| //! Coercion logic. Coercions are certain type conversions that can implicitly |
| //! happen in certain places, e.g. weakening `&mut` to `&` or deref coercions |
| //! like going from `&Vec<T>` to `&[T]`. |
| //! |
| //! See <https://doc.rust-lang.org/nomicon/coercions.html> and |
| //! `rustc_hir_analysis/check/coercion.rs`. |
| |
| use std::iter; |
| |
| use chalk_ir::{cast::Cast, BoundVar, Goal, Mutability, TyKind, TyVariableKind}; |
| use hir_def::{ |
| hir::ExprId, |
| lang_item::{LangItem, LangItemTarget}, |
| }; |
| use stdx::always; |
| use triomphe::Arc; |
| |
| use crate::{ |
| autoderef::{Autoderef, AutoderefKind}, |
| db::HirDatabase, |
| error_lifetime, |
| infer::{ |
| Adjust, Adjustment, AutoBorrow, InferOk, InferenceContext, OverloadedDeref, PointerCast, |
| TypeError, TypeMismatch, |
| }, |
| utils::ClosureSubst, |
| Canonical, DomainGoal, FnAbi, FnPointer, FnSig, Guidance, InEnvironment, Interner, Solution, |
| Substitution, TraitEnvironment, Ty, TyBuilder, TyExt, |
| }; |
| |
| use super::unify::InferenceTable; |
| |
| pub(crate) type CoerceResult = Result<InferOk<(Vec<Adjustment>, Ty)>, TypeError>; |
| |
| /// Do not require any adjustments, i.e. coerce `x -> x`. |
| fn identity(_: Ty) -> Vec<Adjustment> { |
| vec![] |
| } |
| |
| fn simple(kind: Adjust) -> impl FnOnce(Ty) -> Vec<Adjustment> { |
| move |target| vec![Adjustment { kind, target }] |
| } |
| |
| /// This always returns `Ok(...)`. |
| fn success( |
| adj: Vec<Adjustment>, |
| target: Ty, |
| goals: Vec<InEnvironment<Goal<Interner>>>, |
| ) -> CoerceResult { |
| Ok(InferOk { goals, value: (adj, target) }) |
| } |
| |
| pub(super) enum CoercionCause { |
| // FIXME: Make better use of this. Right now things like return and break without a value |
| // use it to point to themselves, causing us to report a mismatch on those expressions even |
| // though technically they themselves are `!` |
| Expr(ExprId), |
| } |
| |
| #[derive(Clone, Debug)] |
| pub(super) struct CoerceMany { |
| expected_ty: Ty, |
| final_ty: Option<Ty>, |
| expressions: Vec<ExprId>, |
| } |
| |
| impl CoerceMany { |
| pub(super) fn new(expected: Ty) -> Self { |
| CoerceMany { expected_ty: expected, final_ty: None, expressions: vec![] } |
| } |
| |
| /// Returns the "expected type" with which this coercion was |
| /// constructed. This represents the "downward propagated" type |
| /// that was given to us at the start of typing whatever construct |
| /// we are typing (e.g., the match expression). |
| /// |
| /// Typically, this is used as the expected type when |
| /// type-checking each of the alternative expressions whose types |
| /// we are trying to merge. |
| pub(super) fn expected_ty(&self) -> Ty { |
| self.expected_ty.clone() |
| } |
| |
| /// Returns the current "merged type", representing our best-guess |
| /// at the LUB of the expressions we've seen so far (if any). This |
| /// isn't *final* until you call `self.complete()`, which will return |
| /// the merged type. |
| pub(super) fn merged_ty(&self) -> Ty { |
| self.final_ty.clone().unwrap_or_else(|| self.expected_ty.clone()) |
| } |
| |
| pub(super) fn complete(self, ctx: &mut InferenceContext<'_>) -> Ty { |
| if let Some(final_ty) = self.final_ty { |
| final_ty |
| } else { |
| ctx.result.standard_types.never.clone() |
