(opaque_ty)) => {
-                    if let Some(bounds) = ty.impl_trait_bounds(db) {
-                        walk_bounds(db, &type_.derived(ty.clone()), &bounds, cb);
-                    }
-
-                    walk_substs(db, type_, &opaque_ty.substitution, cb);
-                }
-                TyKind::Placeholder(_) => {
-                    cb(type_.derived(ty.clone()));
-                    if let Some(bounds) = ty.impl_trait_bounds(db) {
-                        walk_bounds(db, &type_.derived(ty.clone()), &bounds, cb);
-                    }
-                }
-                TyKind::Dyn(bounds) => {
-                    walk_bounds(
-                        db,
-                        &type_.derived(ty.clone()),
-                        bounds.bounds.skip_binders().interned(),
-                        cb,
-                    );
-                }
-
-                TyKind::Ref(_, _, ty)
-                | TyKind::Raw(_, ty)
-                | TyKind::Array(ty, _)
-                | TyKind::Slice(ty) => {
-                    walk_type(db, &type_.derived(ty.clone()), cb);
-                }
-
-                TyKind::FnDef(_, substs)
-                | TyKind::Tuple(_, substs)
-                | TyKind::Closure(.., substs) => {
-                    walk_substs(db, type_, substs, cb);
-                }
-                TyKind::Function(hir_ty::FnPointer { substitution, .. }) => {
-                    walk_substs(db, type_, &substitution.0, cb);
-                }
-
-                _ => {}
-            }
-        }
-
-        walk_type(db, self, &mut cb);
+        let mut visitor =
+            Visitor { db, env: self.env.clone(), callback, visited: FxHashSet::default() };
+        self.ty.visit_with(&mut visitor);
     }
     /// Check if type unifies with another type.
     ///
     /// Note that we consider placeholder types to unify with everything.
     /// For example `Option<T>` and `Option<U>` unify although there is unresolved goal `T = U`.
     pub fn could_unify_with(&self, db: &'db dyn HirDatabase, other: &Type<'db>) -> bool {
-        let tys = hir_ty::replace_errors_with_variables(&(self.ty.clone(), other.ty.clone()));
+        let interner = DbInterner::new_with(db, None, None);
+        let tys = hir_ty::replace_errors_with_variables(interner, &(self.ty, other.ty));
         hir_ty::could_unify(db, self.env.clone(), &tys)
     }
 
@@ -6026,35 +5670,34 @@
     /// This means that placeholder types are not considered to unify if there are any bounds set on
     /// them. For example `Option<T>` and `Option<U>` do not unify as we cannot show that `T = U`
     pub fn could_unify_with_deeply(&self, db: &'db dyn HirDatabase, other: &Type<'db>) -> bool {
-        let tys = hir_ty::replace_errors_with_variables(&(self.ty.clone(), other.ty.clone()));
+        let interner = DbInterner::new_with(db, None, None);
+        let tys = hir_ty::replace_errors_with_variables(interner, &(self.ty, other.ty));
         hir_ty::could_unify_deeply(db, self.env.clone(), &tys)
     }
 
     pub fn could_coerce_to(&self, db: &'db dyn HirDatabase, to: &Type<'db>) -> bool {
-        let tys = hir_ty::replace_errors_with_variables(&(self.ty.clone(), to.ty.clone()));
+        let interner = DbInterner::new_with(db, None, None);
+        let tys = hir_ty::replace_errors_with_variables(interner, &(self.ty, to.ty));
         hir_ty::could_coerce(db, self.env.clone(), &tys)
     }
 
-    pub fn as_type_param(&self, db: &'db dyn HirDatabase) -> Option<TypeParam> {
-        match self.ty.kind(Interner) {
-            TyKind::Placeholder(p) => Some(TypeParam {
-                id: TypeParamId::from_unchecked(hir_ty::from_placeholder_idx(db, *p).0),
-            }),
+    pub fn as_type_param(&self, _db: &'db dyn HirDatabase) -> Option<TypeParam> {
+        match self.ty.kind() {
+            TyKind::Param(param) => Some(TypeParam { id: param.id }),
             _ => None,
         }
     }
 
     /// Returns unique `GenericParam`s contained in this type.
     pub fn generic_params(&self, db: &'db dyn HirDatabase) -> FxHashSet<GenericParam> {
-        hir_ty::collect_placeholders(&self.ty, db)
+        hir_ty::collect_params(&self.ty)
             .into_iter()
             .map(|id| TypeOrConstParam { id }.split(db).either_into())
             .collect()
     }
 
     pub fn layout(&self, db: &'db dyn HirDatabase) -> Result<Layout, LayoutError> {
-        let interner = DbInterner::new_with(db, None, None);
-        db.layout_of_ty(self.ty.to_nextsolver(interner), self.env.clone())
+        db.layout_of_ty(self.ty, self.env.clone())
             .map(|layout| Layout(layout, db.target_data_layout(self.env.krate).unwrap()))
     }
 
@@ -6062,33 +5705,27 @@
         let interner = DbInterner::new_with(db, Some(self.env.krate), self.env.block);
         // FIXME: This should be `PostAnalysis` I believe.
         let infcx = interner.infer_ctxt().build(TypingMode::non_body_analysis());
-        hir_ty::drop::has_drop_glue(&infcx, self.ty.to_nextsolver(interner), self.env.clone())
+        hir_ty::drop::has_drop_glue(&infcx, self.ty, self.env.clone())
     }
 }
 
