| //! # Type Coercion |
| //! |
| //! Under certain circumstances we will coerce from one type to another, |
| //! for example by auto-borrowing. This occurs in situations where the |
| //! compiler has a firm 'expected type' that was supplied from the user, |
| //! and where the actual type is similar to that expected type in purpose |
| //! but not in representation (so actual subtyping is inappropriate). |
| //! |
| //! ## Reborrowing |
| //! |
| //! Note that if we are expecting a reference, we will *reborrow* |
| //! even if the argument provided was already a reference. This is |
| //! useful for freezing mut/const things (that is, when the expected is &T |
| //! but you have &const T or &mut T) and also for avoiding the linearity |
| //! of mut things (when the expected is &mut T and you have &mut T). See |
| //! the various `src/test/ui/coerce-reborrow-*.rs` tests for |
| //! examples of where this is useful. |
| //! |
| //! ## Subtle note |
| //! |
| //! When deciding what type coercions to consider, we do not attempt to |
| //! resolve any type variables we may encounter. This is because `b` |
| //! represents the expected type "as the user wrote it", meaning that if |
| //! the user defined a generic function like |
| //! |
| //! fn foo<A>(a: A, b: A) { ... } |
| //! |
| //! and then we wrote `foo(&1, @2)`, we will not auto-borrow |
| //! either argument. In older code we went to some lengths to |
| //! resolve the `b` variable, which could mean that we'd |
| //! auto-borrow later arguments but not earlier ones, which |
| //! seems very confusing. |
| //! |
| //! ## Subtler note |
| //! |
| //! However, right now, if the user manually specifies the |
| //! values for the type variables, as so: |
| //! |
| //! foo::<&int>(@1, @2) |
| //! |
| //! then we *will* auto-borrow, because we can't distinguish this from a |
| //! function that declared `&int`. This is inconsistent but it's easiest |
| //! at the moment. The right thing to do, I think, is to consider the |
| //! *unsubstituted* type when deciding whether to auto-borrow, but the |
| //! *substituted* type when considering the bounds and so forth. But most |
| //! of our methods don't give access to the unsubstituted type, and |
| //! rightly so because they'd be error-prone. So maybe the thing to do is |
| //! to actually determine the kind of coercions that should occur |
| //! separately and pass them in. Or maybe it's ok as is. Anyway, it's |
| //! sort of a minor point so I've opted to leave it for later -- after all, |
| //! we may want to adjust precisely when coercions occur. |
| |
| use crate::check::{FnCtxt, Needs}; |
| use errors::DiagnosticBuilder; |
| use rustc::hir; |
| use rustc::hir::def_id::DefId; |
| use rustc::hir::ptr::P; |
| use rustc::infer::{Coercion, InferResult, InferOk}; |
| use rustc::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind}; |
| use rustc::traits::{self, ObligationCause, ObligationCauseCode}; |
| use rustc::ty::adjustment::{ |
| Adjustment, Adjust, AllowTwoPhase, AutoBorrow, AutoBorrowMutability, PointerCast |
| }; |
| use rustc::ty::{self, TypeAndMut, Ty}; |
| use rustc::ty::fold::TypeFoldable; |
| use rustc::ty::error::TypeError; |
| use rustc::ty::relate::RelateResult; |
| use rustc::ty::subst::SubstsRef; |
| use smallvec::{smallvec, SmallVec}; |
| use std::ops::Deref; |
| use syntax::feature_gate; |
| use syntax::symbol::sym; |
| use syntax_pos; |
| use rustc_target::spec::abi::Abi; |
| |
| use rustc_error_codes::*; |
| |
| struct Coerce<'a, 'tcx> { |
| fcx: &'a FnCtxt<'a, 'tcx>, |
| cause: ObligationCause<'tcx>, |
| use_lub: bool, |
| /// Determines whether or not allow_two_phase_borrow is set on any |
| /// autoref adjustments we create while coercing. We don't want to |
| /// allow deref coercions to create two-phase borrows, at least initially, |
| /// but we do need two-phase borrows for function argument reborrows. |
| /// See #47489 and #48598 |
| /// See docs on the "AllowTwoPhase" type for a more detailed discussion |
| allow_two_phase: AllowTwoPhase, |
| } |
| |
| impl<'a, 'tcx> Deref for Coerce<'a, 'tcx> { |
| type Target = FnCtxt<'a, 'tcx>; |
| fn deref(&self) -> &Self::Target { |
| &self.fcx |
| } |
| } |
| |
| type CoerceResult<'tcx> = InferResult<'tcx, (Vec<Adjustment<'tcx>>, Ty<'tcx>)>; |
| |
| fn coerce_mutbls<'tcx>(from_mutbl: hir::Mutability, |
| to_mutbl: hir::Mutability) |
| -> RelateResult<'tcx, ()> { |
| match (from_mutbl, to_mutbl) { |
| (hir::Mutability::Mutable, hir::Mutability::Mutable) | |
| (hir::Mutability::Immutable, hir::Mutability::Immutable) | |
| (hir::Mutability::Mutable, hir::Mutability::Immutable) => Ok(()), |
| (hir::Mutability::Immutable, hir::Mutability::Mutable) => Err(TypeError::Mutability), |
| } |
| } |
| |
| fn identity(_: Ty<'_>) -> Vec<Adjustment<'_>> { vec![] } |
| |
| fn simple<'tcx>(kind: Adjust<'tcx>) -> impl FnOnce(Ty<'tcx>) -> Vec<Adjustment<'tcx>> { |
| move |target| vec![Adjustment { kind, target }] |
| } |
| |
| fn success<'tcx>(adj: Vec<Adjustment<'tcx>>, |
| target: Ty<'tcx>, |
| obligations: traits::PredicateObligations<'tcx>) |
| -> CoerceResult<'tcx> { |
| Ok(InferOk { |
| value: (adj, target), |
| obligations |
| }) |
| } |
| |
| impl<'f, 'tcx> Coerce<'f, 'tcx> { |
| fn new( |
| fcx: &'f FnCtxt<'f, 'tcx>, |
| cause: ObligationCause<'tcx>, |
| allow_two_phase: AllowTwoPhase, |
| ) -> Self { |
| Coerce { |
| fcx, |
| cause, |
| allow_two_phase, |
| use_lub: false, |
| } |
| } |
| |
| fn unify(&self, a: Ty<'tcx>, b: Ty<'tcx>) -> InferResult<'tcx, Ty<'tcx>> { |
| self.commit_if_ok(|_| { |
| if self.use_lub { |
| self.at(&self.cause, self.fcx.param_env).lub(b, a) |
| } else { |
| self.at(&self.cause, self.fcx.param_env) |
| .sup(b, a) |
| .map(|InferOk { value: (), obligations }| InferOk { value: a, obligations }) |
| } |
| }) |
| } |
| |
