Merge pull request #20735 from itsjunetime/fix_scip_salsa

fix SCIP panicking due to salsa not attaching
diff --git a/.github/workflows/ci.yaml b/.github/workflows/ci.yaml
index 7706524..0eb57a6 100644
--- a/.github/workflows/ci.yaml
+++ b/.github/workflows/ci.yaml
@@ -56,8 +56,8 @@
       # Install a pinned rustc commit to avoid surprises
       - name: Install Rust toolchain
         run: |
-          RUSTC_VERSION=`cat rust-version`
-          rustup-toolchain-install-master ${RUSTC_VERSION} -c rust-src -c rustfmt
+          RUSTC_VERSION=$(cat rust-version)
+          rustup-toolchain-install-master ${RUSTC_VERSION} -c cargo -c rust-src -c rustfmt
           rustup default ${RUSTC_VERSION}
 
       # Emulate a nightly toolchain, because the toolchain installed above does not have "nightly"
@@ -98,9 +98,9 @@
         run: |
           rustup update --no-self-update stable
           rustup default stable
-          rustup component add --toolchain stable rust-src clippy
-          # We always use a nightly rustfmt, regardless of channel, because we need
-          # --file-lines.
+          rustup component add --toolchain stable rust-src clippy rustfmt
+          # We also install a nightly rustfmt, because we use `--file-lines` in
+          # a test.
           rustup toolchain install nightly --profile minimal --component rustfmt
       # https://github.com/actions-rust-lang/setup-rust-toolchain/blob/main/rust.json
       - name: Install Rust Problem Matcher
diff --git a/Cargo.lock b/Cargo.lock
index 17dea1b..9d0f63d 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -546,6 +546,12 @@
 ]
 
 [[package]]
+name = "fixedbitset"
+version = "0.5.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1d674e81391d1e1ab681a28d99df07927c6d4aa5b027d7da16ba32d1d21ecd99"
+
+[[package]]
 name = "flate2"
 version = "1.1.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -775,6 +781,7 @@
  "itertools",
  "la-arena 0.3.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "oorandom",
+ "petgraph",
  "project-model",
  "query-group-macro",
  "ra-ap-rustc_abi",
@@ -1595,6 +1602,17 @@
 ]
 
 [[package]]
+name = "petgraph"
+version = "0.8.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "54acf3a685220b533e437e264e4d932cfbdc4cc7ec0cd232ed73c08d03b8a7ca"
+dependencies = [
+ "fixedbitset",
+ "hashbrown 0.15.4",
+ "indexmap",
+]
+
+[[package]]
 name = "pin-project-lite"
 version = "0.2.16"
 source = "registry+https://github.com/rust-lang/crates.io-index"
diff --git a/Cargo.toml b/Cargo.toml
index 0401367..d3a4e37 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -170,6 +170,7 @@
 triomphe = { version = "0.1.14", default-features = false, features = ["std"] }
 url = "2.5.4"
 xshell = "0.2.7"
+petgraph = { version = "0.8.2", default-features = false }
 
 # We need to freeze the version of the crate, as the raw-api feature is considered unstable
 dashmap = { version = "=6.1.0", features = ["raw-api", "inline"] }
diff --git a/crates/hir-def/src/lib.rs b/crates/hir-def/src/lib.rs
index 301d4cc..e5c213c 100644
--- a/crates/hir-def/src/lib.rs
+++ b/crates/hir-def/src/lib.rs
@@ -15,10 +15,6 @@
 #[cfg(not(feature = "in-rust-tree"))]
 extern crate ra_ap_rustc_parse_format as rustc_parse_format;
 
-#[cfg(feature = "in-rust-tree")]
-extern crate rustc_abi;
-
-#[cfg(not(feature = "in-rust-tree"))]
 extern crate ra_ap_rustc_abi as rustc_abi;
 
 pub mod db;
diff --git a/crates/hir-ty/Cargo.toml b/crates/hir-ty/Cargo.toml
index 138d02e..4013d19 100644
--- a/crates/hir-ty/Cargo.toml
+++ b/crates/hir-ty/Cargo.toml
@@ -34,6 +34,7 @@
 query-group.workspace = true
 salsa.workspace = true
 salsa-macros.workspace = true
+petgraph.workspace = true
 
 ra-ap-rustc_abi.workspace = true
 ra-ap-rustc_index.workspace = true
diff --git a/crates/hir-ty/src/builder.rs b/crates/hir-ty/src/builder.rs
index 3755175..4957c69 100644
--- a/crates/hir-ty/src/builder.rs
+++ b/crates/hir-ty/src/builder.rs
@@ -3,17 +3,20 @@
 use chalk_ir::{
     AdtId, DebruijnIndex, Scalar,
     cast::{Cast, CastTo, Caster},
-    fold::TypeFoldable,
-    interner::HasInterner,
 };
 use hir_def::{GenericDefId, GenericParamId, TraitId, TypeAliasId, builtin_type::BuiltinType};
 use smallvec::SmallVec;
 
 use crate::{
-    Binders, BoundVar, CallableSig, GenericArg, GenericArgData, Interner, ProjectionTy,
-    Substitution, TraitRef, Ty, TyDefId, TyExt, TyKind, consteval::unknown_const_as_generic,
-    db::HirDatabase, error_lifetime, generics::generics, infer::unify::InferenceTable, primitive,
-    to_assoc_type_id, to_chalk_trait_id,
+    BoundVar, CallableSig, GenericArg, GenericArgData, Interner, ProjectionTy, Substitution,
+    TraitRef, Ty, TyDefId, TyExt, TyKind,
+    consteval::unknown_const_as_generic,
+    db::HirDatabase,
+    error_lifetime,
+    generics::generics,
+    infer::unify::InferenceTable,
+    next_solver::{DbInterner, EarlyBinder, mapping::ChalkToNextSolver},
+    primitive, to_assoc_type_id, to_chalk_trait_id,
 };
 
 #[derive(Debug, Clone, PartialEq, Eq)]
@@ -345,19 +348,20 @@
     }
 }
 
-impl<T: HasInterner<Interner = Interner> + TypeFoldable<Interner>> TyBuilder<Binders<T>> {
-    pub fn build(self) -> T {
+impl<'db, T: rustc_type_ir::TypeFoldable<DbInterner<'db>>> TyBuilder<EarlyBinder<'db, T>> {
+    pub fn build(self, interner: DbInterner<'db>) -> T {
         let (b, subst) = self.build_internal();
-        b.substitute(Interner, &subst)
+        let args: crate::next_solver::GenericArgs<'db> = subst.to_nextsolver(interner);
+        b.instantiate(interner, args)
     }
 }
 
-impl TyBuilder<Binders<Ty>> {
+impl<'db> TyBuilder<EarlyBinder<'db, crate::next_solver::Ty<'db>>> {
     pub fn def_ty(
-        db: &dyn HirDatabase,
+        db: &'db dyn HirDatabase,
         def: TyDefId,
         parent_subst: Option<Substitution>,
-    ) -> TyBuilder<Binders<Ty>> {
+    ) -> TyBuilder<EarlyBinder<'db, crate::next_solver::Ty<'db>>> {
         let poly_ty = db.ty(def);
         let id: GenericDefId = match def {
             TyDefId::BuiltinType(_) => {
@@ -370,7 +374,10 @@
         TyBuilder::subst_for_def(db, id, parent_subst).with_data(poly_ty)
     }
 
-    pub fn impl_self_ty(db: &dyn HirDatabase, def: hir_def::ImplId) -> TyBuilder<Binders<Ty>> {
-        TyBuilder::subst_for_def(db, def, None).with_data(db.impl_self_ty(def))
+    pub fn impl_self_ty(
+        db: &'db dyn HirDatabase,
+        def: hir_def::ImplId,
+    ) -> TyBuilder<EarlyBinder<'db, crate::next_solver::Ty<'db>>> {
+        TyBuilder::subst_for_def(db, def, None).with_data(db.impl_self_ty_ns(def))
     }
 }
diff --git a/crates/hir-ty/src/consteval.rs b/crates/hir-ty/src/consteval.rs
index e2a8d1c..b2daed4 100644
--- a/crates/hir-ty/src/consteval.rs
+++ b/crates/hir-ty/src/consteval.rs
@@ -327,7 +327,7 @@
     debruijn: DebruijnIndex,
 ) -> Const {
     let db = ctx.db;
-    let infer = ctx.clone().resolve_all();
+    let infer = ctx.fixme_resolve_all_clone();
     fn has_closure(body: &Body, expr: ExprId) -> bool {
         if matches!(body[expr], Expr::Closure { .. }) {
             return true;
diff --git a/crates/hir-ty/src/consteval/tests.rs b/crates/hir-ty/src/consteval/tests.rs
index 299b73a..1586846 100644
--- a/crates/hir-ty/src/consteval/tests.rs
+++ b/crates/hir-ty/src/consteval/tests.rs
@@ -36,12 +36,12 @@
     error: impl FnOnce(ConstEvalError) -> bool,
 ) {
     let (db, file_id) = TestDB::with_single_file(ra_fixture);
-    match eval_goal(&db, file_id) {
+    salsa::attach(&db, || match eval_goal(&db, file_id) {
         Ok(_) => panic!("Expected fail, but it succeeded"),
         Err(e) => {
-            assert!(error(simplify(e.clone())), "Actual error was: {}", pretty_print_err(e, db))
+            assert!(error(simplify(e.clone())), "Actual error was: {}", pretty_print_err(e, &db))
         }
-    }
+    })
 }
 
 #[track_caller]
@@ -79,36 +79,38 @@
     check: impl FnOnce(&[u8], &MemoryMap<'_>),
 ) {
     let (db, file_ids) = TestDB::with_many_files(ra_fixture);
-    let file_id = *file_ids.last().unwrap();
-    let r = match eval_goal(&db, file_id) {
-        Ok(t) => t,
-        Err(e) => {
-            let err = pretty_print_err(e, db);
-            panic!("Error in evaluating goal: {err}");
-        }
-    };
-    match &r.data(Interner).value {
-        chalk_ir::ConstValue::Concrete(c) => match &c.interned {
-            ConstScalar::Bytes(b, mm) => {
-                check(b, mm);
+    salsa::attach(&db, || {
+        let file_id = *file_ids.last().unwrap();
+        let r = match eval_goal(&db, file_id) {
+            Ok(t) => t,
+            Err(e) => {
+                let err = pretty_print_err(e, &db);
+                panic!("Error in evaluating goal: {err}");
             }
-            x => panic!("Expected number but found {x:?}"),
-        },
-        _ => panic!("result of const eval wasn't a concrete const"),
-    }
+        };
+        match &r.data(Interner).value {
+            chalk_ir::ConstValue::Concrete(c) => match &c.interned {
+                ConstScalar::Bytes(b, mm) => {
+                    check(b, mm);
+                }
+                x => panic!("Expected number but found {x:?}"),
+            },
+            _ => panic!("result of const eval wasn't a concrete const"),
+        }
+    });
 }
 
-fn pretty_print_err(e: ConstEvalError, db: TestDB) -> String {
+fn pretty_print_err(e: ConstEvalError, db: &TestDB) -> String {
     let mut err = String::new();
     let span_formatter = |file, range| format!("{file:?} {range:?}");
     let display_target =
-        DisplayTarget::from_crate(&db, *db.all_crates().last().expect("no crate graph present"));
+        DisplayTarget::from_crate(db, *db.all_crates().last().expect("no crate graph present"));
     match e {
         ConstEvalError::MirLowerError(e) => {
-            e.pretty_print(&mut err, &db, span_formatter, display_target)
+            e.pretty_print(&mut err, db, span_formatter, display_target)
         }
         ConstEvalError::MirEvalError(e) => {
-            e.pretty_print(&mut err, &db, span_formatter, display_target)
+            e.pretty_print(&mut err, db, span_formatter, display_target)
         }
     }
     .unwrap();
diff --git a/crates/hir-ty/src/consteval_nextsolver.rs b/crates/hir-ty/src/consteval_nextsolver.rs
index 6e07d3a..155f133 100644
--- a/crates/hir-ty/src/consteval_nextsolver.rs
+++ b/crates/hir-ty/src/consteval_nextsolver.rs
@@ -222,7 +222,7 @@
 // and make this function private. See the fixme comment on `InferenceContext::resolve_all`.
 pub(crate) fn eval_to_const<'db>(expr: ExprId, ctx: &mut InferenceContext<'db>) -> Const<'db> {
     let interner = DbInterner::new_with(ctx.db, None, None);
-    let infer = ctx.clone().resolve_all();
+    let infer = ctx.fixme_resolve_all_clone();
     fn has_closure(body: &Body, expr: ExprId) -> bool {
         if matches!(body[expr], Expr::Closure { .. }) {
             return true;
diff --git a/crates/hir-ty/src/db.rs b/crates/hir-ty/src/db.rs
index 44f4806..42f7ec6 100644
--- a/crates/hir-ty/src/db.rs
+++ b/crates/hir-ty/src/db.rs
@@ -16,8 +16,8 @@
 use triomphe::Arc;
 
 use crate::{
-    Binders, Const, ImplTraitId, ImplTraits, InferenceResult, PolyFnSig, Substitution,
-    TraitEnvironment, TraitRef, Ty, TyDefId, ValueTyDefId, chalk_db,
+    Binders, Const, ImplTraitId, ImplTraits, InferenceResult, Substitution, TraitEnvironment,
+    TraitRef, Ty, TyDefId, ValueTyDefId, chalk_db,
     consteval::ConstEvalError,
     drop::DropGlue,
     dyn_compatibility::DynCompatibilityViolation,
@@ -114,55 +114,88 @@
     #[salsa::invoke(crate::dyn_compatibility::dyn_compatibility_of_trait_query)]
     fn dyn_compatibility_of_trait(&self, trait_: TraitId) -> Option<DynCompatibilityViolation>;
 
-    #[salsa::invoke(crate::lower::ty_query)]
+    #[salsa::invoke(crate::lower_nextsolver::ty_query)]
     #[salsa::transparent]
-    fn ty(&self, def: TyDefId) -> Binders<Ty>;
+    fn ty<'db>(
+        &'db self,
+        def: TyDefId,
+    ) -> crate::next_solver::EarlyBinder<'db, crate::next_solver::Ty<'db>>;
 
-    #[salsa::invoke(crate::lower::type_for_type_alias_with_diagnostics_query)]
-    #[salsa::cycle(cycle_result = crate::lower::type_for_type_alias_with_diagnostics_cycle_result)]
-    fn type_for_type_alias_with_diagnostics(&self, def: TypeAliasId) -> (Binders<Ty>, Diagnostics);
+    #[salsa::invoke(crate::lower_nextsolver::type_for_type_alias_with_diagnostics_query)]
+    #[salsa::cycle(cycle_result = crate::lower_nextsolver::type_for_type_alias_with_diagnostics_cycle_result)]
+    fn type_for_type_alias_with_diagnostics<'db>(
+        &'db self,
+        def: TypeAliasId,
+    ) -> (crate::next_solver::EarlyBinder<'db, crate::next_solver::Ty<'db>>, Diagnostics);
 
     /// Returns the type of the value of the given constant, or `None` if the `ValueTyDefId` is
     /// a `StructId` or `EnumVariantId` with a record constructor.
-    #[salsa::invoke(crate::lower::value_ty_query)]
-    fn value_ty(&self, def: ValueTyDefId) -> Option<Binders<Ty>>;
+    #[salsa::invoke(crate::lower_nextsolver::value_ty_query)]
+    fn value_ty<'db>(
+        &'db self,
+        def: ValueTyDefId,
+    ) -> Option<crate::next_solver::EarlyBinder<'db, crate::next_solver::Ty<'db>>>;
 
-    #[salsa::invoke(crate::lower::impl_self_ty_with_diagnostics_query)]
-    #[salsa::cycle(cycle_result = crate::lower::impl_self_ty_with_diagnostics_cycle_result)]
-    fn impl_self_ty_with_diagnostics(&self, def: ImplId) -> (Binders<Ty>, Diagnostics);
+    #[salsa::invoke(crate::lower_nextsolver::impl_self_ty_with_diagnostics_query)]
+    #[salsa::cycle(cycle_result = crate::lower_nextsolver::impl_self_ty_with_diagnostics_cycle_result)]
+    fn impl_self_ty_with_diagnostics<'db>(
+        &'db self,
+        def: ImplId,
+    ) -> (crate::next_solver::EarlyBinder<'db, crate::next_solver::Ty<'db>>, Diagnostics);
 
     #[salsa::invoke(crate::lower::impl_self_ty_query)]
     #[salsa::transparent]
     fn impl_self_ty(&self, def: ImplId) -> Binders<Ty>;
 
     // FIXME: Make this a non-interned query.
-    #[salsa::invoke_interned(crate::lower::const_param_ty_with_diagnostics_query)]
-    #[salsa::cycle(cycle_result = crate::lower::const_param_ty_with_diagnostics_cycle_result)]
-    fn const_param_ty_with_diagnostics(&self, def: ConstParamId) -> (Ty, Diagnostics);
+    #[salsa::invoke_interned(crate::lower_nextsolver::const_param_ty_with_diagnostics_query)]
+    #[salsa::cycle(cycle_result = crate::lower_nextsolver::const_param_ty_with_diagnostics_cycle_result)]
+    fn const_param_ty_with_diagnostics<'db>(
+        &'db self,
+        def: ConstParamId,
+    ) -> (crate::next_solver::Ty<'db>, Diagnostics);
 
-    #[salsa::invoke(crate::lower::const_param_ty_query)]
-    #[salsa::transparent]
+    // FIXME: Make this a non-interned query.
+    #[salsa::invoke_interned(crate::lower::const_param_ty_query)]
+    #[salsa::cycle(cycle_result = crate::lower::const_param_ty_cycle_result)]
     fn const_param_ty(&self, def: ConstParamId) -> Ty;
 
-    #[salsa::invoke(crate::lower::impl_trait_with_diagnostics_query)]
-    fn impl_trait_with_diagnostics(&self, def: ImplId) -> Option<(Binders<TraitRef>, Diagnostics)>;
+    #[salsa::invoke(crate::lower_nextsolver::impl_trait_with_diagnostics_query)]
+    fn impl_trait_with_diagnostics<'db>(
+        &'db self,
+        def: ImplId,
+    ) -> Option<(
+        crate::next_solver::EarlyBinder<'db, crate::next_solver::TraitRef<'db>>,
+        Diagnostics,
+    )>;
 
     #[salsa::invoke(crate::lower::impl_trait_query)]
     #[salsa::transparent]
     fn impl_trait(&self, def: ImplId) -> Option<Binders<TraitRef>>;
 
-    #[salsa::invoke(crate::lower::field_types_with_diagnostics_query)]
-    fn field_types_with_diagnostics(
-        &self,
+    #[salsa::invoke(crate::lower_nextsolver::field_types_with_diagnostics_query)]
+    fn field_types_with_diagnostics<'db>(
+        &'db self,
         var: VariantId,
-    ) -> (Arc<ArenaMap<LocalFieldId, Binders<Ty>>>, Diagnostics);
+    ) -> (
+        Arc<
+            ArenaMap<
+                LocalFieldId,
+                crate::next_solver::EarlyBinder<'db, crate::next_solver::Ty<'db>>,
+            >,
+        >,
+        Diagnostics,
+    );
 
     #[salsa::invoke(crate::lower::field_types_query)]
     #[salsa::transparent]
     fn field_types(&self, var: VariantId) -> Arc<ArenaMap<LocalFieldId, Binders<Ty>>>;
 
-    #[salsa::invoke(crate::lower::callable_item_signature_query)]
-    fn callable_item_signature(&self, def: CallableDefId) -> PolyFnSig;
+    #[salsa::invoke(crate::lower_nextsolver::callable_item_signature_query)]
+    fn callable_item_signature<'db>(
+        &'db self,
+        def: CallableDefId,
+    ) -> crate::next_solver::EarlyBinder<'db, crate::next_solver::PolyFnSig<'db>>;
 
     #[salsa::invoke(crate::lower::return_type_impl_traits)]
     fn return_type_impl_traits(&self, def: FunctionId) -> Option<Arc<Binders<ImplTraits>>>;
@@ -182,6 +215,21 @@
     #[salsa::invoke(crate::lower::generic_predicates_query)]
     fn generic_predicates(&self, def: GenericDefId) -> GenericPredicates;
 