| } |
| } |
| |
| pub(super) fn coerce_forced_unit( |
| &mut self, |
| ctx: &mut InferenceContext<'_>, |
| cause: CoercionCause, |
| ) { |
| self.coerce(ctx, None, &ctx.result.standard_types.unit.clone(), cause) |
| } |
| |
| /// Merge two types from different branches, with possible coercion. |
| /// |
| /// Mostly this means trying to coerce one to the other, but |
| /// - if we have two function types for different functions or closures, we need to |
| /// coerce both to function pointers; |
| /// - if we were concerned with lifetime subtyping, we'd need to look for a |
| /// least upper bound. |
| pub(super) fn coerce( |
| &mut self, |
| ctx: &mut InferenceContext<'_>, |
| expr: Option<ExprId>, |
| expr_ty: &Ty, |
| cause: CoercionCause, |
| ) { |
| let expr_ty = ctx.resolve_ty_shallow(expr_ty); |
| self.expected_ty = ctx.resolve_ty_shallow(&self.expected_ty); |
| |
| // Special case: two function types. Try to coerce both to |
| // pointers to have a chance at getting a match. See |
| // https://github.com/rust-lang/rust/blob/7b805396bf46dce972692a6846ce2ad8481c5f85/src/librustc_typeck/check/coercion.rs#L877-L916 |
| let sig = match (self.merged_ty().kind(Interner), expr_ty.kind(Interner)) { |
| (TyKind::FnDef(x, _), TyKind::FnDef(y, _)) if x == y => None, |
| (TyKind::Closure(x, _), TyKind::Closure(y, _)) if x == y => None, |
| (TyKind::FnDef(..) | TyKind::Closure(..), TyKind::FnDef(..) | TyKind::Closure(..)) => { |
| // FIXME: we're ignoring safety here. To be more correct, if we have one FnDef and one Closure, |
| // we should be coercing the closure to a fn pointer of the safety of the FnDef |
| cov_mark::hit!(coerce_fn_reification); |
| let sig = |
| self.merged_ty().callable_sig(ctx.db).expect("FnDef without callable sig"); |
| Some(sig) |
| } |
| _ => None, |
| }; |
| if let Some(sig) = sig { |
| let target_ty = TyKind::Function(sig.to_fn_ptr()).intern(Interner); |
| let result1 = ctx.table.coerce_inner(self.merged_ty(), &target_ty); |
| let result2 = ctx.table.coerce_inner(expr_ty.clone(), &target_ty); |
| if let (Ok(result1), Ok(result2)) = (result1, result2) { |
| ctx.table.register_infer_ok(InferOk { value: (), goals: result1.goals }); |
| for &e in &self.expressions { |
| ctx.write_expr_adj(e, result1.value.0.clone()); |
| } |
| ctx.table.register_infer_ok(InferOk { value: (), goals: result2.goals }); |
| if let Some(expr) = expr { |
| ctx.write_expr_adj(expr, result2.value.0); |
| self.expressions.push(expr); |
| } |
| return self.final_ty = Some(target_ty); |
| } |
| } |
| |
| // It might not seem like it, but order is important here: If the expected |
| // type is a type variable and the new one is `!`, trying it the other |
| // way around first would mean we make the type variable `!`, instead of |
| // just marking it as possibly diverging. |
| if let Ok(res) = ctx.coerce(expr, &expr_ty, &self.merged_ty()) { |
| self.final_ty = Some(res); |
| } else if let Ok(res) = ctx.coerce(expr, &self.merged_ty(), &expr_ty) { |
| self.final_ty = Some(res); |
| } else { |
| match cause { |
| CoercionCause::Expr(id) => { |
| ctx.result.type_mismatches.insert( |
| id.into(), |
| TypeMismatch { expected: self.merged_ty(), actual: expr_ty.clone() }, |
| ); |
| } |
| } |
| cov_mark::hit!(coerce_merge_fail_fallback); |
