From d8ac334af48075f5d118220051d012f0cf90edd0 Mon Sep 17 00:00:00 2001
From: Ivan Levkivskyi <levkivskyi@gmail.com>
Date: Thu, 7 May 2026 15:05:26 +0100
Subject: [PATCH 1/2] Fix broken refactor of awaitable generator patching

---
 mypy/checker.py                       | 10 ++++-----
 test-data/unit/check-async-await.test | 30 +++++++++++++++++++++++++++
 2 files changed, 35 insertions(+), 5 deletions(-)

diff --git a/mypy/checker.py b/mypy/checker.py
index 7c787d9a42c91..2d23f9c133164 100644
--- a/mypy/checker.py
+++ b/mypy/checker.py
@@ -5721,11 +5721,12 @@ def visit_decorator_inner(
         # Fix the type if decorated with `@types.coroutine` or `@asyncio.coroutine`.
         defn = e.func
         if defn.is_awaitable_coroutine:
-            assert isinstance(defn.type, CallableType)
+            typ = self.function_type(defn)
+            assert isinstance(typ, CallableType)
             # Update the return type to AwaitableGenerator (unless we already did).
             # Note, this doesn't exist in typing.py, only in typing.pyi.
-            if not is_named_instance(defn.type.ret_type, "typing.AwaitableGenerator"):
-                t = defn.type.ret_type
+            if not is_named_instance(typ.ret_type, "typing.AwaitableGenerator"):
+                t = typ.ret_type
                 c = defn.is_coroutine
                 ty = self.get_generator_yield_type(t, c)
                 tc = self.get_generator_receive_type(t, c)
@@ -5734,8 +5735,7 @@ def visit_decorator_inner(
                 else:
                     tr = self.get_generator_return_type(t, c)
                 ret_type = self.named_generic_type("typing.AwaitableGenerator", [ty, tc, tr, t])
-                typ = defn.type.copy_modified(ret_type=ret_type)
-                defn.type = typ
+                defn.type = typ.copy_modified(ret_type=ret_type)
 
         # Type check initialization expressions as part of top-level.
         if not self.can_skip_diagnostics:
diff --git a/test-data/unit/check-async-await.test b/test-data/unit/check-async-await.test
index 907bf6027f657..2e439b9eaeb27 100644
--- a/test-data/unit/check-async-await.test
+++ b/test-data/unit/check-async-await.test
@@ -1091,3 +1091,33 @@ class Launcher(P):
                                           # E: "list[int]" has no attribute "__aiter__" (not async iterable)
 [builtins fixtures/async_await.pyi]
 [typing fixtures/typing-async.pyi]
+
+[case testTypesCoroutineDecoratorUntyped]
+import types
+
+@types.coroutine
+def f(x):
+    yield
+    return 1
+
+async def test() -> None:
+    reveal_type(f)  # N: Revealed type is "def (x: Any) -> typing.AwaitableGenerator[Any, Any, Any, Any]"
+    reveal_type(await f(1))  # N: Revealed type is "Any"
+
+[builtins fixtures/async_await.pyi]
+[typing fixtures/typing-async.pyi]
+
+[case testTypesCoroutineDecoratorPartiallyTyped]
+import types
+
+@types.coroutine
+def f(x: int):
+    yield
+    return 1
+
+async def test() -> None:
+    reveal_type(f)  # N: Revealed type is "def (x: builtins.int) -> typing.AwaitableGenerator[Any, Any, Any, Any]"
+    reveal_type(await f(1))  # N: Revealed type is "Any"
+
+[builtins fixtures/async_await.pyi]
+[typing fixtures/typing-async.pyi]

From 6a6aa4963884a9f34cddd2c946ad12079ea164ea Mon Sep 17 00:00:00 2001
From: Ivan Levkivskyi <levkivskyi@gmail.com>
Date: Thu, 7 May 2026 22:44:32 +0100
Subject: [PATCH 2/2] Make is_dynamic() more correct

---
 mypy/nodes.py                         | 6 +++++-
 test-data/unit/check-async-await.test | 2 ++
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/mypy/nodes.py b/mypy/nodes.py
index 3dafffa5570dd..32a694560b24b 100644
--- a/mypy/nodes.py
+++ b/mypy/nodes.py
@@ -1068,7 +1068,11 @@ def max_fixed_argc(self) -> int:
         return self.max_pos
 
     def is_dynamic(self) -> bool:
-        return self.type is None
+        return (
+            self.type is None
+            or isinstance(self.type, mypy.types.CallableType)
+            and self.type.implicit
+        )
 
 
 FUNCDEF_FLAGS: Final = FUNCITEM_FLAGS + [
diff --git a/test-data/unit/check-async-await.test b/test-data/unit/check-async-await.test
index 2e439b9eaeb27..e887b4c575528 100644
--- a/test-data/unit/check-async-await.test
+++ b/test-data/unit/check-async-await.test
@@ -1098,6 +1098,7 @@ import types
 @types.coroutine
 def f(x):
     yield
+    1 + ""  # OK, in untyped function
     return 1
 
 async def test() -> None:
@@ -1113,6 +1114,7 @@ import types
 @types.coroutine
 def f(x: int):
     yield
+    1 + ""  # E: Unsupported left operand type for + ("int")
     return 1
 
 async def test() -> None: