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Auto merge of #120712 - compiler-errors:async-closures-harmonize, r=oli-obk

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Harmonize `AsyncFn` implementations, make async closures conditionally impl `Fn*` traits

This PR implements several changes to the built-in and libcore-provided implementations of `Fn*` and `AsyncFn*` to address two problems:
1. async closures do not implement the `Fn*` family traits, leading to breakage: https://crater-reports.s3.amazonaws.com/pr-120361/index.html
2. *references* to async closures do not implement `AsyncFn*`, as a consequence of the existing blanket impls of the shape `AsyncFn for F where F: Fn, F::Output: Future`.

In order to fix (1.), we implement `Fn` traits appropriately for async closures. It turns out that async closures can:
* always implement `FnOnce`, meaning that they're drop-in compatible with `FnOnce`-bound combinators like `Option::map`.
* conditionally implement `Fn`/`FnMut` if they have no captures, which means that existing usages of async closures should *probably* work without breakage (crater checking this: https://github.com/rust-lang/rust/pull/120712#issuecomment-1930587805).

In order to fix (2.), we make all of the built-in callables implement `AsyncFn*` via built-in impls, and instead adjust the blanket impls for `AsyncFn*` provided by libcore to match the blanket impls for `Fn*`.
This commit is contained in:
bors 2024-02-10 07:15:15 +00:00
commit 757b8efed4
21 changed files with 706 additions and 263 deletions
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178
compiler/rustc_trait_selection/src/solve/assembly/structural_traits.rs
View file