+    #[salsa::invoke(
+        crate::lower_nextsolver::generic_predicates_without_parent_with_diagnostics_query
+    )]
+    fn generic_predicates_without_parent_with_diagnostics<'db>(
+        &'db self,
+        def: GenericDefId,
+    ) -> (crate::lower_nextsolver::GenericPredicates<'db>, Diagnostics);
+
+    #[salsa::invoke(crate::lower_nextsolver::generic_predicates_without_parent_query)]
+    #[salsa::transparent]
+    fn generic_predicates_without_parent<'db>(
+        &'db self,
+        def: GenericDefId,
+    ) -> crate::lower_nextsolver::GenericPredicates<'db>;
+
     #[salsa::invoke(crate::lower_nextsolver::trait_environment_for_body_query)]
     #[salsa::transparent]
     fn trait_environment_for_body<'db>(&'db self, def: DefWithBodyId)
@@ -277,35 +325,6 @@
 
     // next trait solver
 
-    #[salsa::invoke(crate::lower_nextsolver::ty_query)]
-    #[salsa::transparent]
-    fn ty_ns<'db>(
-        &'db self,
-        def: TyDefId,
-    ) -> crate::next_solver::EarlyBinder<'db, crate::next_solver::Ty<'db>>;
-
-    /// Returns the type of the value of the given constant, or `None` if the `ValueTyDefId` is
-    /// a `StructId` or `EnumVariantId` with a record constructor.
-    #[salsa::invoke(crate::lower_nextsolver::value_ty_query)]
-    fn value_ty_ns<'db>(
-        &'db self,
-        def: ValueTyDefId,
-    ) -> Option<crate::next_solver::EarlyBinder<'db, crate::next_solver::Ty<'db>>>;
-
-    #[salsa::invoke(crate::lower_nextsolver::type_for_type_alias_with_diagnostics_query)]
-    #[salsa::cycle(cycle_result = crate::lower_nextsolver::type_for_type_alias_with_diagnostics_cycle_result)]
-    fn type_for_type_alias_with_diagnostics_ns<'db>(
-        &'db self,
-        def: TypeAliasId,
-    ) -> (crate::next_solver::EarlyBinder<'db, crate::next_solver::Ty<'db>>, Diagnostics);
-
-    #[salsa::invoke(crate::lower_nextsolver::impl_self_ty_with_diagnostics_query)]
-    #[salsa::cycle(cycle_result = crate::lower_nextsolver::impl_self_ty_with_diagnostics_cycle_result)]
-    fn impl_self_ty_with_diagnostics_ns<'db>(
-        &'db self,
-        def: ImplId,
-    ) -> (crate::next_solver::EarlyBinder<'db, crate::next_solver::Ty<'db>>, Diagnostics);
-
     #[salsa::invoke(crate::lower_nextsolver::impl_self_ty_query)]
     #[salsa::transparent]
     fn impl_self_ty_ns<'db>(
@@ -313,26 +332,10 @@
         def: ImplId,
     ) -> crate::next_solver::EarlyBinder<'db, crate::next_solver::Ty<'db>>;
 
-    // FIXME: Make this a non-interned query.
-    #[salsa::invoke_interned(crate::lower_nextsolver::const_param_ty_with_diagnostics_query)]
-    fn const_param_ty_with_diagnostics_ns<'db>(
-        &'db self,
-        def: ConstParamId,
-    ) -> (crate::next_solver::Ty<'db>, Diagnostics);
-
     #[salsa::invoke(crate::lower_nextsolver::const_param_ty_query)]
     #[salsa::transparent]
     fn const_param_ty_ns<'db>(&'db self, def: ConstParamId) -> crate::next_solver::Ty<'db>;
 
-    #[salsa::invoke(crate::lower_nextsolver::impl_trait_with_diagnostics_query)]
-    fn impl_trait_with_diagnostics_ns<'db>(
-        &'db self,
-        def: ImplId,
-    ) -> Option<(
-        crate::next_solver::EarlyBinder<'db, crate::next_solver::TraitRef<'db>>,
-        Diagnostics,
-    )>;
-
     #[salsa::invoke(crate::lower_nextsolver::impl_trait_query)]
     #[salsa::transparent]
     fn impl_trait_ns<'db>(
@@ -340,20 +343,6 @@
         def: ImplId,
     ) -> Option<crate::next_solver::EarlyBinder<'db, crate::next_solver::TraitRef<'db>>>;
 
-    #[salsa::invoke(crate::lower_nextsolver::field_types_with_diagnostics_query)]
-    fn field_types_with_diagnostics_ns<'db>(
-        &'db self,
-        var: VariantId,
-    ) -> (
-        Arc<
-            ArenaMap<
-                LocalFieldId,
-                crate::next_solver::EarlyBinder<'db, crate::next_solver::Ty<'db>>,
-            >,
-        >,
-        Diagnostics,
-    );
-
     #[salsa::invoke(crate::lower_nextsolver::field_types_query)]
     #[salsa::transparent]
     fn field_types_ns<'db>(
@@ -363,12 +352,6 @@
         ArenaMap<LocalFieldId, crate::next_solver::EarlyBinder<'db, crate::next_solver::Ty<'db>>>,
     >;
 
-    #[salsa::invoke(crate::lower_nextsolver::callable_item_signature_query)]
-    fn callable_item_signature_ns<'db>(
-        &'db self,
-        def: CallableDefId,
-    ) -> crate::next_solver::EarlyBinder<'db, crate::next_solver::PolyFnSig<'db>>;
-
     #[salsa::invoke(crate::lower_nextsolver::return_type_impl_traits)]
     fn return_type_impl_traits_ns<'db>(
         &'db self,
@@ -395,21 +378,6 @@
         &'db self,
         def: GenericDefId,
     ) -> crate::lower_nextsolver::GenericPredicates<'db>;
-
-    #[salsa::invoke(
-        crate::lower_nextsolver::generic_predicates_without_parent_with_diagnostics_query
-    )]
-    fn generic_predicates_without_parent_with_diagnostics_ns<'db>(
-        &'db self,
-        def: GenericDefId,
-    ) -> (crate::lower_nextsolver::GenericPredicates<'db>, Diagnostics);
-
-    #[salsa::invoke(crate::lower_nextsolver::generic_predicates_without_parent_query)]
-    #[salsa::transparent]
-    fn generic_predicates_without_parent_ns<'db>(
-        &'db self,
-        def: GenericDefId,
-    ) -> crate::lower_nextsolver::GenericPredicates<'db>;
 }
 
 #[test]
diff --git a/crates/hir-ty/src/display.rs b/crates/hir-ty/src/display.rs
index dc42304..e11ce51 100644
--- a/crates/hir-ty/src/display.rs
+++ b/crates/hir-ty/src/display.rs
@@ -46,8 +46,8 @@
 use stdx::never;
 use triomphe::Arc;
 
-use crate::next_solver::infer::DbInternerInferExt;
 use crate::next_solver::infer::traits::ObligationCause;
+use crate::next_solver::{infer::DbInternerInferExt, mapping::NextSolverToChalk};
 use crate::{
     AliasEq, AliasTy, Binders, CallableDefId, CallableSig, ConcreteConst, Const, ConstScalar,
     ConstValue, DomainGoal, FnAbi, GenericArg, ImplTraitId, Interner, Lifetime, LifetimeData,
@@ -1298,7 +1298,9 @@
                 let def = def.0;
                 let sig = db
                     .callable_item_signature(def)
-                    .substitute(Interner, &convert_args_for_result(interner, args.as_slice()));
+                    .instantiate(interner, args)
+                    .skip_binder()
+                    .to_chalk(interner);
 
                 if f.display_kind.is_source_code() {
                     // `FnDef` is anonymous and there's no surface syntax for it. Show it as a
diff --git a/crates/hir-ty/src/dyn_compatibility.rs b/crates/hir-ty/src/dyn_compatibility.rs
index b87c998..b2406a0 100644
--- a/crates/hir-ty/src/dyn_compatibility.rs
+++ b/crates/hir-ty/src/dyn_compatibility.rs
@@ -329,7 +329,7 @@
         cb(MethodViolationCode::AsyncFn)?;
     }
 
-    let sig = db.callable_item_signature_ns(func.into());
+    let sig = db.callable_item_signature(func.into());
     if sig
         .skip_binder()
         .inputs()
@@ -364,7 +364,7 @@
         cb(MethodViolationCode::UndispatchableReceiver)?;
     }
 
-    let predicates = &*db.generic_predicates_without_parent_ns(func.into());
+    let predicates = &*db.generic_predicates_without_parent(func.into());
     for pred in predicates {
         let pred = pred.kind().skip_binder();
 
diff --git a/crates/hir-ty/src/infer.rs b/crates/hir-ty/src/infer.rs
index 3ece62e..287afb0 100644
--- a/crates/hir-ty/src/infer.rs
+++ b/crates/hir-ty/src/infer.rs
@@ -19,6 +19,7 @@
 mod coerce;
 pub(crate) mod diagnostics;
 mod expr;
+mod fallback;
 mod mutability;
 mod pat;
 mod path;
@@ -53,16 +54,16 @@
 use intern::sym;
 use la_arena::{ArenaMap, Entry};
 use rustc_hash::{FxHashMap, FxHashSet};
+use rustc_type_ir::inherent::Ty as _;
 use stdx::{always, never};
 use triomphe::Arc;
 
-use crate::db::InternedClosureId;
 use crate::{
     AliasEq, AliasTy, Binders, ClosureId, Const, DomainGoal, GenericArg, ImplTraitId, ImplTraitIdx,
     IncorrectGenericsLenKind, Interner, Lifetime, OpaqueTyId, ParamLoweringMode,
     PathLoweringDiagnostic, ProjectionTy, Substitution, TargetFeatures, TraitEnvironment, Ty,
     TyBuilder, TyExt,
-    db::HirDatabase,
+    db::{HirDatabase, InternedClosureId},
     fold_tys,
     generics::Generics,
     infer::{
@@ -75,6 +76,7 @@
     mir::MirSpan,
     next_solver::{
         self, DbInterner,
+        infer::{DefineOpaqueTypes, traits::ObligationCause},
         mapping::{ChalkToNextSolver, NextSolverToChalk},
     },
     static_lifetime, to_assoc_type_id,
@@ -138,6 +140,20 @@
 
     ctx.infer_mut_body();
 
+    ctx.type_inference_fallback();
+
+    // Comment from rustc:
+    // Even though coercion casts provide type hints, we check casts after fallback for
+    // backwards compatibility. This makes fallback a stronger type hint than a cast coercion.
+    let cast_checks = std::mem::take(&mut ctx.deferred_cast_checks);
+    for mut cast in cast_checks.into_iter() {
+        if let Err(diag) = cast.check(&mut ctx) {
+            ctx.diagnostics.push(diag);
+        }
+    }
+
+    ctx.table.select_obligations_where_possible();
+
     ctx.infer_closures();
 
     Arc::new(ctx.resolve_all())
@@ -165,7 +181,6 @@
 
     let ty_with_vars = table.normalize_associated_types_in(ty);
     table.select_obligations_where_possible();
-    table.propagate_diverging_flag();
     table.resolve_completely(ty_with_vars)
 }
 
@@ -632,6 +647,26 @@
     pub fn binding_mode(&self, id: PatId) -> Option<BindingMode> {
         self.binding_modes.get(id).copied()
     }
+
+    // This method is consumed by external tools to run rust-analyzer as a library. Don't remove, please.
+    pub fn expression_types(&self) -> impl Iterator<Item = (ExprId, &Ty)> {
+        self.type_of_expr.iter()
+    }
+
+    // This method is consumed by external tools to run rust-analyzer as a library. Don't remove, please.
+    pub fn pattern_types(&self) -> impl Iterator<Item = (PatId, &Ty)> {
+        self.type_of_pat.iter()
+    }
+
+    // This method is consumed by external tools to run rust-analyzer as a library. Don't remove, please.
+    pub fn binding_types(&self) -> impl Iterator<Item = (BindingId, &Ty)> {
+        self.type_of_binding.iter()
+    }
+
+    // This method is consumed by external tools to run rust-analyzer as a library. Don't remove, please.
+    pub fn return_position_impl_trait_types(&self) -> impl Iterator<Item = (ImplTraitIdx, &Ty)> {
+        self.type_of_rpit.iter()
+    }
 }
 
 impl Index<ExprId> for InferenceResult {
@@ -666,6 +701,25 @@
     }
 }
 
+#[derive(Debug, Clone)]
+struct InternedStandardTypesNextSolver<'db> {
+    unit: crate::next_solver::Ty<'db>,
+    never: crate::next_solver::Ty<'db>,
+    i32: crate::next_solver::Ty<'db>,
+    f64: crate::next_solver::Ty<'db>,
+}
+
+impl<'db> InternedStandardTypesNextSolver<'db> {
+    fn new(interner: DbInterner<'db>) -> Self {
+        Self {
+            unit: crate::next_solver::Ty::new_unit(interner),
+            never: crate::next_solver::Ty::new(interner, crate::next_solver::TyKind::Never),
+            i32: crate::next_solver::Ty::new_int(interner, rustc_type_ir::IntTy::I32),
+            f64: crate::next_solver::Ty::new_float(interner, rustc_type_ir::FloatTy::F64),
+        }
+    }
+}
+
 /// The inference context contains all information needed during type inference.
 #[derive(Clone, Debug)]
 pub(crate) struct InferenceContext<'db> {
@@ -698,6 +752,7 @@
     resume_yield_tys: Option<(Ty, Ty)>,
     diverges: Diverges,
     breakables: Vec<BreakableContext<'db>>,
+    types: InternedStandardTypesNextSolver<'db>,
 
     /// Whether we are inside the pattern of a destructuring assignment.
     inside_assignment: bool,
@@ -778,11 +833,13 @@
         resolver: Resolver<'db>,
     ) -> Self {
         let trait_env = db.trait_environment_for_body(owner);
+        let table = unify::InferenceTable::new(db, trait_env);
         InferenceContext {
+            types: InternedStandardTypesNextSolver::new(table.interner),
             target_features: OnceCell::new(),
             generics: OnceCell::new(),
             result: InferenceResult::default(),
-            table: unify::InferenceTable::new(db, trait_env),
+            table,
             tuple_field_accesses_rev: Default::default(),
             return_ty: TyKind::Error.intern(Interner), // set in collect_* calls
             resume_yield_tys: None,
@@ -845,24 +902,33 @@
         self.result.has_errors = true;
     }
 
-    // FIXME: This function should be private in module. It is currently only used in the consteval, since we need
-    // `InferenceResult` in the middle of inference. See the fixme comment in `consteval::eval_to_const`. If you
-    // used this function for another workaround, mention it here. If you really need this function and believe that
-    // there is no problem in it being `pub(crate)`, remove this comment.
-    pub(crate) fn resolve_all(mut self) -> InferenceResult {
-        self.table.select_obligations_where_possible();
-        self.table.fallback_if_possible();
+    /// Clones `self` and calls `resolve_all()` on it.
+    // FIXME: Remove this.
+    pub(crate) fn fixme_resolve_all_clone(&self) -> InferenceResult {
+        let mut ctx = self.clone();
+
+        ctx.type_inference_fallback();
 
         // Comment from rustc:
         // Even though coercion casts provide type hints, we check casts after fallback for
         // backwards compatibility. This makes fallback a stronger type hint than a cast coercion.
-        let cast_checks = std::mem::take(&mut self.deferred_cast_checks);
+        let cast_checks = std::mem::take(&mut ctx.deferred_cast_checks);
         for mut cast in cast_checks.into_iter() {
-            if let Err(diag) = cast.check(&mut self) {
-                self.diagnostics.push(diag);
+            if let Err(diag) = cast.check(&mut ctx) {
+                ctx.diagnostics.push(diag);
             }
         }
 
+        ctx.table.select_obligations_where_possible();
+
+        ctx.resolve_all()
+    }
+
+    // FIXME: This function should be private in module. It is currently only used in the consteval, since we need
+    // `InferenceResult` in the middle of inference. See the fixme comment in `consteval::eval_to_const`. If you
+    // used this function for another workaround, mention it here. If you really need this function and believe that
+    // there is no problem in it being `pub(crate)`, remove this comment.
+    pub(crate) fn resolve_all(self) -> InferenceResult {
         let InferenceContext {
             mut table, mut result, tuple_field_accesses_rev, diagnostics, ..
         } = self;
@@ -894,11 +960,6 @@
             diagnostics: _,
         } = &mut result;
 
-        // FIXME resolve obligations as well (use Guidance if necessary)
-        table.select_obligations_where_possible();
-
-        // make sure diverging type variables are marked as such
-        table.propagate_diverging_flag();
         for ty in type_of_expr.values_mut() {
             *ty = table.resolve_completely(ty.clone());
             *has_errors = *has_errors || ty.contains_unknown();
@@ -1653,6 +1714,22 @@
         self.resolve_associated_type_with_params(inner_ty, assoc_ty, &[])
     }
 
+    fn demand_eqtype(
+        &mut self,
+        expected: crate::next_solver::Ty<'db>,
+        actual: crate::next_solver::Ty<'db>,
+    ) {
+        let result = self
+            .table
+            .infer_ctxt
+            .at(&ObligationCause::new(), self.table.trait_env.env)
+            .eq(DefineOpaqueTypes::Yes, expected, actual)
+            .map(|infer_ok| self.table.register_infer_ok(infer_ok));
+        if let Err(_err) = result {
+            // FIXME: Emit diagnostic.
+        }
+    }
+
     fn resolve_associated_type_with_params(
         &mut self,
         inner_ty: Ty,
@@ -1708,6 +1785,7 @@
             LifetimeElisionKind::Infer,
         );
         let mut path_ctx = ctx.at_path(path, node);
+        let interner = DbInterner::conjure();
         let (resolution, unresolved) = if value_ns {
             let Some(res) = path_ctx.resolve_path_in_value_ns(HygieneId::ROOT) else {
                 return (self.err_ty(), None);
@@ -1717,15 +1795,27 @@
                     ValueNs::EnumVariantId(var) => {
                         let substs = path_ctx.substs_from_path(var.into(), true, false);
                         drop(ctx);
-                        let ty = self.db.ty(var.lookup(self.db).parent.into());
-                        let ty = self.insert_type_vars(ty.substitute(Interner, &substs));
+                        let args: crate::next_solver::GenericArgs<'_> =
+                            substs.to_nextsolver(interner);
+                        let ty = self
+                            .db
+                            .ty(var.lookup(self.db).parent.into())
+                            .instantiate(interner, args)
+                            .to_chalk(interner);
+                        let ty = self.insert_type_vars(ty);
                         return (ty, Some(var.into()));
                     }
                     ValueNs::StructId(strukt) => {
                         let substs = path_ctx.substs_from_path(strukt.into(), true, false);
                         drop(ctx);
-                        let ty = self.db.ty(strukt.into());
-                        let ty = self.insert_type_vars(ty.substitute(Interner, &substs));
+                        let args: crate::next_solver::GenericArgs<'_> =
+                            substs.to_nextsolver(interner);
+                        let ty = self
+                            .db
+                            .ty(strukt.into())
+                            .instantiate(interner, args)
+                            .to_chalk(interner);
+                        let ty = self.insert_type_vars(ty);
                         return (ty, Some(strukt.into()));
                     }
                     ValueNs::ImplSelf(impl_id) => (TypeNs::SelfType(impl_id), None),
@@ -1746,22 +1836,29 @@
             TypeNs::AdtId(AdtId::StructId(strukt)) => {
                 let substs = path_ctx.substs_from_path(strukt.into(), true, false);
                 drop(ctx);
-                let ty = self.db.ty(strukt.into());
-                let ty = self.insert_type_vars(ty.substitute(Interner, &substs));
+                let args: crate::next_solver::GenericArgs<'_> = substs.to_nextsolver(interner);
+                let ty = self.db.ty(strukt.into()).instantiate(interner, args).to_chalk(interner);
+                let ty = self.insert_type_vars(ty);
                 forbid_unresolved_segments((ty, Some(strukt.into())), unresolved)
             }
             TypeNs::AdtId(AdtId::UnionId(u)) => {
                 let substs = path_ctx.substs_from_path(u.into(), true, false);
                 drop(ctx);
-                let ty = self.db.ty(u.into());
-                let ty = self.insert_type_vars(ty.substitute(Interner, &substs));
+                let args: crate::next_solver::GenericArgs<'_> = substs.to_nextsolver(interner);
+                let ty = self.db.ty(u.into()).instantiate(interner, args).to_chalk(interner);
+                let ty = self.insert_type_vars(ty);
                 forbid_unresolved_segments((ty, Some(u.into())), unresolved)
             }
             TypeNs::EnumVariantId(var) => {
                 let substs = path_ctx.substs_from_path(var.into(), true, false);
                 drop(ctx);
-                let ty = self.db.ty(var.lookup(self.db).parent.into());
-                let ty = self.insert_type_vars(ty.substitute(Interner, &substs));
+                let args: crate::next_solver::GenericArgs<'_> = substs.to_nextsolver(interner);
+                let ty = self
+                    .db
+                    .ty(var.lookup(self.db).parent.into())
+                    .instantiate(interner, args)
+                    .to_chalk(interner);
+                let ty = self.insert_type_vars(ty);
                 forbid_unresolved_segments((ty, Some(var.into())), unresolved)
             }
             TypeNs::SelfType(impl_id) => {
@@ -1844,8 +1941,10 @@
                 };
                 let substs = path_ctx.substs_from_path_segment(it.into(), true, None, false);
                 drop(ctx);
-                let ty = self.db.ty(it.into());
-                let ty = self.insert_type_vars(ty.substitute(Interner, &substs));
+                let interner = DbInterner::conjure();
+                let args: crate::next_solver::GenericArgs<'_> = substs.to_nextsolver(interner);
+                let ty = self.db.ty(it.into()).instantiate(interner, args).to_chalk(interner);
+                let ty = self.insert_type_vars(ty);
 