| } |
| if let Some(expr) = expr { |
| self.expressions.push(expr); |
| } |
| } |
| } |
| |
| pub fn could_coerce( |
| db: &dyn HirDatabase, |
| env: Arc<TraitEnvironment>, |
| tys: &Canonical<(Ty, Ty)>, |
| ) -> bool { |
| coerce(db, env, tys).is_ok() |
| } |
| |
| pub(crate) fn coerce( |
| db: &dyn HirDatabase, |
| env: Arc<TraitEnvironment>, |
| tys: &Canonical<(Ty, Ty)>, |
| ) -> Result<(Vec<Adjustment>, Ty), TypeError> { |
| let mut table = InferenceTable::new(db, env); |
| let vars = table.fresh_subst(tys.binders.as_slice(Interner)); |
| let ty1_with_vars = vars.apply(tys.value.0.clone(), Interner); |
| let ty2_with_vars = vars.apply(tys.value.1.clone(), Interner); |
| let (adjustments, ty) = table.coerce(&ty1_with_vars, &ty2_with_vars)?; |
| // default any type vars that weren't unified back to their original bound vars |
| // (kind of hacky) |
| let find_var = |iv| { |
| vars.iter(Interner).position(|v| match v.interned() { |
| chalk_ir::GenericArgData::Ty(ty) => ty.inference_var(Interner), |
| chalk_ir::GenericArgData::Lifetime(lt) => lt.inference_var(Interner), |
| 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| 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)), |
| }; |
| // FIXME also map the types in the adjustments |
| Ok((adjustments, table.resolve_with_fallback(ty, &fallback))) |
| } |
| |
| impl InferenceContext<'_> { |
| /// Unify two types, but may coerce the first one to the second one |
| /// using "implicit coercion rules" if needed. |
| pub(super) fn coerce( |
| &mut self, |
| expr: Option<ExprId>, |
| from_ty: &Ty, |
| to_ty: &Ty, |
| ) -> Result<Ty, TypeError> { |
| let from_ty = self.resolve_ty_shallow(from_ty); |
| let to_ty = self.resolve_ty_shallow(to_ty); |
| let (adjustments, ty) = self.table.coerce(&from_ty, &to_ty)?; |
| if let Some(expr) = expr { |
| self.write_expr_adj(expr, adjustments); |
| } |
| Ok(ty) |
| } |
| } |
| |
| impl InferenceTable<'_> { |
| /// Unify two types, but may coerce the first one to the second one |
| /// using "implicit coercion rules" if needed. |
| pub(crate) fn coerce( |
| &mut self, |
| from_ty: &Ty, |
| to_ty: &Ty, |
| ) -> Result<(Vec<Adjustment>, Ty), TypeError> { |
| let from_ty = self.resolve_ty_shallow(from_ty); |
| let to_ty = self.resolve_ty_shallow(to_ty); |
| match self.coerce_inner(from_ty, &to_ty) { |
| Ok(InferOk { value: (adjustments, ty), goals }) => { |
| self.register_infer_ok(InferOk { value: (), goals }); |
| Ok((adjustments, ty)) |
| } |
| Err(e) => { |
| // FIXME deal with error |
| Err(e) |
| } |
| } |
| } |
| |
| fn coerce_inner(&mut self, from_ty: Ty, to_ty: &Ty) -> CoerceResult { |
| if from_ty.is_never() { |
| // Subtle: If we are coercing from `!` to `?T`, where `?T` is an unbound |
| // type variable, we want `?T` to fallback to `!` if not |
| // otherwise constrained. An example where this arises: |
| // |
| // let _: Option<?T> = Some({ return; }); |
| // |
| // here, we would coerce from `!` to `?T`. |
| if let TyKind::InferenceVar(tv, TyVariableKind::General) = to_ty.kind(Interner) { |
| self.set_diverging(*tv, true); |
| } |
| return success(simple(Adjust::NeverToAny)(to_ty.clone()), to_ty.clone(), vec![]); |
| } |
| |
| // If we are coercing into an ATPIT, coerce into its proxy inference var, instead. |