| /// Unify two types (using sub or lub) and produce a specific coercion. |
| fn unify_and<F>(&self, a: Ty<'tcx>, b: Ty<'tcx>, f: F) |
| -> CoerceResult<'tcx> |
| where F: FnOnce(Ty<'tcx>) -> Vec<Adjustment<'tcx>> |
| { |
| self.unify(&a, &b).and_then(|InferOk { value: ty, obligations }| { |
| success(f(ty), ty, obligations) |
| }) |
| } |
| |
| fn coerce(&self, a: Ty<'tcx>, b: Ty<'tcx>) -> CoerceResult<'tcx> { |
| let a = self.shallow_resolve(a); |
| debug!("Coerce.tys({:?} => {:?})", a, b); |
| |
| // Just ignore error types. |
| if a.references_error() || b.references_error() { |
| return success(vec![], self.fcx.tcx.types.err, vec![]); |
| } |
| |
| if a.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`. |
| let b = self.shallow_resolve(b); |
| return if self.shallow_resolve(b).is_ty_var() { |
| // Micro-optimization: no need for this if `b` is |
| // already resolved in some way. |
| let diverging_ty = self.next_diverging_ty_var( |
| TypeVariableOrigin { |
| kind: TypeVariableOriginKind::AdjustmentType, |
| span: self.cause.span, |
| }, |
| ); |
| self.unify_and(&b, &diverging_ty, simple(Adjust::NeverToAny)) |
| } else { |
| success(simple(Adjust::NeverToAny)(b), b, vec![]) |
| }; |
| } |
| |
| // Consider coercing the subtype to a DST |
| // |
| // NOTE: this is wrapped in a `commit_if_ok` because it creates |
| // a "spurious" type variable, and we don't want to have that |
| // type variable in memory if the coercion fails. |
| let unsize = self.commit_if_ok(|_| self.coerce_unsized(a, b)); |
| match unsize { |
| Ok(_) => { |
| debug!("coerce: unsize successful"); |
| return unsize; |
| } |
| Err(TypeError::ObjectUnsafeCoercion(did)) => { |
| debug!("coerce: unsize not object safe"); |
| return Err(TypeError::ObjectUnsafeCoercion(did)); |
| } |
| Err(_) => {} |
| } |
| debug!("coerce: unsize failed"); |
| |
| // Examine the supertype and consider auto-borrowing. |
| // |
| // Note: does not attempt to resolve type variables we encounter. |
| // See above for details. |
| match b.kind { |
| ty::RawPtr(mt_b) => { |
| return self.coerce_unsafe_ptr(a, b, mt_b.mutbl); |
| } |
| |
| ty::Ref(r_b, ty, mutbl) => { |
| let mt_b = ty::TypeAndMut { ty, mutbl }; |
| return self.coerce_borrowed_pointer(a, b, r_b, mt_b); |
| } |
| |
| _ => {} |
| } |
| |
| match a.kind { |
| ty::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(a, b) |
| } |
| ty::FnPtr(a_f) => { |
| // We permit coercion of fn pointers to drop the |
| // unsafe qualifier. |
| self.coerce_from_fn_pointer(a, a_f, b) |
| } |
| ty::Closure(def_id_a, substs_a) => { |
| // Non-capturing closures are coercible to |
| // function pointers or unsafe function pointers. |
| // It cannot convert closures that require unsafe. |
| self.coerce_closure_to_fn(a, def_id_a, substs_a, b) |
| } |
| _ => { |
| // Otherwise, just use unification rules. |
| self.unify_and(a, b, 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_borrowed_pointer(&self, |
| a: Ty<'tcx>, |
| b: Ty<'tcx>, |
| r_b: ty::Region<'tcx>, |
| mt_b: TypeAndMut<'tcx>) |
| -> CoerceResult<'tcx> |
| { |
| debug!("coerce_borrowed_pointer(a={:?}, b={:?})", a, b); |
| |
| // If we have a parameter of type `&M T_a` and the value |
| // provided is `expr`, we will be adding an implicit borrow, |
| // meaning that we convert `f(expr)` to `f(&M *expr)`. Therefore, |
| // to type check, we will construct the type that `&M*expr` would |
| // yield. |
| |
| let (r_a, mt_a) = match a.kind { |
| ty::Ref(r_a, ty, mutbl) => { |
| let mt_a = ty::TypeAndMut { ty, mutbl }; |
| coerce_mutbls(mt_a.mutbl, mt_b.mutbl)?; |
| (r_a, mt_a) |
| } |
| _ => return self.unify_and(a, b, identity), |
| }; |
| |
| let span = self.cause.span; |
| |
| let mut first_error = None; |
| let mut r_borrow_var = None; |
| let mut autoderef = self.autoderef(span, a); |
| let mut found = None; |
| |
| for (referent_ty, autoderefs) in autoderef.by_ref() { |
| 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`. |
| // |
| // One fine point concerns the region that we use. We |
| // choose the region such that the region of the final |
| // type that results from `unify` will be the region we |
| // want for the autoref: |
| // |
| // - if in sub mode, that means we want to use `'b` (the |
| // region from the target reference) for both |
| // pointers [2]. This is because sub mode (somewhat |
| // arbitrarily) returns the subtype region. In the case |
| // where we are coercing to a target type, we know we |
| // want to use that target type region (`'b`) because -- |
| // for the program to type-check -- it must be the |
| // smaller of the two. |
| // - One fine point. It may be surprising that we can |
| // use `'b` without relating `'a` and `'b`. The reason |
| // that this is ok is that what we produce is |
| // effectively a `&'b *x` expression (if you could |
| // annotate the region of a borrow), and regionck has |
| // code that adds edges from the region of a borrow |
| // (`'b`, here) into the regions in the borrowed |
| // expression (`*x`, here). (Search for "link".) |
| // - if in lub mode, things can get fairly complicated. The |
| // easiest thing is just to make a fresh |
| // region variable [4], which effectively means we defer |
| // the decision to region inference (and regionck, which will add |
| // some more edges to this variable). However, this can wind up |
| // creating a crippling number of variables in some cases -- |
| // e.g., #32278 -- so we optimize one particular case [3]. |
| // Let me try to explain with some examples: |
| // - The "running example" above represents the simple case, |
| // where we have one `&` reference at the outer level and |
| // ownership all the rest of the way down. In this case, |
| // we want `LUB('a, 'b)` as the resulting region. |
| // - However, if there are nested borrows, that region is |