                 self.resolve_variant_on_alias(ty, unresolved, mod_path)
             }
diff --git a/crates/hir-ty/src/infer/coerce.rs b/crates/hir-ty/src/infer/coerce.rs
index 219b519..62ce00a 100644
--- a/crates/hir-ty/src/infer/coerce.rs
+++ b/crates/hir-ty/src/infer/coerce.rs
@@ -210,9 +210,8 @@
         // Coercing from `!` to any type is allowed:
         if a.is_never() {
             // If we're coercing into an inference var, mark it as possibly diverging.
-            // FIXME: rustc does this differently.
-            if let TyKind::Infer(rustc_type_ir::TyVar(b)) = b.kind() {
-                self.table.set_diverging(b.as_u32().into(), chalk_ir::TyVariableKind::General);
+            if b.is_infer() {
+                self.table.set_diverging(b);
             }
 
             if self.coerce_never {
@@ -1613,16 +1612,21 @@
             chalk_ir::GenericArgData::Const(c) => c.inference_var(Interner),
         } == Some(iv))
     };
-    let fallback = |iv, kind, default, binder| match kind {
-        chalk_ir::VariableKind::Ty(_ty_kind) => find_var(iv)
-            .map_or(default, |i| crate::BoundVar::new(binder, i).to_ty(Interner).cast(Interner)),
-        chalk_ir::VariableKind::Lifetime => find_var(iv).map_or(default, |i| {
-            crate::BoundVar::new(binder, i).to_lifetime(Interner).cast(Interner)
-        }),
-        chalk_ir::VariableKind::Const(ty) => find_var(iv).map_or(default, |i| {
-            crate::BoundVar::new(binder, i).to_const(Interner, ty).cast(Interner)
-        }),
+    let fallback = |iv, kind, binder| match kind {
+        chalk_ir::VariableKind::Ty(_ty_kind) => find_var(iv).map_or_else(
+            || chalk_ir::TyKind::Error.intern(Interner).cast(Interner),
+            |i| crate::BoundVar::new(binder, i).to_ty(Interner).cast(Interner),
+        ),
+        chalk_ir::VariableKind::Lifetime => find_var(iv).map_or_else(
+            || crate::LifetimeData::Error.intern(Interner).cast(Interner),
+            |i| crate::BoundVar::new(binder, i).to_lifetime(Interner).cast(Interner),
+        ),
+        chalk_ir::VariableKind::Const(ty) => find_var(iv).map_or_else(
+            || crate::unknown_const(ty.clone()).cast(Interner),
+            |i| crate::BoundVar::new(binder, i).to_const(Interner, ty.clone()).cast(Interner),
+        ),
     };
     // FIXME also map the types in the adjustments
+    // FIXME: We don't fallback correctly since this is done on `InferenceContext` and we only have `InferenceTable`.
     Ok((adjustments, table.resolve_with_fallback(ty.to_chalk(table.interner), &fallback)))
 }
diff --git a/crates/hir-ty/src/infer/expr.rs b/crates/hir-ty/src/infer/expr.rs
index b4a332f..ddf632c 100644
--- a/crates/hir-ty/src/infer/expr.rs
+++ b/crates/hir-ty/src/infer/expr.rs
@@ -23,13 +23,13 @@
 use tracing::debug;
 
 use crate::autoderef::overloaded_deref_ty;
-use crate::next_solver::ErrorGuaranteed;
 use crate::next_solver::infer::DefineOpaqueTypes;
 use crate::next_solver::obligation_ctxt::ObligationCtxt;
+use crate::next_solver::{DbInterner, ErrorGuaranteed};
 use crate::{
-    Adjust, Adjustment, AdtId, AutoBorrow, Binders, CallableDefId, CallableSig, DeclContext,
-    DeclOrigin, IncorrectGenericsLenKind, Interner, LifetimeElisionKind, Rawness, Scalar,
-    Substitution, TraitEnvironment, TraitRef, Ty, TyBuilder, TyExt, TyKind, consteval,
+    Adjust, Adjustment, AdtId, AutoBorrow, CallableDefId, CallableSig, DeclContext, DeclOrigin,
+    IncorrectGenericsLenKind, Interner, LifetimeElisionKind, Rawness, Scalar, Substitution,
+    TraitEnvironment, TraitRef, Ty, TyBuilder, TyExt, TyKind, consteval,
     generics::generics,
     infer::{
         AllowTwoPhase, BreakableKind,
@@ -1481,7 +1481,10 @@
 
         self.write_method_resolution(tgt_expr, func, subst.clone());
 
-        let method_ty = self.db.value_ty(func.into()).unwrap().substitute(Interner, &subst);
+        let interner = DbInterner::new_with(self.db, None, None);
+        let args: crate::next_solver::GenericArgs<'_> = subst.to_nextsolver(interner);
+        let method_ty =
+            self.db.value_ty(func.into()).unwrap().instantiate(interner, args).to_chalk(interner);
         self.register_obligations_for_call(&method_ty);
 
         self.infer_expr_coerce(rhs, &Expectation::has_type(rhs_ty.clone()), ExprIsRead::Yes);
@@ -1800,11 +1803,17 @@
                         self.write_expr_adj(receiver, adjustments.into_boxed_slice());
                         self.write_method_resolution(tgt_expr, func, substs.clone());
 
+                        let interner = DbInterner::new_with(self.db, None, None);
+                        let args: crate::next_solver::GenericArgs<'_> =
+                            substs.to_nextsolver(interner);
                         self.check_method_call(
                             tgt_expr,
                             &[],
-                            self.db.value_ty(func.into()).unwrap(),
-                            substs,
+                            self.db
+                                .value_ty(func.into())
+                                .unwrap()
+                                .instantiate(interner, args)
+                                .to_chalk(interner),
                             ty,
                             expected,
                         )
@@ -1963,11 +1972,16 @@
 
                 let substs = self.substs_for_method_call(tgt_expr, func.into(), generic_args);
                 self.write_method_resolution(tgt_expr, func, substs.clone());
+                let interner = DbInterner::new_with(self.db, None, None);
+                let gen_args: crate::next_solver::GenericArgs<'_> = substs.to_nextsolver(interner);
                 self.check_method_call(
                     tgt_expr,
                     args,
-                    self.db.value_ty(func.into()).expect("we have a function def"),
-                    substs,
+                    self.db
+                        .value_ty(func.into())
+                        .expect("we have a function def")
+                        .instantiate(interner, gen_args)
+                        .to_chalk(interner),
                     ty,
                     expected,
                 )
@@ -2012,11 +2026,15 @@
                 let recovered = match assoc_func_with_same_name {
                     Some(f) => {
                         let substs = self.substs_for_method_call(tgt_expr, f.into(), generic_args);
+                        let interner = DbInterner::new_with(self.db, None, None);
+                        let args: crate::next_solver::GenericArgs<'_> =
+                            substs.to_nextsolver(interner);
                         let f = self
                             .db
                             .value_ty(f.into())
                             .expect("we have a function def")
-                            .substitute(Interner, &substs);
+                            .instantiate(interner, args)
+                            .to_chalk(interner);
                         let sig = f.callable_sig(self.db).expect("we have a function def");
                         Some((f, sig, true))
                     }
@@ -2056,12 +2074,10 @@
         &mut self,
         tgt_expr: ExprId,
         args: &[ExprId],
-        method_ty: Binders<Ty>,
-        substs: Substitution,
+        method_ty: Ty,
         receiver_ty: Ty,
         expected: &Expectation,
     ) -> Ty {
-        let method_ty = method_ty.substitute(Interner, &substs);
         self.register_obligations_for_call(&method_ty);
         let interner = self.table.interner;
         let ((formal_receiver_ty, param_tys), ret_ty, is_varargs) =
diff --git a/crates/hir-ty/src/infer/fallback.rs b/crates/hir-ty/src/infer/fallback.rs
new file mode 100644
index 0000000..2022447
--- /dev/null
+++ b/crates/hir-ty/src/infer/fallback.rs
@@ -0,0 +1,439 @@
+//! Fallback of infer vars to `!` and `i32`/`f64`.
+
+use intern::sym;
+use petgraph::{
+    Graph,
+    visit::{Dfs, Walker},
+};
+use rustc_hash::{FxBuildHasher, FxHashMap, FxHashSet};
+use rustc_type_ir::{
+    TyVid,
+    inherent::{IntoKind, Ty as _},
+};
+use tracing::debug;
+
+use crate::{
+    infer::InferenceContext,
+    next_solver::{CoercePredicate, PredicateKind, SubtypePredicate, Ty, TyKind},
+};
+
+#[derive(Copy, Clone)]
+pub(crate) enum DivergingFallbackBehavior {
+    /// Always fallback to `()` (aka "always spontaneous decay")
+    ToUnit,
+    /// Sometimes fallback to `!`, but mainly fallback to `()` so that most of the crates are not broken.
+    ContextDependent,
+    /// Always fallback to `!` (which should be equivalent to never falling back + not making
+    /// never-to-any coercions unless necessary)
+    ToNever,
+}
+
+impl<'db> InferenceContext<'db> {
+    pub(super) fn type_inference_fallback(&mut self) {
+        debug!(
+            "type-inference-fallback start obligations: {:#?}",
+            self.table.fulfillment_cx.pending_obligations()
+        );
+
+        // All type checking constraints were added, try to fallback unsolved variables.
+        self.table.select_obligations_where_possible();
+
+        debug!(
+            "type-inference-fallback post selection obligations: {:#?}",
+            self.table.fulfillment_cx.pending_obligations()
+        );
+
+        let fallback_occurred = self.fallback_types();
+
+        if !fallback_occurred {
+            return;
+        }
+
+        // We now see if we can make progress. This might cause us to
+        // unify inference variables for opaque types, since we may
+        // have unified some other type variables during the first
+        // phase of fallback. This means that we only replace
+        // inference variables with their underlying opaque types as a
+        // last resort.
+        //
+        // In code like this:
+        //
+        // ```rust
+        // type MyType = impl Copy;
+        // fn produce() -> MyType { true }
+        // fn bad_produce() -> MyType { panic!() }
+        // ```
+        //
+        // we want to unify the opaque inference variable in `bad_produce`
+        // with the diverging fallback for `panic!` (e.g. `()` or `!`).
+        // This will produce a nice error message about conflicting concrete
+        // types for `MyType`.
+        //
+        // If we had tried to fallback the opaque inference variable to `MyType`,
+        // we will generate a confusing type-check error that does not explicitly
+        // refer to opaque types.
+        self.table.select_obligations_where_possible();
+    }
+
+    fn diverging_fallback_behavior(&self) -> DivergingFallbackBehavior {
+        if self.krate().data(self.db).edition.at_least_2024() {
+            return DivergingFallbackBehavior::ToNever;
+        }
+
+        if self.resolver.def_map().is_unstable_feature_enabled(&sym::never_type_fallback) {
+            return DivergingFallbackBehavior::ContextDependent;
+        }
+
+        DivergingFallbackBehavior::ToUnit
+    }
+
+    fn fallback_types(&mut self) -> bool {
+        // Check if we have any unresolved variables. If not, no need for fallback.
+        let unresolved_variables = self.table.infer_ctxt.unresolved_variables();
+
+        if unresolved_variables.is_empty() {
+            return false;
+        }
+
+        let diverging_fallback_behavior = self.diverging_fallback_behavior();
+
+        let diverging_fallback =
+            self.calculate_diverging_fallback(&unresolved_variables, diverging_fallback_behavior);
+
+        // We do fallback in two passes, to try to generate
+        // better error messages.
+        // The first time, we do *not* replace opaque types.
+        let mut fallback_occurred = false;
+        for ty in unresolved_variables {
+            debug!("unsolved_variable = {:?}", ty);
+            fallback_occurred |= self.fallback_if_possible(ty, &diverging_fallback);
+        }
+
+        fallback_occurred
+    }
+
+    // Tries to apply a fallback to `ty` if it is an unsolved variable.
+    //
+    // - Unconstrained ints are replaced with `i32`.
+    //
+    // - Unconstrained floats are replaced with `f64`.
+    //
+    // - Non-numerics may get replaced with `()` or `!`, depending on
+    //   how they were categorized by `calculate_diverging_fallback`
+    //   (and the setting of `#![feature(never_type_fallback)]`).
+    //
+    // Fallback becomes very dubious if we have encountered
+    // type-checking errors. In that case, fallback to Error.
+    //
+    // Sets `FnCtxt::fallback_has_occurred` if fallback is performed
+    // during this call.
+    fn fallback_if_possible(
+        &mut self,
+        ty: Ty<'db>,
+        diverging_fallback: &FxHashMap<Ty<'db>, Ty<'db>>,
+    ) -> bool {
+        // Careful: we do NOT shallow-resolve `ty`. We know that `ty`
+        // is an unsolved variable, and we determine its fallback
+        // based solely on how it was created, not what other type
+        // variables it may have been unified with since then.
+        //
+        // The reason this matters is that other attempts at fallback
+        // may (in principle) conflict with this fallback, and we wish
+        // to generate a type error in that case. (However, this
+        // actually isn't true right now, because we're only using the
+        // builtin fallback rules. This would be true if we were using
+        // user-supplied fallbacks. But it's still useful to write the
+        // code to detect bugs.)
+        //
+        // (Note though that if we have a general type variable `?T`
+        // that is then unified with an integer type variable `?I`
+        // that ultimately never gets resolved to a special integral
+        // type, `?T` is not considered unsolved, but `?I` is. The
+        // same is true for float variables.)
+        let fallback = match ty.kind() {
+            TyKind::Infer(rustc_type_ir::IntVar(_)) => self.types.i32,
+            TyKind::Infer(rustc_type_ir::FloatVar(_)) => self.types.f64,
+            _ => match diverging_fallback.get(&ty) {
+                Some(&fallback_ty) => fallback_ty,
+                None => return false,
+            },
+        };
+        debug!("fallback_if_possible(ty={:?}): defaulting to `{:?}`", ty, fallback);
+
+        self.demand_eqtype(ty, fallback);
+        true
+    }
+
+    /// The "diverging fallback" system is rather complicated. This is
+    /// a result of our need to balance 'do the right thing' with
+    /// backwards compatibility.
+    ///
+    /// "Diverging" type variables are variables created when we
+    /// coerce a `!` type into an unbound type variable `?X`. If they
+    /// never wind up being constrained, the "right and natural" thing
+    /// is that `?X` should "fallback" to `!`. This means that e.g. an
+    /// expression like `Some(return)` will ultimately wind up with a
+    /// type like `Option<!>` (presuming it is not assigned or
+    /// constrained to have some other type).
+    ///
+    /// However, the fallback used to be `()` (before the `!` type was
+    /// added). Moreover, there are cases where the `!` type 'leaks
+    /// out' from dead code into type variables that affect live
+    /// code. The most common case is something like this:
+    ///
+    /// ```rust
+    /// # fn foo() -> i32 { 4 }
+    /// match foo() {
+    ///     22 => Default::default(), // call this type `?D`
+    ///     _ => return, // return has type `!`
+    /// } // call the type of this match `?M`
+    /// ```
+    ///
+    /// Here, coercing the type `!` into `?M` will create a diverging
+    /// type variable `?X` where `?X <: ?M`. We also have that `?D <:
+    /// ?M`. If `?M` winds up unconstrained, then `?X` will
+    /// fallback. If it falls back to `!`, then all the type variables
+    /// will wind up equal to `!` -- this includes the type `?D`
+    /// (since `!` doesn't implement `Default`, we wind up a "trait
+    /// not implemented" error in code like this). But since the
+    /// original fallback was `()`, this code used to compile with `?D
+    /// = ()`. This is somewhat surprising, since `Default::default()`
+    /// on its own would give an error because the types are
+    /// insufficiently constrained.
+    ///
+    /// Our solution to this dilemma is to modify diverging variables
+    /// so that they can *either* fallback to `!` (the default) or to
+    /// `()` (the backwards compatibility case). We decide which
+    /// fallback to use based on whether there is a coercion pattern
+    /// like this:
+    ///
+    /// ```ignore (not-rust)
+    /// ?Diverging -> ?V
+    /// ?NonDiverging -> ?V
+    /// ?V != ?NonDiverging
+    /// ```
+    ///
+    /// Here `?Diverging` represents some diverging type variable and
+    /// `?NonDiverging` represents some non-diverging type
+    /// variable. `?V` can be any type variable (diverging or not), so
+    /// long as it is not equal to `?NonDiverging`.
+    ///
+    /// Intuitively, what we are looking for is a case where a
+    /// "non-diverging" type variable (like `?M` in our example above)
+    /// is coerced *into* some variable `?V` that would otherwise
+    /// fallback to `!`. In that case, we make `?V` fallback to `!`,
+    /// along with anything that would flow into `?V`.
+    ///
+    /// The algorithm we use:
+    /// * Identify all variables that are coerced *into* by a
+    ///   diverging variable. Do this by iterating over each
+    ///   diverging, unsolved variable and finding all variables
+    ///   reachable from there. Call that set `D`.
+    /// * Walk over all unsolved, non-diverging variables, and find
+    ///   any variable that has an edge into `D`.
+    fn calculate_diverging_fallback(
+        &self,
+        unresolved_variables: &[Ty<'db>],
+        behavior: DivergingFallbackBehavior,
+    ) -> FxHashMap<Ty<'db>, Ty<'db>> {
+        debug!("calculate_diverging_fallback({:?})", unresolved_variables);
+
+        // Construct a coercion graph where an edge `A -> B` indicates
+        // a type variable is that is coerced
+        let coercion_graph = self.create_coercion_graph();
+
+        // Extract the unsolved type inference variable vids; note that some
+        // unsolved variables are integer/float variables and are excluded.
+        let unsolved_vids = unresolved_variables.iter().filter_map(|ty| ty.ty_vid());
+
+        // Compute the diverging root vids D -- that is, the root vid of
+        // those type variables that (a) are the target of a coercion from
+        // a `!` type and (b) have not yet been solved.
+        //
+        // These variables are the ones that are targets for fallback to
+        // either `!` or `()`.
+        let diverging_roots: FxHashSet<TyVid> = self
+            .table
+            .diverging_type_vars
+            .iter()
+            .map(|&ty| self.shallow_resolve(ty))
+            .filter_map(|ty| ty.ty_vid())
+            .map(|vid| self.table.infer_ctxt.root_var(vid))
+            .collect();
+        debug!(
+            "calculate_diverging_fallback: diverging_type_vars={:?}",
+            self.table.diverging_type_vars
+        );
+        debug!("calculate_diverging_fallback: diverging_roots={:?}", diverging_roots);
+
+        // Find all type variables that are reachable from a diverging
+        // type variable. These will typically default to `!`, unless
+        // we find later that they are *also* reachable from some
+        // other type variable outside this set.
+        let mut roots_reachable_from_diverging = Dfs::empty(&coercion_graph);
+        let mut diverging_vids = vec![];
+        let mut non_diverging_vids = vec![];
+        for unsolved_vid in unsolved_vids {
+            let root_vid = self.table.infer_ctxt.root_var(unsolved_vid);
+            debug!(
+                "calculate_diverging_fallback: unsolved_vid={:?} root_vid={:?} diverges={:?}",
+                unsolved_vid,
+                root_vid,
+                diverging_roots.contains(&root_vid),
+            );
+            if diverging_roots.contains(&root_vid) {
+                diverging_vids.push(unsolved_vid);
+                roots_reachable_from_diverging.move_to(root_vid.as_u32().into());
+
+                // drain the iterator to visit all nodes reachable from this node
+                while roots_reachable_from_diverging.next(&coercion_graph).is_some() {}
+            } else {
+                non_diverging_vids.push(unsolved_vid);
+            }
+        }
+
+        debug!(
+            "calculate_diverging_fallback: roots_reachable_from_diverging={:?}",
+            roots_reachable_from_diverging,
+        );
+
+        // Find all type variables N0 that are not reachable from a
+        // diverging variable, and then compute the set reachable from
+        // N0, which we call N. These are the *non-diverging* type
+        // variables. (Note that this set consists of "root variables".)
+        let mut roots_reachable_from_non_diverging = Dfs::empty(&coercion_graph);
+        for &non_diverging_vid in &non_diverging_vids {
+            let root_vid = self.table.infer_ctxt.root_var(non_diverging_vid);
+            if roots_reachable_from_diverging.discovered.contains(root_vid.as_usize()) {
+                continue;
+            }
+            roots_reachable_from_non_diverging.move_to(root_vid.as_u32().into());
+            while roots_reachable_from_non_diverging.next(&coercion_graph).is_some() {}
+        }
+        debug!(
+            "calculate_diverging_fallback: roots_reachable_from_non_diverging={:?}",
+            roots_reachable_from_non_diverging,
+        );
+
+        debug!("obligations: {:#?}", self.table.fulfillment_cx.pending_obligations());
+
+        // For each diverging variable, figure out whether it can
+        // reach a member of N. If so, it falls back to `()`. Else
+        // `!`.
+        let mut diverging_fallback =
+            FxHashMap::with_capacity_and_hasher(diverging_vids.len(), FxBuildHasher);
+
+        for &diverging_vid in &diverging_vids {
+            let diverging_ty = Ty::new_var(self.table.interner, diverging_vid);
+            let root_vid = self.table.infer_ctxt.root_var(diverging_vid);
+            let can_reach_non_diverging = Dfs::new(&coercion_graph, root_vid.as_u32().into())
+                .iter(&coercion_graph)
+                .any(|n| roots_reachable_from_non_diverging.discovered.contains(n.index()));
+
+            let mut fallback_to = |ty| {
+                diverging_fallback.insert(diverging_ty, ty);
+            };
+
+            match behavior {
+                DivergingFallbackBehavior::ToUnit => {
+                    debug!("fallback to () - legacy: {:?}", diverging_vid);
+                    fallback_to(self.types.unit);
+                }
+                DivergingFallbackBehavior::ContextDependent => {
+                    // FIXME: rustc does the following, but given this is only relevant when the unstable
+                    // `never_type_fallback` feature is active, I chose to not port this.
+                    // if found_infer_var_info.self_in_trait && found_infer_var_info.output {
+                    //     // This case falls back to () to ensure that the code pattern in
+                    //     // tests/ui/never_type/fallback-closure-ret.rs continues to
+                    //     // compile when never_type_fallback is enabled.
+                    //     //
+                    //     // This rule is not readily explainable from first principles,
+                    //     // but is rather intended as a patchwork fix to ensure code
+                    //     // which compiles before the stabilization of never type
+                    //     // fallback continues to work.
+                    //     //
+                    //     // Typically this pattern is encountered in a function taking a
+                    //     // closure as a parameter, where the return type of that closure
+                    //     // (checked by `relationship.output`) is expected to implement
+                    //     // some trait (checked by `relationship.self_in_trait`). This
+                    //     // can come up in non-closure cases too, so we do not limit this
+                    //     // rule to specifically `FnOnce`.
+                    //     //
+                    //     // When the closure's body is something like `panic!()`, the
+                    //     // return type would normally be inferred to `!`. However, it
+                    //     // needs to fall back to `()` in order to still compile, as the
+                    //     // trait is specifically implemented for `()` but not `!`.
+                    //     //
+                    //     // For details on the requirements for these relationships to be
+                    //     // set, see the relationship finding module in
+                    //     // compiler/rustc_trait_selection/src/traits/relationships.rs.
+                    //     debug!("fallback to () - found trait and projection: {:?}", diverging_vid);
+                    //     fallback_to(self.types.unit);
+                    // }
+                    if can_reach_non_diverging {
+                        debug!("fallback to () - reached non-diverging: {:?}", diverging_vid);
+                        fallback_to(self.types.unit);
+                    } else {
+                        debug!("fallback to ! - all diverging: {:?}", diverging_vid);
+                        fallback_to(self.types.never);
+                    }
+                }
+                DivergingFallbackBehavior::ToNever => {
+                    debug!(
+                        "fallback to ! - `rustc_never_type_mode = \"fallback_to_never\")`: {:?}",
+                        diverging_vid
+                    );
+                    fallback_to(self.types.never);
+                }
+            }
+        }
+
+        diverging_fallback
+    }
+
+    /// Returns a graph whose nodes are (unresolved) inference variables and where
+    /// an edge `?A -> ?B` indicates that the variable `?A` is coerced to `?B`.
+    fn create_coercion_graph(&self) -> Graph<(), ()> {
+        let pending_obligations = self.table.fulfillment_cx.pending_obligations();
+        let pending_obligations_len = pending_obligations.len();
+        debug!("create_coercion_graph: pending_obligations={:?}", pending_obligations);
+        let coercion_edges = pending_obligations
+            .into_iter()
+            .filter_map(|obligation| {
+                // The predicates we are looking for look like `Coerce(?A -> ?B)`.
+                // They will have no bound variables.
+                obligation.predicate.kind().no_bound_vars()
+            })
+            .filter_map(|atom| {
+                // We consider both subtyping and coercion to imply 'flow' from
+                // some position in the code `a` to a different position `b`.
+                // This is then used to determine which variables interact with
+                // live code, and as such must fall back to `()` to preserve
+                // soundness.
+                //
+                // In practice currently the two ways that this happens is
+                // coercion and subtyping.
+                let (a, b) = match atom {
+                    PredicateKind::Coerce(CoercePredicate { a, b }) => (a, b),
+                    PredicateKind::Subtype(SubtypePredicate { a_is_expected: _, a, b }) => (a, b),
+                    _ => return None,
+                };
+
+                let a_vid = self.root_vid(a)?;
+                let b_vid = self.root_vid(b)?;
+                Some((a_vid.as_u32(), b_vid.as_u32()))
+            });
+        let num_ty_vars = self.table.infer_ctxt.num_ty_vars();
+        let mut graph = Graph::with_capacity(num_ty_vars, pending_obligations_len);
+        for _ in 0..num_ty_vars {
+            graph.add_node(());
+        }
+        graph.extend_with_edges(coercion_edges);
+        graph
+    }
+
+    /// If `ty` is an unresolved type variable, returns its root vid.
+    fn root_vid(&self, ty: Ty<'db>) -> Option<TyVid> {
+        Some(self.table.infer_ctxt.root_var(self.shallow_resolve(ty).ty_vid()?))
+    }
+}
diff --git a/crates/hir-ty/src/infer/path.rs b/crates/hir-ty/src/infer/path.rs
index 80f7324..3a50b83 100644
--- a/crates/hir-ty/src/infer/path.rs
+++ b/crates/hir-ty/src/infer/path.rs
@@ -17,7 +17,10 @@
     generics::generics,
     infer::diagnostics::InferenceTyLoweringContext as TyLoweringContext,
     method_resolution::{self, VisibleFromModule},
-    next_solver::mapping::ChalkToNextSolver,
+    next_solver::{
+        DbInterner,
+        mapping::{ChalkToNextSolver, NextSolverToChalk},
+    },
     to_chalk_trait_id,
 };
 
