3 //! Under certain circumstances we will coerce from one type to another,
4 //! for example by auto-borrowing. This occurs in situations where the
5 //! compiler has a firm 'expected type' that was supplied from the user,
6 //! and where the actual type is similar to that expected type in purpose
7 //! but not in representation (so actual subtyping is inappropriate).
11 //! Note that if we are expecting a reference, we will *reborrow*
12 //! even if the argument provided was already a reference. This is
13 //! useful for freezing mut/const things (that is, when the expected is &T
14 //! but you have &const T or &mut T) and also for avoiding the linearity
15 //! of mut things (when the expected is &mut T and you have &mut T). See
16 //! the various `src/test/ui/coerce-reborrow-*.rs` tests for
17 //! examples of where this is useful.
21 //! When deciding what type coercions to consider, we do not attempt to
22 //! resolve any type variables we may encounter. This is because `b`
23 //! represents the expected type "as the user wrote it", meaning that if
24 //! the user defined a generic function like
26 //! fn foo<A>(a: A, b: A) { ... }
28 //! and then we wrote `foo(&1, @2)`, we will not auto-borrow
29 //! either argument. In older code we went to some lengths to
30 //! resolve the `b` variable, which could mean that we'd
31 //! auto-borrow later arguments but not earlier ones, which
32 //! seems very confusing.
36 //! However, right now, if the user manually specifies the
37 //! values for the type variables, as so:
39 //! foo::<&int>(@1, @2)
41 //! then we *will* auto-borrow, because we can't distinguish this from a
42 //! function that declared `&int`. This is inconsistent but it's easiest
43 //! at the moment. The right thing to do, I think, is to consider the
44 //! *unsubstituted* type when deciding whether to auto-borrow, but the
45 //! *substituted* type when considering the bounds and so forth. But most
46 //! of our methods don't give access to the unsubstituted type, and
47 //! rightly so because they'd be error-prone. So maybe the thing to do is
48 //! to actually determine the kind of coercions that should occur
49 //! separately and pass them in. Or maybe it's ok as is. Anyway, it's
50 //! sort of a minor point so I've opted to leave it for later -- after all,
51 //! we may want to adjust precisely when coercions occur.
53 use crate::check
::{FnCtxt, Needs}
;
54 use errors
::DiagnosticBuilder
;
56 use rustc
::hir
::def_id
::DefId
;
57 use rustc
::hir
::ptr
::P
;
58 use rustc
::infer
::{Coercion, InferResult, InferOk}
;
59 use rustc
::infer
::type_variable
::{TypeVariableOrigin, TypeVariableOriginKind}
;
60 use rustc
::traits
::{self, ObligationCause, ObligationCauseCode}
;
61 use rustc
::ty
::adjustment
::{
62 Adjustment
, Adjust
, AllowTwoPhase
, AutoBorrow
, AutoBorrowMutability
, PointerCast
64 use rustc
::ty
::{self, TypeAndMut, Ty}
;
65 use rustc
::ty
::fold
::TypeFoldable
;
66 use rustc
::ty
::error
::TypeError
;
67 use rustc
::ty
::relate
::RelateResult
;
68 use rustc
::ty
::subst
::SubstsRef
;
69 use smallvec
::{smallvec, SmallVec}
;
71 use syntax
::feature_gate
;
72 use syntax
::symbol
::sym
;
74 use rustc_target
::spec
::abi
::Abi
;
76 struct Coerce
<'a
, 'tcx
> {
77 fcx
: &'a FnCtxt
<'a
, 'tcx
>,
78 cause
: ObligationCause
<'tcx
>,
80 /// Determines whether or not allow_two_phase_borrow is set on any
81 /// autoref adjustments we create while coercing. We don't want to
82 /// allow deref coercions to create two-phase borrows, at least initially,
83 /// but we do need two-phase borrows for function argument reborrows.
84 /// See #47489 and #48598
85 /// See docs on the "AllowTwoPhase" type for a more detailed discussion
86 allow_two_phase
: AllowTwoPhase
,
89 impl<'a
, 'tcx
> Deref
for Coerce
<'a
, 'tcx
> {
90 type Target
= FnCtxt
<'a
, 'tcx
>;
91 fn deref(&self) -> &Self::Target
{
96 type CoerceResult
<'tcx
> = InferResult
<'tcx
, (Vec
<Adjustment
<'tcx
>>, Ty
<'tcx
>)>;
98 fn coerce_mutbls
<'tcx
>(from_mutbl
: hir
::Mutability
,
99 to_mutbl
: hir
::Mutability
)
100 -> RelateResult
<'tcx
, ()> {
101 match (from_mutbl
, to_mutbl
) {
102 (hir
::MutMutable
, hir
::MutMutable
) |
103 (hir
::MutImmutable
, hir
::MutImmutable
) |
104 (hir
::MutMutable
, hir
::MutImmutable
) => Ok(()),
105 (hir
::MutImmutable
, hir
::MutMutable
) => Err(TypeError
::Mutability
),
109 fn identity(_
: Ty
<'_
>) -> Vec
<Adjustment
<'_
>> { vec![] }
111 fn simple
<'tcx
>(kind
: Adjust
<'tcx
>) -> impl FnOnce(Ty
<'tcx
>) -> Vec
<Adjustment
<'tcx
>> {
112 move |target
| vec
![Adjustment { kind, target }
]
115 fn success
<'tcx
>(adj
: Vec
<Adjustment
<'tcx
>>,
117 obligations
: traits
::PredicateObligations
<'tcx
>)
118 -> CoerceResult
<'tcx
> {
120 value
: (adj
, target
),
125 impl<'f
, 'tcx
> Coerce
<'f
, 'tcx
> {
127 fcx
: &'f FnCtxt
<'f
, 'tcx
>,
128 cause
: ObligationCause
<'tcx
>,
129 allow_two_phase
: AllowTwoPhase
,
139 fn unify(&self, a
: Ty
<'tcx
>, b
: Ty
<'tcx
>) -> InferResult
<'tcx
, Ty
<'tcx
>> {
140 self.commit_if_ok(|_
| {
142 self.at(&self.cause
, self.fcx
.param_env
).lub(b
, a
)
144 self.at(&self.cause
, self.fcx
.param_env
)
146 .map(|InferOk { value: (), obligations }
| InferOk { value: a, obligations }
)
151 /// Unify two types (using sub or lub) and produce a specific coercion.