| let mut to_ty = to_ty; |
| let _to; |
| if let Some(atpit_table) = &self.atpit_coercion_table { |
| if let TyKind::OpaqueType(opaque_ty_id, _) = to_ty.kind(Interner) { |
| if !matches!( |
| from_ty.kind(Interner), |
| TyKind::InferenceVar(..) | TyKind::OpaqueType(..) |
| ) { |
| if let Some(ty) = atpit_table.get(opaque_ty_id) { |
| _to = ty.clone(); |
| to_ty = &_to; |
| } |
| } |
| } |
| } |
| |
| // Consider coercing the subtype to a DST |
| if let Ok(ret) = self.try_coerce_unsized(&from_ty, to_ty) { |
| return Ok(ret); |
| } |
| |
| // Examine the supertype and consider auto-borrowing. |
| match to_ty.kind(Interner) { |
| TyKind::Raw(mt, _) => return self.coerce_ptr(from_ty, to_ty, *mt), |
| TyKind::Ref(mt, _, _) => return self.coerce_ref(from_ty, to_ty, *mt), |
| _ => {} |
| } |
| |
| match from_ty.kind(Interner) { |
| TyKind::FnDef(..) => { |
| // Function items are coercible to any closure |
| // type; function pointers are not (that would |
| // require double indirection). |
| // Additionally, we permit coercion of function |
| // items to drop the unsafe qualifier. |
| self.coerce_from_fn_item(from_ty, to_ty) |
| } |
| TyKind::Function(from_fn_ptr) => { |
| // We permit coercion of fn pointers to drop the |
| // unsafe qualifier. |
| self.coerce_from_fn_pointer(from_ty.clone(), from_fn_ptr, to_ty) |
| } |
| TyKind::Closure(_, from_substs) => { |
| // Non-capturing closures are coercible to |
| // function pointers or unsafe function pointers. |
| // It cannot convert closures that require unsafe. |
| self.coerce_closure_to_fn(from_ty.clone(), from_substs, to_ty) |
| } |
| _ => { |
| // Otherwise, just use unification rules. |
| self.unify_and(&from_ty, to_ty, identity) |
| } |
| } |
| } |
| |
| /// Unify two types (using sub or lub) and produce a specific coercion. |
| fn unify_and<F>(&mut self, t1: &Ty, t2: &Ty, f: F) -> CoerceResult |
| where |
| F: FnOnce(Ty) -> Vec<Adjustment>, |
| { |
| self.try_unify(t1, t2) |
| .and_then(|InferOk { goals, .. }| success(f(t1.clone()), t1.clone(), goals)) |
| } |
| |
| fn coerce_ptr(&mut self, from_ty: Ty, to_ty: &Ty, to_mt: Mutability) -> CoerceResult { |
| let (is_ref, from_mt, from_inner) = match from_ty.kind(Interner) { |
| TyKind::Ref(mt, _, ty) => (true, mt, ty), |
| TyKind::Raw(mt, ty) => (false, mt, ty), |
| _ => return self.unify_and(&from_ty, to_ty, identity), |
| }; |
| |
| coerce_mutabilities(*from_mt, to_mt)?; |
| |
| // Check that the types which they point at are compatible. |
| let from_raw = TyKind::Raw(to_mt, from_inner.clone()).intern(Interner); |
| |
| // Although references and unsafe ptrs have the same |
| // representation, we still register an Adjust::DerefRef so that |
| // regionck knows that the region for `a` must be valid here. |
| if is_ref { |
| self.unify_and(&from_raw, to_ty, |target| { |
| vec![ |
| Adjustment { kind: Adjust::Deref(None), target: from_inner.clone() }, |
| Adjustment { kind: Adjust::Borrow(AutoBorrow::RawPtr(to_mt)), target }, |
| ] |
| }) |
| } else if *from_mt != to_mt { |
| self.unify_and( |
| &from_raw, |
| to_ty, |
| simple(Adjust::Pointer(PointerCast::MutToConstPointer)), |
| ) |
| } else { |
| self.unify_and(&from_raw, to_ty, identity) |
| } |
| } |
| |
| /// Reborrows `&mut A` to `&mut B` and `&(mut) A` to `&B`. |
