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Rollup merge of #141359 - compiler-errors:async-fn-once, r=lcnr

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Fix `FnOnce` impl for `AsyncFn`/`AsyncFnMut` self-borrowing closures in new solver

This only affects closures that are "`AsyncFn`/`AsyncFnMut`" in their calling capability that are being called with the `FnOnce` trait.

fixes https://github.com/rust-lang/trait-system-refactor-initiative/issues/217

r? lcnr
This commit is contained in:
Matthias Krüger 2025-05-22 16:04:12 +02:00 • committed by GitHub
commit 654b2f39f1
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3 changed files with 21 additions and 8 deletions
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2
compiler/rustc_next_trait_solver/src/solve/assembly/structural_traits.rs
View file

@ -327,7 +327,7 @@ pub(in crate::solve) fn extract_tupled_inputs_and_output_from_callable<I: Intern
// always be called once. It additionally implements `Fn`/`FnMut`
// only if it has no upvars referencing the closure-env lifetime,
// and if the closure kind permits it.
if closure_kind != ty::ClosureKind::FnOnce && args.has_self_borrows() {
if goal_kind != ty::ClosureKind::FnOnce && args.has_self_borrows() {
return Err(NoSolution);
}

12
compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs
View file

@ -841,16 +841,17 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
return None;
};
let (closure_def_id, found_args, by_ref_captures) = match *self_ty.kind() {
let (closure_def_id, found_args, has_self_borrows) = match *self_ty.kind() {
ty::Closure(def_id, args) => {
(def_id, args.as_closure().sig().map_bound(|sig| sig.inputs()[0]), None)
(def_id, args.as_closure().sig().map_bound(|sig| sig.inputs()[0]), false)
}
ty::CoroutineClosure(def_id, args) => (
def_id,
args.as_coroutine_closure()
.coroutine_closure_sig()
.map_bound(|sig| sig.tupled_inputs_ty),
Some(args.as_coroutine_closure().coroutine_captures_by_ref_ty()),
!args.as_coroutine_closure().tupled_upvars_ty().is_ty_var()
&& args.as_coroutine_closure().has_self_borrows(),
),
_ => return None,
};
@ -884,10 +885,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
// If the closure has captures, then perhaps the reason that the trait
// is unimplemented is because async closures don't implement `Fn`/`FnMut`
// if they have captures.
if let Some(by_ref_captures) = by_ref_captures
&& let ty::FnPtr(sig_tys, _) = by_ref_captures.kind()
&& !sig_tys.skip_binder().output().is_unit()
{
if has_self_borrows && expected_kind != ty::ClosureKind::FnOnce {
let mut err = self.dcx().create_err(AsyncClosureNotFn {
span: self.tcx.def_span(closure_def_id),
kind: expected_kind.as_str(),

15
tests/ui/async-await/async-closures/async-fn-mut-impl-fn-once.rs Normal file
View file

@ -0,0 +1,15 @@
//@ edition:2021
//@ check-pass
//@ revisions: current next
//@ ignore-compare-mode-next-solver (explicit revisions)
//@[next] compile-flags: -Znext-solver
fn call_once<F>(_: impl FnOnce() -> F) {}
fn main() {
let mut i = 0;
let c = async || {
i += 1;
};
call_once(c);
}