 #[derive(Clone, PartialEq, Eq, Debug, Hash)]
 pub struct TypeNs<'db> {
     env: Arc<TraitEnvironment<'db>>,
-    ty: hir_ty::next_solver::Ty<'db>,
-    _pd: PhantomCovariantLifetime<'db>,
+    ty: Ty<'db>,
 }
 
 impl<'db> TypeNs<'db> {
-    fn new(
-        db: &'db dyn HirDatabase,
-        lexical_env: impl HasResolver,
-        ty: hir_ty::next_solver::Ty<'db>,
-    ) -> Self {
+    fn new(db: &'db dyn HirDatabase, lexical_env: impl HasResolver, ty: Ty<'db>) -> Self {
         let resolver = lexical_env.resolver(db);
         let environment = resolver
             .generic_def()
             .map_or_else(|| TraitEnvironment::empty(resolver.krate()), |d| db.trait_environment(d));
-        TypeNs { env: environment, ty, _pd: PhantomCovariantLifetime::new() }
+        TypeNs { env: environment, ty }
     }
 
-    pub fn to_type(&self, db: &'db dyn HirDatabase) -> Type<'db> {
-        let interner = DbInterner::new_with(db, Some(self.env.krate), self.env.block);
-        Type { env: self.env.clone(), ty: convert_ty_for_result(interner, self.ty), _pd: self._pd }
+    pub fn to_type(&self, _db: &'db dyn HirDatabase) -> Type<'db> {
+        Type { env: self.env.clone(), ty: self.ty }
     }
 
     // FIXME: Find better API that also handles const generics
@@ -6144,40 +5781,38 @@
 #[derive(Debug)]
 pub struct Callable<'db> {
     ty: Type<'db>,
-    sig: CallableSig,
-    callee: Callee,
+    sig: PolyFnSig<'db>,
+    callee: Callee<'db>,
     /// Whether this is a method that was called with method call syntax.
     is_bound_method: bool,
 }
 
 #[derive(Clone, PartialEq, Eq, Hash, Debug)]
-enum Callee {
+enum Callee<'db> {
     Def(CallableDefId),
-    Closure(ClosureId, Substitution),
+    Closure(InternedClosureId, GenericArgs<'db>),
     FnPtr,
     FnImpl(FnTrait),
 }
 
-pub enum CallableKind {
+pub enum CallableKind<'db> {
     Function(Function),
     TupleStruct(Struct),
     TupleEnumVariant(Variant),
-    Closure(Closure),
+    Closure(Closure<'db>),
     FnPtr,
     FnImpl(FnTrait),
 }
 
 impl<'db> Callable<'db> {
-    pub fn kind(&self) -> CallableKind {
+    pub fn kind(&self) -> CallableKind<'db> {
         match self.callee {
             Callee::Def(CallableDefId::FunctionId(it)) => CallableKind::Function(it.into()),
             Callee::Def(CallableDefId::StructId(it)) => CallableKind::TupleStruct(it.into()),
             Callee::Def(CallableDefId::EnumVariantId(it)) => {
                 CallableKind::TupleEnumVariant(it.into())
             }
-            Callee::Closure(id, ref subst) => {
-                CallableKind::Closure(Closure { id, subst: subst.clone() })
-            }
+            Callee::Closure(id, ref subst) => CallableKind::Closure(Closure { id, subst: *subst }),
             Callee::FnPtr => CallableKind::FnPtr,
             Callee::FnImpl(fn_) => CallableKind::FnImpl(fn_),
         }
@@ -6188,25 +5823,31 @@
             _ => return None,
         };
         let func = Function { id: func };
-        Some((func.self_param(db)?, self.ty.derived(self.sig.params()[0].clone())))
+        Some((
+            func.self_param(db)?,
+            self.ty.derived(self.sig.skip_binder().inputs_and_output.inputs()[0]),
+        ))
     }
     pub fn n_params(&self) -> usize {
-        self.sig.params().len() - if self.is_bound_method { 1 } else { 0 }
+        self.sig.skip_binder().inputs_and_output.inputs().len()
+            - if self.is_bound_method { 1 } else { 0 }
     }
     pub fn params(&self) -> Vec<Param<'db>> {
         self.sig
-            .params()
+            .skip_binder()
+            .inputs_and_output
+            .inputs()
             .iter()
             .enumerate()
             .skip(if self.is_bound_method { 1 } else { 0 })
-            .map(|(idx, ty)| (idx, self.ty.derived(ty.clone())))
+            .map(|(idx, ty)| (idx, self.ty.derived(*ty)))
             .map(|(idx, ty)| Param { func: self.callee.clone(), idx, ty })
             .collect()
     }
     pub fn return_type(&self) -> Type<'db> {
-        self.ty.derived(self.sig.ret().clone())
+        self.ty.derived(self.sig.skip_binder().output())
     }
-    pub fn sig(&self) -> &CallableSig {
+    pub fn sig(&self) -> impl Eq {
         &self.sig
     }
 
@@ -6758,5 +6399,37 @@
     name.map_or_else(Name::missing, |name| name.as_name())
 }
 
