Fix false positive for not-async-context-manager when contextlib.asynccontextmanager is used

Close #3862

Author: PCManticore

ChangeLog

@@ -24,6 +24,10 @@ What's New in Pylint 2.6.1?
 ===========================
 Release date: TBA
 
+* Fix false positive for `not-async-context-manager` when `contextlib.asynccontextmanager` is used
+
+  Close #3862
+
 * Fix linter multiprocessing pool shutdown (triggered warnings when runned in parallels with other pytest plugins)
 
   Closes #3779

pylint/checkers/async.py

@@ -58,7 +58,12 @@ def visit_asyncwith(self, node):
             if inferred is None or inferred is astroid.Uninferable:
                 continue
 
-            if isinstance(inferred, bases.AsyncGenerator):
+            if isinstance(inferred, astroid.AsyncFunctionDef):
+                # Check if we are dealing with a function decorated
+                # with contextlib.asynccontextmanager.
+                if decorated_with(inferred, self._async_generators):
+                    continue
+            elif isinstance(inferred, bases.AsyncGenerator):
                 # Check if we are dealing with a function decorated
                 # with contextlib.asynccontextmanager.
                 if decorated_with(inferred.parent, self._async_generators):
@@ -79,7 +84,6 @@ def visit_asyncwith(self, node):
                                 continue
                 else:
                     continue
-
             self.add_message(
                 "not-async-context-manager", node=node, args=(inferred.name,)
             )

tests/functional/n/not_async_context_manager_py37.py

@@ -10,3 +10,14 @@ async def context_manager(value):
 
 async with context_manager(42) as ans:
     assert ans == 42
+
+
+def async_context_manager():
+    @asynccontextmanager
+    async def wrapper():
+        pass
+    return wrapper
+
+async def func():
+    async with async_context_manager():
+        pass