More precise type for TypeAliasType.__getitem__ (#12354)

JelleZijlstra · web-flow · commit d482d4e83c9d · 2024-07-17T06:37:31.000-07:00
At runtime, this always returns a GenericAlias; see typealias_subscript in Objects/typevarobject.c. See microsoft/pyright#8444.
diff --git a/stdlib/typing.pyi b/stdlib/typing.pyi
@@ -1056,7 +1056,7 @@ if sys.version_info >= (3, 12):
         # It's writable on types, but not on instances of TypeAliasType.
         @property
         def __module__(self) -> str | None: ...  # type: ignore[override]
-        def __getitem__(self, parameters: Any) -> Any: ...
+        def __getitem__(self, parameters: Any) -> GenericAlias: ...
         def __or__(self, right: Any) -> _SpecialForm: ...
         def __ror__(self, left: Any) -> _SpecialForm: ...
 
diff --git a/stdlib/typing_extensions.pyi b/stdlib/typing_extensions.pyi
@@ -403,6 +403,7 @@ else:
         # It's writable on types, but not on instances of TypeAliasType.
         @property
         def __module__(self) -> str | None: ...  # type: ignore[override]
+        # Returns typing._GenericAlias, which isn't stubbed.
         def __getitem__(self, parameters: Any) -> Any: ...
         if sys.version_info >= (3, 10):
             def __or__(self, right: Any) -> _SpecialForm: ...