@@ -36,7 +39,9 @@
 
         self.add_required_obligations_for_value_path(generic_def, &substs);
 
-        let ty = self.db.value_ty(value_def)?.substitute(Interner, &substs);
+        let interner = DbInterner::new_with(self.db, None, None);
+        let args: crate::next_solver::GenericArgs<'_> = substs.to_nextsolver(interner);
+        let ty = self.db.value_ty(value_def)?.instantiate(interner, args).to_chalk(interner);
         let ty = self.process_remote_user_written_ty(ty);
         Some(ty)
     }
@@ -89,9 +94,9 @@
 
         let generic_def = value_def.to_generic_def_id(self.db);
         if let GenericDefId::StaticId(_) = generic_def {
+            let interner = DbInterner::new_with(self.db, None, None);
             // `Static` is the kind of item that can never be generic currently. We can just skip the binders to get its type.
-            let (ty, binders) = self.db.value_ty(value_def)?.into_value_and_skipped_binders();
-            stdx::always!(binders.is_empty(Interner), "non-empty binders for non-generic def",);
+            let ty = self.db.value_ty(value_def)?.skip_binder().to_chalk(interner);
             return Some(ValuePathResolution::NonGeneric(ty));
         };
 
diff --git a/crates/hir-ty/src/infer/unify.rs b/crates/hir-ty/src/infer/unify.rs
index 6df9cba..108cf5b 100644
--- a/crates/hir-ty/src/infer/unify.rs
+++ b/crates/hir-ty/src/infer/unify.rs
@@ -3,8 +3,7 @@
 use std::fmt;
 
 use chalk_ir::{
-    CanonicalVarKind, FloatTy, IntTy, TyVariableKind, cast::Cast, fold::TypeFoldable,
-    interner::HasInterner,
+    CanonicalVarKind, TyVariableKind, cast::Cast, fold::TypeFoldable, interner::HasInterner,
 };
 use either::Either;
 use hir_def::{AdtId, lang_item::LangItem};
@@ -12,7 +11,7 @@
 use intern::sym;
 use rustc_hash::{FxHashMap, FxHashSet};
 use rustc_type_ir::{
-    FloatVid, IntVid, TyVid, TypeVisitableExt, UpcastFrom,
+    TyVid, TypeVisitableExt, UpcastFrom,
     inherent::{IntoKind, Span, Term as _, Ty as _},
     relate::{Relate, solver_relating::RelateExt},
     solve::{Certainty, GoalSource},
@@ -23,8 +22,8 @@
 use super::{InferResult, InferenceContext, TypeError};
 use crate::{
     AliasTy, BoundVar, Canonical, Const, ConstValue, DebruijnIndex, GenericArg, GenericArgData,
-    InferenceVar, Interner, Lifetime, OpaqueTyId, ProjectionTy, Scalar, Substitution,
-    TraitEnvironment, Ty, TyExt, TyKind, VariableKind,
+    InferenceVar, Interner, Lifetime, OpaqueTyId, ProjectionTy, Substitution, TraitEnvironment, Ty,
+    TyExt, TyKind, VariableKind,
     consteval::unknown_const,
     db::HirDatabase,
     fold_generic_args, fold_tys_and_consts,
@@ -143,7 +142,6 @@
     let ty1_with_vars = table.normalize_associated_types_in(ty1_with_vars);
     let ty2_with_vars = table.normalize_associated_types_in(ty2_with_vars);
     table.select_obligations_where_possible();
-    table.propagate_diverging_flag();
     let ty1_with_vars = table.resolve_completely(ty1_with_vars);
     let ty2_with_vars = table.resolve_completely(ty2_with_vars);
     table.unify_deeply(&ty1_with_vars, &ty2_with_vars)
@@ -170,13 +168,19 @@
             GenericArgData::Const(c) => c.inference_var(Interner),
         } == Some(iv))
     };
-    let fallback = |iv, kind, default, binder| match kind {
-        chalk_ir::VariableKind::Ty(_ty_kind) => find_var(iv)
-            .map_or(default, |i| BoundVar::new(binder, i).to_ty(Interner).cast(Interner)),
-        chalk_ir::VariableKind::Lifetime => find_var(iv)
-            .map_or(default, |i| BoundVar::new(binder, i).to_lifetime(Interner).cast(Interner)),
-        chalk_ir::VariableKind::Const(ty) => find_var(iv)
-            .map_or(default, |i| BoundVar::new(binder, i).to_const(Interner, ty).cast(Interner)),
+    let fallback = |iv, kind, binder| match kind {
+        chalk_ir::VariableKind::Ty(_ty_kind) => find_var(iv).map_or_else(
+            || TyKind::Error.intern(Interner).cast(Interner),
+            |i| BoundVar::new(binder, i).to_ty(Interner).cast(Interner),
+        ),
+        chalk_ir::VariableKind::Lifetime => find_var(iv).map_or_else(
+            || crate::error_lifetime().cast(Interner),
+            |i| BoundVar::new(binder, i).to_lifetime(Interner).cast(Interner),
+        ),
+        chalk_ir::VariableKind::Const(ty) => find_var(iv).map_or_else(
+            || crate::unknown_const(ty.clone()).cast(Interner),
+            |i| BoundVar::new(binder, i).to_const(Interner, ty.clone()).cast(Interner),
+        ),
     };
     Some(Substitution::from_iter(
         Interner,
@@ -215,14 +219,13 @@
     pub(crate) trait_env: Arc<TraitEnvironment<'db>>,
     pub(crate) tait_coercion_table: Option<FxHashMap<OpaqueTyId, Ty>>,
     pub(crate) infer_ctxt: InferCtxt<'db>,
-    diverging_tys: FxHashSet<Ty>,
     pub(super) fulfillment_cx: FulfillmentCtxt<'db>,
+    pub(super) diverging_type_vars: FxHashSet<crate::next_solver::Ty<'db>>,
 }
 
 pub(crate) struct InferenceTableSnapshot<'db> {
     ctxt_snapshot: CombinedSnapshot,
     obligations: FulfillmentCtxt<'db>,
-    diverging_tys: FxHashSet<Ty>,
 }
 
 impl<'db> InferenceTable<'db> {
@@ -238,7 +241,7 @@
             tait_coercion_table: None,
             fulfillment_cx: FulfillmentCtxt::new(&infer_ctxt),
             infer_ctxt,
-            diverging_tys: FxHashSet::default(),
+            diverging_type_vars: FxHashSet::default(),
         }
     }
 
@@ -321,74 +324,8 @@
         }
     }
 
-    /// Chalk doesn't know about the `diverging` flag, so when it unifies two
-    /// type variables of which one is diverging, the chosen root might not be
-    /// diverging and we have no way of marking it as such at that time. This
-    /// function goes through all type variables and make sure their root is
-    /// marked as diverging if necessary, so that resolving them gives the right
-    /// result.
-    pub(super) fn propagate_diverging_flag(&mut self) {
-        let mut new_tys = FxHashSet::default();
-        for ty in self.diverging_tys.iter() {
-            match ty.kind(Interner) {
-                TyKind::InferenceVar(var, kind) => match kind {
-                    TyVariableKind::General => {
-                        let root = InferenceVar::from(
-                            self.infer_ctxt.root_var(TyVid::from_u32(var.index())).as_u32(),
-                        );
-                        if root.index() != var.index() {
-                            new_tys.insert(TyKind::InferenceVar(root, *kind).intern(Interner));
-                        }
-                    }
-                    TyVariableKind::Integer => {
-                        let root = InferenceVar::from(
-                            self.infer_ctxt
-                                .inner
-                                .borrow_mut()
-                                .int_unification_table()
-                                .find(IntVid::from_usize(var.index() as usize))
-                                .as_u32(),
-                        );
-                        if root.index() != var.index() {
-                            new_tys.insert(TyKind::InferenceVar(root, *kind).intern(Interner));
-                        }
-                    }
-                    TyVariableKind::Float => {
-                        let root = InferenceVar::from(
-                            self.infer_ctxt
-                                .inner
-                                .borrow_mut()
-                                .float_unification_table()
-                                .find(FloatVid::from_usize(var.index() as usize))
-                                .as_u32(),
-                        );
-                        if root.index() != var.index() {
-                            new_tys.insert(TyKind::InferenceVar(root, *kind).intern(Interner));
-                        }
-                    }
-                },
-                _ => {}
-            }
-        }
-        self.diverging_tys.extend(new_tys);
-    }
-
-    pub(super) fn set_diverging(&mut self, iv: InferenceVar, kind: TyVariableKind) {
-        self.diverging_tys.insert(TyKind::InferenceVar(iv, kind).intern(Interner));
-    }
-
-    fn fallback_value(&self, iv: InferenceVar, kind: TyVariableKind) -> Ty {
-        let is_diverging =
-            self.diverging_tys.contains(&TyKind::InferenceVar(iv, kind).intern(Interner));
-        if is_diverging {
-            return TyKind::Never.intern(Interner);
-        }
-        match kind {
-            TyVariableKind::General => TyKind::Error,
-            TyVariableKind::Integer => TyKind::Scalar(Scalar::Int(IntTy::I32)),
-            TyVariableKind::Float => TyKind::Scalar(Scalar::Float(FloatTy::F64)),
-        }
-        .intern(Interner)
+    pub(super) fn set_diverging(&mut self, ty: crate::next_solver::Ty<'db>) {
+        self.diverging_type_vars.insert(ty);
     }
 
     pub(crate) fn canonicalize<T>(&mut self, t: T) -> rustc_type_ir::Canonical<DbInterner<'db>, T>
@@ -529,7 +466,7 @@
 
         let ty = var.to_ty(Interner, kind);
         if diverging {
-            self.diverging_tys.insert(ty.clone());
+            self.diverging_type_vars.insert(ty.to_nextsolver(self.interner));
         }
         ty
     }
@@ -573,7 +510,7 @@
     pub(crate) fn resolve_with_fallback<T>(
         &mut self,
         t: T,
-        fallback: &dyn Fn(InferenceVar, VariableKind, GenericArg, DebruijnIndex) -> GenericArg,
+        fallback: &dyn Fn(InferenceVar, VariableKind, DebruijnIndex) -> GenericArg,
     ) -> T
     where
         T: HasInterner<Interner = Interner> + TypeFoldable<Interner>,
@@ -615,7 +552,7 @@
     fn resolve_with_fallback_inner<T>(
         &mut self,
         t: T,
-        fallback: &dyn Fn(InferenceVar, VariableKind, GenericArg, DebruijnIndex) -> GenericArg,
+        fallback: &dyn Fn(InferenceVar, VariableKind, DebruijnIndex) -> GenericArg,
     ) -> T
     where
         T: HasInterner<Interner = Interner> + TypeFoldable<Interner>,
@@ -632,53 +569,15 @@
         T: HasInterner<Interner = Interner> + TypeFoldable<Interner> + ChalkToNextSolver<'db, U>,
         U: NextSolverToChalk<'db, T> + rustc_type_ir::TypeFoldable<DbInterner<'db>>,
     {
-        let t = self.resolve_with_fallback(t, &|_, _, d, _| d);
-        let t = self.normalize_associated_types_in(t);
-        // let t = self.resolve_opaque_tys_in(t);
-        // Resolve again, because maybe normalization inserted infer vars.
-        self.resolve_with_fallback(t, &|_, _, d, _| d)
-    }
+        let value = t.to_nextsolver(self.interner);
+        let value = self.infer_ctxt.resolve_vars_if_possible(value);
 
-    /// Apply a fallback to unresolved scalar types. Integer type variables and float type
-    /// variables are replaced with i32 and f64, respectively.
-    ///
-    /// This method is only intended to be called just before returning inference results (i.e. in
-    /// `InferenceContext::resolve_all()`).
-    ///
-    /// FIXME: This method currently doesn't apply fallback to unconstrained general type variables
-    /// whereas rustc replaces them with `()` or `!`.
-    pub(super) fn fallback_if_possible(&mut self) {
-        let int_fallback = TyKind::Scalar(Scalar::Int(IntTy::I32)).intern(Interner);
-        let float_fallback = TyKind::Scalar(Scalar::Float(FloatTy::F64)).intern(Interner);
+        let mut goals = vec![];
+        let value = value.fold_with(&mut resolve_completely::Resolver::new(self, true, &mut goals));
 