+fn generic_args_from_tys<'db>(
+    interner: DbInterner<'db>,
+    def_id: SolverDefId,
+    args: impl IntoIterator<Item = Ty<'db>>,
+) -> GenericArgs<'db> {
+    let mut args = args.into_iter();
+    GenericArgs::for_item(interner, def_id, |_, _, id, _| {
+        if matches!(id, GenericParamId::TypeParamId(_))
+            && let Some(arg) = args.next()
+        {
+            arg.into()
+        } else {
+            next_solver::GenericArg::error_from_id(interner, id)
+        }
+    })
+}
+
+fn has_non_default_type_params(db: &dyn HirDatabase, generic_def: GenericDefId) -> bool {
+    let params = db.generic_params(generic_def);
+    let defaults = db.generic_defaults_ns(generic_def);
+    params
+        .iter_type_or_consts()
+        .filter(|(_, param)| matches!(param, TypeOrConstParamData::TypeParamData(_)))
+        .map(|(local_id, _)| TypeOrConstParamId { parent: generic_def, local_id })
+        .any(|param| {
+            let Some(param) = hir_ty::param_idx(db, param) else {
+                return false;
+            };
+            defaults.get(param).is_none()
+        })
+}
+
 pub use hir_ty::next_solver;
 pub use hir_ty::setup_tracing;
diff --git a/crates/hir/src/semantics.rs b/crates/hir/src/semantics.rs
index 45c2020..eecca02 100644
--- a/crates/hir/src/semantics.rs
+++ b/crates/hir/src/semantics.rs
@@ -28,9 +28,10 @@
     mod_path::{ModPath, PathKind},
     name::AsName,
 };
-use hir_ty::diagnostics::{unsafe_operations, unsafe_operations_for_body};
-use hir_ty::next_solver::DbInterner;
-use hir_ty::next_solver::mapping::{ChalkToNextSolver, NextSolverToChalk};
+use hir_ty::{
+    diagnostics::{unsafe_operations, unsafe_operations_for_body},
+    next_solver::DbInterner,
+};
 use intern::{Interned, Symbol, sym};
 use itertools::Itertools;
 use rustc_hash::{FxHashMap, FxHashSet};
@@ -1563,16 +1564,11 @@
 
         let (mut source_ty, _) = analyzer.type_of_expr(self.db, expr)?;
 
-        let interner = DbInterner::new_with(self.db, None, None);
-
         analyzer.expr_adjustments(expr).map(|it| {
             it.iter()
                 .map(|adjust| {
-                    let target = Type::new_with_resolver(
-                        self.db,
-                        &analyzer.resolver,
-                        adjust.target.to_chalk(interner),
-                    );
+                    let target =
+                        Type::new_with_resolver(self.db, &analyzer.resolver, adjust.target);
                     let kind = match adjust.kind {
                         hir_ty::Adjust::NeverToAny => Adjust::NeverToAny,
                         hir_ty::Adjust::Deref(Some(hir_ty::OverloadedDeref(m))) => {
@@ -1666,7 +1662,7 @@
             trait_.id.into(),
             |_, _, id, _| {
                 assert!(matches!(id, hir_def::GenericParamId::TypeParamId(_)), "expected a type");
-                subst.next().expect("too few subst").ty.to_nextsolver(interner).into()
+                subst.next().expect("too few subst").ty.into()
             },
         );
         assert!(subst.next().is_none(), "too many subst");
diff --git a/crates/hir/src/source_analyzer.rs b/crates/hir/src/source_analyzer.rs
index a4bc3e8..8d2ba7e 100644
--- a/crates/hir/src/source_analyzer.rs
+++ b/crates/hir/src/source_analyzer.rs
@@ -7,13 +7,6 @@
 //! purely for "IDE needs".
 use std::iter::{self, once};
 
-use crate::{
-    Adt, AssocItem, BindingMode, BuiltinAttr, BuiltinType, Callable, Const, DeriveHelper, Field,
-    Function, GenericSubstitution, Local, Macro, ModuleDef, Static, Struct, ToolModule, Trait,
-    TupleField, Type, TypeAlias, Variant,
-    db::HirDatabase,
-    semantics::{PathResolution, PathResolutionPerNs},
-};
 use either::Either;
 use hir_def::{
     AdtId, AssocItemId, CallableDefId, ConstId, DefWithBodyId, FieldId, FunctionId, GenericDefId,
@@ -36,23 +29,24 @@
     name::{AsName, Name},
 };
 use hir_ty::{
-    Adjustment, AliasTy, InferenceResult, Interner, LifetimeElisionKind, ProjectionTy,
-    Substitution, ToChalk, TraitEnvironment, Ty, TyKind, TyLoweringContext,
+    Adjustment, InferenceResult, LifetimeElisionKind, TraitEnvironment, TyLoweringContext,
     diagnostics::{
         InsideUnsafeBlock, record_literal_missing_fields, record_pattern_missing_fields,
         unsafe_operations,
     },
-    from_assoc_type_id,
     lang_items::lang_items_for_bin_op,
     method_resolution,
     next_solver::{
-        DbInterner, GenericArgs, TypingMode,
-        infer::DbInternerInferExt,
-        mapping::{ChalkToNextSolver, NextSolverToChalk},
+        DbInterner, ErrorGuaranteed, GenericArgs, Ty, TyKind, TypingMode, infer::DbInternerInferExt,
     },
+    traits::structurally_normalize_ty,
 };
 use intern::sym;
 use itertools::Itertools;
+use rustc_type_ir::{
+    AliasTyKind,
+    inherent::{AdtDef, IntoKind, Ty as _},
+};
 use smallvec::SmallVec;
 use stdx::never;
 use syntax::{
@@ -61,6 +55,14 @@
 };
 use triomphe::Arc;
 