152 fn unify_and
<F
>(&self, a
: Ty
<'tcx
>, b
: Ty
<'tcx
>, f
: F
)
153 -> CoerceResult
<'tcx
>
154 where F
: FnOnce(Ty
<'tcx
>) -> Vec
<Adjustment
<'tcx
>>
156 self.unify(&a
, &b
).and_then(|InferOk { value: ty, obligations }
| {
157 success(f(ty
), ty
, obligations
)
161 fn coerce(&self, a
: Ty
<'tcx
>, b
: Ty
<'tcx
>) -> CoerceResult
<'tcx
> {
162 let a
= self.shallow_resolve(a
);
163 debug
!("Coerce.tys({:?} => {:?})", a
, b
);
165 // Just ignore error types.
166 if a
.references_error() || b
.references_error() {
167 return success(vec
![], self.fcx
.tcx
.types
.err
, vec
![]);
171 // Subtle: If we are coercing from `!` to `?T`, where `?T` is an unbound
172 // type variable, we want `?T` to fallback to `!` if not
173 // otherwise constrained. An example where this arises:
175 // let _: Option<?T> = Some({ return; });
177 // here, we would coerce from `!` to `?T`.
178 let b
= self.shallow_resolve(b
);
179 return if self.shallow_resolve(b
).is_ty_var() {
180 // Micro-optimization: no need for this if `b` is
181 // already resolved in some way.
182 let diverging_ty
= self.next_diverging_ty_var(
184 kind
: TypeVariableOriginKind
::AdjustmentType
,
185 span
: self.cause
.span
,
188 self.unify_and(&b
, &diverging_ty
, simple(Adjust
::NeverToAny
))
190 success(simple(Adjust
::NeverToAny
)(b
), b
, vec
![])
194 // Consider coercing the subtype to a DST
196 // NOTE: this is wrapped in a `commit_if_ok` because it creates
197 // a "spurious" type variable, and we don't want to have that
198 // type variable in memory if the coercion fails.
199 let unsize
= self.commit_if_ok(|_
| self.coerce_unsized(a
, b
));
202 debug
!("coerce: unsize successful");
205 Err(TypeError
::ObjectUnsafeCoercion(did
)) => {
206 debug
!("coerce: unsize not object safe");
207 return Err(TypeError
::ObjectUnsafeCoercion(did
));
211 debug
!("coerce: unsize failed");
213 // Examine the supertype and consider auto-borrowing.
215 // Note: does not attempt to resolve type variables we encounter.
216 // See above for details.
218 ty
::RawPtr(mt_b
) => {
219 return self.coerce_unsafe_ptr(a
, b
, mt_b
.mutbl
);
222 ty
::Ref(r_b
, ty
, mutbl
) => {
223 let mt_b
= ty
::TypeAndMut { ty, mutbl }
;
224 return self.coerce_borrowed_pointer(a
, b
, r_b
, mt_b
);
232 // Function items are coercible to any closure
233 // type; function pointers are not (that would
234 // require double indirection).
235 // Additionally, we permit coercion of function
236 // items to drop the unsafe qualifier.
237 self.coerce_from_fn_item(a
, b
)
240 // We permit coercion of fn pointers to drop the
242 self.coerce_from_fn_pointer(a
, a_f
, b
)
244 ty
::Closure(def_id_a
, substs_a
) => {
245 // Non-capturing closures are coercible to
246 // function pointers or unsafe function pointers.
247 // It cannot convert closures that require unsafe.
248 self.coerce_closure_to_fn(a
, def_id_a
, substs_a
, b
)
251 // Otherwise, just use unification rules.
252 self.unify_and(a
, b
, identity
)
257 /// Reborrows `&mut A` to `&mut B` and `&(mut) A` to `&B`.
258 /// To match `A` with `B`, autoderef will be performed,
259 /// calling `deref`/`deref_mut` where necessary.
260 fn coerce_borrowed_pointer(&self,
263 r_b
: ty
::Region
<'tcx
>,
264 mt_b
: TypeAndMut
<'tcx
>)
265 -> CoerceResult
<'tcx
>
267 debug
!("coerce_borrowed_pointer(a={:?}, b={:?})", a
, b
);
269 // If we have a parameter of type `&M T_a` and the value
270 // provided is `expr`, we will be adding an implicit borrow,
271 // meaning that we convert `f(expr)` to `f(&M *expr)`. Therefore,
272 // to type check, we will construct the type that `&M*expr` would
275 let (r_a
, mt_a
) = match a
.kind
{
276 ty
::Ref(r_a
, ty
, mutbl
) => {
277 let mt_a
= ty
::TypeAndMut { ty, mutbl }
;
278 coerce_mutbls(mt_a
.mutbl
, mt_b
.mutbl
)?
;
281 _
=> return self.unify_and(a
, b
, identity
),
284 let span
= self.cause
.span
;
286 let mut first_error
= None
;
287 let mut r_borrow_var
= None
;
288 let mut autoderef
= self.autoderef(span
, a
);
289 let mut found
= None
;
291 for (referent_ty
, autoderefs
) in autoderef
.by_ref() {
293 // Don't let this pass, otherwise it would cause
294 // &T to autoref to &&T.
298 // At this point, we have deref'd `a` to `referent_ty`. So
299 // imagine we are coercing from `&'a mut Vec<T>` to `&'b mut [T]`.
300 // In the autoderef loop for `&'a mut Vec<T>`, we would get
303 // - `&'a mut Vec<T>` -- 0 derefs, just ignore it
304 // - `Vec<T>` -- 1 deref
305 // - `[T]` -- 2 deref
307 // At each point after the first callback, we want to
308 // check to see whether this would match out target type
309 // (`&'b mut [T]`) if we autoref'd it. We can't just
310 // compare the referent types, though, because we still
311 // have to consider the mutability. E.g., in the case
312 // we've been considering, we have an `&mut` reference, so
313 // the `T` in `[T]` needs to be unified with equality.
315 // Therefore, we construct reference types reflecting what
316 // the types will be after we do the final auto-ref and
317 // compare those. Note that this means we use the target
318 // mutability [1], since it may be that we are coercing
319 // from `&mut T` to `&U`.
321 // One fine point concerns the region that we use. We
322 // choose the region such that the region of the final
323 // type that results from `unify` will be the region we
324 // want for the autoref:
326 // - if in sub mode, that means we want to use `'b` (the
327 // region from the target reference) for both
328 // pointers [2]. This is because sub mode (somewhat
329 // arbitrarily) returns the subtype region. In the case
330 // where we are coercing to a target type, we know we
331 // want to use that target type region (`'b`) because --
332 // for the program to type-check -- it must be the
333 // smaller of the two.
334 // - One fine point. It may be surprising that we can
335 // use `'b` without relating `'a` and `'b`. The reason
336 // that this is ok is that what we produce is
337 // effectively a `&'b *x` expression (if you could
338 // annotate the region of a borrow), and regionck has
339 // code that adds edges from the region of a borrow
340 // (`'b`, here) into the regions in the borrowed
341 // expression (`*x`, here). (Search for "link".)