| // too strong. Consider a coercion from `&'a &'x Rc<T>` to |
| // `&'b T`. In this case, `'a` is actually irrelevant. |
| // The pointer we want is `LUB('x, 'b`). If we choose `LUB('a,'b)` |
| // we get spurious errors (`ui/regions-lub-ref-ref-rc.rs`). |
| // (The errors actually show up in borrowck, typically, because |
| // this extra edge causes the region `'a` to be inferred to something |
| // too big, which then results in borrowck errors.) |
| // - We could track the innermost shared reference, but there is already |
| // code in regionck that has the job of creating links between |
| // the region of a borrow and the regions in the thing being |
| // borrowed (here, `'a` and `'x`), and it knows how to handle |
| // all the various cases. So instead we just make a region variable |
| // and let regionck figure it out. |
| let r = if !self.use_lub { |
| r_b // [2] above |
| } else if autoderefs == 1 { |
| r_a // [3] above |
| } else { |
| if r_borrow_var.is_none() { |
| // create var lazilly, at most once |
| let coercion = Coercion(span); |
| let r = self.next_region_var(coercion); |
| r_borrow_var = Some(r); // [4] above |
| } |
| r_borrow_var.unwrap() |
| }; |
| let derefd_ty_a = self.tcx.mk_ref(r, |
| TypeAndMut { |
| ty: referent_ty, |
| mutbl: mt_b.mutbl, // [1] above |
| }); |
| match self.unify(derefd_ty_a, b) { |
| Ok(ok) => { |
| found = Some(ok); |
| 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, mut obligations } = match found { |
| Some(d) => d, |
| None => { |
| let err = first_error.expect("coerce_borrowed_pointer had no error"); |
| debug!("coerce_borrowed_pointer: failed with err = {:?}", err); |
| return Err(err); |
| } |
| }; |
| |
| if ty == a && mt_a.mutbl == hir::Mutability::Immutable && 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. |
| assert_eq!(mt_b.mutbl, hir::Mutability::Immutable); // can only coerce &T -> &U |
| return success(vec![], ty, obligations); |
| } |
| |
| let needs = Needs::maybe_mut_place(mt_b.mutbl); |
| let InferOk { value: mut adjustments, obligations: o } |
| = autoderef.adjust_steps_as_infer_ok(self, needs); |
| obligations.extend(o); |
| obligations.extend(autoderef.into_obligations()); |
| |
| // Now apply the autoref. We have to extract the region out of |
| // the final ref type we got. |
| let r_borrow = match ty.kind { |
| ty::Ref(r_borrow, _, _) => r_borrow, |
| _ => span_bug!(span, "expected a ref type, got {:?}", ty), |
| }; |
| let mutbl = match mt_b.mutbl { |
| hir::Mutability::Immutable => AutoBorrowMutability::Immutable, |
| hir::Mutability::Mutable => AutoBorrowMutability::Mutable { |
| allow_two_phase_borrow: self.allow_two_phase, |
| } |
| }; |
| adjustments.push(Adjustment { |
| kind: Adjust::Borrow(AutoBorrow::Ref(r_borrow, mutbl)), |
| target: ty |
| }); |
| |
| debug!("coerce_borrowed_pointer: succeeded ty={:?} adjustments={:?}", |
| ty, |
| adjustments); |
| |
| success(adjustments, ty, obligations) |
| } |
| |
| |
| // &[T; n] or &mut [T; n] -> &[T] |
| // or &mut [T; n] -> &mut [T] |
| // or &Concrete -> &Trait, etc. |
| fn coerce_unsized(&self, source: Ty<'tcx>, target: Ty<'tcx>) -> CoerceResult<'tcx> { |
| debug!("coerce_unsized(source={:?}, target={:?})", source, target); |
| |
| let traits = (self.tcx.lang_items().unsize_trait(), |
| self.tcx.lang_items().coerce_unsized_trait()); |
| let (unsize_did, coerce_unsized_did) = if let (Some(u), Some(cu)) = traits { |
| (u, cu) |
| } else { |
| debug!("missing Unsize or CoerceUnsized traits"); |
| return Err(TypeError::Mismatch); |
| }; |
| |
| // Note, we want to avoid unnecessary unsizing. We don't want to coerce to |
| // a DST unless we have to. This currently comes out in the wash since |
| // we can't unify [T] with U. But to properly support DST, we need to allow |
| // that, at which point we will need extra checks on the target here. |
| |
| // Handle reborrows before selecting `Source: CoerceUnsized<Target>`. |
| let reborrow = match (&source.kind, &target.kind) { |
| (&ty::Ref(_, ty_a, mutbl_a), &ty::Ref(_, _, mutbl_b)) => { |
| coerce_mutbls(mutbl_a, mutbl_b)?; |
| |
| let coercion = Coercion(self.cause.span); |
| let r_borrow = self.next_region_var(coercion); |
| let mutbl = match mutbl_b { |
| hir::Mutability::Immutable => AutoBorrowMutability::Immutable, |
| hir::Mutability::Mutable => AutoBorrowMutability::Mutable { |
| // We don't allow two-phase borrows here, at least for initial |
| // implementation. If it happens that this coercion is a function argument, |
| // the reborrow in coerce_borrowed_ptr will pick it up. |
| allow_two_phase_borrow: AllowTwoPhase::No, |
| } |
| }; |
| Some((Adjustment { |
| kind: Adjust::Deref(None), |
| target: ty_a |
| }, Adjustment { |
| kind: Adjust::Borrow(AutoBorrow::Ref(r_borrow, mutbl)), |
| target: self.tcx.mk_ref(r_borrow, ty::TypeAndMut { |
| mutbl: mutbl_b, |
| ty: ty_a |
| }) |
| })) |
| } |
| (&ty::Ref(_, ty_a, mt_a), &ty::RawPtr(ty::TypeAndMut { mutbl: mt_b, .. })) => { |
| coerce_mutbls(mt_a, mt_b)?; |
| |
| Some((Adjustment { |
| kind: Adjust::Deref(None), |
| target: ty_a |
| }, Adjustment { |
| kind: Adjust::Borrow(AutoBorrow::RawPtr(mt_b)), |
| target: self.tcx.mk_ptr(ty::TypeAndMut { |
| mutbl: mt_b, |
| ty: ty_a |
| }) |
| })) |
| } |
| _ => None, |
| }; |
| let coerce_source = reborrow.as_ref().map_or(source, |&(_, ref r)| r.target); |
| |
| // Setup either a subtyping or a LUB relationship between |
| // the `CoerceUnsized` target type and the expected type. |
| // We only have the latter, so we use an inference variable |
| // for the former and let type inference do the rest. |
| let origin = TypeVariableOrigin { |
| kind: TypeVariableOriginKind::MiscVariable, |
| span: self.cause.span, |
| }; |
| let coerce_target = self.next_ty_var(origin); |
| let mut coercion = self.unify_and(coerce_target, target, |target| { |
| let unsize = Adjustment { |
