From d5a9a005188322cd08dca018402e1593d3a5ebd5 Mon Sep 17 00:00:00 2001
From: Andrew Zhogin <andrew.zhogin@gmail.com>
Date: Tue, 3 Jun 2025 03:27:21 +0700
Subject: Fix for async drop inside async gen fn

---
 compiler/rustc_mir_transform/src/coroutine/drop.rs | 34 ++++++++++++++++++----
 tests/crashes/140530.rs                            |  8 -----
 .../async-drop/assign-incompatible-types.rs        |  9 ++++++
 3 files changed, 37 insertions(+), 14 deletions(-)
 delete mode 100644 tests/crashes/140530.rs
 create mode 100644 tests/ui/async-await/async-drop/assign-incompatible-types.rs

diff --git a/compiler/rustc_mir_transform/src/coroutine/drop.rs b/compiler/rustc_mir_transform/src/coroutine/drop.rs
index 6b266da5a69..625e53f9959 100644
--- a/compiler/rustc_mir_transform/src/coroutine/drop.rs
+++ b/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));
 
diff --git a/tests/crashes/140530.rs b/tests/crashes/140530.rs
deleted file mode 100644
index 7e0372a4bd8..00000000000
--- a/tests/crashes/140530.rs
+++ /dev/null
@@ -1,8 +0,0 @@
-//@ known-bug: #140530
-//@ edition: 2024
-
-#![feature(async_drop, gen_blocks)]
-async gen fn a() {
-  _ = async {}
-}
-fn main() {}
diff --git a/tests/ui/async-await/async-drop/assign-incompatible-types.rs b/tests/ui/async-await/async-drop/assign-incompatible-types.rs
new file mode 100644
index 00000000000..359939ff9ac
--- /dev/null
+++ b/tests/ui/async-await/async-drop/assign-incompatible-types.rs
@@ -0,0 +1,9 @@
+// ex-ice: #140530
+//@ edition: 2024
+//@ build-pass
+#![feature(async_drop, gen_blocks)]
+#![allow(incomplete_features)]
+async gen fn a() {
+  _ = async {}
+}
+fn main() {}
-- 
cgit 1.4.1-3-g733a5