-        let int_vars = self.infer_ctxt.inner.borrow_mut().int_unification_table().len();
-        for v in 0..int_vars {
-            let var = InferenceVar::from(v as u32).to_ty(Interner, TyVariableKind::Integer);
-            let maybe_resolved = self.resolve_ty_shallow(&var);
-            if let TyKind::InferenceVar(_, kind) = maybe_resolved.kind(Interner) {
-                // I don't think we can ever unify these vars with float vars, but keep this here for now
-                let fallback = match kind {
-                    TyVariableKind::Integer => &int_fallback,
-                    TyVariableKind::Float => &float_fallback,
-                    TyVariableKind::General => unreachable!(),
-                };
-                self.unify(&var, fallback);
-            }
-        }
-        let float_vars = self.infer_ctxt.inner.borrow_mut().float_unification_table().len();
-        for v in 0..float_vars {
-            let var = InferenceVar::from(v as u32).to_ty(Interner, TyVariableKind::Float);
-            let maybe_resolved = self.resolve_ty_shallow(&var);
-            if let TyKind::InferenceVar(_, kind) = maybe_resolved.kind(Interner) {
-                // I don't think we can ever unify these vars with float vars, but keep this here for now
-                let fallback = match kind {
-                    TyVariableKind::Integer => &int_fallback,
-                    TyVariableKind::Float => &float_fallback,
-                    TyVariableKind::General => unreachable!(),
-                };
-                self.unify(&var, fallback);
-            }
-        }
+        // FIXME(next-solver): Handle `goals`.
+
+        value.to_chalk(self.interner)
     }
 
     /// Unify two relatable values (e.g. `Ty`) and register new trait goals that arise from that.
@@ -780,7 +679,7 @@
     }
 
     pub(crate) fn structurally_resolve_type(&mut self, ty: &Ty) -> Ty {
-        if let TyKind::Alias(..) = ty.kind(Interner) {
+        if let TyKind::Alias(chalk_ir::AliasTy::Projection(..)) = ty.kind(Interner) {
             self.structurally_normalize_ty(ty)
         } else {
             self.resolve_vars_with_obligations(ty.to_nextsolver(self.interner))
@@ -829,15 +728,13 @@
 
     pub(crate) fn snapshot(&mut self) -> InferenceTableSnapshot<'db> {
         let ctxt_snapshot = self.infer_ctxt.start_snapshot();
-        let diverging_tys = self.diverging_tys.clone();
         let obligations = self.fulfillment_cx.clone();
-        InferenceTableSnapshot { ctxt_snapshot, diverging_tys, obligations }
+        InferenceTableSnapshot { ctxt_snapshot, obligations }
     }
 
     #[tracing::instrument(skip_all)]
     pub(crate) fn rollback_to(&mut self, snapshot: InferenceTableSnapshot<'db>) {
         self.infer_ctxt.rollback_to(snapshot.ctxt_snapshot);
-        self.diverging_tys = snapshot.diverging_tys;
         self.fulfillment_cx = snapshot.obligations;
     }
 
@@ -1166,14 +1063,10 @@
 mod resolve {
     use super::InferenceTable;
     use crate::{
-        ConcreteConst, Const, ConstData, ConstScalar, ConstValue, DebruijnIndex, GenericArg,
-        InferenceVar, Interner, Lifetime, Ty, TyVariableKind, VariableKind,
-        next_solver::mapping::NextSolverToChalk,
+        Const, DebruijnIndex, GenericArg, InferenceVar, Interner, Lifetime, Ty, TyVariableKind,
+        VariableKind, next_solver::mapping::NextSolverToChalk,
     };
-    use chalk_ir::{
-        cast::Cast,
-        fold::{TypeFoldable, TypeFolder},
-    };
+    use chalk_ir::fold::{TypeFoldable, TypeFolder};
     use rustc_type_ir::{FloatVid, IntVid, TyVid};
 
     #[derive(Debug, Copy, Clone, PartialEq, Eq)]
@@ -1187,7 +1080,7 @@
     pub(super) struct Resolver<
         'a,
         'b,
-        F: Fn(InferenceVar, VariableKind, GenericArg, DebruijnIndex) -> GenericArg,
+        F: Fn(InferenceVar, VariableKind, DebruijnIndex) -> GenericArg,
     > {
         pub(super) table: &'a mut InferenceTable<'b>,
         pub(super) var_stack: &'a mut Vec<(InferenceVar, VarKind)>,
@@ -1195,7 +1088,7 @@
     }
     impl<F> TypeFolder<Interner> for Resolver<'_, '_, F>
     where
-        F: Fn(InferenceVar, VariableKind, GenericArg, DebruijnIndex) -> GenericArg,
+        F: Fn(InferenceVar, VariableKind, DebruijnIndex) -> GenericArg,
     {
         fn as_dyn(&mut self) -> &mut dyn TypeFolder<Interner> {
             self
@@ -1217,8 +1110,7 @@
                     let var = InferenceVar::from(vid.as_u32());
                     if self.var_stack.contains(&(var, VarKind::Ty(kind))) {
                         // recursive type
-                        let default = self.table.fallback_value(var, kind).cast(Interner);
-                        return (self.fallback)(var, VariableKind::Ty(kind), default, outer_binder)
+                        return (self.fallback)(var, VariableKind::Ty(kind), outer_binder)
                             .assert_ty_ref(Interner)
                             .clone();
                     }
@@ -1230,8 +1122,7 @@
                         self.var_stack.pop();
                         result
                     } else {
-                        let default = self.table.fallback_value(var, kind).cast(Interner);
-                        (self.fallback)(var, VariableKind::Ty(kind), default, outer_binder)
+                        (self.fallback)(var, VariableKind::Ty(kind), outer_binder)
                             .assert_ty_ref(Interner)
                             .clone()
                     }
@@ -1247,8 +1138,7 @@
                     let var = InferenceVar::from(vid.as_u32());
                     if self.var_stack.contains(&(var, VarKind::Ty(kind))) {
                         // recursive type
-                        let default = self.table.fallback_value(var, kind).cast(Interner);
-                        return (self.fallback)(var, VariableKind::Ty(kind), default, outer_binder)
+                        return (self.fallback)(var, VariableKind::Ty(kind), outer_binder)
                             .assert_ty_ref(Interner)
                             .clone();
                     }
@@ -1260,8 +1150,7 @@
                         self.var_stack.pop();
                         result
                     } else {
-                        let default = self.table.fallback_value(var, kind).cast(Interner);
-                        (self.fallback)(var, VariableKind::Ty(kind), default, outer_binder)
+                        (self.fallback)(var, VariableKind::Ty(kind), outer_binder)
                             .assert_ty_ref(Interner)
                             .clone()
                     }
@@ -1277,8 +1166,7 @@
                     let var = InferenceVar::from(vid.as_u32());
                     if self.var_stack.contains(&(var, VarKind::Ty(kind))) {
                         // recursive type
-                        let default = self.table.fallback_value(var, kind).cast(Interner);
-                        return (self.fallback)(var, VariableKind::Ty(kind), default, outer_binder)
+                        return (self.fallback)(var, VariableKind::Ty(kind), outer_binder)
                             .assert_ty_ref(Interner)
                             .clone();
                     }
@@ -1290,8 +1178,7 @@
                         self.var_stack.pop();
                         result
                     } else {
-                        let default = self.table.fallback_value(var, kind).cast(Interner);
-                        (self.fallback)(var, VariableKind::Ty(kind), default, outer_binder)
+                        (self.fallback)(var, VariableKind::Ty(kind), outer_binder)
                             .assert_ty_ref(Interner)
                             .clone()
                     }
@@ -1310,15 +1197,9 @@
                 .infer_ctxt
                 .root_const_var(rustc_type_ir::ConstVid::from_u32(var.index()));
             let var = InferenceVar::from(vid.as_u32());
-            let default = ConstData {
-                ty: ty.clone(),
-                value: ConstValue::Concrete(ConcreteConst { interned: ConstScalar::Unknown }),
-            }
-            .intern(Interner)
-            .cast(Interner);
             if self.var_stack.contains(&(var, VarKind::Const)) {
                 // recursive
-                return (self.fallback)(var, VariableKind::Const(ty), default, outer_binder)
+                return (self.fallback)(var, VariableKind::Const(ty), outer_binder)
                     .assert_const_ref(Interner)
                     .clone();
             }
@@ -1330,7 +1211,7 @@
                 self.var_stack.pop();
                 result
             } else {
-                (self.fallback)(var, VariableKind::Const(ty), default, outer_binder)
+                (self.fallback)(var, VariableKind::Const(ty), outer_binder)
                     .assert_const_ref(Interner)
                     .clone()
             }
@@ -1349,3 +1230,124 @@
         }
     }
 }
+
+mod resolve_completely {
+    use rustc_type_ir::{
+        DebruijnIndex, Flags, TypeFolder, TypeSuperFoldable,
+        inherent::{Const as _, Ty as _},
+    };
+
+    use crate::next_solver::Region;
+    use crate::{
+        infer::unify::InferenceTable,
+        next_solver::{
+            Const, DbInterner, ErrorGuaranteed, Goal, Predicate, Term, Ty,
+            infer::traits::ObligationCause,
+            normalize::deeply_normalize_with_skipped_universes_and_ambiguous_coroutine_goals,
+        },
+    };
+
+    pub(super) struct Resolver<'a, 'db> {
+        ctx: &'a mut InferenceTable<'db>,
+        /// Whether we should normalize, disabled when resolving predicates.
+        should_normalize: bool,
+        nested_goals: &'a mut Vec<Goal<'db, Predicate<'db>>>,
+    }
+
+    impl<'a, 'db> Resolver<'a, 'db> {
+        pub(super) fn new(
+            ctx: &'a mut InferenceTable<'db>,
+            should_normalize: bool,
+            nested_goals: &'a mut Vec<Goal<'db, Predicate<'db>>>,
+        ) -> Resolver<'a, 'db> {
+            Resolver { ctx, nested_goals, should_normalize }
+        }
+
+        fn handle_term<T>(
+            &mut self,
+            value: T,
+            outer_exclusive_binder: impl FnOnce(T) -> DebruijnIndex,
+        ) -> T
+        where
+            T: Into<Term<'db>> + TypeSuperFoldable<DbInterner<'db>> + Copy,
+        {
+            let value = if self.should_normalize {
+                let cause = ObligationCause::new();
+                let at = self.ctx.infer_ctxt.at(&cause, self.ctx.trait_env.env);
+                let universes = vec![None; outer_exclusive_binder(value).as_usize()];
+                match deeply_normalize_with_skipped_universes_and_ambiguous_coroutine_goals(
+                    at, value, universes,
+                ) {
+                    Ok((value, goals)) => {
+                        self.nested_goals.extend(goals);
+                        value
+                    }
+                    Err(_errors) => {
+                        // FIXME: Report the error.
+                        value
+                    }
+                }
+            } else {
+                value
+            };
+
+            value.fold_with(&mut ReplaceInferWithError { interner: self.ctx.interner })
+        }
+    }
+
+    impl<'cx, 'db> TypeFolder<DbInterner<'db>> for Resolver<'cx, 'db> {
+        fn cx(&self) -> DbInterner<'db> {
+            self.ctx.interner
+        }
+
+        fn fold_region(&mut self, r: Region<'db>) -> Region<'db> {
+            if r.is_var() { Region::error(self.ctx.interner) } else { r }
+        }
+
+        fn fold_ty(&mut self, ty: Ty<'db>) -> Ty<'db> {
+            self.handle_term(ty, |it| it.outer_exclusive_binder())
+        }
+
+        fn fold_const(&mut self, ct: Const<'db>) -> Const<'db> {
+            self.handle_term(ct, |it| it.outer_exclusive_binder())
+        }
+
+        fn fold_predicate(&mut self, predicate: Predicate<'db>) -> Predicate<'db> {
+            assert!(
+                !self.should_normalize,
+                "normalizing predicates in writeback is not generally sound"
+            );
+            predicate.super_fold_with(self)
+        }
+    }
+
+    struct ReplaceInferWithError<'db> {
+        interner: DbInterner<'db>,
+    }
+
+    impl<'db> TypeFolder<DbInterner<'db>> for ReplaceInferWithError<'db> {
+        fn cx(&self) -> DbInterner<'db> {
+            self.interner
+        }
+
+        fn fold_ty(&mut self, t: Ty<'db>) -> Ty<'db> {
+            if t.is_infer() {
+                Ty::new_error(self.interner, ErrorGuaranteed)
+            } else {
+                t.super_fold_with(self)
+            }
+        }
+
+        fn fold_const(&mut self, c: Const<'db>) -> Const<'db> {
+            if c.is_ct_infer() {
+                Const::new_error(self.interner, ErrorGuaranteed)
+            } else {
+                c.super_fold_with(self)
+            }
+        }
+
+        fn fold_region(&mut self, r: Region<'db>) -> Region<'db> {
+            if r.is_var() { Region::error(self.interner) } else { r }
+        }
+    }
+}
diff --git a/crates/hir-ty/src/layout/tests.rs b/crates/hir-ty/src/layout/tests.rs
index 523ddad..6960e23 100644
--- a/crates/hir-ty/src/layout/tests.rs
+++ b/crates/hir-ty/src/layout/tests.rs
@@ -1,18 +1,17 @@
 use base_db::target::TargetData;
-use chalk_ir::{AdtId, TyKind};
 use either::Either;
 use hir_def::db::DefDatabase;
 use project_model::{Sysroot, toolchain_info::QueryConfig};
 use rustc_hash::FxHashMap;
+use rustc_type_ir::inherent::{GenericArgs as _, Ty as _};
 use syntax::ToSmolStr;
 use test_fixture::WithFixture;
 use triomphe::Arc;
 
 use crate::{
-    Interner, Substitution,
     db::HirDatabase,
     layout::{Layout, LayoutError},
-    next_solver::{DbInterner, mapping::ChalkToNextSolver},
+    next_solver::{AdtDef, DbInterner, GenericArgs, mapping::ChalkToNextSolver},
     setup_tracing,
     test_db::TestDB,
 };
@@ -80,18 +79,18 @@
             Some(adt_or_type_alias_id)
         })
         .unwrap();
-    let goal_ty = match adt_or_type_alias_id {
-        Either::Left(adt_id) => {
-            TyKind::Adt(AdtId(adt_id), Substitution::empty(Interner)).intern(Interner)
-        }
-        Either::Right(ty_id) => {
-            db.ty(ty_id.into()).substitute(Interner, &Substitution::empty(Interner))
-        }
-    };
     salsa::attach(&db, || {
         let interner = DbInterner::new_with(&db, None, None);
+        let goal_ty = match adt_or_type_alias_id {
+            Either::Left(adt_id) => crate::next_solver::Ty::new_adt(
+                interner,
+                AdtDef::new(adt_id, interner),
+                GenericArgs::identity_for_item(interner, adt_id.into()),
+            ),
+            Either::Right(ty_id) => db.ty(ty_id.into()).instantiate_identity(),
+        };
         db.layout_of_ty(
-            goal_ty.to_nextsolver(interner),
+            goal_ty,
             db.trait_environment(match adt_or_type_alias_id {
                 Either::Left(adt) => hir_def::GenericDefId::AdtId(adt),
                 Either::Right(ty) => hir_def::GenericDefId::TypeAliasId(ty),
diff --git a/crates/hir-ty/src/lib.rs b/crates/hir-ty/src/lib.rs
index 05c5a7a..281cf6b 100644
--- a/crates/hir-ty/src/lib.rs
+++ b/crates/hir-ty/src/lib.rs
@@ -3,45 +3,24 @@
 
 #![cfg_attr(feature = "in-rust-tree", feature(rustc_private))]
 
-#[cfg(feature = "in-rust-tree")]
-extern crate rustc_index;
+// FIXME: We used to import `rustc_*` deps from `rustc_private` with `feature = "in-rust-tree" but
+// temporarily switched to crates.io versions due to hardships that working on them from rustc
+// demands corresponding changes on rust-analyzer at the same time.
+// For details, see the zulip discussion below:
+// https://rust-lang.zulipchat.com/#narrow/channel/185405-t-compiler.2Frust-analyzer/topic/relying.20on.20in-tree.20.60rustc_type_ir.60.2F.60rustc_next_trait_solver.60/with/541055689
 
-#[cfg(not(feature = "in-rust-tree"))]
 extern crate ra_ap_rustc_index as rustc_index;
 
-#[cfg(feature = "in-rust-tree")]
-extern crate rustc_abi;
-
-#[cfg(not(feature = "in-rust-tree"))]
 extern crate ra_ap_rustc_abi as rustc_abi;
 
-#[cfg(feature = "in-rust-tree")]
-extern crate rustc_pattern_analysis;
-
-#[cfg(not(feature = "in-rust-tree"))]
 extern crate ra_ap_rustc_pattern_analysis as rustc_pattern_analysis;
 
-#[cfg(feature = "in-rust-tree")]
-extern crate rustc_ast_ir;
-
-#[cfg(not(feature = "in-rust-tree"))]
 extern crate ra_ap_rustc_ast_ir as rustc_ast_ir;
 
-#[cfg(feature = "in-rust-tree")]
-extern crate rustc_type_ir;
-
-#[cfg(not(feature = "in-rust-tree"))]
 extern crate ra_ap_rustc_type_ir as rustc_type_ir;
 
-#[cfg(feature = "in-rust-tree")]
-extern crate rustc_next_trait_solver;
-
-#[cfg(not(feature = "in-rust-tree"))]
 extern crate ra_ap_rustc_next_trait_solver as rustc_next_trait_solver;
 
-#[cfg(feature = "in-rust-tree")]
-extern crate rustc_data_structures as ena;
-
 mod builder;
 mod chalk_db;
 mod chalk_ext;
@@ -578,8 +557,10 @@
 
     pub fn from_def(db: &dyn HirDatabase, def: FnDefId, substs: &Substitution) -> CallableSig {
         let callable_def = ToChalk::from_chalk(db, def);
+        let interner = DbInterner::new_with(db, None, None);
+        let args: crate::next_solver::GenericArgs<'_> = substs.to_nextsolver(interner);
         let sig = db.callable_item_signature(callable_def);
-        sig.substitute(Interner, substs)
+        sig.instantiate(interner, args).skip_binder().to_chalk(interner)
     }
     pub fn from_fn_ptr(fn_ptr: &FnPointer) -> CallableSig {
         CallableSig {
diff --git a/crates/hir-ty/src/lower.rs b/crates/hir-ty/src/lower.rs
index 20f421d..b55f9cd 100644
--- a/crates/hir-ty/src/lower.rs
+++ b/crates/hir-ty/src/lower.rs
@@ -24,16 +24,15 @@
 
 use either::Either;
 use hir_def::{
-    AdtId, AssocItemId, CallableDefId, ConstId, ConstParamId, EnumId, EnumVariantId, FunctionId,
-    GenericDefId, GenericParamId, ImplId, ItemContainerId, LocalFieldId, Lookup, StaticId,
-    StructId, TypeAliasId, TypeOrConstParamId, UnionId, VariantId,
+    AdtId, AssocItemId, ConstId, ConstParamId, EnumId, EnumVariantId, FunctionId, GenericDefId,
+    GenericParamId, ImplId, ItemContainerId, LocalFieldId, Lookup, StaticId, StructId, TypeAliasId,
+    TypeOrConstParamId, UnionId, VariantId,
     builtin_type::BuiltinType,
     expr_store::{ExpressionStore, path::Path},
     hir::generics::{GenericParamDataRef, TypeOrConstParamData, WherePredicate},
-    item_tree::FieldsShape,
     lang_item::LangItem,
     resolver::{HasResolver, LifetimeNs, Resolver, TypeNs},
-    signatures::{FunctionSignature, TraitFlags, TypeAliasFlags},
+    signatures::{FunctionSignature, TraitFlags},
     type_ref::{
         ConstRef, LifetimeRefId, LiteralConstRef, PathId, TraitBoundModifier,
         TraitRef as HirTraitRef, TypeBound, TypeRef, TypeRefId,
@@ -46,10 +45,10 @@
 use triomphe::{Arc, ThinArc};
 
 use crate::{
-    AliasTy, Binders, BoundVar, CallableSig, Const, DebruijnIndex, DynTy, FnAbi, FnPointer, FnSig,
-    FnSubst, ImplTrait, ImplTraitId, ImplTraits, Interner, Lifetime, LifetimeData,
-    LifetimeOutlives, PolyFnSig, QuantifiedWhereClause, QuantifiedWhereClauses, Substitution,
-    TraitRef, TraitRefExt, Ty, TyBuilder, TyKind, WhereClause, all_super_traits,
+    AliasTy, Binders, BoundVar, Const, DebruijnIndex, DynTy, FnAbi, FnPointer, FnSig, FnSubst,
+    ImplTrait, ImplTraitId, ImplTraits, Interner, Lifetime, LifetimeData, LifetimeOutlives,
+    QuantifiedWhereClause, QuantifiedWhereClauses, Substitution, TraitRef, TraitRefExt, Ty,
+    TyBuilder, TyKind, WhereClause, all_super_traits,
     consteval::{intern_const_ref, path_to_const, unknown_const, unknown_const_as_generic},
     db::HirDatabase,
     error_lifetime,
@@ -59,7 +58,7 @@
         path::{PathDiagnosticCallback, PathLoweringContext},
     },
     make_binders,
-    mapping::{ToChalk, from_chalk_trait_id, lt_to_placeholder_idx},
+    mapping::{from_chalk_trait_id, lt_to_placeholder_idx},
     static_lifetime, to_chalk_trait_id, to_placeholder_idx,
     utils::all_super_trait_refs,
     variable_kinds_from_iter,
@@ -825,15 +824,6 @@
     }
 }
 