| /// To match `A` with `B`, autoderef will be performed, |
| /// calling `deref`/`deref_mut` where necessary. |
| fn coerce_ref(&mut self, from_ty: Ty, to_ty: &Ty, to_mt: Mutability) -> CoerceResult { |
| let from_mt = match from_ty.kind(Interner) { |
| &TyKind::Ref(mt, _, _) => { |
| coerce_mutabilities(mt, to_mt)?; |
| mt |
| } |
| _ => return self.unify_and(&from_ty, to_ty, identity), |
| }; |
| |
| // NOTE: this code is mostly copied and adapted from rustc, and |
| // currently more complicated than necessary, carrying errors around |
| // etc.. This complication will become necessary when we actually track |
| // details of coercion errors though, so I think it's useful to leave |
| // the structure like it is. |
| |
| let snapshot = self.snapshot(); |
| |
| let mut autoderef = Autoderef::new(self, from_ty.clone(), false); |
| let mut first_error = None; |
| let mut found = None; |
| |
| while let Some((referent_ty, autoderefs)) = autoderef.next() { |
| if autoderefs == 0 { |
| // Don't let this pass, otherwise it would cause |
| // &T to autoref to &&T. |
| continue; |
| } |
| |
| // At this point, we have deref'd `a` to `referent_ty`. So |
| // imagine we are coercing from `&'a mut Vec<T>` to `&'b mut [T]`. |
| // In the autoderef loop for `&'a mut Vec<T>`, we would get |
| // three callbacks: |
| // |
| // - `&'a mut Vec<T>` -- 0 derefs, just ignore it |
| // - `Vec<T>` -- 1 deref |
| // - `[T]` -- 2 deref |
| // |
| // At each point after the first callback, we want to |
| // check to see whether this would match out target type |
| // (`&'b mut [T]`) if we autoref'd it. We can't just |
| // compare the referent types, though, because we still |
| // have to consider the mutability. E.g., in the case |
| // we've been considering, we have an `&mut` reference, so |
| // the `T` in `[T]` needs to be unified with equality. |
| // |
| // Therefore, we construct reference types reflecting what |
| // the types will be after we do the final auto-ref and |
| // compare those. Note that this means we use the target |
| // mutability [1], since it may be that we are coercing |
| // from `&mut T` to `&U`. |
| let lt = error_lifetime(); // FIXME: handle lifetimes correctly, see rustc |
| let derefd_from_ty = TyKind::Ref(to_mt, lt, referent_ty).intern(Interner); |
| match autoderef.table.try_unify(&derefd_from_ty, to_ty) { |
| Ok(result) => { |
| found = Some(result.map(|()| derefd_from_ty)); |
| break; |
| } |
| Err(err) => { |
| if first_error.is_none() { |
| first_error = Some(err); |
| } |
| } |
| } |
| } |
| |
| // Extract type or return an error. We return the first error |
| // we got, which should be from relating the "base" type |
| // (e.g., in example above, the failure from relating `Vec<T>` |
| // to the target type), since that should be the least |
| // confusing. |
| let InferOk { value: ty, goals } = match found { |
| Some(d) => d, |
| None => { |
| self.rollback_to(snapshot); |
| let err = first_error.expect("coerce_borrowed_pointer had no error"); |
| return Err(err); |
| } |
| }; |
| if ty == from_ty && from_mt == Mutability::Not && autoderef.step_count() == 1 { |
| // As a special case, if we would produce `&'a *x`, that's |
| // a total no-op. We end up with the type `&'a T` just as |