@ -323,34 +323,27 @@ pub(in crate::solve) fn extract_tupled_inputs_and_output_from_async_callable<'tc
self_ty: Ty<'tcx>,
goal_kind: ty::ClosureKind,
env_region: ty::Region<'tcx>,
) -> Result<
(ty::Binder<'tcx, (Ty<'tcx>, Ty<'tcx>, Ty<'tcx>)>, Option<ty::Predicate<'tcx>>),
NoSolution,
> {
) -> Result<(ty::Binder<'tcx, (Ty<'tcx>, Ty<'tcx>, Ty<'tcx>)>, Vec<ty::Predicate<'tcx>>), NoSolution>
{
match *self_ty.kind() {
ty::CoroutineClosure(def_id, args) => {
let args = args.as_coroutine_closure();
let kind_ty = args.kind_ty();
if let Some(closure_kind) = kind_ty.to_opt_closure_kind() {
let sig = args.coroutine_closure_sig().skip_binder();
let mut nested = vec![];
let coroutine_ty = if let Some(closure_kind) = kind_ty.to_opt_closure_kind() {
if !closure_kind.extends(goal_kind) {
return Err(NoSolution);
}
Ok((
args.coroutine_closure_sig().map_bound(|sig| {
let coroutine_ty = sig.to_coroutine_given_kind_and_upvars(
tcx,
args.parent_args(),
tcx.coroutine_for_closure(def_id),
goal_kind,
env_region,
args.tupled_upvars_ty(),
args.coroutine_captures_by_ref_ty(),
);
(sig.tupled_inputs_ty, sig.return_ty, coroutine_ty)
}),
None,
))
sig.to_coroutine_given_kind_and_upvars(
tcx,
args.parent_args(),
tcx.coroutine_for_closure(def_id),
goal_kind,
env_region,
args.tupled_upvars_ty(),
args.coroutine_captures_by_ref_ty(),
)
} else {
let async_fn_kind_trait_def_id =
tcx.require_lang_item(LangItem::AsyncFnKindHelper, None);
@ -367,42 +360,117 @@ pub(in crate::solve) fn extract_tupled_inputs_and_output_from_async_callable<'tc
// the goal kind <= the closure kind. As a projection `AsyncFnKindHelper::Upvars`
// will project to the right upvars for the generator, appending the inputs and
// coroutine upvars respecting the closure kind.
Ok((
args.coroutine_closure_sig().map_bound(|sig| {
let tupled_upvars_ty = Ty::new_projection(
tcx,
upvars_projection_def_id,
[
ty::GenericArg::from(kind_ty),
Ty::from_closure_kind(tcx, goal_kind).into(),
env_region.into(),
sig.tupled_inputs_ty.into(),
args.tupled_upvars_ty().into(),
args.coroutine_captures_by_ref_ty().into(),
],
);
let coroutine_ty = sig.to_coroutine(
tcx,
args.parent_args(),
Ty::from_closure_kind(tcx, goal_kind),
tcx.coroutine_for_closure(def_id),
tupled_upvars_ty,
);
(sig.tupled_inputs_ty, sig.return_ty, coroutine_ty)
}),
Some(
ty::TraitRef::new(
tcx,
async_fn_kind_trait_def_id,
[kind_ty, Ty::from_closure_kind(tcx, goal_kind)],
)
.to_predicate(tcx),
),
))
}
nested.push(
ty::TraitRef::new(
tcx,
async_fn_kind_trait_def_id,
[kind_ty, Ty::from_closure_kind(tcx, goal_kind)],
)
.to_predicate(tcx),
);
let tupled_upvars_ty = Ty::new_projection(
tcx,
upvars_projection_def_id,
[
ty::GenericArg::from(kind_ty),
Ty::from_closure_kind(tcx, goal_kind).into(),
env_region.into(),
sig.tupled_inputs_ty.into(),
args.tupled_upvars_ty().into(),
args.coroutine_captures_by_ref_ty().into(),
],
);
sig.to_coroutine(
tcx,
args.parent_args(),
Ty::from_closure_kind(tcx, goal_kind),
tcx.coroutine_for_closure(def_id),
tupled_upvars_ty,
)
};
Ok((
args.coroutine_closure_sig().rebind((
sig.tupled_inputs_ty,
sig.return_ty,
coroutine_ty,
)),
nested,
))
}
ty::FnDef(..) | ty::FnPtr(..) | ty::Closure(..) => Err(NoSolution),
ty::FnDef(..) | ty::FnPtr(..) => {
let bound_sig = self_ty.fn_sig(tcx);
let sig = bound_sig.skip_binder();
let future_trait_def_id = tcx.require_lang_item(LangItem::Future, None);
// `FnDef` and `FnPtr` only implement `AsyncFn*` when their
// return type implements `Future`.
let nested = vec![
bound_sig
.rebind(ty::TraitRef::new(tcx, future_trait_def_id, [sig.output()]))
.to_predicate(tcx),
];
let future_output_def_id = tcx
.associated_items(future_trait_def_id)
.filter_by_name_unhygienic(sym::Output)
.next()
.unwrap()
.def_id;
let future_output_ty = Ty::new_projection(tcx, future_output_def_id, [sig.output()]);
Ok((
bound_sig.rebind((Ty::new_tup(tcx, sig.inputs()), sig.output(), future_output_ty)),
nested,
))
}
ty::Closure(_, args) => {
let args = args.as_closure();
let bound_sig = args.sig();
let sig = bound_sig.skip_binder();
let future_trait_def_id = tcx.require_lang_item(LangItem::Future, None);
// `Closure`s only implement `AsyncFn*` when their return type
// implements `Future`.
let mut nested = vec![
bound_sig
.rebind(ty::TraitRef::new(tcx, future_trait_def_id, [sig.output()]))
.to_predicate(tcx),
];
// Additionally, we need to check that the closure kind
// is still compatible.
let kind_ty = args.kind_ty();
if let Some(closure_kind) = kind_ty.to_opt_closure_kind() {
if !closure_kind.extends(goal_kind) {
return Err(NoSolution);
}
} else {
let async_fn_kind_trait_def_id =
tcx.require_lang_item(LangItem::AsyncFnKindHelper, None);
// When we don't know the closure kind (and therefore also the closure's upvars,
// which are computed at the same time), we must delay the computation of the
// generator's upvars. We do this using the `AsyncFnKindHelper`, which as a trait
// goal functions similarly to the old `ClosureKind` predicate, and ensures that
// the goal kind <= the closure kind. As a projection `AsyncFnKindHelper::Upvars`
// will project to the right upvars for the generator, appending the inputs and
// coroutine upvars respecting the closure kind.
nested.push(
ty::TraitRef::new(
tcx,
async_fn_kind_trait_def_id,
[kind_ty, Ty::from_closure_kind(tcx, goal_kind)],
)
.to_predicate(tcx),
);
}
let future_output_def_id = tcx
.associated_items(future_trait_def_id)
.filter_by_name_unhygienic(sym::Output)
.next()
.unwrap()
.def_id;
let future_output_ty = Ty::new_projection(tcx, future_output_def_id, [sig.output()]);
Ok((bound_sig.rebind((sig.inputs()[0], sig.output(), future_output_ty)), nested))
}
ty::Bool
| ty::Char