+use crate::{
+    Adt, AssocItem, BindingMode, BuiltinAttr, BuiltinType, Callable, Const, DeriveHelper, Field,
+    Function, GenericSubstitution, Local, Macro, ModuleDef, Static, Struct, ToolModule, Trait,
+    TupleField, Type, TypeAlias, Variant,
+    db::HirDatabase,
+    semantics::{PathResolution, PathResolutionPerNs},
+};
+
 /// `SourceAnalyzer` is a convenience wrapper which exposes HIR API in terms of
 /// original source files. It should not be used inside the HIR itself.
 #[derive(Debug)]
@@ -292,9 +294,7 @@
             .and_then(|expr_id| infer.expr_adjustment(expr_id))
             .and_then(|adjusts| adjusts.last().map(|adjust| adjust.target));
         let ty = infer[expr_id];
-        let mk_ty = |ty: hir_ty::next_solver::Ty<'_>| {
-            Type::new_with_resolver(db, &self.resolver, ty.to_chalk(DbInterner::conjure()))
-        };
+        let mk_ty = |ty: Ty<'db>| Type::new_with_resolver(db, &self.resolver, ty);
         Some((mk_ty(ty), coerced.map(mk_ty)))
     }
 
@@ -316,9 +316,7 @@
         };
 
         let ty = infer[expr_or_pat_id];
-        let mk_ty = |ty: hir_ty::next_solver::Ty<'db>| {
-            Type::new_with_resolver(db, &self.resolver, ty.to_chalk(DbInterner::conjure()))
-        };
+        let mk_ty = |ty: Ty<'db>| Type::new_with_resolver(db, &self.resolver, ty);
         Some((mk_ty(ty), coerced.map(mk_ty)))
     }
 
@@ -330,9 +328,7 @@
         let binding_id = self.binding_id_of_pat(pat)?;
         let infer = self.infer()?;
         let ty = infer[binding_id];
-        let mk_ty = |ty: hir_ty::next_solver::Ty<'db>| {
-            Type::new_with_resolver(db, &self.resolver, ty.to_chalk(DbInterner::conjure()))
-        };
+        let mk_ty = |ty: Ty<'db>| Type::new_with_resolver(db, &self.resolver, ty);
         Some(mk_ty(ty))
     }
 
@@ -343,7 +339,7 @@
     ) -> Option<Type<'db>> {
         let binding = self.body()?.self_param?;
         let ty = self.infer()?[binding];
-        Some(Type::new_with_resolver(db, &self.resolver, ty.to_chalk(DbInterner::conjure())))
+        Some(Type::new_with_resolver(db, &self.resolver, ty))
     }
 
     pub(crate) fn binding_mode_of_pat(
@@ -374,9 +370,7 @@
             infer
                 .pat_adjustment(pat_id.as_pat()?)?
                 .iter()
-                .map(|ty| {
-                    Type::new_with_resolver(db, &self.resolver, ty.to_chalk(DbInterner::conjure()))
-                })
+                .map(|ty| Type::new_with_resolver(db, &self.resolver, *ty))
                 .collect(),
         )
     }
@@ -390,7 +384,7 @@
         let (func, args) = self.infer()?.method_resolution(expr_id)?;
         let interner = DbInterner::new_with(db, None, None);
         let ty = db.value_ty(func.into())?.instantiate(interner, args);
-        let ty = Type::new_with_resolver(db, &self.resolver, ty.to_chalk(interner));
+        let ty = Type::new_with_resolver(db, &self.resolver, ty);
         let mut res = ty.as_callable(db)?;
         res.is_bound_method = true;
         Some(res)
@@ -414,18 +408,13 @@
     ) -> Option<(Either<Function, Field>, Option<GenericSubstitution<'db>>)> {
         let expr_id = self.expr_id(call.clone().into())?.as_expr()?;
         let inference_result = self.infer()?;
-        let interner = DbInterner::new_with(db, None, None);
         match inference_result.method_resolution(expr_id) {
             Some((f_in_trait, substs)) => {
                 let (fn_, subst) =
                     self.resolve_impl_method_or_trait_def_with_subst(db, f_in_trait, substs);
                 Some((
                     Either::Left(fn_.into()),
-                    Some(GenericSubstitution::new(
-                        fn_.into(),
-                        subst.to_chalk(interner),
-                        self.trait_environment(db),
-                    )),
+                    Some(GenericSubstitution::new(fn_.into(), subst, self.trait_environment(db))),
                 ))
             }
             None => {
@@ -465,11 +454,7 @@
         let body = self.store()?;
         if let Expr::Field { expr: object_expr, name: _ } = body[field_expr] {
             let (adt, subst) = infer.type_of_expr_with_adjust(object_expr)?.as_adt()?;
-            return Some(GenericSubstitution::new(
-                adt.into(),
-                subst.to_chalk(DbInterner::conjure()),
-                self.trait_environment(db),
-            ));
+            return Some(GenericSubstitution::new(adt.into(), subst, self.trait_environment(db)));
         }
         None
     }
@@ -483,7 +468,6 @@
         let (def, ..) = self.body_()?;
         let expr_id = self.expr_id(field.clone().into())?.as_expr()?;
         let inference_result = self.infer()?;
-        let interner = DbInterner::new_with(db, None, None);
         match inference_result.field_resolution(expr_id) {
             Some(field) => match field {
                 Either::Left(field) => Some((
@@ -503,11 +487,7 @@
                 let (f, subst) = self.resolve_impl_method_or_trait_def_with_subst(db, f, substs);
                 (
                     Either::Right(f.into()),
-                    Some(GenericSubstitution::new(
-                        f.into(),
-                        subst.to_chalk(interner),
-                        self.trait_environment(db),
-                    )),
+                    Some(GenericSubstitution::new(f.into(), subst, self.trait_environment(db))),
                 )
             }),
         }
@@ -557,7 +537,7 @@
         db: &'db dyn HirDatabase,
         await_expr: &ast::AwaitExpr,
     ) -> Option<FunctionId> {
-        let mut ty = self.ty_of_expr(await_expr.expr()?)?.clone();
+        let mut ty = self.ty_of_expr(await_expr.expr()?)?;
 