| // we started with. In that case, just skip it |
| // altogether. This is just an optimization. |
| // |
| // Note that for `&mut`, we DO want to reborrow -- |
| // otherwise, this would be a move, which might be an |
| // error. For example `foo(self.x)` where `self` and |
| // `self.x` both have `&mut `type would be a move of |
| // `self.x`, but we auto-coerce it to `foo(&mut *self.x)`, |
| // which is a borrow. |
| always!(to_mt == Mutability::Not); // can only coerce &T -> &U |
| return success(vec![], ty, goals); |
| } |
| |
| let mut adjustments = auto_deref_adjust_steps(&autoderef); |
| adjustments |
| .push(Adjustment { kind: Adjust::Borrow(AutoBorrow::Ref(to_mt)), target: ty.clone() }); |
| |
| success(adjustments, ty, goals) |
| } |
| |
| /// Attempts to coerce from the type of a Rust function item into a function pointer. |
| fn coerce_from_fn_item(&mut self, from_ty: Ty, to_ty: &Ty) -> CoerceResult { |
| match to_ty.kind(Interner) { |
| TyKind::Function(_) => { |
| let from_sig = from_ty.callable_sig(self.db).expect("FnDef had no sig"); |
| |
| // FIXME check ABI: Intrinsics are not coercible to function pointers |
| // FIXME Safe `#[target_feature]` functions are not assignable to safe fn pointers (RFC 2396) |
| |
| // FIXME rustc normalizes assoc types in the sig here, not sure if necessary |
| |
| let from_sig = from_sig.to_fn_ptr(); |
| let from_fn_pointer = TyKind::Function(from_sig.clone()).intern(Interner); |
| let ok = self.coerce_from_safe_fn( |
| from_fn_pointer.clone(), |
| &from_sig, |
| to_ty, |
| |unsafe_ty| { |
| vec![ |
| Adjustment { |
| kind: Adjust::Pointer(PointerCast::ReifyFnPointer), |
| target: from_fn_pointer, |
| }, |
| Adjustment { |
| kind: Adjust::Pointer(PointerCast::UnsafeFnPointer), |
| target: unsafe_ty, |
| }, |
| ] |
| }, |
| simple(Adjust::Pointer(PointerCast::ReifyFnPointer)), |
| )?; |
| |
| Ok(ok) |
| } |
| _ => self.unify_and(&from_ty, to_ty, identity), |
| } |
| } |
| |
| fn coerce_from_fn_pointer( |
| &mut self, |
| from_ty: Ty, |
| from_f: &FnPointer, |
| to_ty: &Ty, |
| ) -> CoerceResult { |
| self.coerce_from_safe_fn( |
| from_ty, |
| from_f, |
| to_ty, |
| simple(Adjust::Pointer(PointerCast::UnsafeFnPointer)), |
| identity, |
| ) |
| } |
| |
| fn coerce_from_safe_fn<F, G>( |
| &mut self, |
| from_ty: Ty, |
| from_fn_ptr: &FnPointer, |
| to_ty: &Ty, |
| to_unsafe: F, |
| normal: G, |
| ) -> CoerceResult |
| where |
| F: FnOnce(Ty) -> Vec<Adjustment>, |
| G: FnOnce(Ty) -> Vec<Adjustment>, |
| { |
| if let TyKind::Function(to_fn_ptr) = to_ty.kind(Interner) { |
| if let (chalk_ir::Safety::Safe, chalk_ir::Safety::Unsafe) = |
| (from_fn_ptr.sig.safety, to_fn_ptr.sig.safety) |
| { |
| let from_unsafe = |
| TyKind::Function(safe_to_unsafe_fn_ty(from_fn_ptr.clone())).intern(Interner); |
| return self.unify_and(&from_unsafe, to_ty, to_unsafe); |
| } |
| } |
| self.unify_and(&from_ty, to_ty, normal) |
| } |
| |
| /// Attempts to coerce from the type of a non-capturing closure into a |
| /// function pointer. |
| fn coerce_closure_to_fn( |
| &mut self, |
| from_ty: Ty, |
| from_substs: &Substitution, |
| to_ty: &Ty, |
| ) -> CoerceResult { |
| match to_ty.kind(Interner) { |
| // if from_substs is non-capturing (FIXME) |
| TyKind::Function(fn_ty) => { |
| // We coerce the closure, which has fn type |