-/// Build the signature of a callable item (function, struct or enum variant).
-pub(crate) fn callable_item_signature_query(db: &dyn HirDatabase, def: CallableDefId) -> PolyFnSig {
-    match def {
-        CallableDefId::FunctionId(f) => fn_sig_for_fn(db, f),
-        CallableDefId::StructId(s) => fn_sig_for_struct_constructor(db, s),
-        CallableDefId::EnumVariantId(e) => fn_sig_for_enum_variant_constructor(db, e),
-    }
-}
-
 fn named_associated_type_shorthand_candidates<R>(
     db: &dyn HirDatabase,
     // If the type parameter is defined in an impl and we're in a method, there
@@ -918,7 +908,7 @@
     db: &dyn HirDatabase,
     variant_id: VariantId,
 ) -> Arc<ArenaMap<LocalFieldId, Binders<Ty>>> {
-    db.field_types_with_diagnostics(variant_id).0
+    field_types_with_diagnostics_query(db, variant_id).0
 }
 
 /// Build the type of all specific fields of a struct or enum variant.
@@ -1313,208 +1303,6 @@
     (GenericDefaults(None), None)
 }
 
-fn fn_sig_for_fn(db: &dyn HirDatabase, def: FunctionId) -> PolyFnSig {
-    let data = db.function_signature(def);
-    let resolver = def.resolver(db);
-    let mut ctx_params = TyLoweringContext::new(
-        db,
-        &resolver,
-        &data.store,
-        def.into(),
-        LifetimeElisionKind::for_fn_params(&data),
-    )
-    .with_type_param_mode(ParamLoweringMode::Variable);
-    let params = data.params.iter().map(|&tr| ctx_params.lower_ty(tr));
-
-    let ret = match data.ret_type {
-        Some(ret_type) => {
-            let mut ctx_ret = TyLoweringContext::new(
-                db,
-                &resolver,
-                &data.store,
-                def.into(),
-                LifetimeElisionKind::for_fn_ret(),
-            )
-            .with_impl_trait_mode(ImplTraitLoweringMode::Opaque)
-            .with_type_param_mode(ParamLoweringMode::Variable);
-            ctx_ret.lower_ty(ret_type)
-        }
-        None => TyKind::Tuple(0, Substitution::empty(Interner)).intern(Interner),
-    };
-    let generics = generics(db, def.into());
-    let sig = CallableSig::from_params_and_return(
-        params,
-        ret,
-        data.is_varargs(),
-        if data.is_unsafe() { Safety::Unsafe } else { Safety::Safe },
-        data.abi.as_ref().map_or(FnAbi::Rust, FnAbi::from_symbol),
-    );
-    make_binders(db, &generics, sig)
-}
-
-/// Build the declared type of a function. This should not need to look at the
-/// function body.
-fn type_for_fn(db: &dyn HirDatabase, def: FunctionId) -> Binders<Ty> {
-    let generics = generics(db, def.into());
-    let substs = generics.bound_vars_subst(db, DebruijnIndex::INNERMOST);
-    make_binders(
-        db,
-        &generics,
-        TyKind::FnDef(CallableDefId::FunctionId(def).to_chalk(db), substs).intern(Interner),
-    )
-}
-
-/// Build the declared type of a const.
-fn type_for_const(db: &dyn HirDatabase, def: ConstId) -> Binders<Ty> {
-    let data = db.const_signature(def);
-    let generics = generics(db, def.into());
-    let resolver = def.resolver(db);
-    let parent = def.loc(db).container;
-    let mut ctx = TyLoweringContext::new(
-        db,
-        &resolver,
-        &data.store,
-        def.into(),
-        LifetimeElisionKind::for_const(parent),
-    )
-    .with_type_param_mode(ParamLoweringMode::Variable);
-
-    make_binders(db, &generics, ctx.lower_ty(data.type_ref))
-}
-
-/// Build the declared type of a static.
-fn type_for_static(db: &dyn HirDatabase, def: StaticId) -> Binders<Ty> {
-    let data = db.static_signature(def);
-    let resolver = def.resolver(db);
-    let mut ctx = TyLoweringContext::new(
-        db,
-        &resolver,
-        &data.store,
-        def.into(),
-        LifetimeElisionKind::Elided(static_lifetime()),
-    );
-
-    Binders::empty(Interner, ctx.lower_ty(data.type_ref))
-}
-
-fn fn_sig_for_struct_constructor(db: &dyn HirDatabase, def: StructId) -> PolyFnSig {
-    let field_tys = db.field_types(def.into());
-    let params = field_tys.iter().map(|(_, ty)| ty.skip_binders().clone());
-    let (ret, binders) = type_for_adt(db, def.into()).into_value_and_skipped_binders();
-    Binders::new(
-        binders,
-        CallableSig::from_params_and_return(params, ret, false, Safety::Safe, FnAbi::RustCall),
-    )
-}
-
-/// Build the type of a tuple struct constructor.
-fn type_for_struct_constructor(db: &dyn HirDatabase, def: StructId) -> Option<Binders<Ty>> {
-    let struct_data = def.fields(db);
-    match struct_data.shape {
-        FieldsShape::Record => None,
-        FieldsShape::Unit => Some(type_for_adt(db, def.into())),
-        FieldsShape::Tuple => {
-            let generics = generics(db, AdtId::from(def).into());
-            let substs = generics.bound_vars_subst(db, DebruijnIndex::INNERMOST);
-            Some(make_binders(
-                db,
-                &generics,
-                TyKind::FnDef(CallableDefId::StructId(def).to_chalk(db), substs).intern(Interner),
-            ))
-        }
-    }
-}
-
-fn fn_sig_for_enum_variant_constructor(db: &dyn HirDatabase, def: EnumVariantId) -> PolyFnSig {
-    let field_tys = db.field_types(def.into());
-    let params = field_tys.iter().map(|(_, ty)| ty.skip_binders().clone());
-    let parent = def.lookup(db).parent;
-    let (ret, binders) = type_for_adt(db, parent.into()).into_value_and_skipped_binders();
-    Binders::new(
-        binders,
-        CallableSig::from_params_and_return(params, ret, false, Safety::Safe, FnAbi::RustCall),
-    )
-}
-
-/// Build the type of a tuple enum variant constructor.
-fn type_for_enum_variant_constructor(
-    db: &dyn HirDatabase,
-    def: EnumVariantId,
-) -> Option<Binders<Ty>> {
-    let e = def.lookup(db).parent;
-    match def.fields(db).shape {
-        FieldsShape::Record => None,
-        FieldsShape::Unit => Some(type_for_adt(db, e.into())),
-        FieldsShape::Tuple => {
-            let generics = generics(db, e.into());
-            let substs = generics.bound_vars_subst(db, DebruijnIndex::INNERMOST);
-            Some(make_binders(
-                db,
-                &generics,
-                TyKind::FnDef(CallableDefId::EnumVariantId(def).to_chalk(db), substs)
-                    .intern(Interner),
-            ))
-        }
-    }
-}
-
-#[salsa_macros::tracked(cycle_result = type_for_adt_cycle_result)]
-fn type_for_adt_tracked(db: &dyn HirDatabase, adt: AdtId) -> Binders<Ty> {
-    type_for_adt(db, adt)
-}
-
-fn type_for_adt_cycle_result(db: &dyn HirDatabase, adt: AdtId) -> Binders<Ty> {
-    let generics = generics(db, adt.into());
-    make_binders(db, &generics, TyKind::Error.intern(Interner))
-}
-
-fn type_for_adt(db: &dyn HirDatabase, adt: AdtId) -> Binders<Ty> {
-    let generics = generics(db, adt.into());
-    let subst = generics.bound_vars_subst(db, DebruijnIndex::INNERMOST);
-    let ty = TyKind::Adt(crate::AdtId(adt), subst).intern(Interner);
-    make_binders(db, &generics, ty)
-}
-
-pub(crate) fn type_for_type_alias_with_diagnostics_query(
-    db: &dyn HirDatabase,
-    t: TypeAliasId,
-) -> (Binders<Ty>, Diagnostics) {
-    let generics = generics(db, t.into());
-    let type_alias_data = db.type_alias_signature(t);
-    let mut diags = None;
-    let inner = if type_alias_data.flags.contains(TypeAliasFlags::IS_EXTERN) {
-        TyKind::Foreign(crate::to_foreign_def_id(t)).intern(Interner)
-    } else {
-        let resolver = t.resolver(db);
-        let alias = db.type_alias_signature(t);
-        let mut ctx = TyLoweringContext::new(
-            db,
-            &resolver,
-            &alias.store,
-            t.into(),
-            LifetimeElisionKind::AnonymousReportError,
-        )
-        .with_impl_trait_mode(ImplTraitLoweringMode::Opaque)
-        .with_type_param_mode(ParamLoweringMode::Variable);
-        let res = alias
-            .ty
-            .map(|type_ref| ctx.lower_ty(type_ref))
-            .unwrap_or_else(|| TyKind::Error.intern(Interner));
-        diags = create_diagnostics(ctx.diagnostics);
-        res
-    };
-
-    (make_binders(db, &generics, inner), diags)
-}
-
-pub(crate) fn type_for_type_alias_with_diagnostics_cycle_result(
-    db: &dyn HirDatabase,
-    adt: TypeAliasId,
-) -> (Binders<Ty>, Diagnostics) {
-    let generics = generics(db, adt.into());
-    (make_binders(db, &generics, TyKind::Error.intern(Interner)), None)
-}
-
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
 pub enum TyDefId {
     BuiltinType(BuiltinType),
@@ -1547,31 +1335,8 @@
     }
 }
 
-/// Build the declared type of an item. This depends on the namespace; e.g. for
-/// `struct Foo(usize)`, we have two types: The type of the struct itself, and
-/// the constructor function `(usize) -> Foo` which lives in the values
-/// namespace.
-pub(crate) fn ty_query(db: &dyn HirDatabase, def: TyDefId) -> Binders<Ty> {
-    match def {
-        TyDefId::BuiltinType(it) => Binders::empty(Interner, TyBuilder::builtin(it)),
-        TyDefId::AdtId(it) => type_for_adt_tracked(db, it),
-        TyDefId::TypeAliasId(it) => db.type_for_type_alias_with_diagnostics(it).0,
-    }
-}
-
-pub(crate) fn value_ty_query(db: &dyn HirDatabase, def: ValueTyDefId) -> Option<Binders<Ty>> {
-    match def {
-        ValueTyDefId::FunctionId(it) => Some(type_for_fn(db, it)),
-        ValueTyDefId::StructId(it) => type_for_struct_constructor(db, it),
-        ValueTyDefId::UnionId(it) => Some(type_for_adt(db, it.into())),
-        ValueTyDefId::EnumVariantId(it) => type_for_enum_variant_constructor(db, it),
-        ValueTyDefId::ConstId(it) => Some(type_for_const(db, it)),
-        ValueTyDefId::StaticId(it) => Some(type_for_static(db, it)),
-    }
-}
-
 pub(crate) fn impl_self_ty_query(db: &dyn HirDatabase, impl_id: ImplId) -> Binders<Ty> {
-    db.impl_self_ty_with_diagnostics(impl_id).0
+    impl_self_ty_with_diagnostics_query(db, impl_id).0
 }
 
 pub(crate) fn impl_self_ty_with_diagnostics_query(
@@ -1595,16 +1360,8 @@
     )
 }
 
-pub(crate) fn impl_self_ty_with_diagnostics_cycle_result(
-    db: &dyn HirDatabase,
-    impl_id: ImplId,
-) -> (Binders<Ty>, Diagnostics) {
-    let generics = generics(db, impl_id.into());
-    (make_binders(db, &generics, TyKind::Error.intern(Interner)), None)
-}
-
 pub(crate) fn const_param_ty_query(db: &dyn HirDatabase, def: ConstParamId) -> Ty {
-    db.const_param_ty_with_diagnostics(def).0
+    const_param_ty_with_diagnostics_query(db, def).0
 }
 
 // returns None if def is a type arg
@@ -1632,16 +1389,16 @@
     (ty, create_diagnostics(ctx.diagnostics))
 }
 
-pub(crate) fn const_param_ty_with_diagnostics_cycle_result(
+pub(crate) fn const_param_ty_cycle_result(
     _: &dyn HirDatabase,
     _: crate::db::HirDatabaseData,
     _: ConstParamId,
-) -> (Ty, Diagnostics) {
-    (TyKind::Error.intern(Interner), None)
+) -> Ty {
+    TyKind::Error.intern(Interner)
 }
 
 pub(crate) fn impl_trait_query(db: &dyn HirDatabase, impl_id: ImplId) -> Option<Binders<TraitRef>> {
-    db.impl_trait_with_diagnostics(impl_id).map(|it| it.0)
+    impl_trait_with_diagnostics_query(db, impl_id).map(|it| it.0)
 }
 
 pub(crate) fn impl_trait_with_diagnostics_query(
diff --git a/crates/hir-ty/src/lower/path.rs b/crates/hir-ty/src/lower/path.rs
index bc03298..279bbff 100644
--- a/crates/hir-ty/src/lower/path.rs
+++ b/crates/hir-ty/src/lower/path.rs
@@ -28,6 +28,10 @@
     error_lifetime,
     generics::{Generics, generics},
     lower::{LifetimeElisionKind, named_associated_type_shorthand_candidates},
+    next_solver::{
+        DbInterner,
+        mapping::{ChalkToNextSolver, NextSolverToChalk},
+    },
     static_lifetime, to_assoc_type_id, to_chalk_trait_id, to_placeholder_idx,
     utils::associated_type_by_name_including_super_traits,
 };
@@ -256,7 +260,8 @@
                     }
                     ParamLoweringMode::Variable => TyBuilder::impl_self_ty(self.ctx.db, impl_id)
                         .fill_with_bound_vars(self.ctx.in_binders, 0)
-                        .build(),
+                        .build(DbInterner::conjure())
+                        .to_chalk(DbInterner::conjure()),
                 }
             }
             TypeNs::AdtSelfType(adt) => {
@@ -267,7 +272,9 @@
                         generics.bound_vars_subst(self.ctx.db, self.ctx.in_binders)
                     }
                 };
-                self.ctx.db.ty(adt.into()).substitute(Interner, &substs)
+                let interner = DbInterner::conjure();
+                let args: crate::next_solver::GenericArgs<'_> = substs.to_nextsolver(interner);
+                self.ctx.db.ty(adt.into()).instantiate(interner, args).to_chalk(interner)
             }
 
             TypeNs::AdtId(it) => self.lower_path_inner(it.into(), infer_args),
@@ -537,7 +544,9 @@
             TyDefId::TypeAliasId(it) => it.into(),
         };
         let substs = self.substs_from_path_segment(generic_def, infer_args, None, false);
-        self.ctx.db.ty(typeable).substitute(Interner, &substs)
+        let interner = DbInterner::conjure();
+        let args: crate::next_solver::GenericArgs<'_> = substs.to_nextsolver(interner);
+        self.ctx.db.ty(typeable).instantiate(interner, args).to_chalk(interner)
     }
 
     /// Collect generic arguments from a path into a `Substs`. See also
diff --git a/crates/hir-ty/src/lower_nextsolver.rs b/crates/hir-ty/src/lower_nextsolver.rs
index 1ca56fe..02774a6 100644
--- a/crates/hir-ty/src/lower_nextsolver.rs
+++ b/crates/hir-ty/src/lower_nextsolver.rs
@@ -904,7 +904,7 @@
     db: &'db dyn HirDatabase,
     impl_id: ImplId,
 ) -> Option<EarlyBinder<'db, TraitRef<'db>>> {
-    db.impl_trait_with_diagnostics_ns(impl_id).map(|it| it.0)
+    db.impl_trait_with_diagnostics(impl_id).map(|it| it.0)
 }
 
 pub(crate) fn impl_trait_with_diagnostics_query<'db>(
@@ -986,7 +986,7 @@
             AdtDef::new(it, interner),
             GenericArgs::identity_for_item(interner, it.into()),
         )),
-        TyDefId::TypeAliasId(it) => db.type_for_type_alias_with_diagnostics_ns(it).0,
+        TyDefId::TypeAliasId(it) => db.type_for_type_alias_with_diagnostics(it).0,
     }
 }
 
@@ -1131,7 +1131,7 @@
     db: &'db dyn HirDatabase,
     impl_id: ImplId,
 ) -> EarlyBinder<'db, Ty<'db>> {
-    db.impl_self_ty_with_diagnostics_ns(impl_id).0
+    db.impl_self_ty_with_diagnostics(impl_id).0
 }
 
 pub(crate) fn impl_self_ty_with_diagnostics_query<'db>(
@@ -1162,7 +1162,7 @@
 }
 
 pub(crate) fn const_param_ty_query<'db>(db: &'db dyn HirDatabase, def: ConstParamId) -> Ty<'db> {
-    db.const_param_ty_with_diagnostics_ns(def).0
+    db.const_param_ty_with_diagnostics(def).0
 }
 
 // returns None if def is a type arg
@@ -1191,11 +1191,21 @@
     (ty, create_diagnostics(ctx.diagnostics))
 }
 
+pub(crate) fn const_param_ty_with_diagnostics_cycle_result<'db>(
+    db: &'db dyn HirDatabase,
+    _: crate::db::HirDatabaseData,
+    def: ConstParamId,
+) -> (Ty<'db>, Diagnostics) {
+    let resolver = def.parent().resolver(db);
+    let interner = DbInterner::new_with(db, Some(resolver.krate()), None);
+    (Ty::new_error(interner, ErrorGuaranteed), None)
+}
+
 pub(crate) fn field_types_query<'db>(
     db: &'db dyn HirDatabase,
     variant_id: VariantId,
 ) -> Arc<ArenaMap<LocalFieldId, EarlyBinder<'db, Ty<'db>>>> {
-    db.field_types_with_diagnostics_ns(variant_id).0
+    db.field_types_with_diagnostics(variant_id).0
 }
 
 /// Build the type of all specific fields of a struct or enum variant.
@@ -1960,7 +1970,8 @@
     let mut search = |t: TraitRef<'db>| -> Option<R> {
         let trait_id = t.def_id.0;
         let mut checked_traits = FxHashSet::default();
-        let mut check_trait = |trait_id: TraitId| {
+        let mut check_trait = |trait_ref: TraitRef<'db>| {
+            let trait_id = trait_ref.def_id.0;
             let name = &db.trait_signature(trait_id).name;
             tracing::debug!(?trait_id, ?name);
             if !checked_traits.insert(trait_id) {
@@ -1971,37 +1982,39 @@
             tracing::debug!(?data.items);
             for (name, assoc_id) in &data.items {
                 if let &AssocItemId::TypeAliasId(alias) = assoc_id
-                    && let Some(ty) = check_alias(name, t, alias)
+                    && let Some(ty) = check_alias(name, trait_ref, alias)
                 {
                     return Some(ty);
                 }
             }
             None
         };
-        let mut stack: SmallVec<[_; 4]> = smallvec![trait_id];
-        while let Some(trait_def_id) = stack.pop() {
-            if let Some(alias) = check_trait(trait_def_id) {
+        let mut stack: SmallVec<[_; 4]> = smallvec![t];
+        while let Some(trait_ref) = stack.pop() {
+            if let Some(alias) = check_trait(trait_ref) {
                 return Some(alias);
             }
             for pred in generic_predicates_filtered_by(
                 db,
-                GenericDefId::TraitId(trait_def_id),
+                GenericDefId::TraitId(trait_ref.def_id.0),
                 PredicateFilter::SelfTrait,
                 // We are likely in the midst of lowering generic predicates of `def`.
                 // So, if we allow `pred == def` we might fall into an infinite recursion.
                 // Actually, we have already checked for the case `pred == def` above as we started
                 // with a stack including `trait_id`
-                |pred| pred != def && pred == GenericDefId::TraitId(trait_def_id),
+                |pred| pred != def && pred == GenericDefId::TraitId(trait_ref.def_id.0),
             )
             .0
             .deref()
             {
                 tracing::debug!(?pred);
-                let trait_id = match pred.kind().skip_binder() {
-                    rustc_type_ir::ClauseKind::Trait(pred) => pred.def_id(),
+                let sup_trait_ref = match pred.kind().skip_binder() {
+                    rustc_type_ir::ClauseKind::Trait(pred) => pred.trait_ref,
                     _ => continue,
                 };
-                stack.push(trait_id.0);
+                let sup_trait_ref =
+                    EarlyBinder::bind(sup_trait_ref).instantiate(interner, trait_ref.args);
+                stack.push(sup_trait_ref);
             }
             tracing::debug!(?stack);
         }
diff --git a/crates/hir-ty/src/method_resolution.rs b/crates/hir-ty/src/method_resolution.rs
index fd28159..93ef642 100644
--- a/crates/hir-ty/src/method_resolution.rs
+++ b/crates/hir-ty/src/method_resolution.rs
@@ -1697,8 +1697,10 @@
                 return IsValidCandidate::NotVisible;
             }
             let self_ty_matches = table.run_in_snapshot(|table| {
-                let expected_self_ty =
-                    TyBuilder::impl_self_ty(db, impl_id).fill_with_inference_vars(table).build();
+                let expected_self_ty = TyBuilder::impl_self_ty(db, impl_id)
+                    .fill_with_inference_vars(table)
+                    .build(DbInterner::conjure())
+                    .to_chalk(DbInterner::conjure());
                 table.unify(&expected_self_ty, self_ty)
             });
             if !self_ty_matches {
@@ -1744,9 +1746,13 @@
                         .fill_with_inference_vars(table)
                         .build();
 