342 // - if in lub mode, things can get fairly complicated. The
343 // easiest thing is just to make a fresh
344 // region variable [4], which effectively means we defer
345 // the decision to region inference (and regionck, which will add
346 // some more edges to this variable). However, this can wind up
347 // creating a crippling number of variables in some cases --
348 // e.g., #32278 -- so we optimize one particular case [3].
349 // Let me try to explain with some examples:
350 // - The "running example" above represents the simple case,
351 // where we have one `&` reference at the outer level and
352 // ownership all the rest of the way down. In this case,
353 // we want `LUB('a, 'b)` as the resulting region.
354 // - However, if there are nested borrows, that region is
355 // too strong. Consider a coercion from `&'a &'x Rc<T>` to
356 // `&'b T`. In this case, `'a` is actually irrelevant.
357 // The pointer we want is `LUB('x, 'b`). If we choose `LUB('a,'b)`
358 // we get spurious errors (`ui/regions-lub-ref-ref-rc.rs`).
359 // (The errors actually show up in borrowck, typically, because
360 // this extra edge causes the region `'a` to be inferred to something
361 // too big, which then results in borrowck errors.)
362 // - We could track the innermost shared reference, but there is already
363 // code in regionck that has the job of creating links between
364 // the region of a borrow and the regions in the thing being
365 // borrowed (here, `'a` and `'x`), and it knows how to handle
366 // all the various cases. So instead we just make a region variable
367 // and let regionck figure it out.
368 let r
= if !self.use_lub
{
370 } else if autoderefs
== 1 {
373 if r_borrow_var
.is_none() {
374 // create var lazilly, at most once
375 let coercion
= Coercion(span
);
376 let r
= self.next_region_var(coercion
);
377 r_borrow_var
= Some(r
); // [4] above
379 r_borrow_var
.unwrap()
381 let derefd_ty_a
= self.tcx
.mk_ref(r
,
384 mutbl
: mt_b
.mutbl
, // [1] above
386 match self.unify(derefd_ty_a
, b
) {
392 if first_error
.is_none() {
393 first_error
= Some(err
);
399 // Extract type or return an error. We return the first error
400 // we got, which should be from relating the "base" type
401 // (e.g., in example above, the failure from relating `Vec<T>`
402 // to the target type), since that should be the least
404 let InferOk { value: ty, mut obligations }
= match found
{
407 let err
= first_error
.expect("coerce_borrowed_pointer had no error");
408 debug
!("coerce_borrowed_pointer: failed with err = {:?}", err
);
413 if ty
== a
&& mt_a
.mutbl
== hir
::MutImmutable
&& autoderef
.step_count() == 1 {
414 // As a special case, if we would produce `&'a *x`, that's
415 // a total no-op. We end up with the type `&'a T` just as
416 // we started with. In that case, just skip it
417 // altogether. This is just an optimization.
419 // Note that for `&mut`, we DO want to reborrow --
420 // otherwise, this would be a move, which might be an
421 // error. For example `foo(self.x)` where `self` and
422 // `self.x` both have `&mut `type would be a move of
423 // `self.x`, but we auto-coerce it to `foo(&mut *self.x)`,
424 // which is a borrow.
425 assert_eq
!(mt_b
.mutbl
, hir
::MutImmutable
); // can only coerce &T -> &U
426 return success(vec
![], ty
, obligations
);
429 let needs
= Needs
::maybe_mut_place(mt_b
.mutbl
);
430 let InferOk { value: mut adjustments, obligations: o }
431 = autoderef
.adjust_steps_as_infer_ok(self, needs
);
432 obligations
.extend(o
);
433 obligations
.extend(autoderef
.into_obligations());
435 // Now apply the autoref. We have to extract the region out of
436 // the final ref type we got.
437 let r_borrow
= match ty
.kind
{
438 ty
::Ref(r_borrow
, _
, _
) => r_borrow
,
439 _
=> span_bug
!(span
, "expected a ref type, got {:?}", ty
),
441 let mutbl
= match mt_b
.mutbl
{
442 hir
::MutImmutable
=> AutoBorrowMutability
::Immutable
,
443 hir
::MutMutable
=> AutoBorrowMutability
::Mutable
{
444 allow_two_phase_borrow
: self.allow_two_phase
,
447 adjustments
.push(Adjustment
{
448 kind
: Adjust
::Borrow(AutoBorrow
::Ref(r_borrow
, mutbl
)),
452 debug
!("coerce_borrowed_pointer: succeeded ty={:?} adjustments={:?}",
456 success(adjustments
, ty
, obligations
)
460 // &[T; n] or &mut [T; n] -> &[T]
461 // or &mut [T; n] -> &mut [T]
462 // or &Concrete -> &Trait, etc.
463 fn coerce_unsized(&self, source
: Ty
<'tcx
>, target
: Ty
<'tcx
>) -> CoerceResult
<'tcx
> {
464 debug
!("coerce_unsized(source={:?}, target={:?})", source
, target
);
466 let traits
= (self.tcx
.lang_items().unsize_trait(),
467 self.tcx
.lang_items().coerce_unsized_trait());
468 let (unsize_did
, coerce_unsized_did
) = if let (Some(u
), Some(cu
)) = traits
{
471 debug
!("missing Unsize or CoerceUnsized traits");
472 return Err(TypeError
::Mismatch
);
475 // Note, we want to avoid unnecessary unsizing. We don't want to coerce to
476 // a DST unless we have to. This currently comes out in the wash since
477 // we can't unify [T] with U. But to properly support DST, we need to allow
478 // that, at which point we will need extra checks on the target here.
480 // Handle reborrows before selecting `Source: CoerceUnsized<Target>`.
481 let reborrow
= match (&source
.kind
, &target
.kind
) {
482 (&ty
::Ref(_
, ty_a
, mutbl_a
), &ty
::Ref(_
, _
, mutbl_b
)) => {
483 coerce_mutbls(mutbl_a
, mutbl_b
)?
;
485 let coercion
= Coercion(self.cause
.span
);
486 let r_borrow
= self.next_region_var(coercion
);
487 let mutbl
= match mutbl_b
{
488 hir
::MutImmutable
=> AutoBorrowMutability
::Immutable
,
489 hir
::MutMutable
=> AutoBorrowMutability
::Mutable
{
490 // We don't allow two-phase borrows here, at least for initial
491 // implementation. If it happens that this coercion is a function argument,
492 // the reborrow in coerce_borrowed_ptr will pick it up.