| // `extern "rust-call" fn((arg0,arg1,...)) -> _` |
| // to |
| // `fn(arg0,arg1,...) -> _` |
| // or |
| // `unsafe fn(arg0,arg1,...) -> _` |
| let safety = fn_ty.sig.safety; |
| let pointer_ty = coerce_closure_fn_ty(from_substs, safety); |
| self.unify_and( |
| &pointer_ty, |
| to_ty, |
| simple(Adjust::Pointer(PointerCast::ClosureFnPointer(safety))), |
| ) |
| } |
| _ => self.unify_and(&from_ty, to_ty, identity), |
| } |
| } |
| |
| /// Coerce a type using `from_ty: CoerceUnsized<ty_ty>` |
| /// |
| /// See: <https://doc.rust-lang.org/nightly/std/marker/trait.CoerceUnsized.html> |
| fn try_coerce_unsized(&mut self, from_ty: &Ty, to_ty: &Ty) -> CoerceResult { |
| // These 'if' statements require some explanation. |
| // The `CoerceUnsized` trait is special - it is only |
| // possible to write `impl CoerceUnsized<B> for A` where |
| // A and B have 'matching' fields. This rules out the following |
| // two types of blanket impls: |
| // |
| // `impl<T> CoerceUnsized<T> for SomeType` |
| // `impl<T> CoerceUnsized<SomeType> for T` |
| // |
| // Both of these trigger a special `CoerceUnsized`-related error (E0376) |
| // |
| // We can take advantage of this fact to avoid performing unnecessary work. |
| // If either `source` or `target` is a type variable, then any applicable impl |
| // would need to be generic over the self-type (`impl<T> CoerceUnsized<SomeType> for T`) |
| // or generic over the `CoerceUnsized` type parameter (`impl<T> CoerceUnsized<T> for |
| // SomeType`). |
| // |
| // However, these are exactly the kinds of impls which are forbidden by |
| // the compiler! Therefore, we can be sure that coercion will always fail |
| // when either the source or target type is a type variable. This allows us |
| // to skip performing any trait selection, and immediately bail out. |
| if from_ty.is_ty_var() { |
| return Err(TypeError); |
| } |
| if to_ty.is_ty_var() { |
| return Err(TypeError); |
| } |
| |
| // Handle reborrows before trying to solve `Source: CoerceUnsized<Target>`. |
| let reborrow = match (from_ty.kind(Interner), to_ty.kind(Interner)) { |
| (TyKind::Ref(from_mt, _, from_inner), &TyKind::Ref(to_mt, _, _)) => { |
| coerce_mutabilities(*from_mt, to_mt)?; |
| |
| let lt = error_lifetime(); |
| Some(( |
| Adjustment { kind: Adjust::Deref(None), target: from_inner.clone() }, |
| Adjustment { |
| kind: Adjust::Borrow(AutoBorrow::Ref(to_mt)), |
| target: TyKind::Ref(to_mt, lt, from_inner.clone()).intern(Interner), |
| }, |
| )) |
| } |
| (TyKind::Ref(from_mt, _, from_inner), &TyKind::Raw(to_mt, _)) => { |
| coerce_mutabilities(*from_mt, to_mt)?; |
| |
| Some(( |
| Adjustment { kind: Adjust::Deref(None), target: from_inner.clone() }, |
| Adjustment { |
| kind: Adjust::Borrow(AutoBorrow::RawPtr(to_mt)), |
| target: TyKind::Raw(to_mt, from_inner.clone()).intern(Interner), |
| }, |
| )) |
| } |
| _ => None, |
| }; |
| let coerce_from = |
| reborrow.as_ref().map_or_else(|| from_ty.clone(), |(_, adj)| adj.target.clone()); |
| |
| let krate = self.trait_env.krate; |
| let coerce_unsized_trait = match self.db.lang_item(krate, LangItem::CoerceUnsized) { |
| Some(LangItemTarget::Trait(trait_)) => trait_, |
| _ => return Err(TypeError), |
| }; |
| |
| let coerce_unsized_tref = { |
