Fix stubtest false positives with TypedDicts at runtime (#14984)

Fixes #14983

Author: AlexWaygood

mypy/stubtest.py

@@ -26,7 +26,7 @@
 from functools import singledispatch
 from pathlib import Path
 from typing import Any, Generic, Iterator, TypeVar, Union
-from typing_extensions import get_origin
+from typing_extensions import get_origin, is_typeddict
 
 import mypy.build
 import mypy.modulefinder
@@ -436,12 +436,12 @@ class SubClass(runtime):  # type: ignore[misc]
 
 
 def _verify_metaclass(
-    stub: nodes.TypeInfo, runtime: type[Any], object_path: list[str]
+    stub: nodes.TypeInfo, runtime: type[Any], object_path: list[str], *, is_runtime_typeddict: bool
 ) -> Iterator[Error]:
     # We exclude protocols, because of how complex their implementation is in different versions of
-    # python. Enums are also hard, ignoring.
+    # python. Enums are also hard, as are runtime TypedDicts; ignoring.
     # TODO: check that metaclasses are identical?
-    if not stub.is_protocol and not stub.is_enum:
+    if not stub.is_protocol and not stub.is_enum and not is_runtime_typeddict:
         runtime_metaclass = type(runtime)
         if runtime_metaclass is not type and stub.metaclass_type is None:
             # This means that runtime has a custom metaclass, but a stub does not.
@@ -485,22 +485,27 @@ def verify_typeinfo(
         return
 
     yield from _verify_final(stub, runtime, object_path)
-    yield from _verify_metaclass(stub, runtime, object_path)
+    is_runtime_typeddict = stub.typeddict_type is not None and is_typeddict(runtime)
+    yield from _verify_metaclass(
+        stub, runtime, object_path, is_runtime_typeddict=is_runtime_typeddict
+    )
 
     # Check everything already defined on the stub class itself (i.e. not inherited)
     to_check = set(stub.names)
     # Check all public things on the runtime class
     to_check.update(
         m for m in vars(runtime) if not is_probably_private(m) and m not in IGNORABLE_CLASS_DUNDERS
     )
-    # Special-case the __init__ method for Protocols
+    # Special-case the __init__ method for Protocols and the __new__ method for TypedDicts
     #
     # TODO: On Python <3.11, __init__ methods on Protocol classes
     # are silently discarded and replaced.
     # However, this is not the case on Python 3.11+.
     # Ideally, we'd figure out a good way of validating Protocol __init__ methods on 3.11+.
     if stub.is_protocol:
         to_check.discard("__init__")
+    if is_runtime_typeddict:
+        to_check.discard("__new__")
 
     for entry in sorted(to_check):
         mangled_entry = entry

mypy/test/teststubtest.py

@@ -1572,24 +1572,36 @@ class _Options(TypedDict):
         )
 
     @collect_cases
-    def test_protocol(self) -> Iterator[Case]:
+    def test_runtime_typing_objects(self) -> Iterator[Case]:
+        yield Case(
+            stub="from typing_extensions import Protocol, TypedDict",
+            runtime="from typing_extensions import Protocol, TypedDict",
+            error=None,
+        )
         yield Case(
             stub="""
-            from typing_extensions import Protocol
-
             class X(Protocol):
                 bar: int
                 def foo(self, x: int, y: bytes = ...) -> str: ...
             """,
             runtime="""
-            from typing_extensions import Protocol
-
             class X(Protocol):
                 bar: int
                 def foo(self, x: int, y: bytes = ...) -> str: ...
             """,
             error=None,
         )
+        yield Case(
+            stub="""
+            class Y(TypedDict):
+                a: int
+            """,
+            runtime="""
+            class Y(TypedDict):
+                a: int
+            """,
+            error=None,
+        )
 
     @collect_cases
     def test_type_var(self) -> Iterator[Case]:

test-data/unit/lib-stub/typing_extensions.pyi

@@ -56,6 +56,10 @@ class _TypedDict(Mapping[str, object]):
     if sys.version_info < (3, 0):
         def has_key(self, k: str) -> bool: ...
     def __delitem__(self, k: NoReturn) -> None: ...
+    # Stubtest's tests need the following items:
+    __required_keys__: frozenset[str]
+    __optional_keys__: frozenset[str]
+    __total__: bool
 
 def TypedDict(typename: str, fields: Dict[str, Type[_T]], *, total: Any = ...) -> Type[dict]: ...