gh-119600: mock: do not access attributes of original when new_callable is set (#119601)

In order to patch flask.g e.g. as in #84982, that
proxies getattr must not be invoked. For that,
mock must not try to read from the original
object. In some cases that is unavoidable, e.g.
when doing autospec. However, patch("flask.g",
new_callable=MagicMock) should be entirely safe.

4 files changed, 29 insertions, 5 deletions

diff --git a/Lib/test/test_unittest/testmock/support.py b/Lib/test/test_unittest/testmock/support.py
index 49986d6..6c535b7 100644
--- a/Lib/test/test_unittest/testmock/support.py
+++ b/Lib/test/test_unittest/testmock/support.py
@@ -14,3 +14,14 @@ class SomeClass(object):
 
 class X(object):
     pass
+
+# A standin for weurkzeug.local.LocalProxy - issue 119600
+def _inaccessible(*args, **kwargs):
+    raise AttributeError
+
+
+class OpaqueProxy:
+    __getattribute__ = _inaccessible
+
+
+g = OpaqueProxy()
diff --git a/Lib/test/test_unittest/testmock/testpatch.py b/Lib/test/test_unittest/testmock/testpatch.py
index be75fda..f26e74c 100644
--- a/Lib/test/test_unittest/testmock/testpatch.py
+++ b/Lib/test/test_unittest/testmock/testpatch.py
@@ -2045,6 +2045,13 @@ class PatchTest(unittest.TestCase):
         with self.assertRaises(TypeError):
             test()
 
+    def test_patch_proxy_object(self):
+        @patch("test.test_unittest.testmock.support.g", new_callable=MagicMock())
+        def test(_):
+            pass
+
+        test()
+
 
 if __name__ == '__main__':
     unittest.main()
diff --git a/Lib/unittest/mock.py b/Lib/unittest/mock.py
index 3ef83e2..edabb45 100644
--- a/Lib/unittest/mock.py
+++ b/Lib/unittest/mock.py
@@ -1508,13 +1508,12 @@ class _patch(object):
                 if isinstance(original, type):
                     # If we're patching out a class and there is a spec
                     inherit = True
-            if spec is None and _is_async_obj(original):
-                Klass = AsyncMock
-            else:
-                Klass = MagicMock
-            _kwargs = {}
+
+            # Determine the Klass to use
             if new_callable is not None:
                 Klass = new_callable
+            elif spec is None and _is_async_obj(original):
+                Klass = AsyncMock
             elif spec is not None or spec_set is not None:
                 this_spec = spec
                 if spec_set is not None:
@@ -1527,7 +1526,12 @@ class _patch(object):
                     Klass = AsyncMock
                 elif not_callable:
                     Klass = NonCallableMagicMock
+                else:
+                    Klass = MagicMock
+            else:
+                Klass = MagicMock
 
+            _kwargs = {}
             if spec is not None:
                 _kwargs['spec'] = spec
             if spec_set is not None:
diff --git a/Misc/NEWS.d/next/Library/2024-06-10-14-00-40.gh-issue-119600.jJMf4C.rst b/Misc/NEWS.d/next/Library/2024-06-10-14-00-40.gh-issue-119600.jJMf4C.rst
new file mode 100644
index 0000000..04c9ca9
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2024-06-10-14-00-40.gh-issue-119600.jJMf4C.rst
@@ -0,0 +1,2 @@
+Fix :func:`unittest.mock.patch` to not read attributes of the target when
+``new_callable`` is set. Patch by Robert Collins.