         let into_future_trait = self
             .resolver
@@ -565,7 +545,7 @@
             .map(Trait::from);
 
         if let Some(into_future_trait) = into_future_trait {
-            let type_ = Type::new_with_resolver(db, &self.resolver, ty.clone());
+            let type_ = Type::new_with_resolver(db, &self.resolver, ty);
             if type_.impls_trait(db, into_future_trait, &[]) {
                 let items = into_future_trait.items(db);
                 let into_future_type = items.into_iter().find_map(|item| match item {
@@ -585,7 +565,7 @@
         // HACK: subst for `poll()` coincides with that for `Future` because `poll()` itself
         // doesn't have any generic parameters, so we skip building another subst for `poll()`.
         let interner = DbInterner::new_with(db, None, None);
-        let substs = GenericArgs::new_from_iter(interner, [ty.to_nextsolver(interner).into()]);
+        let substs = GenericArgs::new_from_iter(interner, [ty.into()]);
         Some(self.resolve_impl_method_or_trait_def(db, poll_fn, substs))
     }
 
@@ -627,7 +607,7 @@
         let interner = DbInterner::new_with(db, None, None);
         // HACK: subst for all methods coincides with that for their trait because the methods
         // don't have any generic parameters, so we skip building another subst for the methods.
-        let substs = GenericArgs::new_from_iter(interner, [ty.to_nextsolver(interner).into()]);
+        let substs = GenericArgs::new_from_iter(interner, [ty.into()]);
 
         Some(self.resolve_impl_method_or_trait_def(db, op_fn, substs))
     }
@@ -658,10 +638,7 @@
         // HACK: subst for all methods coincides with that for their trait because the methods
         // don't have any generic parameters, so we skip building another subst for the methods.
         let interner = DbInterner::new_with(db, None, None);
-        let substs = GenericArgs::new_from_iter(
-            interner,
-            [base_ty.to_nextsolver(interner).into(), index_ty.to_nextsolver(interner).into()],
-        );
+        let substs = GenericArgs::new_from_iter(interner, [base_ty.into(), index_ty.into()]);
         Some(self.resolve_impl_method_or_trait_def(db, op_fn, substs))
     }
 
@@ -679,10 +656,7 @@
         // HACK: subst for `index()` coincides with that for `Index` because `index()` itself
         // doesn't have any generic parameters, so we skip building another subst for `index()`.
         let interner = DbInterner::new_with(db, None, None);
-        let substs = GenericArgs::new_from_iter(
-            interner,
-            [lhs.to_nextsolver(interner).into(), rhs.to_nextsolver(interner).into()],
-        );
+        let substs = GenericArgs::new_from_iter(interner, [lhs.into(), rhs.into()]);
 
         Some(self.resolve_impl_method_or_trait_def(db, op_fn, substs))
     }
@@ -698,7 +672,7 @@
         // HACK: subst for `branch()` coincides with that for `Try` because `branch()` itself
         // doesn't have any generic parameters, so we skip building another subst for `branch()`.
         let interner = DbInterner::new_with(db, None, None);
-        let substs = GenericArgs::new_from_iter(interner, [ty.to_nextsolver(interner).into()]);
+        let substs = GenericArgs::new_from_iter(interner, [ty.into()]);
 
         Some(self.resolve_impl_method_or_trait_def(db, op_fn, substs))
     }
@@ -735,12 +709,11 @@
             }
         };
         let (adt, subst) = self.infer()?.type_of_expr_or_pat(expr_id)?.as_adt()?;
-        let subst = subst.to_chalk(interner);
         let variant = self.infer()?.variant_resolution_for_expr_or_pat(expr_id)?;
         let variant_data = variant.fields(db);
         let field = FieldId { parent: variant, local_id: variant_data.field(&local_name)? };
         let field_ty =
-            db.field_types(variant).get(field.local_id)?.clone().substitute(Interner, &subst);
+            (*db.field_types_ns(variant).get(field.local_id)?).instantiate(interner, subst);
         Some((
             field.into(),
             local,
@@ -762,9 +735,8 @@
         let variant_data = variant.fields(db);
         let field = FieldId { parent: variant, local_id: variant_data.field(&field_name)? };
         let (adt, subst) = self.infer()?[pat_id.as_pat()?].as_adt()?;
-        let subst = subst.to_chalk(interner);
         let field_ty =
-            db.field_types(variant).get(field.local_id)?.clone().substitute(Interner, &subst);
+            (*db.field_types_ns(variant).get(field.local_id)?).instantiate(interner, subst);
         Some((
             field.into(),
             Type::new_with_resolver(db, &self.resolver, field_ty),
@@ -817,43 +789,40 @@
         let container = self.type_of_type(db, &container)?;
 