493 allow_two_phase_borrow
: AllowTwoPhase
::No
,
497 kind
: Adjust
::Deref(None
),
500 kind
: Adjust
::Borrow(AutoBorrow
::Ref(r_borrow
, mutbl
)),
501 target
: self.tcx
.mk_ref(r_borrow
, ty
::TypeAndMut
{
507 (&ty
::Ref(_
, ty_a
, mt_a
), &ty
::RawPtr(ty
::TypeAndMut { mutbl: mt_b, .. }
)) => {
508 coerce_mutbls(mt_a
, mt_b
)?
;
511 kind
: Adjust
::Deref(None
),
514 kind
: Adjust
::Borrow(AutoBorrow
::RawPtr(mt_b
)),
515 target
: self.tcx
.mk_ptr(ty
::TypeAndMut
{
523 let coerce_source
= reborrow
.as_ref().map_or(source
, |&(_
, ref r
)| r
.target
);
525 // Setup either a subtyping or a LUB relationship between
526 // the `CoerceUnsized` target type and the expected type.
527 // We only have the latter, so we use an inference variable
528 // for the former and let type inference do the rest.
529 let origin
= TypeVariableOrigin
{
530 kind
: TypeVariableOriginKind
::MiscVariable
,
531 span
: self.cause
.span
,
533 let coerce_target
= self.next_ty_var(origin
);
534 let mut coercion
= self.unify_and(coerce_target
, target
, |target
| {
535 let unsize
= Adjustment
{
536 kind
: Adjust
::Pointer(PointerCast
::Unsize
),
540 None
=> vec
![unsize
],
541 Some((ref deref
, ref autoref
)) => {
542 vec
![deref
.clone(), autoref
.clone(), unsize
]
547 let mut selcx
= traits
::SelectionContext
::new(self);
549 // Create an obligation for `Source: CoerceUnsized<Target>`.
550 let cause
= ObligationCause
::new(
553 ObligationCauseCode
::Coercion { source, target }
,
556 // Use a FIFO queue for this custom fulfillment procedure.
558 // A Vec (or SmallVec) is not a natural choice for a queue. However,
559 // this code path is hot, and this queue usually has a max length of 1
560 // and almost never more than 3. By using a SmallVec we avoid an
561 // allocation, at the (very small) cost of (occasionally) having to
562 // shift subsequent elements down when removing the front element.
563 let mut queue
: SmallVec
<[_
; 4]> =
564 smallvec
![self.tcx
.predicate_for_trait_def(self.fcx
.param_env
,
569 &[coerce_target
.into()])];
571 let mut has_unsized_tuple_coercion
= false;
573 // Keep resolving `CoerceUnsized` and `Unsize` predicates to avoid
574 // emitting a coercion in cases like `Foo<$1>` -> `Foo<$2>`, where
575 // inference might unify those two inner type variables later.
576 let traits
= [coerce_unsized_did
, unsize_did
];
577 while !queue
.is_empty() {
578 let obligation
= queue
.remove(0);
579 debug
!("coerce_unsized resolve step: {:?}", obligation
);
580 let trait_ref
= match obligation
.predicate
{
581 ty
::Predicate
::Trait(ref tr
) if traits
.contains(&tr
.def_id()) => {
582 if unsize_did
== tr
.def_id() {
583 let sty
= &tr
.skip_binder().input_types().nth(1).unwrap().kind
;
584 if let ty
::Tuple(..) = sty
{
585 debug
!("coerce_unsized: found unsized tuple coercion");
586 has_unsized_tuple_coercion
= true;
592 coercion
.obligations
.push(obligation
);
596 match selcx
.select(&obligation
.with(trait_ref
)) {
597 // Uncertain or unimplemented.
599 if trait_ref
.def_id() == unsize_did
{
600 let trait_ref
= self.resolve_vars_if_possible(&trait_ref
);
601 let self_ty
= trait_ref
.skip_binder().self_ty();
602 let unsize_ty
= trait_ref
.skip_binder().input_types().nth(1).unwrap();
603 debug
!("coerce_unsized: ambiguous unsize case for {:?}", trait_ref
);
604 match (&self_ty
.kind
, &unsize_ty
.kind
) {
605 (ty
::Infer(ty
::TyVar(v
)),
606 ty
::Dynamic(..)) if self.type_var_is_sized(*v
) => {
607 debug
!("coerce_unsized: have sized infer {:?}", v
);
608 coercion
.obligations
.push(obligation
);
609 // `$0: Unsize<dyn Trait>` where we know that `$0: Sized`, try going
613 // Some other case for `$0: Unsize<Something>`. Note that we
614 // hit this case even if `Something` is a sized type, so just
615 // don't do the coercion.
616 debug
!("coerce_unsized: ambiguous unsize");
617 return Err(TypeError
::Mismatch
);
621 debug
!("coerce_unsized: early return - ambiguous");
622 return Err(TypeError
::Mismatch
);
625 Err(traits
::Unimplemented
) => {
626 debug
!("coerce_unsized: early return - can't prove obligation");
627 return Err(TypeError
::Mismatch
);
630 // Object safety violations or miscellaneous.
632 self.report_selection_error(&obligation
, &err
, false, false);
633 // Treat this like an obligation and follow through
634 // with the unsizing - the lack of a coercion should
635 // be silent, as it causes a type mismatch later.
638 Ok(Some(vtable
)) => {
639 queue
.extend(vtable
.nested_obligations())
644 if has_unsized_tuple_coercion
&& !self.tcx
.features().unsized_tuple_coercion
{
645 feature_gate
::emit_feature_err(&self.tcx
.sess
.parse_sess
,
646 sym
::unsized_tuple_coercion
,
648 feature_gate
::GateIssue
::Language
,
649 feature_gate
::EXPLAIN_UNSIZED_TUPLE_COERCION
);
655 fn coerce_from_safe_fn
<F
, G
>(&self,
657 fn_ty_a
: ty
::PolyFnSig
<'tcx
>,
661 -> CoerceResult
<'tcx
>
662 where F
: FnOnce(Ty
<'tcx
>) -> Vec
<Adjustment
<'tcx
>>,
663 G
: FnOnce(Ty
<'tcx
>) -> Vec
<Adjustment
<'tcx
>>
665 if let ty
::FnPtr(fn_ty_b
) = b
.kind
{
666 if let (hir
::Unsafety
::Normal
, hir
::Unsafety
::Unsafe
)
667 = (fn_ty_a
.unsafety(), fn_ty_b
.unsafety())
669 let unsafe_a
= self.tcx
.safe_to_unsafe_fn_ty(fn_ty_a
);
670 return self.unify_and(unsafe_a
, b
, to_unsafe
);
673 self.unify_and(a
, b
, normal
)
676 fn coerce_from_fn_pointer(&self,
678 fn_ty_a
: ty
::PolyFnSig
<'tcx
>,
680 -> CoerceResult
<'tcx
> {
681 //! Attempts to coerce from the type of a Rust function item
682 //! into a closure or a `proc`.