| let b = TyBuilder::trait_ref(self.db, coerce_unsized_trait); |
| if b.remaining() != 2 { |
| // The CoerceUnsized trait should have two generic params: Self and T. |
| return Err(TypeError); |
| } |
| b.push(coerce_from).push(to_ty.clone()).build() |
| }; |
| |
| let goal: InEnvironment<DomainGoal> = |
| InEnvironment::new(&self.trait_env.env, coerce_unsized_tref.cast(Interner)); |
| |
| let canonicalized = self.canonicalize_with_free_vars(goal); |
| |
| // FIXME: rustc's coerce_unsized is more specialized -- it only tries to |
| // solve `CoerceUnsized` and `Unsize` goals at this point and leaves the |
| // rest for later. Also, there's some logic about sized type variables. |
| // Need to find out in what cases this is necessary |
| let solution = self |
| .db |
| .trait_solve(krate, self.trait_env.block, canonicalized.value.clone().cast(Interner)) |
| .ok_or(TypeError)?; |
| |
| match solution { |
| Solution::Unique(v) => { |
| canonicalized.apply_solution( |
| self, |
| Canonical { |
| binders: v.binders, |
| // FIXME handle constraints |
| value: v.value.subst, |
| }, |
| ); |
| } |
| Solution::Ambig(Guidance::Definite(subst)) => { |
| // FIXME need to record an obligation here |
| canonicalized.apply_solution(self, subst) |
| } |
| // FIXME actually we maybe should also accept unknown guidance here |
| _ => return Err(TypeError), |
| }; |
| let unsize = |
| Adjustment { kind: Adjust::Pointer(PointerCast::Unsize), target: to_ty.clone() }; |
| let adjustments = match reborrow { |
| None => vec![unsize], |
| Some((deref, autoref)) => vec![deref, autoref, unsize], |
| }; |
| success(adjustments, to_ty.clone(), vec![]) |
| } |
| } |
| |
| fn coerce_closure_fn_ty(closure_substs: &Substitution, safety: chalk_ir::Safety) -> Ty { |
| let closure_sig = ClosureSubst(closure_substs).sig_ty().clone(); |
| match closure_sig.kind(Interner) { |
| TyKind::Function(fn_ty) => TyKind::Function(FnPointer { |
| num_binders: fn_ty.num_binders, |
| sig: FnSig { safety, abi: FnAbi::Rust, variadic: fn_ty.sig.variadic }, |
| substitution: fn_ty.substitution.clone(), |
| }) |
| .intern(Interner), |
| _ => TyKind::Error.intern(Interner), |
| } |
| } |
| |
| fn safe_to_unsafe_fn_ty(fn_ty: FnPointer) -> FnPointer { |
| FnPointer { |
| num_binders: fn_ty.num_binders, |
| sig: FnSig { safety: chalk_ir::Safety::Unsafe, ..fn_ty.sig }, |
| substitution: fn_ty.substitution, |
| } |
| } |
| |
| fn coerce_mutabilities(from: Mutability, to: Mutability) -> Result<(), TypeError> { |
| match (from, to) { |
| (Mutability::Mut, Mutability::Mut | Mutability::Not) |
| | (Mutability::Not, Mutability::Not) => Ok(()), |
| (Mutability::Not, Mutability::Mut) => Err(TypeError), |
| } |
| } |
| |
| pub(super) fn auto_deref_adjust_steps(autoderef: &Autoderef<'_, '_>) -> Vec<Adjustment> { |
| let steps = autoderef.steps(); |
| let targets = |
| steps.iter().skip(1).map(|(_, ty)| ty.clone()).chain(iter::once(autoderef.final_ty())); |
| steps |
| .iter() |
| .map(|(kind, _source)| match kind { |
| // We do not know what kind of deref we require at this point yet |
| AutoderefKind::Overloaded => Some(OverloadedDeref(None)), |
| AutoderefKind::Builtin => None, |
| }) |
| .zip(targets) |
| .map(|(autoderef, target)| Adjustment { kind: Adjust::Deref(autoderef), target }) |
| .collect() |
| } |