         let trait_env = container.env;
+
+        let interner = DbInterner::new_with(db, Some(trait_env.krate), trait_env.block);
+        let infcx = interner.infer_ctxt().build(TypingMode::PostAnalysis);
+
         let mut container = Either::Right(container.ty);
         for field_name in offset_of_expr.fields() {
-            if let Some(
-                TyKind::Alias(AliasTy::Projection(ProjectionTy { associated_ty_id, substitution }))
-                | TyKind::AssociatedType(associated_ty_id, substitution),
-            ) = container.as_ref().right().map(|it| it.kind(Interner))
-            {
-                let projection = ProjectionTy {
-                    associated_ty_id: *associated_ty_id,
-                    substitution: substitution.clone(),
-                };
-                container = Either::Right(db.normalize_projection(projection, trait_env.clone()));
+            if let Either::Right(container) = &mut container {
+                *container = structurally_normalize_ty(&infcx, *container, trait_env.clone());
             }
-            let handle_variants = |variant: VariantId, subst: &Substitution, container: &mut _| {
-                let fields = variant.fields(db);
-                let field = fields.field(&field_name.as_name())?;
-                let field_types = db.field_types(variant);
-                *container = Either::Right(field_types[field].clone().substitute(Interner, subst));
-                let generic_def = match variant {
-                    VariantId::EnumVariantId(it) => it.loc(db).parent.into(),
-                    VariantId::StructId(it) => it.into(),
-                    VariantId::UnionId(it) => it.into(),
+            let handle_variants =
+                |variant: VariantId, subst: GenericArgs<'db>, container: &mut _| {
+                    let fields = variant.fields(db);
+                    let field = fields.field(&field_name.as_name())?;
+                    let field_types = db.field_types_ns(variant);
+                    *container = Either::Right(field_types[field].instantiate(interner, subst));
+                    let generic_def = match variant {
+                        VariantId::EnumVariantId(it) => it.loc(db).parent.into(),
+                        VariantId::StructId(it) => it.into(),
+                        VariantId::UnionId(it) => it.into(),
+                    };
+                    Some((
+                        Either::Right(Field { parent: variant.into(), id: field }),
+                        generic_def,
+                        subst,
+                    ))
                 };
-                Some((
-                    Either::Right(Field { parent: variant.into(), id: field }),
-                    generic_def,
-                    subst.clone(),
-                ))
-            };
-            let temp_ty = TyKind::Error.intern(Interner);
+            let temp_ty = Ty::new_error(interner, ErrorGuaranteed);
             let (field_def, generic_def, subst) =
-                match std::mem::replace(&mut container, Either::Right(temp_ty.clone())) {
+                match std::mem::replace(&mut container, Either::Right(temp_ty)) {
                     Either::Left((variant_id, subst)) => {
-                        handle_variants(VariantId::from(variant_id), &subst, &mut container)?
+                        handle_variants(VariantId::from(variant_id), subst, &mut container)?
                     }
-                    Either::Right(container_ty) => match container_ty.kind(Interner) {
-                        TyKind::Adt(adt_id, subst) => match adt_id.0 {
+                    Either::Right(container_ty) => match container_ty.kind() {
+                        TyKind::Adt(adt_def, subst) => match adt_def.def_id().0 {
                             AdtId::StructId(id) => {
                                 handle_variants(id.into(), subst, &mut container)?
                             }
@@ -863,8 +832,8 @@
                             AdtId::EnumId(id) => {
                                 let variants = id.enum_variants(db);
                                 let variant = variants.variant(&field_name.as_name())?;
-                                container = Either::Left((variant, subst.clone()));
-                                (Either::Left(Variant { id: variant }), id.into(), subst.clone())
+                                container = Either::Left((variant, subst));
+                                (Either::Left(Variant { id: variant }), id.into(), subst)
                             }
                         },
                         _ => return None,
@@ -884,7 +853,6 @@
         db: &'db dyn HirDatabase,
         path: &ast::Path,
     ) -> Option<(PathResolution, Option<GenericSubstitution<'db>>)> {
-        let interner = DbInterner::new_with(db, None, None);
         let parent = path.syntax().parent();
         let parent = || parent.clone();
 