+                    let args: crate::next_solver::GenericArgs<'_> =
+                        fn_subst.to_nextsolver(table.interner);
                     let sig = db.callable_item_signature(fn_id.into());
-                    let expected_receiver =
-                        sig.map(|s| s.params()[0].clone()).substitute(Interner, &fn_subst);
+                    let expected_receiver = sig
+                        .map_bound(|s| s.skip_binder().inputs_and_output.as_slice()[0])
+                        .instantiate(table.interner, args)
+                        .to_chalk(table.interner);
 
                     // FIXME: Clean up this mess with some context struct like rustc's `ProbeContext`
                     let variance = match mode {
@@ -1831,9 +1837,12 @@
             let fn_subst: crate::Substitution =
                 table.infer_ctxt.fresh_args_for_item(fn_id.into()).to_chalk(table.interner);
 
+            let args: crate::next_solver::GenericArgs<'_> = fn_subst.to_nextsolver(table.interner);
             let sig = db.callable_item_signature(fn_id.into());
-            let expected_receiver =
-                sig.map(|s| s.params()[0].clone()).substitute(Interner, &fn_subst);
+            let expected_receiver = sig
+                .map_bound(|s| s.skip_binder().inputs_and_output.as_slice()[0])
+                .instantiate(table.interner, args)
+                .to_chalk(table.interner);
 
             check_that!(table.unify(receiver_ty, &expected_receiver));
         }
diff --git a/crates/hir-ty/src/mir/eval/shim.rs b/crates/hir-ty/src/mir/eval/shim.rs
index f67778b..bb0d1f7 100644
--- a/crates/hir-ty/src/mir/eval/shim.rs
+++ b/crates/hir-ty/src/mir/eval/shim.rs
@@ -14,6 +14,7 @@
 use intern::{Symbol, sym};
 use stdx::never;
 
+use crate::next_solver::mapping::NextSolverToChalk;
 use crate::{
     DropGlue,
     display::DisplayTarget,
@@ -1371,9 +1372,8 @@
                     result = (l as i8).cmp(&(r as i8));
                 }
                 if let Some(e) = LangItem::Ordering.resolve_enum(self.db, self.crate_id) {
-                    let ty = self.db.ty(e.into());
-                    let r = self
-                        .compute_discriminant(ty.skip_binders().clone(), &[result as i8 as u8])?;
+                    let ty = self.db.ty(e.into()).skip_binder().to_chalk(interner);
+                    let r = self.compute_discriminant(ty.clone(), &[result as i8 as u8])?;
                     destination.write_from_bytes(self, &r.to_le_bytes()[0..destination.size])?;
                     Ok(())
                 } else {
diff --git a/crates/hir-ty/src/mir/lower.rs b/crates/hir-ty/src/mir/lower.rs
index 0416f43..3e44e8c 100644
--- a/crates/hir-ty/src/mir/lower.rs
+++ b/crates/hir-ty/src/mir/lower.rs
@@ -43,7 +43,10 @@
         Terminator, TerminatorKind, TupleFieldId, Ty, UnOp, VariantId, intern_const_scalar,
         return_slot,
     },
-    next_solver::{DbInterner, mapping::ChalkToNextSolver},
+    next_solver::{
+        DbInterner,
+        mapping::{ChalkToNextSolver, NextSolverToChalk},
+    },
     static_lifetime,
     traits::FnTrait,
     utils::ClosureSubst,
@@ -2207,8 +2210,13 @@
             // otherwise it's an inline const, and has no parameter
             if let DefWithBodyId::FunctionId(fid) = owner {
                 let substs = TyBuilder::placeholder_subst(db, fid);
-                let callable_sig =
-                    db.callable_item_signature(fid.into()).substitute(Interner, &substs);
+                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(fid.into())
+                    .instantiate(interner, args)
+                    .skip_binder()
+                    .to_chalk(interner);
                 let mut params = callable_sig.params().iter();
                 let self_param = body.self_param.and_then(|id| Some((id, params.next()?.clone())));
                 break 'b ctx.lower_params_and_bindings(
diff --git a/crates/hir-ty/src/next_solver.rs b/crates/hir-ty/src/next_solver.rs
index 073a029..ab167e8 100644
--- a/crates/hir-ty/src/next_solver.rs
+++ b/crates/hir-ty/src/next_solver.rs
@@ -13,7 +13,7 @@
 pub mod interner;
 mod ir_print;
 pub mod mapping;
-mod normalize;
+pub mod normalize;
 pub mod obligation_ctxt;
 mod opaques;
 pub mod predicate;
diff --git a/crates/hir-ty/src/next_solver/consts.rs b/crates/hir-ty/src/next_solver/consts.rs
index 7ebefa7..0b35820 100644
--- a/crates/hir-ty/src/next_solver/consts.rs
+++ b/crates/hir-ty/src/next_solver/consts.rs
@@ -36,8 +36,6 @@
             internee: kind,
             flags: flags.flags,
             outer_exclusive_binder: flags.outer_exclusive_binder,
-            #[cfg(feature = "in-rust-tree")]
-            stable_hash: ena::fingerprint::Fingerprint::ZERO,
         };
         Const::new_(interner.db(), InternedWrapperNoDebug(cached))
     }
diff --git a/crates/hir-ty/src/next_solver/interner.rs b/crates/hir-ty/src/next_solver/interner.rs
index 9cf56be..3ff9fde 100644
--- a/crates/hir-ty/src/next_solver/interner.rs
+++ b/crates/hir-ty/src/next_solver/interner.rs
@@ -1091,23 +1091,21 @@
                     ItemContainerId::ImplId(it) => it,
                     _ => panic!("assoc ty value should be in impl"),
                 };
-                self.db().ty_ns(id.into())
+                self.db().ty(id.into())
             }
-            SolverDefId::AdtId(id) => self.db().ty_ns(id.into()),
+            SolverDefId::AdtId(id) => self.db().ty(id.into()),
             // FIXME(next-solver): This uses the types of `query mir_borrowck` in rustc.
             //
             // We currently always use the type from HIR typeck which ignores regions. This
             // should be fine.
             SolverDefId::InternedOpaqueTyId(_) => self.type_of_opaque_hir_typeck(def_id),
-            SolverDefId::FunctionId(id) => self.db.value_ty_ns(id.into()).unwrap(),
+            SolverDefId::FunctionId(id) => self.db.value_ty(id.into()).unwrap(),
             SolverDefId::Ctor(id) => {
                 let id = match id {
                     Ctor::Struct(id) => id.into(),
                     Ctor::Enum(id) => id.into(),
                 };
-                self.db
-                    .value_ty_ns(id)
-                    .expect("`SolverDefId::Ctor` should have a function-like ctor")
+                self.db.value_ty(id).expect("`SolverDefId::Ctor` should have a function-like ctor")
             }
             _ => panic!("Unexpected def_id `{def_id:?}` provided for `type_of`"),
         }
@@ -1227,7 +1225,7 @@
         self,
         def_id: Self::FunctionId,
     ) -> EarlyBinder<Self, rustc_type_ir::Binder<Self, rustc_type_ir::FnSig<Self>>> {
-        self.db().callable_item_signature_ns(def_id.0)
+        self.db().callable_item_signature(def_id.0)
     }
 
     fn coroutine_movability(self, def_id: Self::CoroutineId) -> rustc_ast_ir::Movability {
@@ -1322,7 +1320,7 @@
         self,
         def_id: Self::DefId,
     ) -> EarlyBinder<Self, impl IntoIterator<Item = Self::Clause>> {
-        let predicates = self.db().generic_predicates_without_parent_ns(def_id.try_into().unwrap());
+        let predicates = self.db().generic_predicates_without_parent(def_id.try_into().unwrap());
         let predicates: Vec<_> = predicates.iter().cloned().collect();
         EarlyBinder::bind(predicates.into_iter())
     }
diff --git a/crates/hir-ty/src/next_solver/mapping.rs b/crates/hir-ty/src/next_solver/mapping.rs
index 5dcb1e6..f3f74f6 100644
--- a/crates/hir-ty/src/next_solver/mapping.rs
+++ b/crates/hir-ty/src/next_solver/mapping.rs
@@ -575,6 +575,17 @@
     }
 }
 
+impl<'db, T: NextSolverToChalk<'db, U>, U: HasInterner<Interner = Interner>>
+    NextSolverToChalk<'db, chalk_ir::Binders<U>> for rustc_type_ir::Binder<DbInterner<'db>, T>
+{
+    fn to_chalk(self, interner: DbInterner<'db>) -> chalk_ir::Binders<U> {
+        chalk_ir::Binders::new(
+            self.bound_vars().to_chalk(interner),
+            self.skip_binder().to_chalk(interner),
+        )
+    }
+}
+
 impl<'db> ChalkToNextSolver<'db, BoundVarKinds> for chalk_ir::VariableKinds<Interner> {
     fn to_nextsolver(&self, interner: DbInterner<'db>) -> BoundVarKinds {
         BoundVarKinds::new_from_iter(
@@ -584,6 +595,12 @@
     }
 }
 
+impl<'db> NextSolverToChalk<'db, chalk_ir::VariableKinds<Interner>> for BoundVarKinds {
+    fn to_chalk(self, interner: DbInterner<'db>) -> chalk_ir::VariableKinds<Interner> {
+        chalk_ir::VariableKinds::from_iter(Interner, self.iter().map(|v| v.to_chalk(interner)))
+    }
+}
+
 impl<'db> ChalkToNextSolver<'db, BoundVarKind> for chalk_ir::VariableKind<Interner> {
     fn to_nextsolver(&self, interner: DbInterner<'db>) -> BoundVarKind {
         match self {
@@ -594,6 +611,18 @@
     }
 }
 
+impl<'db> NextSolverToChalk<'db, chalk_ir::VariableKind<Interner>> for BoundVarKind {
+    fn to_chalk(self, interner: DbInterner<'db>) -> chalk_ir::VariableKind<Interner> {
+        match self {
+            BoundVarKind::Ty(_) => chalk_ir::VariableKind::Ty(chalk_ir::TyVariableKind::General),
+            BoundVarKind::Region(_) => chalk_ir::VariableKind::Lifetime,
+            BoundVarKind::Const => {
+                chalk_ir::VariableKind::Const(chalk_ir::TyKind::Error.intern(Interner))
+            }
+        }
+    }
+}
+
 impl<'db> ChalkToNextSolver<'db, GenericArg<'db>> for chalk_ir::GenericArg<Interner> {
     fn to_nextsolver(&self, interner: DbInterner<'db>) -> GenericArg<'db> {
         match self.data(Interner) {
@@ -1233,6 +1262,22 @@
     }
 }
 
+impl<'db> NextSolverToChalk<'db, crate::CallableSig> for rustc_type_ir::FnSig<DbInterner<'db>> {
+    fn to_chalk(self, interner: DbInterner<'db>) -> crate::CallableSig {
+        crate::CallableSig {
+            abi: self.abi,
+            is_varargs: self.c_variadic,
+            safety: match self.safety {
+                super::abi::Safety::Safe => chalk_ir::Safety::Safe,
+                super::abi::Safety::Unsafe => chalk_ir::Safety::Unsafe,
+            },
+            params_and_return: triomphe::Arc::from_iter(
+                self.inputs_and_output.iter().map(|ty| convert_ty_for_result(interner, ty)),
+            ),
+        }
+    }
+}
+
 pub fn convert_canonical_args_for_result<'db>(
     interner: DbInterner<'db>,
     args: Canonical<'db, Vec<GenericArg<'db>>>,
diff --git a/crates/hir-ty/src/next_solver/predicate.rs b/crates/hir-ty/src/next_solver/predicate.rs
index 8654541..99b1354 100644
--- a/crates/hir-ty/src/next_solver/predicate.rs
+++ b/crates/hir-ty/src/next_solver/predicate.rs
@@ -227,8 +227,6 @@
             internee: kind,
             flags: flags.flags,
             outer_exclusive_binder: flags.outer_exclusive_binder,
-            #[cfg(feature = "in-rust-tree")]
-            stable_hash: ena::fingerprint::Fingerprint::ZERO,
         };
         Predicate::new_(interner.db(), InternedWrapperNoDebug(cached))
     }
diff --git a/crates/hir-ty/src/next_solver/region.rs b/crates/hir-ty/src/next_solver/region.rs
index d6214d9..0bfd2b8 100644
--- a/crates/hir-ty/src/next_solver/region.rs
+++ b/crates/hir-ty/src/next_solver/region.rs
@@ -15,7 +15,7 @@
     interner::{BoundVarKind, DbInterner, Placeholder},
 };
 
-type RegionKind<'db> = rustc_type_ir::RegionKind<DbInterner<'db>>;
+pub type RegionKind<'db> = rustc_type_ir::RegionKind<DbInterner<'db>>;
 
 #[salsa::interned(constructor = new_, debug)]
 pub struct Region<'db> {
@@ -53,6 +53,10 @@
         Region::new(interner, RegionKind::ReVar(v))
     }
 
+    pub fn new_erased(interner: DbInterner<'db>) -> Region<'db> {
+        Region::new(interner, RegionKind::ReErased)
+    }
+
     pub fn is_placeholder(&self) -> bool {
         matches!(self.inner(), RegionKind::RePlaceholder(..))
     }
@@ -61,6 +65,10 @@
         matches!(self.inner(), RegionKind::ReStatic)
     }
 
+    pub fn is_var(&self) -> bool {
+        matches!(self.inner(), RegionKind::ReVar(_))
+    }
+
     pub fn error(interner: DbInterner<'db>) -> Self {
         Region::new(interner, RegionKind::ReError(ErrorGuaranteed))
     }
diff --git a/crates/hir-ty/src/next_solver/ty.rs b/crates/hir-ty/src/next_solver/ty.rs
index c7a747a..a25996a 100644
--- a/crates/hir-ty/src/next_solver/ty.rs
+++ b/crates/hir-ty/src/next_solver/ty.rs
@@ -7,6 +7,7 @@
 use intern::{Interned, Symbol, sym};
 use rustc_abi::{Float, Integer, Size};
 use rustc_ast_ir::{Mutability, try_visit, visit::VisitorResult};
+use rustc_type_ir::TyVid;
 use rustc_type_ir::{
     BoundVar, ClosureKind, CollectAndApply, FlagComputation, Flags, FloatTy, FloatVid, InferTy,
     IntTy, IntVid, Interner, TypeFoldable, TypeSuperFoldable, TypeSuperVisitable, TypeVisitable,
@@ -60,8 +61,6 @@
             internee: kind,
             flags: flags.flags,
             outer_exclusive_binder: flags.outer_exclusive_binder,
-            #[cfg(feature = "in-rust-tree")]
-            stable_hash: ena::fingerprint::Fingerprint::ZERO,
         };
         Ty::new_(interner.db(), InternedWrapperNoDebug(cached))
     }
@@ -338,6 +337,14 @@
         matches!(self.kind(), TyKind::Tuple(tys) if tys.inner().is_empty())
     }
 
+    #[inline]
+    pub fn ty_vid(self) -> Option<TyVid> {
+        match self.kind() {
+            TyKind::Infer(rustc_type_ir::TyVar(vid)) => Some(vid),
+            _ => None,
+        }
+    }
+
     /// Given a `fn` type, returns an equivalent `unsafe fn` type;
     /// that is, a `fn` type that is equivalent in every way for being
     /// unsafe.
diff --git a/crates/hir-ty/src/tests/incremental.rs b/crates/hir-ty/src/tests/incremental.rs
index c0b930e..cc5ad20 100644
--- a/crates/hir-ty/src/tests/incremental.rs
+++ b/crates/hir-ty/src/tests/incremental.rs
@@ -504,14 +504,11 @@
                 "crate_local_def_map",
                 "trait_impls_in_crate_shim",
                 "attrs_shim",
-                "impl_trait_with_diagnostics_shim",
                 "impl_signature_shim",
                 "impl_signature_with_source_map_shim",
-                "impl_self_ty_with_diagnostics_shim",
                 "struct_signature_shim",
                 "struct_signature_with_source_map_shim",
                 "attrs_shim",
-                "type_for_adt_tracked",
             ]
         "#]],
     );
@@ -609,9 +606,6 @@
                 "trait_impls_in_crate_shim",
                 "impl_trait_with_diagnostics_shim",
                 "impl_self_ty_with_diagnostics_shim",
-                "type_for_adt_tracked",
-                "impl_trait_with_diagnostics_ns_shim",
-                "impl_self_ty_with_diagnostics_ns_shim",
                 "generic_predicates_ns_shim",
                 "value_ty_shim",
                 "generic_predicates_shim",
@@ -700,8 +694,6 @@
                 "trait_impls_in_crate_shim",
                 "impl_trait_with_diagnostics_shim",
                 "impl_self_ty_with_diagnostics_shim",
-                "impl_trait_with_diagnostics_ns_shim",
-                "impl_self_ty_with_diagnostics_ns_shim",
                 "generic_predicates_ns_shim",
                 "generic_predicates_shim",
             ]
diff --git a/crates/hir-ty/src/tests/method_resolution.rs b/crates/hir-ty/src/tests/method_resolution.rs
index b14ce35..5ada14b 100644
--- a/crates/hir-ty/src/tests/method_resolution.rs
+++ b/crates/hir-ty/src/tests/method_resolution.rs
@@ -2053,7 +2053,7 @@
                                // ^^^^ expected Box<dyn Error + '?>, got Box<dyn Error + Send + '?>
                                // FIXME, type mismatch should not occur
         <dyn Error>::downcast(err).map_err(|_| loop {})
-      //^^^^^^^^^^^^^^^^^^^^^ type: fn downcast<{unknown}>(Box<dyn Error + '?>) -> Result<Box<{unknown}>, Box<dyn Error + '?>>
+      //^^^^^^^^^^^^^^^^^^^^^ type: fn downcast<{unknown}>(Box<dyn Error + 'static>) -> Result<Box<{unknown}>, Box<dyn Error + 'static>>
     }
 }
 "#,
diff --git a/crates/hir-ty/src/tests/never_type.rs b/crates/hir-ty/src/tests/never_type.rs
index af5290d..4d68179 100644
--- a/crates/hir-ty/src/tests/never_type.rs
+++ b/crates/hir-ty/src/tests/never_type.rs
@@ -14,8 +14,6 @@
     );
 }
 