| kind: Adjust::Pointer(PointerCast::Unsize), |
| target |
| }; |
| match reborrow { |
| None => vec![unsize], |
| Some((ref deref, ref autoref)) => { |
| vec![deref.clone(), autoref.clone(), unsize] |
| } |
| } |
| })?; |
| |
| let mut selcx = traits::SelectionContext::new(self); |
| |
| // Create an obligation for `Source: CoerceUnsized<Target>`. |
| let cause = ObligationCause::new( |
| self.cause.span, |
| self.body_id, |
| ObligationCauseCode::Coercion { source, target }, |
| ); |
| |
| // Use a FIFO queue for this custom fulfillment procedure. |
| // |
| // A Vec (or SmallVec) is not a natural choice for a queue. However, |
| // this code path is hot, and this queue usually has a max length of 1 |
| // and almost never more than 3. By using a SmallVec we avoid an |
| // allocation, at the (very small) cost of (occasionally) having to |
| // shift subsequent elements down when removing the front element. |
| let mut queue: SmallVec<[_; 4]> = |
| smallvec![self.tcx.predicate_for_trait_def(self.fcx.param_env, |
| cause, |
| coerce_unsized_did, |
| 0, |
| coerce_source, |
| &[coerce_target.into()])]; |
| |
| let mut has_unsized_tuple_coercion = false; |
| |
| // Keep resolving `CoerceUnsized` and `Unsize` predicates to avoid |
| // emitting a coercion in cases like `Foo<$1>` -> `Foo<$2>`, where |
| // inference might unify those two inner type variables later. |
| let traits = [coerce_unsized_did, unsize_did]; |
| while !queue.is_empty() { |
| let obligation = queue.remove(0); |
| debug!("coerce_unsized resolve step: {:?}", obligation); |
| let trait_ref = match obligation.predicate { |
| ty::Predicate::Trait(ref tr) if traits.contains(&tr.def_id()) => { |
| if unsize_did == tr.def_id() { |
| let sty = &tr.skip_binder().input_types().nth(1).unwrap().kind; |
| if let ty::Tuple(..) = sty { |
| debug!("coerce_unsized: found unsized tuple coercion"); |
| has_unsized_tuple_coercion = true; |
| } |
| } |
| tr.clone() |
| } |
| _ => { |
| coercion.obligations.push(obligation); |
| continue; |
| } |
| }; |
| match selcx.select(&obligation.with(trait_ref)) { |
| // Uncertain or unimplemented. |
| Ok(None) => { |
| if trait_ref.def_id() == unsize_did { |
| let trait_ref = self.resolve_vars_if_possible(&trait_ref); |
| let self_ty = trait_ref.skip_binder().self_ty(); |
| let unsize_ty = trait_ref.skip_binder().input_types().nth(1).unwrap(); |
| debug!("coerce_unsized: ambiguous unsize case for {:?}", trait_ref); |
| match (&self_ty.kind, &unsize_ty.kind) { |
| (ty::Infer(ty::TyVar(v)), |
| ty::Dynamic(..)) if self.type_var_is_sized(*v) => { |
| debug!("coerce_unsized: have sized infer {:?}", v); |
| coercion.obligations.push(obligation); |
| // `$0: Unsize<dyn Trait>` where we know that `$0: Sized`, try going |
| // for unsizing. |
| } |
| _ => { |
| // Some other case for `$0: Unsize<Something>`. Note that we |
| // hit this case even if `Something` is a sized type, so just |
| // don't do the coercion. |
| debug!("coerce_unsized: ambiguous unsize"); |
| return Err(TypeError::Mismatch); |
| } |
| } |
| } else { |
| debug!("coerce_unsized: early return - ambiguous"); |
| return Err(TypeError::Mismatch); |
| } |
| } |
| Err(traits::Unimplemented) => { |
| debug!("coerce_unsized: early return - can't prove obligation"); |
| return Err(TypeError::Mismatch); |
| } |
| |
| // Object safety violations or miscellaneous. |
| Err(err) => { |
| self.report_selection_error(&obligation, &err, false, false); |
| // Treat this like an obligation and follow through |
| // with the unsizing - the lack of a coercion should |
| // be silent, as it causes a type mismatch later. |
| } |
| |
| Ok(Some(vtable)) => { |
| queue.extend(vtable.nested_obligations()) |
| } |
| } |
| } |
| |
| if has_unsized_tuple_coercion && !self.tcx.features().unsized_tuple_coercion { |
| feature_gate::feature_err( |
| &self.tcx.sess.parse_sess, |
| sym::unsized_tuple_coercion, |
| self.cause.span, |
| "unsized tuple coercion is not stable enough for use and is subject to change", |
| ) |
| .emit(); |
| } |
| |
| Ok(coercion) |
| } |
| |
| fn coerce_from_safe_fn<F, G>(&self, |
| a: Ty<'tcx>, |
| fn_ty_a: ty::PolyFnSig<'tcx>, |
| b: Ty<'tcx>, |
| to_unsafe: F, |
| normal: G) |
| -> CoerceResult<'tcx> |
| where F: FnOnce(Ty<'tcx>) -> Vec<Adjustment<'tcx>>, |
| G: FnOnce(Ty<'tcx>) -> Vec<Adjustment<'tcx>> |
| { |
| if let ty::FnPtr(fn_ty_b) = b.kind { |
| if let (hir::Unsafety::Normal, hir::Unsafety::Unsafe) |
| = (fn_ty_a.unsafety(), fn_ty_b.unsafety()) |
| { |
| let unsafe_a = self.tcx.safe_to_unsafe_fn_ty(fn_ty_a); |
| return self.unify_and(unsafe_a, b, to_unsafe); |
| } |
| } |
| self.unify_and(a, b, normal) |
| } |
| |
| fn coerce_from_fn_pointer(&self, |
| a: Ty<'tcx>, |
| fn_ty_a: ty::PolyFnSig<'tcx>, |
| b: Ty<'tcx>) |
| -> CoerceResult<'tcx> { |
| //! Attempts to coerce from the type of a Rust function item |
| //! into a closure or a `proc`. |
| //! |
| |
| let b = self.shallow_resolve(b); |
| debug!("coerce_from_fn_pointer(a={:?}, b={:?})", a, b); |
| |
| self.coerce_from_safe_fn(a, fn_ty_a, b, |
| simple(Adjust::Pointer(PointerCast::UnsafeFnPointer)), identity) |
| } |
| |
| fn coerce_from_fn_item(&self, |
| a: Ty<'tcx>, |
| b: Ty<'tcx>) |
| -> CoerceResult<'tcx> { |
| //! Attempts to coerce from the type of a Rust function item |
| //! into a closure or a `proc`. |
| |
| let b = self.shallow_resolve(b); |
| debug!("coerce_from_fn_item(a={:?}, b={:?})", a, b); |
| |
| match b.kind { |
| ty::FnPtr(_) => { |
| let a_sig = a.fn_sig(self.tcx); |
| // Intrinsics are not coercible to function pointers |
| if a_sig.abi() == Abi::RustIntrinsic || |
| a_sig.abi() == Abi::PlatformIntrinsic { |
| return Err(TypeError::IntrinsicCast); |
| } |
| let InferOk { value: a_sig, mut obligations } = |
| self.normalize_associated_types_in_as_infer_ok(self.cause.span, &a_sig); |
| |
