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Unrolled build for rust-lang#134017
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Rollup merge of rust-lang#134017 - compiler-errors:call-once-deduction, r=jieyouxu

Don't use `AsyncFnOnce::CallOnceFuture` bounds for signature deduction

We shouldn't be using `AsyncFnOnce::CallOnceFuture` projection bounds to deduce anything about the return type of an async closure, **only** `AsyncFnOnce::Output`. This was accidental b/c all we were looking at was the def id of the trait, rather than the projection. This PR fixes that.

This doesn't affect stable code, since `CallOnceFuture` bounds cannot be written on stable.

Fixes rust-lang#134015
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rust-timer authored Dec 10, 2024
2 parents 4996052 + 88669ae commit c4f4dcd
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Showing 2 changed files with 18 additions and 8 deletions.
12 changes: 4 additions & 8 deletions compiler/rustc_hir_typeck/src/closure.rs
Original file line number Diff line number Diff line change
Expand Up @@ -454,28 +454,24 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
closure_kind: hir::ClosureKind,
projection: ty::PolyProjectionPredicate<'tcx>,
) -> Option<ExpectedSig<'tcx>> {
let tcx = self.tcx;

let trait_def_id = projection.trait_def_id(tcx);
let def_id = projection.projection_def_id();

// For now, we only do signature deduction based off of the `Fn` and `AsyncFn` traits,
// for closures and async closures, respectively.
match closure_kind {
hir::ClosureKind::Closure
if self.tcx.fn_trait_kind_from_def_id(trait_def_id).is_some() =>
{
hir::ClosureKind::Closure if self.tcx.is_lang_item(def_id, LangItem::FnOnceOutput) => {
self.extract_sig_from_projection(cause_span, projection)
}
hir::ClosureKind::CoroutineClosure(hir::CoroutineDesugaring::Async)
if self.tcx.async_fn_trait_kind_from_def_id(trait_def_id).is_some() =>
if self.tcx.is_lang_item(def_id, LangItem::AsyncFnOnceOutput) =>
{
self.extract_sig_from_projection(cause_span, projection)
}
// It's possible we've passed the closure to a (somewhat out-of-fashion)
// `F: FnOnce() -> Fut, Fut: Future<Output = T>` style bound. Let's still
// guide inference here, since it's beneficial for the user.
hir::ClosureKind::CoroutineClosure(hir::CoroutineDesugaring::Async)
if self.tcx.fn_trait_kind_from_def_id(trait_def_id).is_some() =>
if self.tcx.is_lang_item(def_id, LangItem::FnOnceOutput) =>
{
self.extract_sig_from_projection_and_future_bound(cause_span, projection)
}
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14 changes: 14 additions & 0 deletions tests/ui/async-await/async-closures/call-once-deduction.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,14 @@
//@ edition: 2021
//@ check-pass

#![feature(async_closure, async_fn_traits, unboxed_closures)]

fn bar<F, O>(_: F)
where
F: AsyncFnOnce<(), CallOnceFuture = O>,
{
}

fn main() {
bar(async move || {});
}

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