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

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

2 files changed, 6 insertions, 8 deletions

diff --git a/compiler/rustc_next_trait_solver/src/solve/assembly/structural_traits.rs b/compiler/rustc_next_trait_solver/src/solve/assembly/structural_traits.rs
index 2a2b462a36c..26ad72bea80 100644
--- a/compiler/rustc_next_trait_solver/src/solve/assembly/structural_traits.rs
+++ b/compiler/rustc_next_trait_solver/src/solve/assembly/structural_traits.rs
@@ -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);
                 }
 
diff --git a/compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs b/compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs
index 970160ba212..7d8c4df6341 100644
--- a/compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs
+++ b/compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs
@@ -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(),