| let a_fn_pointer = self.tcx.mk_fn_ptr(a_sig); |
| let InferOk { value, obligations: o2 } = self.coerce_from_safe_fn( |
| a_fn_pointer, |
| a_sig, |
| b, |
| |unsafe_ty| { |
| vec![ |
| Adjustment { |
| kind: Adjust::Pointer(PointerCast::ReifyFnPointer), |
| target: a_fn_pointer |
| }, |
| Adjustment { |
| kind: Adjust::Pointer(PointerCast::UnsafeFnPointer), |
| target: unsafe_ty |
| }, |
| ] |
| }, |
| simple(Adjust::Pointer(PointerCast::ReifyFnPointer)) |
| )?; |
| |
| obligations.extend(o2); |
| Ok(InferOk { value, obligations }) |
| } |
| _ => self.unify_and(a, b, identity), |
| } |
| } |
| |
| fn coerce_closure_to_fn(&self, |
| a: Ty<'tcx>, |
| def_id_a: DefId, |
| substs_a: SubstsRef<'tcx>, |
| b: Ty<'tcx>) |
| -> CoerceResult<'tcx> { |
| //! Attempts to coerce from the type of a non-capturing closure |
| //! into a function pointer. |
| //! |
| |
| let b = self.shallow_resolve(b); |
| |
| match b.kind { |
| ty::FnPtr(fn_ty) if self.tcx.upvars(def_id_a).map_or(true, |v| v.is_empty()) => { |
| // We coerce the closure, which has fn type |
| // `extern "rust-call" fn((arg0,arg1,...)) -> _` |
| // to |
| // `fn(arg0,arg1,...) -> _` |
| // or |
| // `unsafe fn(arg0,arg1,...) -> _` |
| let sig = self.closure_sig(def_id_a, substs_a); |
| let unsafety = fn_ty.unsafety(); |
| let pointer_ty = self.tcx.coerce_closure_fn_ty(sig, unsafety); |
| debug!("coerce_closure_to_fn(a={:?}, b={:?}, pty={:?})", |
| a, b, pointer_ty); |
| self.unify_and(pointer_ty, b, simple( |
| Adjust::Pointer(PointerCast::ClosureFnPointer(unsafety)) |
| )) |
| } |
| _ => self.unify_and(a, b, identity), |
| } |
| } |
| |
| fn coerce_unsafe_ptr(&self, |
| a: Ty<'tcx>, |
| b: Ty<'tcx>, |
| mutbl_b: hir::Mutability) |
| -> CoerceResult<'tcx> { |
| debug!("coerce_unsafe_ptr(a={:?}, b={:?})", a, b); |
| |
| let (is_ref, mt_a) = match a.kind { |
| ty::Ref(_, ty, mutbl) => (true, ty::TypeAndMut { ty, mutbl }), |
| ty::RawPtr(mt) => (false, mt), |
| _ => return self.unify_and(a, b, identity) |
| }; |
| |
| // Check that the types which they point at are compatible. |
| let a_unsafe = self.tcx.mk_ptr(ty::TypeAndMut { |
| mutbl: mutbl_b, |
| ty: mt_a.ty, |
| }); |
| coerce_mutbls(mt_a.mutbl, mutbl_b)?; |
| // 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(a_unsafe, b, |target| { |
| vec![Adjustment { |
| kind: Adjust::Deref(None), |
| target: mt_a.ty |
| }, Adjustment { |
| kind: Adjust::Borrow(AutoBorrow::RawPtr(mutbl_b)), |
| target |
| }] |
| }) |
| } else if mt_a.mutbl != mutbl_b { |
| self.unify_and( |
| a_unsafe, b, simple(Adjust::Pointer(PointerCast::MutToConstPointer)) |
| ) |
| } else { |
| self.unify_and(a_unsafe, b, identity) |
| } |
| } |
| } |
| |
| impl<'a, 'tcx> FnCtxt<'a, 'tcx> { |
| /// Attempt to coerce an expression to a type, and return the |
| /// adjusted type of the expression, if successful. |
| /// Adjustments are only recorded if the coercion succeeded. |
| /// The expressions *must not* have any pre-existing adjustments. |
| pub fn try_coerce( |
| &self, |
| expr: &hir::Expr, |
| expr_ty: Ty<'tcx>, |
| target: Ty<'tcx>, |
| allow_two_phase: AllowTwoPhase, |
| ) -> RelateResult<'tcx, Ty<'tcx>> { |
| let source = self.resolve_vars_with_obligations(expr_ty); |
| debug!("coercion::try({:?}: {:?} -> {:?})", expr, source, target); |
| |
| let cause = self.cause(expr.span, ObligationCauseCode::ExprAssignable); |
| let coerce = Coerce::new(self, cause, allow_two_phase); |
| let ok = self.commit_if_ok(|_| coerce.coerce(source, target))?; |
| |
| let (adjustments, _) = self.register_infer_ok_obligations(ok); |
| self.apply_adjustments(expr, adjustments); |
| Ok(if expr_ty.references_error() { |
| self.tcx.types.err |
| } else { |
| target |
| }) |
| } |
| |
| /// Same as `try_coerce()`, but without side-effects. |
| pub fn can_coerce(&self, expr_ty: Ty<'tcx>, target: Ty<'tcx>) -> bool { |
| let source = self.resolve_vars_with_obligations(expr_ty); |
| debug!("coercion::can({:?} -> {:?})", source, target); |
| |
| let cause = self.cause(syntax_pos::DUMMY_SP, ObligationCauseCode::ExprAssignable); |
| // We don't ever need two-phase here since we throw out the result of the coercion |
| let coerce = Coerce::new(self, cause, AllowTwoPhase::No); |
| self.probe(|_| coerce.coerce(source, target)).is_ok() |
| } |
| |
| /// Given some expressions, their known unified type and another expression, |
| /// tries to unify the types, potentially inserting coercions on any of the |
| /// provided expressions and returns their LUB (aka "common supertype"). |
| /// |
| /// This is really an internal helper. From outside the coercion |
| /// module, you should instantiate a `CoerceMany` instance. |
| fn try_find_coercion_lub<E>(&self, |
| cause: &ObligationCause<'tcx>, |
| exprs: &[E], |
| prev_ty: Ty<'tcx>, |
| new: &hir::Expr, |
| new_ty: Ty<'tcx>) |
| -> RelateResult<'tcx, Ty<'tcx>> |
| where E: AsCoercionSite |
| { |
| let prev_ty = self.resolve_vars_with_obligations(prev_ty); |
| let new_ty = self.resolve_vars_with_obligations(new_ty); |
| debug!("coercion::try_find_coercion_lub({:?}, {:?})", prev_ty, new_ty); |
| |
| // Special-case that coercion alone cannot handle: |
| // Two function item types of differing IDs or InternalSubsts. |
| if let (&ty::FnDef(..), &ty::FnDef(..)) = (&prev_ty.kind, &new_ty.kind) { |
| // Don't reify if the function types have a LUB, i.e., they |
| // are the same function and their parameters have a LUB. |
| let lub_ty = self.commit_if_ok(|_| { |
| self.at(cause, self.param_env) |
| .lub(prev_ty, new_ty) |
| }).map(|ok| self.register_infer_ok_obligations(ok)); |
| |
| if lub_ty.is_ok() { |
| // We have a LUB of prev_ty and new_ty, just return it. |
| return lub_ty; |
| } |
| |
| // The signature must match. |
| let a_sig = prev_ty.fn_sig(self.tcx); |
| let a_sig = self.normalize_associated_types_in(new.span, &a_sig); |
| let b_sig = new_ty.fn_sig(self.tcx); |