685 let b
= self.shallow_resolve(b
);
686 debug
!("coerce_from_fn_pointer(a={:?}, b={:?})", a
, b
);
688 self.coerce_from_safe_fn(a
, fn_ty_a
, b
,
689 simple(Adjust
::Pointer(PointerCast
::UnsafeFnPointer
)), identity
)
692 fn coerce_from_fn_item(&self,
695 -> CoerceResult
<'tcx
> {
696 //! Attempts to coerce from the type of a Rust function item
697 //! into a closure or a `proc`.
699 let b
= self.shallow_resolve(b
);
700 debug
!("coerce_from_fn_item(a={:?}, b={:?})", a
, b
);
704 let a_sig
= a
.fn_sig(self.tcx
);
705 // Intrinsics are not coercible to function pointers
706 if a_sig
.abi() == Abi
::RustIntrinsic
||
707 a_sig
.abi() == Abi
::PlatformIntrinsic
{
708 return Err(TypeError
::IntrinsicCast
);
710 let InferOk { value: a_sig, mut obligations }
=
711 self.normalize_associated_types_in_as_infer_ok(self.cause
.span
, &a_sig
);
713 let a_fn_pointer
= self.tcx
.mk_fn_ptr(a_sig
);
714 let InferOk { value, obligations: o2 }
= self.coerce_from_safe_fn(
721 kind
: Adjust
::Pointer(PointerCast
::ReifyFnPointer
),
725 kind
: Adjust
::Pointer(PointerCast
::UnsafeFnPointer
),
730 simple(Adjust
::Pointer(PointerCast
::ReifyFnPointer
))
733 obligations
.extend(o2
);
734 Ok(InferOk { value, obligations }
)
736 _
=> self.unify_and(a
, b
, identity
),
740 fn coerce_closure_to_fn(&self,
743 substs_a
: SubstsRef
<'tcx
>,
745 -> CoerceResult
<'tcx
> {
746 //! Attempts to coerce from the type of a non-capturing closure
747 //! into a function pointer.
750 let b
= self.shallow_resolve(b
);
753 ty
::FnPtr(fn_ty
) if self.tcx
.upvars(def_id_a
).map_or(true, |v
| v
.is_empty()) => {
754 // We coerce the closure, which has fn type
755 // `extern "rust-call" fn((arg0,arg1,...)) -> _`
757 // `fn(arg0,arg1,...) -> _`
759 // `unsafe fn(arg0,arg1,...) -> _`
760 let sig
= self.closure_sig(def_id_a
, substs_a
);
761 let unsafety
= fn_ty
.unsafety();
762 let pointer_ty
= self.tcx
.coerce_closure_fn_ty(sig
, unsafety
);
763 debug
!("coerce_closure_to_fn(a={:?}, b={:?}, pty={:?})",
765 self.unify_and(pointer_ty
, b
, simple(
766 Adjust
::Pointer(PointerCast
::ClosureFnPointer(unsafety
))
769 _
=> self.unify_and(a
, b
, identity
),
773 fn coerce_unsafe_ptr(&self,
776 mutbl_b
: hir
::Mutability
)
777 -> CoerceResult
<'tcx
> {
778 debug
!("coerce_unsafe_ptr(a={:?}, b={:?})", a
, b
);
780 let (is_ref
, mt_a
) = match a
.kind
{
781 ty
::Ref(_
, ty
, mutbl
) => (true, ty
::TypeAndMut { ty, mutbl }
),
782 ty
::RawPtr(mt
) => (false, mt
),
783 _
=> return self.unify_and(a
, b
, identity
)
786 // Check that the types which they point at are compatible.
787 let a_unsafe
= self.tcx
.mk_ptr(ty
::TypeAndMut
{
791 coerce_mutbls(mt_a
.mutbl
, mutbl_b
)?
;
792 // Although references and unsafe ptrs have the same
793 // representation, we still register an Adjust::DerefRef so that
794 // regionck knows that the region for `a` must be valid here.
796 self.unify_and(a_unsafe
, b
, |target
| {
798 kind
: Adjust
::Deref(None
),
801 kind
: Adjust
::Borrow(AutoBorrow
::RawPtr(mutbl_b
)),
805 } else if mt_a
.mutbl
!= mutbl_b
{
807 a_unsafe
, b
, simple(Adjust
::Pointer(PointerCast
::MutToConstPointer
))
810 self.unify_and(a_unsafe
, b
, identity
)
815 impl<'a
, 'tcx
> FnCtxt
<'a
, 'tcx
> {
816 /// Attempt to coerce an expression to a type, and return the
817 /// adjusted type of the expression, if successful.
818 /// Adjustments are only recorded if the coercion succeeded.
819 /// The expressions *must not* have any pre-existing adjustments.
825 allow_two_phase
: AllowTwoPhase
,
826 ) -> RelateResult
<'tcx
, Ty
<'tcx
>> {
827 let source
= self.resolve_vars_with_obligations(expr_ty
);
828 debug
!("coercion::try({:?}: {:?} -> {:?})", expr
, source
, target
);
830 let cause
= self.cause(expr
.span
, ObligationCauseCode
::ExprAssignable
);
831 let coerce
= Coerce
::new(self, cause
, allow_two_phase
);
832 let ok
= self.commit_if_ok(|_
| coerce
.coerce(source
, target
))?
;
834 let (adjustments
, _
) = self.register_infer_ok_obligations(ok
);
835 self.apply_adjustments(expr
, adjustments
);
836 Ok(if expr_ty
.references_error() {
843 /// Same as `try_coerce()`, but without side-effects.
844 pub fn can_coerce(&self, expr_ty
: Ty
<'tcx
>, target
: Ty
<'tcx
>) -> bool
{
845 let source
= self.resolve_vars_with_obligations(expr_ty
);
846 debug
!("coercion::can({:?} -> {:?})", source
, target
);
848 let cause
= self.cause(syntax_pos
::DUMMY_SP
, ObligationCauseCode
::ExprAssignable
);
849 // We don't ever need two-phase here since we throw out the result of the coercion
850 let coerce
= Coerce
::new(self, cause
, AllowTwoPhase
::No
);
851 self.probe(|_
| coerce
.coerce(source
, target
)).is_ok()
854 /// Given some expressions, their known unified type and another expression,
855 /// tries to unify the types, potentially inserting coercions on any of the
856 /// provided expressions and returns their LUB (aka "common supertype").
858 /// This is really an internal helper. From outside the coercion
859 /// module, you should instantiate a `CoerceMany` instance.