@@ -900,31 +868,27 @@
                                 None => {
                                     let subst = GenericSubstitution::new(
                                         f_in_trait.into(),
-                                        subs.to_chalk(interner),
+                                        subs,
                                         self.trait_environment(db),
                                     );
                                     (assoc, subst)
                                 }
                                 Some(func_ty) => {
-                                    if let TyKind::FnDef(_fn_def, subs) =
-                                        func_ty.to_chalk(interner).kind(Interner)
-                                    {
+                                    if let TyKind::FnDef(_fn_def, subs) = func_ty.kind() {
                                         let (fn_, subst) = self
                                             .resolve_impl_method_or_trait_def_with_subst(
-                                                db,
-                                                f_in_trait,
-                                                subs.to_nextsolver(interner),
+                                                db, f_in_trait, subs,
                                             );
                                         let subst = GenericSubstitution::new(
                                             fn_.into(),
-                                            subst.to_chalk(interner),
+                                            subst,
                                             self.trait_environment(db),
                                         );
                                         (fn_.into(), subst)
                                     } else {
                                         let subst = GenericSubstitution::new(
                                             f_in_trait.into(),
-                                            subs.to_chalk(interner),
+                                            subs,
                                             self.trait_environment(db),
                                         );
                                         (assoc, subst)
@@ -937,7 +901,7 @@
                                 self.resolve_impl_const_or_trait_def_with_subst(db, const_id, subs);
                             let subst = GenericSubstitution::new(
                                 konst.into(),
-                                subst.to_chalk(interner),
+                                subst,
                                 self.trait_environment(db),
                             );
                             (konst.into(), subst)
@@ -946,7 +910,7 @@
                             assoc,
                             GenericSubstitution::new(
                                 type_alias.into(),
-                                subs.to_chalk(interner),
+                                subs,
                                 self.trait_environment(db),
                             ),
                         ),
@@ -970,7 +934,7 @@
                                 self.resolve_impl_const_or_trait_def_with_subst(db, const_id, subs);
                             let subst = GenericSubstitution::new(
                                 konst.into(),
-                                subst.to_chalk(interner),
+                                subst,
                                 self.trait_environment(db),
                             );
                             (konst.into(), subst)
@@ -979,7 +943,7 @@
                             assoc,
                             GenericSubstitution::new(
                                 assoc.into(),
-                                subs.to_chalk(interner),
+                                subs,
                                 self.trait_environment(db),
                             ),
                         ),
@@ -1177,36 +1141,38 @@
                 let parent = parent()?;
                 let ty = if let Some(expr) = ast::Expr::cast(parent.clone()) {
                     let expr_id = self.expr_id(expr)?;
-                    self.infer()?.type_of_expr_or_pat(expr_id)?.to_chalk(interner)
+                    self.infer()?.type_of_expr_or_pat(expr_id)?
                 } else if let Some(pat) = ast::Pat::cast(parent) {
                     let pat_id = self.pat_id(&pat)?;
-                    self.infer()?[pat_id].to_chalk(interner)
+                    self.infer()?[pat_id]
                 } else {
                     return None;
                 };
                 let env = self.trait_environment(db);
-                let (subst, expected_resolution) = match ty.kind(Interner) {
-                    TyKind::Adt(adt_id, subst) => (
-                        GenericSubstitution::new(adt_id.0.into(), subst.clone(), env),
-                        PathResolution::Def(ModuleDef::Adt(adt_id.0.into())),
-                    ),
-                    TyKind::AssociatedType(assoc_id, subst) => {
-                        let assoc_id = from_assoc_type_id(*assoc_id);
+                let (subst, expected_resolution) = match ty.kind() {
+                    TyKind::Adt(adt_def, subst) => {
+                        let adt_id = adt_def.def_id().0;
                         (
-                            GenericSubstitution::new(assoc_id.into(), subst.clone(), env),
+                            GenericSubstitution::new(adt_id.into(), subst, env),
+                            PathResolution::Def(ModuleDef::Adt(adt_id.into())),
+                        )
+                    }
+                    TyKind::Alias(AliasTyKind::Projection, alias) => {
+                        let assoc_id = alias.def_id.expect_type_alias();
+                        (
+                            GenericSubstitution::new(assoc_id.into(), alias.args, env),
                             PathResolution::Def(ModuleDef::TypeAlias(assoc_id.into())),
                         )
                     }
                     TyKind::FnDef(fn_id, subst) => {
-                        let fn_id = ToChalk::from_chalk(db, *fn_id);
-                        let generic_def_id = match fn_id {
+                        let generic_def_id = match fn_id.0 {
                             CallableDefId::StructId(id) => id.into(),
                             CallableDefId::FunctionId(id) => id.into(),
                             CallableDefId::EnumVariantId(_) => return None,
                         };
                         (
-                            GenericSubstitution::new(generic_def_id, subst.clone(), env),
-                            PathResolution::Def(ModuleDefId::from(fn_id).into()),
+                            GenericSubstitution::new(generic_def_id, subst, env),
+                            PathResolution::Def(ModuleDefId::from(fn_id.0).into()),
                         )
                     }
                     _ => return None,
@@ -1260,8 +1226,7 @@
                 record_pattern_missing_fields(db, infer, pat_id, &body[pat_id])?
             }
         };
-        let interner = DbInterner::new_with(db, None, None);
-        let res = self.missing_fields(db, &substs.to_chalk(interner), variant, missing_fields);
+        let res = self.missing_fields(db, substs, variant, missing_fields);
         Some(res)
     }
 