| let b_sig = self.normalize_associated_types_in(new.span, &b_sig); |
| let sig = self.at(cause, self.param_env) |
| .trace(prev_ty, new_ty) |
| .lub(&a_sig, &b_sig) |
| .map(|ok| self.register_infer_ok_obligations(ok))?; |
| |
| // Reify both sides and return the reified fn pointer type. |
| let fn_ptr = self.tcx.mk_fn_ptr(sig); |
| for expr in exprs.iter().map(|e| e.as_coercion_site()).chain(Some(new)) { |
| // The only adjustment that can produce an fn item is |
| // `NeverToAny`, so this should always be valid. |
| self.apply_adjustments(expr, vec![Adjustment { |
| kind: Adjust::Pointer(PointerCast::ReifyFnPointer), |
| target: fn_ptr |
| }]); |
| } |
| return Ok(fn_ptr); |
| } |
| |
| // Configure a Coerce instance to compute the LUB. |
| // We don't allow two-phase borrows on any autorefs this creates since we |
| // probably aren't processing function arguments here and even if we were, |
| // they're going to get autorefed again anyway and we can apply 2-phase borrows |
| // at that time. |
| let mut coerce = Coerce::new(self, cause.clone(), AllowTwoPhase::No); |
| coerce.use_lub = true; |
| |
| // First try to coerce the new expression to the type of the previous ones, |
| // but only if the new expression has no coercion already applied to it. |
| let mut first_error = None; |
| if !self.tables.borrow().adjustments().contains_key(new.hir_id) { |
| let result = self.commit_if_ok(|_| coerce.coerce(new_ty, prev_ty)); |
| match result { |
| Ok(ok) => { |
| let (adjustments, target) = self.register_infer_ok_obligations(ok); |
| self.apply_adjustments(new, adjustments); |
| return Ok(target); |
| } |
| Err(e) => first_error = Some(e), |
| } |
| } |
| |
| // Then try to coerce the previous expressions to the type of the new one. |
| // This requires ensuring there are no coercions applied to *any* of the |
| // previous expressions, other than noop reborrows (ignoring lifetimes). |
| for expr in exprs { |
| let expr = expr.as_coercion_site(); |
| let noop = match self.tables.borrow().expr_adjustments(expr) { |
| &[ |
| Adjustment { kind: Adjust::Deref(_), .. }, |
| Adjustment { kind: Adjust::Borrow(AutoBorrow::Ref(_, mutbl_adj)), .. } |
| ] => { |
| match self.node_ty(expr.hir_id).kind { |
| ty::Ref(_, _, mt_orig) => { |
| let mutbl_adj: hir::Mutability = mutbl_adj.into(); |
| // Reborrow that we can safely ignore, because |
| // the next adjustment can only be a Deref |
| // which will be merged into it. |
| mutbl_adj == mt_orig |
| } |
| _ => false, |
| } |
| } |
| &[Adjustment { kind: Adjust::NeverToAny, .. }] | &[] => true, |
| _ => false, |
| }; |
| |
| if !noop { |
| return self.commit_if_ok(|_| |
| self.at(cause, self.param_env) |
| .lub(prev_ty, new_ty) |
| ).map(|ok| self.register_infer_ok_obligations(ok)); |
| } |
| } |
| |
| match self.commit_if_ok(|_| coerce.coerce(prev_ty, new_ty)) { |
| Err(_) => { |
| // Avoid giving strange errors on failed attempts. |
| if let Some(e) = first_error { |
| Err(e) |
| } else { |
| self.commit_if_ok(|_| |
| self.at(cause, self.param_env) |
| .lub(prev_ty, new_ty) |
| ).map(|ok| self.register_infer_ok_obligations(ok)) |
| } |
| } |
| Ok(ok) => { |
| let (adjustments, target) = self.register_infer_ok_obligations(ok); |
| for expr in exprs { |
| let expr = expr.as_coercion_site(); |
| self.apply_adjustments(expr, adjustments.clone()); |
| } |
| Ok(target) |
| } |
| } |
| } |
| } |
| |
| /// CoerceMany encapsulates the pattern you should use when you have |
| /// many expressions that are all getting coerced to a common |
| /// type. This arises, for example, when you have a match (the result |
| /// of each arm is coerced to a common type). It also arises in less |
| /// obvious places, such as when you have many `break foo` expressions |
| /// that target the same loop, or the various `return` expressions in |
| /// a function. |
| /// |
| /// The basic protocol is as follows: |
| /// |
| /// - Instantiate the `CoerceMany` with an initial `expected_ty`. |
| /// This will also serve as the "starting LUB". The expectation is |
| /// that this type is something which all of the expressions *must* |
| /// be coercible to. Use a fresh type variable if needed. |
| /// - For each expression whose result is to be coerced, invoke `coerce()` with. |
| /// - In some cases we wish to coerce "non-expressions" whose types are implicitly |
| /// unit. This happens for example if you have a `break` with no expression, |
| /// or an `if` with no `else`. In that case, invoke `coerce_forced_unit()`. |
| /// - `coerce()` and `coerce_forced_unit()` may report errors. They hide this |
| /// from you so that you don't have to worry your pretty head about it. |
| /// But if an error is reported, the final type will be `err`. |
| /// - Invoking `coerce()` may cause us to go and adjust the "adjustments" on |
| /// previously coerced expressions. |
| /// - When all done, invoke `complete()`. This will return the LUB of |
| /// all your expressions. |
| /// - WARNING: I don't believe this final type is guaranteed to be |
| /// related to your initial `expected_ty` in any particular way, |
| /// although it will typically be a subtype, so you should check it. |
| /// - Invoking `complete()` may cause us to go and adjust the "adjustments" on |
| /// previously coerced expressions. |
| /// |
| /// Example: |
| /// |
| /// ``` |
| /// let mut coerce = CoerceMany::new(expected_ty); |
| /// for expr in exprs { |
| /// let expr_ty = fcx.check_expr_with_expectation(expr, expected); |
| /// coerce.coerce(fcx, &cause, expr, expr_ty); |
| /// } |
| /// let final_ty = coerce.complete(fcx); |
| /// ``` |
| pub struct CoerceMany<'tcx, 'exprs, E: AsCoercionSite> { |
| expected_ty: Ty<'tcx>, |
| final_ty: Option<Ty<'tcx>>, |
| expressions: Expressions<'tcx, 'exprs, E>, |
| pushed: usize, |
| } |
| |