860 fn try_find_coercion_lub
<E
>(&self,
861 cause
: &ObligationCause
<'tcx
>,
866 -> RelateResult
<'tcx
, Ty
<'tcx
>>
867 where E
: AsCoercionSite
869 let prev_ty
= self.resolve_vars_with_obligations(prev_ty
);
870 let new_ty
= self.resolve_vars_with_obligations(new_ty
);
871 debug
!("coercion::try_find_coercion_lub({:?}, {:?})", prev_ty
, new_ty
);
873 // Special-case that coercion alone cannot handle:
874 // Two function item types of differing IDs or InternalSubsts.
875 if let (&ty
::FnDef(..), &ty
::FnDef(..)) = (&prev_ty
.kind
, &new_ty
.kind
) {
876 // Don't reify if the function types have a LUB, i.e., they
877 // are the same function and their parameters have a LUB.
878 let lub_ty
= self.commit_if_ok(|_
| {
879 self.at(cause
, self.param_env
)
880 .lub(prev_ty
, new_ty
)
881 }).map(|ok
| self.register_infer_ok_obligations(ok
));
884 // We have a LUB of prev_ty and new_ty, just return it.
888 // The signature must match.
889 let a_sig
= prev_ty
.fn_sig(self.tcx
);
890 let a_sig
= self.normalize_associated_types_in(new
.span
, &a_sig
);
891 let b_sig
= new_ty
.fn_sig(self.tcx
);
892 let b_sig
= self.normalize_associated_types_in(new
.span
, &b_sig
);
893 let sig
= self.at(cause
, self.param_env
)
894 .trace(prev_ty
, new_ty
)
896 .map(|ok
| self.register_infer_ok_obligations(ok
))?
;
898 // Reify both sides and return the reified fn pointer type.
899 let fn_ptr
= self.tcx
.mk_fn_ptr(sig
);
900 for expr
in exprs
.iter().map(|e
| e
.as_coercion_site()).chain(Some(new
)) {
901 // The only adjustment that can produce an fn item is
902 // `NeverToAny`, so this should always be valid.
903 self.apply_adjustments(expr
, vec
![Adjustment
{
904 kind
: Adjust
::Pointer(PointerCast
::ReifyFnPointer
),
911 // Configure a Coerce instance to compute the LUB.
912 // We don't allow two-phase borrows on any autorefs this creates since we
913 // probably aren't processing function arguments here and even if we were,
914 // they're going to get autorefed again anyway and we can apply 2-phase borrows
916 let mut coerce
= Coerce
::new(self, cause
.clone(), AllowTwoPhase
::No
);
917 coerce
.use_lub
= true;
919 // First try to coerce the new expression to the type of the previous ones,
920 // but only if the new expression has no coercion already applied to it.
921 let mut first_error
= None
;
922 if !self.tables
.borrow().adjustments().contains_key(new
.hir_id
) {
923 let result
= self.commit_if_ok(|_
| coerce
.coerce(new_ty
, prev_ty
));
926 let (adjustments
, target
) = self.register_infer_ok_obligations(ok
);
927 self.apply_adjustments(new
, adjustments
);
930 Err(e
) => first_error
= Some(e
),
934 // Then try to coerce the previous expressions to the type of the new one.
935 // This requires ensuring there are no coercions applied to *any* of the
936 // previous expressions, other than noop reborrows (ignoring lifetimes).
938 let expr
= expr
.as_coercion_site();
939 let noop
= match self.tables
.borrow().expr_adjustments(expr
) {
941 Adjustment { kind: Adjust::Deref(_), .. }
,
942 Adjustment { kind: Adjust::Borrow(AutoBorrow::Ref(_, mutbl_adj)), .. }
944 match self.node_ty(expr
.hir_id
).kind
{
945 ty
::Ref(_
, _
, mt_orig
) => {
946 let mutbl_adj
: hir
::Mutability
= mutbl_adj
.into();
947 // Reborrow that we can safely ignore, because
948 // the next adjustment can only be a Deref
949 // which will be merged into it.
955 &[Adjustment { kind: Adjust::NeverToAny, .. }
] | &[] => true,
960 return self.commit_if_ok(|_
|
961 self.at(cause
, self.param_env
)
962 .lub(prev_ty
, new_ty
)
963 ).map(|ok
| self.register_infer_ok_obligations(ok
));
967 match self.commit_if_ok(|_
| coerce
.coerce(prev_ty
, new_ty
)) {
969 // Avoid giving strange errors on failed attempts.
970 if let Some(e
) = first_error
{
973 self.commit_if_ok(|_
|
974 self.at(cause
, self.param_env
)
975 .lub(prev_ty
, new_ty
)
976 ).map(|ok
| self.register_infer_ok_obligations(ok
))
980 let (adjustments
, target
) = self.register_infer_ok_obligations(ok
);
982 let expr
= expr
.as_coercion_site();
983 self.apply_adjustments(expr
, adjustments
.clone());
991 /// CoerceMany encapsulates the pattern you should use when you have
992 /// many expressions that are all getting coerced to a common
993 /// type. This arises, for example, when you have a match (the result
994 /// of each arm is coerced to a common type). It also arises in less
995 /// obvious places, such as when you have many `break foo` expressions
996 /// that target the same loop, or the various `return` expressions in
999 /// The basic protocol is as follows:
1001 /// - Instantiate the `CoerceMany` with an initial `expected_ty`.
1002 /// This will also serve as the "starting LUB". The expectation is
1003 /// that this type is something which all of the expressions *must*
1004 /// be coercible to. Use a fresh type variable if needed.
1005 /// - For each expression whose result is to be coerced, invoke `coerce()` with.
1006 /// - In some cases we wish to coerce "non-expressions" whose types are implicitly
1007 /// unit. This happens for example if you have a `break` with no expression,
1008 /// or an `if` with no `else`. In that case, invoke `coerce_forced_unit()`.
1009 /// - `coerce()` and `coerce_forced_unit()` may report errors. They hide this
1010 /// from you so that you don't have to worry your pretty head about it.
1011 /// But if an error is reported, the final type will be `err`.
1012 /// - Invoking `coerce()` may cause us to go and adjust the "adjustments" on
1013 /// previously coerced expressions.
1014 /// - When all done, invoke `complete()`. This will return the LUB of
1015 /// all your expressions.
1016 /// - WARNING: I don't believe this final type is guaranteed to be
1017 /// related to your initial `expected_ty` in any particular way,
1018 /// although it will typically be a subtype, so you should check it.
1019 /// - Invoking `complete()` may cause us to go and adjust the "adjustments" on
1020 /// previously coerced expressions.
