Fix async iterator body stripping (#15491)

Fixes #15489

Author: hauntsaninja

mypy/fastparse.py

@@ -521,40 +521,48 @@ def translate_stmt_list(
             return [block]
 
         stack = self.class_and_function_stack
-        if self.strip_function_bodies and len(stack) == 1 and stack[0] == "F":
+        # Fast case for stripping function bodies
+        if (
+            can_strip
+            and self.strip_function_bodies
+            and len(stack) == 1
+            and stack[0] == "F"
+            and not is_coroutine
+        ):
             return []
 
         res: list[Statement] = []
         for stmt in stmts:
             node = self.visit(stmt)
             res.append(node)
 
-        if (
-            self.strip_function_bodies
-            and can_strip
-            and stack[-2:] == ["C", "F"]
-            and not is_possible_trivial_body(res)
-        ):
-            # We only strip method bodies if they don't assign to an attribute, as
-            # this may define an attribute which has an externally visible effect.
-            visitor = FindAttributeAssign()
-            for s in res:
-                s.accept(visitor)
-                if visitor.found:
-                    break
-            else:
-                if is_coroutine:
-                    # Yields inside an async function affect the return type and should not
-                    # be stripped.
-                    yield_visitor = FindYield()
+        # Slow case for stripping function bodies
+        if can_strip and self.strip_function_bodies:
+            if stack[-2:] == ["C", "F"]:
+                if is_possible_trivial_body(res):
+                    can_strip = False
+                else:
+                    # We only strip method bodies if they don't assign to an attribute, as
+                    # this may define an attribute which has an externally visible effect.
+                    visitor = FindAttributeAssign()
                     for s in res:
-                        s.accept(yield_visitor)
-                        if yield_visitor.found:
+                        s.accept(visitor)
+                        if visitor.found:
+                            can_strip = False
                             break
-                    else:
-                        return []
-                else:
-                    return []
+
+            if can_strip and stack[-1] == "F" and is_coroutine:
+                # Yields inside an async function affect the return type and should not
+                # be stripped.
+                yield_visitor = FindYield()
+                for s in res:
+                    s.accept(yield_visitor)
+                    if yield_visitor.found:
+                        can_strip = False
+                        break
+
+            if can_strip:
+                return []
         return res
 
     def translate_type_comment(

test-data/unit/check-async-await.test

@@ -945,17 +945,21 @@ async def bar(x: Union[A, B]) -> None:
 [typing fixtures/typing-async.pyi]
 
 [case testAsyncIteratorWithIgnoredErrors]
-from m import L
+import m
 
-async def func(l: L) -> None:
+async def func(l: m.L) -> None:
     reveal_type(l.get_iterator)  # N: Revealed type is "def () -> typing.AsyncIterator[builtins.str]"
     reveal_type(l.get_iterator2)  # N: Revealed type is "def () -> typing.AsyncIterator[builtins.str]"
     async for i in l.get_iterator():
         reveal_type(i)  # N: Revealed type is "builtins.str"
 
+    reveal_type(m.get_generator)  # N: Revealed type is "def () -> typing.AsyncGenerator[builtins.int, None]"
+    async for i2 in m.get_generator():
+        reveal_type(i2)  # N: Revealed type is "builtins.int"
+
 [file m.py]
 # mypy: ignore-errors=True
-from typing import AsyncIterator
+from typing import AsyncIterator, AsyncGenerator
 
 class L:
     async def some_func(self, i: int) -> str:
@@ -968,6 +972,9 @@ class L:
         if self:
             a = (yield 'x')
 
+async def get_generator() -> AsyncGenerator[int, None]:
+    yield 1
+
 [builtins fixtures/async_await.pyi]
 [typing fixtures/typing-async.pyi]