bpo-37838: get_type_hints for wrapped functions with forward reference (GH-17126)

https://bugs.python.org/issue37838
(cherry picked from commit 0aca3a3)

Co-authored-by: benedwards14 <53377856+benedwards14@users.noreply.github.com>

Author: miss-islington

Lib/test/ann_module.py

@@ -6,6 +6,7 @@
 """
 
 from typing import Optional
+from functools import wraps
 
 __annotations__[1] = 2
 
@@ -51,3 +52,9 @@ def foo(x: int = 10):
     def bar(y: List[str]):
         x: str = 'yes'
     bar()
+
+def dec(func):
+    @wraps(func)
+    def wrapper(*args, **kwargs):
+        return func(*args, **kwargs)
+    return wrapper

Lib/test/test_typing.py

@@ -2778,6 +2778,16 @@ async def g_with(am: AsyncContextManager[int]):
 
 gth = get_type_hints
 
+class ForRefExample:
+    @ann_module.dec
+    def func(self: 'ForRefExample'):
+        pass
+
+    @ann_module.dec
+    @ann_module.dec
+    def nested(self: 'ForRefExample'):
+        pass
+
 
 class GetTypeHintTests(BaseTestCase):
     def test_get_type_hints_from_various_objects(self):
@@ -2876,6 +2886,11 @@ def test_get_type_hints_ClassVar(self):
                           'x': ClassVar[Optional[B]]})
         self.assertEqual(gth(G), {'lst': ClassVar[List[T]]})
 
+    def test_get_type_hints_wrapped_decoratored_func(self):
+        expects = {'self': ForRefExample}
+        self.assertEqual(gth(ForRefExample.func), expects)
+        self.assertEqual(gth(ForRefExample.nested), expects)
+
 
 class GetUtilitiesTestCase(TestCase):
     def test_get_origin(self):

Lib/typing.py

@@ -1234,7 +1234,11 @@ def get_type_hints(obj, globalns=None, localns=None):
         if isinstance(obj, types.ModuleType):
             globalns = obj.__dict__
         else:
-            globalns = getattr(obj, '__globals__', {})
+            nsobj = obj
+            # Find globalns for the unwrapped object.
+            while hasattr(nsobj, '__wrapped__'):
+                nsobj = nsobj.__wrapped__
+            globalns = getattr(nsobj, '__globals__', {})
         if localns is None:
             localns = globalns
     elif localns is None:

Misc/NEWS.d/next/Library/2019-11-21-11-39-17.bpo-37838.lRFcEC.rst

@@ -0,0 +1 @@
+:meth:`typing.get_type_hints` properly handles functions decorated with :meth:`functools.wraps`.