1025 /// let mut coerce = CoerceMany::new(expected_ty);
1026 /// for expr in exprs {
1027 /// let expr_ty = fcx.check_expr_with_expectation(expr, expected);
1028 /// coerce.coerce(fcx, &cause, expr, expr_ty);
1030 /// let final_ty = coerce.complete(fcx);
1032 pub struct CoerceMany
<'tcx
, 'exprs
, E
: AsCoercionSite
> {
1033 expected_ty
: Ty
<'tcx
>,
1034 final_ty
: Option
<Ty
<'tcx
>>,
1035 expressions
: Expressions
<'tcx
, 'exprs
, E
>,
1039 /// The type of a `CoerceMany` that is storing up the expressions into
1040 /// a buffer. We use this in `check/mod.rs` for things like `break`.
1041 pub type DynamicCoerceMany
<'tcx
> = CoerceMany
<'tcx
, 'tcx
, P
<hir
::Expr
>>;
1043 enum Expressions
<'tcx
, 'exprs
, E
: AsCoercionSite
> {
1044 Dynamic(Vec
<&'tcx hir
::Expr
>),
1045 UpFront(&'exprs
[E
]),
1048 impl<'tcx
, 'exprs
, E
: AsCoercionSite
> CoerceMany
<'tcx
, 'exprs
, E
> {
1049 /// The usual case; collect the set of expressions dynamically.
1050 /// If the full set of coercion sites is known before hand,
1051 /// consider `with_coercion_sites()` instead to avoid allocation.
1052 pub fn new(expected_ty
: Ty
<'tcx
>) -> Self {
1053 Self::make(expected_ty
, Expressions
::Dynamic(vec
![]))
1056 /// As an optimization, you can create a `CoerceMany` with a
1057 /// pre-existing slice of expressions. In this case, you are
1058 /// expected to pass each element in the slice to `coerce(...)` in
1059 /// order. This is used with arrays in particular to avoid
1060 /// needlessly cloning the slice.
1061 pub fn with_coercion_sites(expected_ty
: Ty
<'tcx
>,
1062 coercion_sites
: &'exprs
[E
])
1064 Self::make(expected_ty
, Expressions
::UpFront(coercion_sites
))
1067 fn make(expected_ty
: Ty
<'tcx
>, expressions
: Expressions
<'tcx
, 'exprs
, E
>) -> Self {
1076 /// Returns the "expected type" with which this coercion was
1077 /// constructed. This represents the "downward propagated" type
1078 /// that was given to us at the start of typing whatever construct
1079 /// we are typing (e.g., the match expression).
1081 /// Typically, this is used as the expected type when
1082 /// type-checking each of the alternative expressions whose types
1083 /// we are trying to merge.
1084 pub fn expected_ty(&self) -> Ty
<'tcx
> {
1088 /// Returns the current "merged type", representing our best-guess
1089 /// at the LUB of the expressions we've seen so far (if any). This
1090 /// isn't *final* until you call `self.final()`, which will return
1091 /// the merged type.
1092 pub fn merged_ty(&self) -> Ty
<'tcx
> {
1093 self.final_ty
.unwrap_or(self.expected_ty
)
1096 /// Indicates that the value generated by `expression`, which is
1097 /// of type `expression_ty`, is one of the possibilities that we
1098 /// could coerce from. This will record `expression`, and later
1099 /// calls to `coerce` may come back and add adjustments and things
1103 fcx
: &FnCtxt
<'a
, 'tcx
>,
1104 cause
: &ObligationCause
<'tcx
>,
1105 expression
: &'tcx hir
::Expr
,
1106 expression_ty
: Ty
<'tcx
>,
1108 self.coerce_inner(fcx
,
1115 /// Indicates that one of the inputs is a "forced unit". This
1116 /// occurs in a case like `if foo { ... };`, where the missing else
1117 /// generates a "forced unit". Another example is a `loop { break;
1118 /// }`, where the `break` has no argument expression. We treat
1119 /// these cases slightly differently for error-reporting
1120 /// purposes. Note that these tend to correspond to cases where
1121 /// the `()` expression is implicit in the source, and hence we do
1122 /// not take an expression argument.
1124 /// The `augment_error` gives you a chance to extend the error
1125 /// message, in case any results (e.g., we use this to suggest
1126 /// removing a `;`).
1127 pub fn coerce_forced_unit
<'a
>(
1129 fcx
: &FnCtxt
<'a
, 'tcx
>,
1130 cause
: &ObligationCause
<'tcx
>,
1131 augment_error
: &mut dyn FnMut(&mut DiagnosticBuilder
<'_
>),
1132 label_unit_as_expected
: bool
,
1134 self.coerce_inner(fcx
,
1138 Some(augment_error
),
1139 label_unit_as_expected
)
1142 /// The inner coercion "engine". If `expression` is `None`, this
1143 /// is a forced-unit case, and hence `expression_ty` must be
1145 fn coerce_inner
<'a
>(
1147 fcx
: &FnCtxt
<'a
, 'tcx
>,
1148 cause
: &ObligationCause
<'tcx
>,
1149 expression
: Option
<&'tcx hir
::Expr
>,
1150 mut expression_ty
: Ty
<'tcx
>,
1151 augment_error
: Option
<&mut dyn FnMut(&mut DiagnosticBuilder
<'_
>)>,
1152 label_expression_as_expected
: bool
,
1154 // Incorporate whatever type inference information we have
1155 // until now; in principle we might also want to process
1156 // pending obligations, but doing so should only improve
1157 // compatibility (hopefully that is true) by helping us
1158 // uncover never types better.
1159 if expression_ty
.is_ty_var() {
1160 expression_ty
= fcx
.infcx
.shallow_resolve(expression_ty
);
1163 // If we see any error types, just propagate that error
1165 if expression_ty
.references_error() || self.merged_ty().references_error() {
1166 self.final_ty
= Some(fcx
.tcx
.types
.err
);
1170 // Handle the actual type unification etc.
1171 let result
= if let Some(expression
) = expression
{
1172 if self.pushed
== 0 {
1173 // Special-case the first expression we are coercing.
1174 // To be honest, I'm not entirely sure why we do this.
1175 // We don't allow two-phase borrows, see comment in try_find_coercion_lub for why
1176 fcx
.try_coerce(expression
, expression_ty
, self.expected_ty
, AllowTwoPhase
::No
)
1178 match self.expressions
{
1179 Expressions
::Dynamic(ref exprs
) => fcx
.try_find_coercion_lub(
1186 Expressions
::UpFront(ref coercion_sites
) => fcx
.try_find_coercion_lub(
1188 &coercion_sites
[0..self.pushed
],
1196 // this is a hack for cases where we default to `()` because
1197 // the expression etc has been omitted from the source. An
1198 // example is an `if let` without an else:
1200 // if let Some(x) = ... { }
1202 // we wind up with a second match arm that is like `_ =>
1203 // ()`. That is the case we are considering here. We take
1204 // a different path to get the right "expected, found"
1205 // message and so forth (and because we know that
1206 // `expression_ty` will be unit).