| /// The type of a `CoerceMany` that is storing up the expressions into |
| /// a buffer. We use this in `check/mod.rs` for things like `break`. |
| pub type DynamicCoerceMany<'tcx> = CoerceMany<'tcx, 'tcx, P<hir::Expr>>; |
| |
| enum Expressions<'tcx, 'exprs, E: AsCoercionSite> { |
| Dynamic(Vec<&'tcx hir::Expr>), |
| UpFront(&'exprs [E]), |
| } |
| |
| impl<'tcx, 'exprs, E: AsCoercionSite> CoerceMany<'tcx, 'exprs, E> { |
| /// The usual case; collect the set of expressions dynamically. |
| /// If the full set of coercion sites is known before hand, |
| /// consider `with_coercion_sites()` instead to avoid allocation. |
| pub fn new(expected_ty: Ty<'tcx>) -> Self { |
| Self::make(expected_ty, Expressions::Dynamic(vec![])) |
| } |
| |
| /// As an optimization, you can create a `CoerceMany` with a |
| /// pre-existing slice of expressions. In this case, you are |
| /// expected to pass each element in the slice to `coerce(...)` in |
| /// order. This is used with arrays in particular to avoid |
| /// needlessly cloning the slice. |
| pub fn with_coercion_sites(expected_ty: Ty<'tcx>, |
| coercion_sites: &'exprs [E]) |
| -> Self { |
| Self::make(expected_ty, Expressions::UpFront(coercion_sites)) |
| } |
| |
| fn make(expected_ty: Ty<'tcx>, expressions: Expressions<'tcx, 'exprs, E>) -> Self { |
| CoerceMany { |
| expected_ty, |
| final_ty: None, |
| expressions, |
| pushed: 0, |
| } |
| } |
| |
| /// 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 fn expected_ty(&self) -> Ty<'tcx> { |
| self.expected_ty |
| } |
| |
| /// 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.final()`, which will return |
| /// the merged type. |
| pub fn merged_ty(&self) -> Ty<'tcx> { |
| self.final_ty.unwrap_or(self.expected_ty) |
| } |
| |
| /// Indicates that the value generated by `expression`, which is |
| /// of type `expression_ty`, is one of the possibilities that we |
| /// could coerce from. This will record `expression`, and later |
| /// calls to `coerce` may come back and add adjustments and things |
| /// if necessary. |
| pub fn coerce<'a>( |
| &mut self, |
| fcx: &FnCtxt<'a, 'tcx>, |
| cause: &ObligationCause<'tcx>, |
| expression: &'tcx hir::Expr, |
| expression_ty: Ty<'tcx>, |
| ) { |
| self.coerce_inner(fcx, |
| cause, |
| Some(expression), |
| expression_ty, |
| None, false) |
| } |
| |
| /// Indicates that one of the inputs is a "forced unit". This |
| /// occurs in a case like `if foo { ... };`, where the missing else |
| /// generates a "forced unit". Another example is a `loop { break; |
| /// }`, where the `break` has no argument expression. We treat |
| /// these cases slightly differently for error-reporting |
| /// purposes. Note that these tend to correspond to cases where |
| /// the `()` expression is implicit in the source, and hence we do |
| /// not take an expression argument. |
| /// |
| /// The `augment_error` gives you a chance to extend the error |
| /// message, in case any results (e.g., we use this to suggest |
| /// removing a `;`). |
| pub fn coerce_forced_unit<'a>( |
| &mut self, |
| fcx: &FnCtxt<'a, 'tcx>, |
| cause: &ObligationCause<'tcx>, |
| augment_error: &mut dyn FnMut(&mut DiagnosticBuilder<'_>), |
| label_unit_as_expected: bool, |
| ) { |
| self.coerce_inner(fcx, |
| cause, |
| None, |
| fcx.tcx.mk_unit(), |
| Some(augment_error), |
| label_unit_as_expected) |
| } |
| |
| /// The inner coercion "engine". If `expression` is `None`, this |
| /// is a forced-unit case, and hence `expression_ty` must be |
| /// `Nil`. |
| fn coerce_inner<'a>( |
| &mut self, |
| fcx: &FnCtxt<'a, 'tcx>, |
| cause: &ObligationCause<'tcx>, |
| expression: Option<&'tcx hir::Expr>, |
| mut expression_ty: Ty<'tcx>, |
| augment_error: Option<&mut dyn FnMut(&mut DiagnosticBuilder<'_>)>, |
| label_expression_as_expected: bool, |
| ) { |
| // Incorporate whatever type inference information we have |
| // until now; in principle we might also want to process |
| // pending obligations, but doing so should only improve |
| // compatibility (hopefully that is true) by helping us |
| // uncover never types better. |
| if expression_ty.is_ty_var() { |
| expression_ty = fcx.infcx.shallow_resolve(expression_ty); |
| } |
| |
| // If we see any error types, just propagate that error |
| // upwards. |
| if expression_ty.references_error() || self.merged_ty().references_error() { |
| self.final_ty = Some(fcx.tcx.types.err); |
| return; |
| } |
| |
| // Handle the actual type unification etc. |
| let result = if let Some(expression) = expression { |
| if self.pushed == 0 { |
| // Special-case the first expression we are coercing. |
| // To be honest, I'm not entirely sure why we do this. |
| // We don't allow two-phase borrows, see comment in try_find_coercion_lub for why |
| fcx.try_coerce(expression, expression_ty, self.expected_ty, AllowTwoPhase::No) |
| } else { |
| match self.expressions { |
| Expressions::Dynamic(ref exprs) => fcx.try_find_coercion_lub( |
| cause, |
| exprs, |
| self.merged_ty(), |
| expression, |
| expression_ty, |
| ), |
| Expressions::UpFront(ref coercion_sites) => fcx.try_find_coercion_lub( |
| cause, |
| &coercion_sites[0..self.pushed], |
| self.merged_ty(), |
| expression, |
| expression_ty, |
| ), |
| } |
| } |
| } else { |
| // this is a hack for cases where we default to `()` because |
| // the expression etc has been omitted from the source. An |
| // example is an `if let` without an else: |
| // |
| // if let Some(x) = ... { } |
| // |
| // we wind up with a second match arm that is like `_ => |
| // ()`. That is the case we are considering here. We take |
| // a different path to get the right "expected, found" |
| // message and so forth (and because we know that |
| // `expression_ty` will be unit). |
| // |
| // Another example is `break` with no argument expression. |
| assert!(expression_ty.is_unit(), "if let hack without unit type"); |
