[WIP/RFC] Revisit patching of mypy builtins (reveal_{type,locals}) (#615)

* Revisit patching of mypy builtins (reveal_{type,locals})

Fixes https://github.com/typeddjango/django-stubs/issues/609
Reverts ee58b18f15

* Create test_patching.yml

Co-authored-by: Nikita Sobolev <mail@sobolevn.me>

django_stubs_ext/tests/test_monkeypatching.py

@@ -29,9 +29,6 @@ def make_generic_classes(
             with suppress(AttributeError):
                 delattr(el.cls, "__class_getitem__")
 
-        del builtins.reveal_type
-        del builtins.reveal_locals
-
     def factory(django_version: Optional[_VersionSpec] = None) -> None:
         if django_version is not None:
             monkeypatch.setattr(patch, "VERSION", django_version)
@@ -71,11 +68,15 @@ def test_patched_version_specific(
             assert el.cls[int] is el.cls
 
 
-def test_patched_mypy_builtins(
+def test_mypy_builtins_not_patched_globally(
     make_generic_classes: _MakeGenericClasses,
 ) -> None:
-    """Ensures that we properly patch builtins with `mypy` specific helpers."""
+    """Ensures that builtins are not patched with `mypy` specific helpers.
+
+    This should only happend during `django.setup()`
+    (https://github.com/typeddjango/django-stubs/issues/609).
+    """
     make_generic_classes()
 
-    assert builtins.reveal_type
-    assert builtins.reveal_locals
+    assert not hasattr(builtins, "reveal_type")
+    assert not hasattr(builtins, "reveal_locals")

django_stubs_ext/tests/typecheck/test_patching.yml

@@ -0,0 +1,15 @@
+-   case: patch_reveal_type_during_django_setup
+    main: |
+        # `main` is empty on purpose, because we test the `django.setup()` step.
+        # It executes the `myapp/models.py` file and should not produce anything,
+        # because `reveal_type` and `reveal_locals` are patched.
+    installed_apps:
+        - myapp
+    files:
+        -   path: myapp/__init__.py
+        -   path: myapp/models.py
+            content: |
+                # Will be executed during `django.setup()`:
+                a = 1
+                reveal_type(a)
+                reveal_locals()