@@ -1278,25 +1243,25 @@
 
         let (variant, missing_fields, _exhaustive) =
             record_pattern_missing_fields(db, infer, pat_id, &body[pat_id])?;
-        let interner = DbInterner::new_with(db, None, None);
-        let res = self.missing_fields(db, &substs.to_chalk(interner), variant, missing_fields);
+        let res = self.missing_fields(db, substs, variant, missing_fields);
         Some(res)
     }
 
     fn missing_fields(
         &self,
         db: &'db dyn HirDatabase,
-        substs: &Substitution,
+        substs: GenericArgs<'db>,
         variant: VariantId,
         missing_fields: Vec<LocalFieldId>,
     ) -> Vec<(Field, Type<'db>)> {
-        let field_types = db.field_types(variant);
+        let interner = DbInterner::new_with(db, None, None);
+        let field_types = db.field_types_ns(variant);
 
         missing_fields
             .into_iter()
             .map(|local_id| {
                 let field = FieldId { parent: variant, local_id };
-                let ty = field_types[local_id].clone().substitute(Interner, substs);
+                let ty = field_types[local_id].instantiate(interner, substs);
                 (field.into(), Type::new_with_resolver_inner(db, &self.resolver, ty))
             })
             .collect()
@@ -1455,10 +1420,8 @@
         Some((trait_id, fn_id))
     }
 
-    fn ty_of_expr(&self, expr: ast::Expr) -> Option<Ty> {
-        self.infer()?
-            .type_of_expr_or_pat(self.expr_id(expr)?)
-            .map(|ty| ty.to_chalk(DbInterner::conjure()))
+    fn ty_of_expr(&self, expr: ast::Expr) -> Option<Ty<'db>> {
+        self.infer()?.type_of_expr_or_pat(self.expr_id(expr)?)
     }
 }
 
diff --git a/crates/hir/src/term_search/tactics.rs b/crates/hir/src/term_search/tactics.rs
index 9df131f..dddc035 100644
--- a/crates/hir/src/term_search/tactics.rs
+++ b/crates/hir/src/term_search/tactics.rs
@@ -10,20 +10,21 @@
 
 use std::iter;
 
-use hir_ty::TyBuilder;
-use hir_ty::db::HirDatabase;
-use hir_ty::mir::BorrowKind;
+use hir_ty::{
+    db::HirDatabase,
+    mir::BorrowKind,
+    next_solver::{DbInterner, Ty},
+};
 use itertools::Itertools;
 use rustc_hash::FxHashSet;
+use rustc_type_ir::inherent::Ty as _;
 use span::Edition;
 
 use crate::{
     Adt, AssocItem, GenericDef, GenericParam, HasAttrs, HasVisibility, Impl, ModuleDef, ScopeDef,
-    Type, TypeParam,
+    Type, TypeParam, term_search::Expr,
 };
 
-use crate::term_search::Expr;
-
 use super::{LookupTable, NewTypesKey, TermSearchCtx};
 
 /// # Trivial tactic
@@ -596,10 +597,13 @@
 ) -> impl Iterator<Item = Expr<'db>> + use<'a, 'db, 'lt, DB> {
     let db = ctx.sema.db;
     let module = ctx.scope.module();
+    let interner = DbInterner::new_with(db, None, None);
+    let bool_ty = Ty::new_bool(interner);
+    let unit_ty = Ty::new_unit(interner);
     [
-        Expr::FamousType { ty: Type::new(db, module.id, TyBuilder::bool()), value: "true" },
-        Expr::FamousType { ty: Type::new(db, module.id, TyBuilder::bool()), value: "false" },
-        Expr::FamousType { ty: Type::new(db, module.id, TyBuilder::unit()), value: "()" },
+        Expr::FamousType { ty: Type::new(db, module.id, bool_ty), value: "true" },
+        Expr::FamousType { ty: Type::new(db, module.id, bool_ty), value: "false" },
+        Expr::FamousType { ty: Type::new(db, module.id, unit_ty), value: "()" },
     ]
     .into_iter()
     .inspect(|exprs| {
diff --git a/crates/ide/src/hover/render.rs b/crates/ide/src/hover/render.rs
index c5d695c..f29ccc9 100644
--- a/crates/ide/src/hover/render.rs
+++ b/crates/ide/src/hover/render.rs
@@ -695,7 +695,7 @@
                 DropInfo { drop_glue: field.ty(db).to_type(db).drop_glue(db), has_dtor: None }
             }
             Definition::Adt(Adt::Struct(strukt)) => {
-                let struct_drop_glue = strukt.ty_placeholders(db).drop_glue(db);
+                let struct_drop_glue = strukt.ty_params(db).drop_glue(db);
                 let mut fields_drop_glue = strukt
                     .fields(db)
                     .iter()
@@ -716,10 +716,10 @@
             // Unions cannot have fields with drop glue.
             Definition::Adt(Adt::Union(union)) => DropInfo {
                 drop_glue: DropGlue::None,
-                has_dtor: Some(union.ty_placeholders(db).drop_glue(db) != DropGlue::None),
+                has_dtor: Some(union.ty_params(db).drop_glue(db) != DropGlue::None),
             },
             Definition::Adt(Adt::Enum(enum_)) => {
-                let enum_drop_glue = enum_.ty_placeholders(db).drop_glue(db);
+                let enum_drop_glue = enum_.ty_params(db).drop_glue(db);
                 let fields_drop_glue = enum_
                     .variants(db)
                     .iter()
@@ -748,7 +748,7 @@
                 DropInfo { drop_glue: fields_drop_glue, has_dtor: None }
             }
             Definition::TypeAlias(type_alias) => {
-                DropInfo { drop_glue: type_alias.ty_placeholders(db).drop_glue(db), has_dtor: None }
+                DropInfo { drop_glue: type_alias.ty_params(db).drop_glue(db), has_dtor: None }
             }
             Definition::Local(local) => {
                 DropInfo { drop_glue: local.ty(db).drop_glue(db), has_dtor: None }