Rollup merge of #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 #134015

2 files changed, 18 insertions, 8 deletions

diff --git a/compiler/rustc_hir_typeck/src/closure.rs b/compiler/rustc_hir_typeck/src/closure.rs
index e715a7f7e15..9037caf0066 100644
--- a/compiler/rustc_hir_typeck/src/closure.rs
+++ b/compiler/rustc_hir_typeck/src/closure.rs
@@ -454,20 +454,16 @@ 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)
             }
@@ -475,7 +471,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             // `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)
             }
diff --git a/tests/ui/async-await/async-closures/call-once-deduction.rs b/tests/ui/async-await/async-closures/call-once-deduction.rs
new file mode 100644
index 00000000000..41d92bc3d78
--- /dev/null
+++ b/tests/ui/async-await/async-closures/call-once-deduction.rs
@@ -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 || {});
+}