1208 // Another example is `break` with no argument expression.
1209 assert
!(expression_ty
.is_unit(), "if let hack without unit type");
1210 fcx
.at(cause
, fcx
.param_env
)
1211 .eq_exp(label_expression_as_expected
, expression_ty
, self.merged_ty())
1213 fcx
.register_infer_ok_obligations(infer_ok
);
1220 self.final_ty
= Some(v
);
1221 if let Some(e
) = expression
{
1222 match self.expressions
{
1223 Expressions
::Dynamic(ref mut buffer
) => buffer
.push(e
),
1224 Expressions
::UpFront(coercion_sites
) => {
1225 // if the user gave us an array to validate, check that we got
1226 // the next expression in the list, as expected
1227 assert_eq
!(coercion_sites
[self.pushed
].as_coercion_site().hir_id
,
1234 Err(coercion_error
) => {
1235 let (expected
, found
) = if label_expression_as_expected
{
1236 // In the case where this is a "forced unit", like
1237 // `break`, we want to call the `()` "expected"
1238 // since it is implied by the syntax.
1239 // (Note: not all force-units work this way.)"
1240 (expression_ty
, self.final_ty
.unwrap_or(self.expected_ty
))
1242 // Otherwise, the "expected" type for error
1243 // reporting is the current unification type,
1244 // which is basically the LUB of the expressions
1245 // we've seen so far (combined with the expected
1247 (self.final_ty
.unwrap_or(self.expected_ty
), expression_ty
)
1252 ObligationCauseCode
::ReturnNoExpression
=> {
1253 err
= struct_span_err
!(
1254 fcx
.tcx
.sess
, cause
.span
, E0069
,
1255 "`return;` in a function whose return type is not `()`");
1256 err
.span_label(cause
.span
, "return type is not `()`");
1258 ObligationCauseCode
::BlockTailExpression(blk_id
) => {
1259 let parent_id
= fcx
.tcx
.hir().get_parent_node(blk_id
);
1260 err
= self.report_return_mismatched_types(
1267 expression
.map(|expr
| (expr
, blk_id
)),
1270 ObligationCauseCode
::ReturnValue(id
) => {
1271 err
= self.report_return_mismatched_types(
1272 cause
, expected
, found
, coercion_error
, fcx
, id
, None
);
1275 err
= fcx
.report_mismatched_types(cause
, expected
, found
, coercion_error
);
1279 if let Some(augment_error
) = augment_error
{
1280 augment_error(&mut err
);
1283 // Error possibly reported in `check_assign` so avoid emitting error again.
1284 err
.emit_unless(expression
.filter(|e
| fcx
.is_assign_to_bool(e
, expected
))
1287 self.final_ty
= Some(fcx
.tcx
.types
.err
);
1292 fn report_return_mismatched_types
<'a
>(
1294 cause
: &ObligationCause
<'tcx
>,
1297 ty_err
: TypeError
<'tcx
>,
1298 fcx
: &FnCtxt
<'a
, 'tcx
>,
1300 expression
: Option
<(&'tcx hir
::Expr
, hir
::HirId
)>,
1301 ) -> DiagnosticBuilder
<'a
> {
1302 let mut err
= fcx
.report_mismatched_types(cause
, expected
, found
, ty_err
);
1304 let mut pointing_at_return_type
= false;
1305 let mut return_sp
= None
;
1307 // Verify that this is a tail expression of a function, otherwise the
1308 // label pointing out the cause for the type coercion will be wrong
1309 // as prior return coercions would not be relevant (#57664).
1310 let parent_id
= fcx
.tcx
.hir().get_parent_node(id
);
1311 let fn_decl
= if let Some((expr
, blk_id
)) = expression
{
1312 pointing_at_return_type
= fcx
.suggest_mismatched_types_on_tail(
1320 let parent
= fcx
.tcx
.hir().get(parent_id
);
1321 if let (Some(match_expr
), true, false) = (
1322 fcx
.tcx
.hir().get_match_if_cause(expr
.hir_id
),
1324 pointing_at_return_type
,
1326 if match_expr
.span
.desugaring_kind().is_none() {
1327 err
.span_label(match_expr
.span
, "expected this to be `()`");
1328 fcx
.suggest_semicolon_at_end(match_expr
.span
, &mut err
);
1331 fcx
.get_node_fn_decl(parent
).map(|(fn_decl
, _
, is_main
)| (fn_decl
, is_main
))
1333 fcx
.get_fn_decl(parent_id
)
1336 if let (Some((fn_decl
, can_suggest
)), _
) = (fn_decl
, pointing_at_return_type
) {
1337 if expression
.is_none() {
1338 pointing_at_return_type
|= fcx
.suggest_missing_return_type(
1339 &mut err
, &fn_decl
, expected
, found
, can_suggest
);
1341 if !pointing_at_return_type
{
1342 return_sp
= Some(fn_decl
.output
.span()); // `impl Trait` return type
1345 if let (Some(sp
), Some(return_sp
)) = (fcx
.ret_coercion_span
.borrow().as_ref(), return_sp
) {
1346 err
.span_label(return_sp
, "expected because this return type...");
1347 err
.span_label( *sp
, format
!(
1348 "...is found to be `{}` here",
1349 fcx
.resolve_vars_with_obligations(expected
),
1355 pub fn complete
<'a
>(self, fcx
: &FnCtxt
<'a
, 'tcx
>) -> Ty
<'tcx
> {
1356 if let Some(final_ty
) = self.final_ty
{
1359 // If we only had inputs that were of type `!` (or no
1360 // inputs at all), then the final type is `!`.
1361 assert_eq
!(self.pushed
, 0);
1367 /// Something that can be converted into an expression to which we can
1368 /// apply a coercion.
1369 pub trait AsCoercionSite
{
1370 fn as_coercion_site(&self) -> &hir
::Expr
;
1373 impl AsCoercionSite
for hir
::Expr
{
1374 fn as_coercion_site(&self) -> &hir
::Expr
{
1379 impl AsCoercionSite
for P
<hir
::Expr
> {
1380 fn as_coercion_site(&self) -> &hir
::Expr
{
1385 impl<'a
, T
> AsCoercionSite
for &'a T
1386 where T
: AsCoercionSite
1388 fn as_coercion_site(&self) -> &hir
::Expr
{
1389 (**self).as_coercion_site()
1393 impl AsCoercionSite
for ! {
1394 fn as_coercion_site(&self) -> &hir
::Expr
{
1399 impl AsCoercionSite
for hir
::Arm
{
1400 fn as_coercion_site(&self) -> &hir
::Expr
{