| fcx.at(cause, fcx.param_env) |
| .eq_exp(label_expression_as_expected, expression_ty, self.merged_ty()) |
| .map(|infer_ok| { |
| fcx.register_infer_ok_obligations(infer_ok); |
| expression_ty |
| }) |
| }; |
| |
| match result { |
| Ok(v) => { |
| self.final_ty = Some(v); |
| if let Some(e) = expression { |
| match self.expressions { |
| Expressions::Dynamic(ref mut buffer) => buffer.push(e), |
| Expressions::UpFront(coercion_sites) => { |
| // if the user gave us an array to validate, check that we got |
| // the next expression in the list, as expected |
| assert_eq!(coercion_sites[self.pushed].as_coercion_site().hir_id, |
| e.hir_id); |
| } |
| } |
| self.pushed += 1; |
| } |
| } |
| Err(coercion_error) => { |
| let (expected, found) = if label_expression_as_expected { |
| // In the case where this is a "forced unit", like |
| // `break`, we want to call the `()` "expected" |
| // since it is implied by the syntax. |
| // (Note: not all force-units work this way.)" |
| (expression_ty, self.final_ty.unwrap_or(self.expected_ty)) |
| } else { |
| // Otherwise, the "expected" type for error |
| // reporting is the current unification type, |
| // which is basically the LUB of the expressions |
| // we've seen so far (combined with the expected |
| // type) |
| (self.final_ty.unwrap_or(self.expected_ty), expression_ty) |
| }; |
| |
| let mut err; |
| match cause.code { |
| ObligationCauseCode::ReturnNoExpression => { |
| err = struct_span_err!( |
| fcx.tcx.sess, cause.span, E0069, |
| "`return;` in a function whose return type is not `()`"); |
| err.span_label(cause.span, "return type is not `()`"); |
| } |
| ObligationCauseCode::BlockTailExpression(blk_id) => { |
| let parent_id = fcx.tcx.hir().get_parent_node(blk_id); |
| err = self.report_return_mismatched_types( |
| cause, |
| expected, |
| found, |
| coercion_error, |
| fcx, |
| parent_id, |
| expression.map(|expr| (expr, blk_id)), |
| ); |
| } |
| ObligationCauseCode::ReturnValue(id) => { |
| err = self.report_return_mismatched_types( |
| cause, expected, found, coercion_error, fcx, id, None); |
| } |
| _ => { |
| err = fcx.report_mismatched_types(cause, expected, found, coercion_error); |
| } |
| } |
| |
| if let Some(augment_error) = augment_error { |
| augment_error(&mut err); |
| } |
| |
| // Error possibly reported in `check_assign` so avoid emitting error again. |
| err.emit_unless(expression.filter(|e| fcx.is_assign_to_bool(e, expected)) |
| .is_some()); |
| |
| self.final_ty = Some(fcx.tcx.types.err); |
| } |
| } |
| } |
| |
| fn report_return_mismatched_types<'a>( |
| &self, |
| cause: &ObligationCause<'tcx>, |
| expected: Ty<'tcx>, |
| found: Ty<'tcx>, |
| ty_err: TypeError<'tcx>, |
| fcx: &FnCtxt<'a, 'tcx>, |
| id: hir::HirId, |
| expression: Option<(&'tcx hir::Expr, hir::HirId)>, |
| ) -> DiagnosticBuilder<'a> { |
| let mut err = fcx.report_mismatched_types(cause, expected, found, ty_err); |
| |
| let mut pointing_at_return_type = false; |
| let mut return_sp = None; |
| |
| // Verify that this is a tail expression of a function, otherwise the |
| // label pointing out the cause for the type coercion will be wrong |
| // as prior return coercions would not be relevant (#57664). |
| let parent_id = fcx.tcx.hir().get_parent_node(id); |
| let fn_decl = if let Some((expr, blk_id)) = expression { |
| pointing_at_return_type = fcx.suggest_mismatched_types_on_tail( |
| &mut err, |
| expr, |
| expected, |
| found, |
| cause.span, |
| blk_id, |
| ); |
| let parent = fcx.tcx.hir().get(parent_id); |
| if let (Some(match_expr), true, false) = ( |
| fcx.tcx.hir().get_match_if_cause(expr.hir_id), |
| expected.is_unit(), |
| pointing_at_return_type, |
| ) { |
| if match_expr.span.desugaring_kind().is_none() { |
| err.span_label(match_expr.span, "expected this to be `()`"); |
| fcx.suggest_semicolon_at_end(match_expr.span, &mut err); |
| } |
| } |
| fcx.get_node_fn_decl(parent).map(|(fn_decl, _, is_main)| (fn_decl, is_main)) |
| } else { |
| fcx.get_fn_decl(parent_id) |
| }; |
| |
| if let (Some((fn_decl, can_suggest)), _) = (fn_decl, pointing_at_return_type) { |
| if expression.is_none() { |
| pointing_at_return_type |= fcx.suggest_missing_return_type( |
| &mut err, &fn_decl, expected, found, can_suggest); |
| } |
| if !pointing_at_return_type { |
| return_sp = Some(fn_decl.output.span()); // `impl Trait` return type |
| } |
| } |
| if let (Some(sp), Some(return_sp)) = (fcx.ret_coercion_span.borrow().as_ref(), return_sp) { |
| err.span_label(return_sp, "expected because this return type..."); |
| err.span_label( *sp, format!( |
| "...is found to be `{}` here", |
| fcx.resolve_vars_with_obligations(expected), |
| )); |
| } |
| err |
| } |
| |
| pub fn complete<'a>(self, fcx: &FnCtxt<'a, 'tcx>) -> Ty<'tcx> { |
| if let Some(final_ty) = self.final_ty { |
| final_ty |
| } else { |
| // If we only had inputs that were of type `!` (or no |
| // inputs at all), then the final type is `!`. |
| assert_eq!(self.pushed, 0); |
| fcx.tcx.types.never |
| } |
| } |
| } |
| |
| /// Something that can be converted into an expression to which we can |
| /// apply a coercion. |
| pub trait AsCoercionSite { |
| fn as_coercion_site(&self) -> &hir::Expr; |
| } |
| |
| impl AsCoercionSite for hir::Expr { |
| fn as_coercion_site(&self) -> &hir::Expr { |
| self |
| } |
| } |
| |
| impl AsCoercionSite for P<hir::Expr> { |
| fn as_coercion_site(&self) -> &hir::Expr { |
| self |
| } |
| } |
| |
| impl<'a, T> AsCoercionSite for &'a T |
| where T: AsCoercionSite |
| { |
| fn as_coercion_site(&self) -> &hir::Expr { |
| (**self).as_coercion_site() |
| } |
| } |
| |
| impl AsCoercionSite for ! { |
| fn as_coercion_site(&self) -> &hir::Expr { |
| unreachable!() |
| } |
| } |
| |
| impl AsCoercionSite for hir::Arm { |
| fn as_coercion_site(&self) -> &hir::Expr { |
| &self.body |
| } |
| } |
