Extend contextmanager to asynccontextmanager

mypy/plugins/default.py

@@ -24,7 +24,7 @@ def get_function_hook(self, fullname: str
                           ) -> Optional[Callable[[FunctionContext], Type]]:
         from mypy.plugins import ctypes
 
-        if fullname == 'contextlib.contextmanager':
+        if fullname in ('contextlib.contextmanager', 'contextlib.asynccontextmanager'):
             return contextmanager_callback
         elif fullname == 'builtins.open' and self.python_version[0] == 3:
             return open_callback

test-data/unit/check-default-plugin.test

@@ -24,6 +24,43 @@ f = g # E: Incompatible types in assignment (expression has type "Callable[[Any,
 [typing fixtures/typing-medium.pyi]
 [builtins fixtures/tuple.pyi]
 
+[case testAsyncContextManagerWithGenericFunction]
+# flags: --python-version 3.7
+from contextlib import asynccontextmanager
+from typing import TypeVar, AsyncGenerator
+
+T = TypeVar('T')
+
+@asynccontextmanager
+async def yield_id(item: T) -> AsyncGenerator[T, None]:
+    yield item
+
+reveal_type(yield_id) # N: Revealed type is "def [T] (item: T`-1) -> typing.AsyncContextManager[T`-1]"
+
+async with yield_id(1) as x:
+    reveal_type(x) # N: Revealed type is "builtins.int*"
+[typing fixtures/typing-async.pyi]
+[builtins fixtures/tuple.pyi]
+
+[case testAsyncContextManagerWithGenericFunctionAndSendType]
+# flags: --python-version 3.7
+from contextlib import asynccontextmanager
+from typing import TypeVar, AsyncGenerator
+
+T = TypeVar('T')
+S = TypeVar('S')
+
+@asynccontextmanager
+async def yield_id(item: T) -> AsyncGenerator[T, S]:
+    yield item
+
+reveal_type(yield_id) # N: Revealed type is "def [T, S] (item: T`-1) -> typing.AsyncContextManager[T`-1]"
+
+async with yield_id(1) as x:
+    reveal_type(x) # N: Revealed type is "builtins.int*"
+[typing fixtures/typing-async.pyi]
+[builtins fixtures/tuple.pyi]
+
 [case testContextManagerWithUnspecifiedArguments]
 from contextlib import contextmanager
 from typing import Callable, Iterator