Rollup merge of #141932 - azhogin:azhogin/async-drop-inside-asyncgen-fix, r=oli-obk

Fix for async drop inside async gen fn

Return value (for yield) is corrected for async drop inside async gen function.
In CFG, when internal async drop future is polled and returned `Poll<()>::Pending`, then async gen resume function returns `Poll<(OptRet)>::Pending`.

Fixes #140530

Author: matthiaskrgr

compiler/rustc_mir_transform/src/coroutine/drop.rs

@@ -382,12 +382,34 @@ pub(super) fn expand_async_drops<'tcx>(
             dropline_call_bb = Some(drop_call_bb);
         }
 
-        // value needed only for return-yields or gen-coroutines, so just const here
-        let value = Operand::Constant(Box::new(ConstOperand {
-            span: body.span,
-            user_ty: None,
-            const_: Const::from_bool(tcx, false),
-        }));
+        let value =
+            if matches!(coroutine_kind, CoroutineKind::Desugared(CoroutineDesugaring::AsyncGen, _))
+            {
+                // For AsyncGen we need `yield Poll<OptRet>::Pending`
+                let full_yield_ty = body.yield_ty().unwrap();
+                let ty::Adt(_poll_adt, args) = *full_yield_ty.kind() else { bug!() };
+                let ty::Adt(_option_adt, args) = *args.type_at(0).kind() else { bug!() };
+                let yield_ty = args.type_at(0);
+                Operand::Constant(Box::new(ConstOperand {
+                    span: source_info.span,
+                    const_: Const::Unevaluated(
+                        UnevaluatedConst::new(
+                            tcx.require_lang_item(LangItem::AsyncGenPending, None),
+                            tcx.mk_args(&[yield_ty.into()]),
+                        ),
+                        full_yield_ty,
+                    ),
+                    user_ty: None,
+                }))
+            } else {
+                // value needed only for return-yields or gen-coroutines, so just const here
+                Operand::Constant(Box::new(ConstOperand {
+                    span: body.span,
+                    user_ty: None,
+                    const_: Const::from_bool(tcx, false),
+                }))
+            };
+
         use rustc_middle::mir::AssertKind::ResumedAfterDrop;
         let panic_bb = insert_panic_block(tcx, body, ResumedAfterDrop(coroutine_kind));
 

tests/crashes/140530.rs renamed to tests/ui/async-await/async-drop/assign-incompatible-types.rs

@@ -1,7 +1,8 @@
-//@ known-bug: #140530
+// ex-ice: #140530
 //@ edition: 2024
-
+//@ build-pass
 #![feature(async_drop, gen_blocks)]
+#![allow(incomplete_features)]
 async gen fn a() {
   _ = async {}
 }