bjoernager/rust
bjoernager/rust
1
Fork 0
Code Issues Pull requests Activity

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

Browse source 
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
Download patch file Download diff file Expand all files Collapse all files

31
compiler/rustc_ty_utils/src/instance.rs
View file

@ -278,6 +278,24 @@ fn resolve_associated_item<'tcx>(
def: ty::InstanceDef::FnPtrShim(trait_item_id, rcvr_args.type_at(0)),
args: rcvr_args,
}),
ty::CoroutineClosure(coroutine_closure_def_id, args) => {
// When a coroutine-closure implements the `Fn` traits, then it
// always dispatches to the `FnOnce` implementation. This is to
// ensure that the `closure_kind` of the resulting closure is in
// sync with the built-in trait implementations (since all of the
// implementations return `FnOnce::Output`).
if ty::ClosureKind::FnOnce == args.as_coroutine_closure().kind() {
Some(Instance::new(coroutine_closure_def_id, args))
} else {
Some(Instance {
def: ty::InstanceDef::ConstructCoroutineInClosureShim {
coroutine_closure_def_id,
target_kind: ty::ClosureKind::FnOnce,
},
args,
})
}
}
_ => bug!(
"no built-in definition for `{trait_ref}::{}` for non-fn type",
tcx.item_name(trait_item_id)
@ -306,6 +324,19 @@ fn resolve_associated_item<'tcx>(
Some(Instance::new(coroutine_closure_def_id, args))
}
}
ty::Closure(closure_def_id, args) => {
let trait_closure_kind = tcx.fn_trait_kind_from_def_id(trait_id).unwrap();
Some(Instance::resolve_closure(
tcx,
closure_def_id,
args,
trait_closure_kind,
))
}
ty::FnDef(..) | ty::FnPtr(..) => Some(Instance {
def: ty::InstanceDef::FnPtrShim(trait_item_id, rcvr_args.type_at(0)),
args: rcvr_args,
}),
_ => bug!(
"no built-in definition for `{trait_ref}::{}` for non-lending-closure type",
tcx.item_name(trait_item_id)