-// FIXME(next-solver): The never type fallback implemented in r-a no longer works properly because of
-// `Coerce` predicates. We should reimplement fallback like rustc.
 #[test]
 fn infer_never2() {
     check_types(
@@ -26,7 +24,7 @@
     let a = gen();
     if false { a } else { loop {} };
     a;
-} //^ {unknown}
+} //^ !
 "#,
     );
 }
@@ -41,7 +39,7 @@
     let a = gen();
     if false { loop {} } else { a };
     a;
-  //^ {unknown}
+  //^ !
 }
 "#,
     );
@@ -56,7 +54,7 @@
 fn test() {
     let a = if true { Option::None } else { Option::Some(return) };
     a;
-} //^ Option<{unknown}>
+} //^ Option<!>
 "#,
     );
 }
@@ -220,7 +218,7 @@
         _ => loop {},
     };
     i;
-} //^ {unknown}
+} //^ !
 "#,
     );
 }
diff --git a/crates/hir-ty/src/tests/regression.rs b/crates/hir-ty/src/tests/regression.rs
index a6215ef..00835aa 100644
--- a/crates/hir-ty/src/tests/regression.rs
+++ b/crates/hir-ty/src/tests/regression.rs
@@ -1951,7 +1951,7 @@
     Alias::Braced;
   //^^^^^^^^^^^^^ {unknown}
     let Alias::Braced = loop {};
-      //^^^^^^^^^^^^^ {unknown}
+      //^^^^^^^^^^^^^ !
   let Alias::Braced(..) = loop {};
     //^^^^^^^^^^^^^^^^^ Enum
 
diff --git a/crates/hir-ty/src/tests/traits.rs b/crates/hir-ty/src/tests/traits.rs
index 41f8d4e..66faac0 100644
--- a/crates/hir-ty/src/tests/traits.rs
+++ b/crates/hir-ty/src/tests/traits.rs
@@ -1487,8 +1487,8 @@
             268..269 'x': Box<dyn Trait<u64> + '?>
             275..276 'y': &'? (dyn Trait<u64> + '?)
             286..287 'z': Box<dyn Trait<u64> + '?>
-            290..293 'bar': fn bar() -> Box<dyn Trait<u64> + '?>
-            290..295 'bar()': Box<dyn Trait<u64> + '?>
+            290..293 'bar': fn bar() -> Box<dyn Trait<u64> + 'static>
+            290..295 'bar()': Box<dyn Trait<u64> + 'static>
             301..302 'x': Box<dyn Trait<u64> + '?>
             301..308 'x.foo()': u64
             314..315 'y': &'? (dyn Trait<u64> + '?)
@@ -1535,7 +1535,7 @@
             251..252 's': S<u32, i32>
             267..289 '{     ...z(); }': ()
             273..274 's': S<u32, i32>
-            273..280 's.bar()': &'? (dyn Trait<u32, i32> + '?)
+            273..280 's.bar()': &'? (dyn Trait<u32, i32> + 'static)
             273..286 's.bar().baz()': (u32, i32)
         "#]],
     );
@@ -1568,8 +1568,8 @@
             106..107 'x': dyn Trait + '?
             113..114 'y': &'? (dyn Trait + '?)
             124..125 'z': dyn Trait + '?
-            128..131 'bar': fn bar() -> dyn Trait + '?
-            128..133 'bar()': dyn Trait + '?
+            128..131 'bar': fn bar() -> dyn Trait + 'static
+            128..133 'bar()': dyn Trait + 'static
             139..140 'x': dyn Trait + '?
             139..146 'x.foo()': u64
             152..153 'y': &'? (dyn Trait + '?)
@@ -1597,7 +1597,7 @@
             47..48 '_': &'? (dyn Fn(S) + '?)
             58..60 '{}': ()
             71..105 '{     ...()); }': ()
-            77..78 'f': fn f(&'? (dyn Fn(S) + '?))
+            77..78 'f': fn f(&'? (dyn Fn(S) + 'static))
             77..102 'f(&|nu...foo())': ()
             79..101 '&|numb....foo()': &'? impl Fn(S)
             80..101 '|numbe....foo()': impl Fn(S)
@@ -2952,7 +2952,7 @@
             34..36 '{}': ()
             46..47 'x': &'? (dyn Foo + '?)
             59..74 '{     foo(x); }': ()
-            65..68 'foo': fn foo(&'? (dyn Foo + '?))
+            65..68 'foo': fn foo(&'? (dyn Foo + 'static))
             65..71 'foo(x)': ()
             69..70 'x': &'? (dyn Foo + '?)
         "#]],
diff --git a/crates/hir-ty/src/variance.rs b/crates/hir-ty/src/variance.rs
index 8593dba..a17cf37 100644
--- a/crates/hir-ty/src/variance.rs
+++ b/crates/hir-ty/src/variance.rs
@@ -15,6 +15,8 @@
 
 use crate::db::HirDatabase;
 use crate::generics::{Generics, generics};
+use crate::next_solver::DbInterner;
+use crate::next_solver::mapping::{ChalkToNextSolver, NextSolverToChalk};
 use crate::{
     AliasTy, Const, ConstScalar, DynTyExt, GenericArg, GenericArgData, Interner, Lifetime,
     LifetimeData, Ty, TyKind,
@@ -238,14 +240,15 @@
             }
             GenericDefId::FunctionId(f) => {
                 let subst = self.generics.placeholder_subst(self.db);
-                self.add_constraints_from_sig(
-                    self.db
-                        .callable_item_signature(f.into())
-                        .substitute(Interner, &subst)
-                        .params_and_return
-                        .iter(),
-                    Variance::Covariant,
-                );
+                let interner = DbInterner::new_with(self.db, None, None);
+                let args: crate::next_solver::GenericArgs<'_> = subst.to_nextsolver(interner);
+                let sig = self
+                    .db
+                    .callable_item_signature(f.into())
+                    .instantiate(interner, args)
+                    .skip_binder()
+                    .to_chalk(interner);
+                self.add_constraints_from_sig(sig.params_and_return.iter(), Variance::Covariant);
             }
             _ => {}
         }
diff --git a/crates/hir/src/lib.rs b/crates/hir/src/lib.rs
index 862067e..93f6f63 100644
--- a/crates/hir/src/lib.rs
+++ b/crates/hir/src/lib.rs
@@ -20,10 +20,6 @@
 #![cfg_attr(feature = "in-rust-tree", feature(rustc_private))]
 #![recursion_limit = "512"]
 
-#[cfg(feature = "in-rust-tree")]
-extern crate rustc_type_ir;
-
-#[cfg(not(feature = "in-rust-tree"))]
 extern crate ra_ap_rustc_type_ir as rustc_type_ir;
 
 mod attrs;
@@ -682,7 +678,7 @@
                             push_ty_diagnostics(
                                 db,
                                 acc,
-                                db.field_types_with_diagnostics_ns(s.id.into()).1,
+                                db.field_types_with_diagnostics(s.id.into()).1,
                                 source_map,
                             );
                         }
@@ -694,7 +690,7 @@
                             push_ty_diagnostics(
                                 db,
                                 acc,
-                                db.field_types_with_diagnostics_ns(u.id.into()).1,
+                                db.field_types_with_diagnostics(u.id.into()).1,
                                 source_map,
                             );
                         }
@@ -724,7 +720,7 @@
                                 push_ty_diagnostics(
                                     db,
                                     acc,
-                                    db.field_types_with_diagnostics_ns(v.into()).1,
+                                    db.field_types_with_diagnostics(v.into()).1,
                                     source_map,
                                 );
                                 expr_store_diagnostics(db, acc, source_map);
@@ -740,7 +736,7 @@
                     push_ty_diagnostics(
                         db,
                         acc,
-                        db.type_for_type_alias_with_diagnostics_ns(type_alias.id).1,
+                        db.type_for_type_alias_with_diagnostics(type_alias.id).1,
                         &source_map,
                     );
                     acc.extend(def.diagnostics(db, style_lints));
@@ -915,13 +911,13 @@
             push_ty_diagnostics(
                 db,
                 acc,
-                db.impl_self_ty_with_diagnostics_ns(impl_def.id).1,
+                db.impl_self_ty_with_diagnostics(impl_def.id).1,
                 &source_map,
             );
             push_ty_diagnostics(
                 db,
                 acc,
-                db.impl_trait_with_diagnostics_ns(impl_def.id).and_then(|it| it.1),
+                db.impl_trait_with_diagnostics(impl_def.id).and_then(|it| it.1),
                 &source_map,
             );
 
@@ -1504,7 +1500,7 @@
         let krate = self.inner.krate(db);
         let interner = DbInterner::new_with(db, Some(krate.base()), None);
 
-        let ty = db.ty_ns(self.inner.id.into());
+        let ty = db.ty(self.inner.id.into());
         TypeNs::new(db, self.inner.id, ty.instantiate(interner, self.args))
     }
 }
@@ -1664,7 +1660,7 @@
         let krate = self.inner.krate(db);
         let interner = DbInterner::new_with(db, Some(krate.base()), None);
 
-        let ty = db.ty_ns(self.inner.id.into());
+        let ty = db.ty(self.inner.id.into());
         TypeNs::new(db, self.inner.id, ty.instantiate(interner, self.args))
     }
 }
@@ -1851,7 +1847,8 @@
                     ParamKind::Lifetime => error_lifetime().cast(Interner),
                 }
             })
-            .build();
+            .build(DbInterner::conjure())
+            .to_chalk(DbInterner::conjure());
         Type::new(db, id, ty)
     }
 
@@ -2286,7 +2283,13 @@
     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 callable_sig = db.callable_item_signature(self.id.into()).substitute(Interner, &substs);
+        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);
         Type::new_with_resolver_inner(db, &resolver, ty)
     }
@@ -2295,8 +2298,14 @@
     pub fn ret_type(self, db: &dyn HirDatabase) -> Type<'_> {
         let resolver = self.id.resolver(db);
         let substs = TyBuilder::placeholder_subst(db, self.id);
-        let callable_sig = db.callable_item_signature(self.id.into()).substitute(Interner, &substs);
-        let ty = callable_sig.ret().clone();
+        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);
         Type::new_with_resolver_inner(db, &resolver, ty)
     }
 
@@ -2325,8 +2334,14 @@
             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 callable_sig = db.callable_item_signature(self.id.into()).substitute(Interner, &substs);
-        let ty = callable_sig.ret().clone();
+        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);
         Type::new_with_resolver_inner(db, &resolver, ty)
     }
 
@@ -2336,8 +2351,14 @@
         }
         let resolver = self.id.resolver(db);
         let substs = TyBuilder::placeholder_subst(db, self.id);
-        let callable_sig = db.callable_item_signature(self.id.into()).substitute(Interner, &substs);
-        let ret_ty = callable_sig.ret().clone();
+        let interner = DbInterner::new_with(db, None, None);
+        let args: crate::next_solver::GenericArgs<'_> = substs.to_nextsolver(interner);
+        let ret_ty = db
+            .callable_item_signature(self.id.into())
+            .instantiate(interner, args)
+            .skip_binder()
+            .output()
+            .to_chalk(interner);
         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();
@@ -2357,7 +2378,13 @@
     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 callable_sig = db.callable_item_signature(self.id.into()).substitute(Interner, &substs);
+        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);
         callable_sig
             .params()
             .iter()
@@ -2385,7 +2412,13 @@
     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 callable_sig = db.callable_item_signature(self.id.into()).substitute(Interner, &substs);
+        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 skip = if db.function_signature(self.id).has_self_param() { 1 } else { 0 };
         callable_sig
             .params()
@@ -2435,7 +2468,13 @@
                 GenericArg::new(Interner, GenericArgData::Ty(ty))
             })
             .build();
-        let callable_sig = db.callable_item_signature(self.id.into()).substitute(Interner, &substs);
+        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 skip = if db.function_signature(self.id).has_self_param() { 1 } else { 0 };
         callable_sig
             .params()
@@ -2730,8 +2769,13 @@
 
     pub fn ty<'db>(&self, db: &'db dyn HirDatabase) -> Type<'db> {
         let substs = TyBuilder::placeholder_subst(db, self.func);
-        let callable_sig =
-            db.callable_item_signature(self.func.into()).substitute(Interner, &substs);
+        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 environment = db.trait_environment(self.func.into());
         let ty = callable_sig.params()[0].clone();
         Type { env: environment, ty, _pd: PhantomCovariantLifetime::new() }
@@ -2763,8 +2807,13 @@
         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 callable_sig =
-            db.callable_item_signature(self.func.into()).substitute(Interner, &substs);
+        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 environment = db.trait_environment(self.func.into());
         let ty = callable_sig.params()[0].clone();
         Type { env: environment, ty, _pd: PhantomCovariantLifetime::new() }
@@ -3640,7 +3689,7 @@
                 push_ty_diagnostics(
                     db,
                     acc,
-                    db.type_for_type_alias_with_diagnostics_ns(type_alias.id).1,
+                    db.type_for_type_alias_with_diagnostics(type_alias.id).1,
                     &db.type_alias_signature_with_source_map(type_alias.id).1,
                 );
                 for diag in hir_ty::diagnostics::incorrect_case(db, type_alias.id.into()) {
@@ -3768,7 +3817,7 @@
         push_ty_diagnostics(
             db,
             acc,
-            db.generic_predicates_without_parent_with_diagnostics_ns(def).1,
+            db.generic_predicates_without_parent_with_diagnostics(def).1,
             &source_map,
         );
         for (param_id, param) in generics.iter_type_or_consts() {
@@ -3776,7 +3825,7 @@
                 push_ty_diagnostics(
                     db,
                     acc,
-                    db.const_param_ty_with_diagnostics_ns(ConstParamId::from_unchecked(
+                    db.const_param_ty_with_diagnostics(ConstParamId::from_unchecked(
                         TypeOrConstParamId { parent: def, local_id: param_id },
                     ))
                     .1,
@@ -4828,32 +4877,40 @@
     }
 
     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_binders().clone()),
+                TyDefId::BuiltinType(_) => {
+                    return Type::new(db, def, ty.skip_binder().to_chalk(interner));
+                }
             },
         );
-        Type::new(db, def, ty.substitute(Interner, &substs))
+        let args: hir_ty::next_solver::GenericArgs<'_> = substs.to_nextsolver(interner);
+        Type::new(db, def, ty.instantiate(interner, args).to_chalk(interner))
     }
 
     fn from_def_placeholders(
         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::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_binders().clone()),
+                TyDefId::BuiltinType(_) => {
+                    return Type::new(db, def, ty.skip_binder().to_chalk(interner));
+                }
             },
         );
-        Type::new(db, def, ty.substitute(Interner, &substs))
+        let args: hir_ty::next_solver::GenericArgs<'_> = substs.to_nextsolver(interner);
+        Type::new(db, def, ty.instantiate(interner, args).to_chalk(interner))
     }
 
     fn from_value_def(
@@ -4863,6 +4920,7 @@
         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() {
@@ -4873,10 +4931,13 @@
                 ValueTyDefId::EnumVariantId(it) => {
                     GenericDefId::AdtId(AdtId::EnumId(it.lookup(db).parent))
                 }
-                ValueTyDefId::StaticId(_) => return Type::new(db, def, ty.skip_binders().clone()),
+                ValueTyDefId::StaticId(_) => {
+                    return Type::new(db, def, ty.skip_binder().to_chalk(interner));
+                }
             },
         );
-        Type::new(db, def, ty.substitute(Interner, &substs))
+        let args: crate::next_solver::GenericArgs<'_> = substs.to_nextsolver(interner);
+        Type::new(db, def, ty.instantiate(interner, args).to_chalk(interner))
     }
 
     pub fn new_slice(ty: Self) -> Self {
diff --git a/crates/hir/src/source_analyzer.rs b/crates/hir/src/source_analyzer.rs
index a19183f..c6b7e84 100644
--- a/crates/hir/src/source_analyzer.rs
+++ b/crates/hir/src/source_analyzer.rs
@@ -46,6 +46,10 @@
     from_assoc_type_id,
     lang_items::lang_items_for_bin_op,
     method_resolution,
+    next_solver::{
+        DbInterner,
+        mapping::{ChalkToNextSolver, NextSolverToChalk},
+    },
 };
 use intern::sym;
 use itertools::Itertools;
@@ -372,8 +376,10 @@
     ) -> Option<Callable<'db>> {
         let expr_id = self.expr_id(call.clone().into())?.as_expr()?;
         let (func, substs) = self.infer()?.method_resolution(expr_id)?;
-        let ty = db.value_ty(func.into())?.substitute(Interner, &substs);
-        let ty = Type::new_with_resolver(db, &self.resolver, ty);
+        let interner = DbInterner::new_with(db, None, None);
+        let args: hir_ty::next_solver::GenericArgs<'_> = substs.to_nextsolver(interner);
+        let ty = db.value_ty(func.into())?.instantiate(interner, args);
+        let ty = Type::new_with_resolver(db, &self.resolver, ty.to_chalk(interner));
         let mut res = ty.as_callable(db)?;
         res.is_bound_method = true;
         Some(res)
diff --git a/crates/ide-completion/src/context/analysis.rs b/crates/ide-completion/src/context/analysis.rs
index cdb1ad8..77a9440 100644
--- a/crates/ide-completion/src/context/analysis.rs
+++ b/crates/ide-completion/src/context/analysis.rs
@@ -1,6 +1,7 @@
 //! Module responsible for analyzing the code surrounding the cursor for completion.
 use std::iter;
 
+use base_db::salsa;
 use hir::{ExpandResult, InFile, Semantics, Type, TypeInfo, Variant};
 use ide_db::{RootDatabase, active_parameter::ActiveParameter};
 use itertools::Either;
@@ -85,9 +86,15 @@
     let original_offset = expansion.original_offset + relative_offset;
     let token = expansion.original_file.token_at_offset(original_offset).left_biased()?;
 
-    analyze(sema, expansion, original_token, &token).map(|(analysis, expected, qualifier_ctx)| {
-        AnalysisResult { analysis, expected, qualifier_ctx, token, original_offset }
-    })
+    salsa::attach(sema.db, || analyze(sema, expansion, original_token, &token)).map(
+        |(analysis, expected, qualifier_ctx)| AnalysisResult {
+            analysis,
+            expected,
+            qualifier_ctx,
+            token,
+            original_offset,
+        },
+    )
 }
 
 fn token_at_offset_ignore_whitespace(file: &SyntaxNode, offset: TextSize) -> Option<SyntaxToken> {
diff --git a/crates/ide-db/src/syntax_helpers/suggest_name.rs b/crates/ide-db/src/syntax_helpers/suggest_name.rs
index 995bf72..2e03665 100644
--- a/crates/ide-db/src/syntax_helpers/suggest_name.rs
+++ b/crates/ide-db/src/syntax_helpers/suggest_name.rs
@@ -473,7 +473,7 @@
             frange.range,
             "selection is not an expression(yet contained in one)"
         );
-        let name = NameGenerator::default().for_variable(&expr, &sema);
+        let name = salsa::attach(sema.db, || NameGenerator::default().for_variable(&expr, &sema));
         assert_eq!(&name, expected);
     }
 
diff --git a/crates/ide/src/inlay_hints/bind_pat.rs b/crates/ide/src/inlay_hints/bind_pat.rs
index 104740c..b7c1241 100644
--- a/crates/ide/src/inlay_hints/bind_pat.rs
+++ b/crates/ide/src/inlay_hints/bind_pat.rs
@@ -380,7 +380,7 @@
     let foo = foo4();
      // ^^^ &dyn Fn(f64, f64) -> u32
     let foo = foo5();
-     // ^^^ &dyn Fn(&dyn Fn(f64, f64) -> u32, f64) -> u32
+     // ^^^ &dyn Fn(&(dyn Fn(f64, f64) -> u32 + 'static), f64) -> u32
     let foo = foo6();
      // ^^^ impl Fn(f64, f64) -> u32
     let foo = foo7();
diff --git a/crates/ide/src/view_memory_layout.rs b/crates/ide/src/view_memory_layout.rs
index 04537f9..ddd58a0 100644
--- a/crates/ide/src/view_memory_layout.rs
+++ b/crates/ide/src/view_memory_layout.rs
@@ -94,8 +94,8 @@
     let def = get_definition(&sema, token)?;
 
     let ty = match def {
-        Definition::Adt(it) => it.ty(db),
-        Definition::TypeAlias(it) => it.ty(db),
+        Definition::Adt(it) => salsa::attach(db, || it.ty(db)),
+        Definition::TypeAlias(it) => salsa::attach(db, || it.ty(db)),
         Definition::BuiltinType(it) => it.ty(db),
         Definition::SelfType(it) => it.self_ty(db),
         Definition::Local(it) => it.ty(db),
diff --git a/crates/intern/src/symbol/symbols.rs b/crates/intern/src/symbol/symbols.rs
index 1db4f8e..920bdd9 100644
--- a/crates/intern/src/symbol/symbols.rs
+++ b/crates/intern/src/symbol/symbols.rs
@@ -516,4 +516,5 @@
     flags,
     precision,
     width,
+    never_type_fallback,
 }
diff --git a/rust-version b/rust-version
index 02b217f..8854fb9 100644
--- a/rust-version
+++ b/rust-version
@@ -1 +1 @@
-21a19c297d4f5a03501d92ca251bd7a17073c08a
+caccb4d0368bd918ef6668af8e13834d07040417