Make captures state error more precise

Author: compiler-errors

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(),