Resolve bare Protocol and Generic references in type position

mypy/typeanal.py

@@ -67,6 +67,7 @@
     LITERAL_TYPE_NAMES,
     MYPYC_NATIVE_INT_NAMES,
     NEVER_NAMES,
+    PROTOCOL_NAMES,
     TUPLE_NAMES,
     TYPE_ALIAS_NAMES,
     TYPE_NAMES,
@@ -702,6 +703,29 @@ def try_analyze_special_unbound_type(self, t: UnboundType, fullname: str) -> Typ
                 self.fail(f'{type_str} can\'t contain "{bad_item_name}"', t, code=codes.VALID_TYPE)
                 item = AnyType(TypeOfAny.from_error)
             return TypeType.make_normalized(item, line=t.line, column=t.column)
+        elif fullname in PROTOCOL_NAMES or fullname == "typing.Generic":
+            # A bare reference to Protocol or Generic in type expression position.
+            # Stubs declare both as X: type[_X] (mirroring the runtime, where they
+            # are classes on 3.12+), so e.g. 'type[Protocol]' must accept the
+            # special form itself.
+            # https://github.com/python/mypy/issues/21940
+            if t.args or t.empty_tuple_index:
+                # 'Protocol[...]'/ 'Generic[...]' are class base syntax, not a type.
+                return None
+            private = "_Protocol" if fullname in PROTOCOL_NAMES else "_Generic"
+            module = "typing_extensions" if fullname.startswith("typing_extensions.") else "typing"
+            sym = self.api.lookup_fully_qualified_or_none(f"{module}.{private}")
+            if sym is not None and isinstance(sym.node, PlaceholderNode):
+                if self.api.is_incomplete_namespace(module):
+                    # The private class is not defined yet, defer until it is.
+                    self.api.record_incomplete_ref()
+                    return AnyType(TypeOfAny.special_form)
+                return None
+            if sym is None or not isinstance(sym.node, TypeInfo):
+                # Stub sets that do not declare the private class yet: keep the
+                # regular 'not valid as a type' error instead of resolving to Any.
+                return None
+            return Instance(sym.node, [], line=t.line, column=t.column)
         elif fullname in ("typing_extensions.TypeForm", "typing.TypeForm"):
             if len(t.args) == 0:
                 any_type = self.get_omitted_any(t)

test-data/unit/check-generics.test

@@ -3737,3 +3737,11 @@ def test(tp: type[T]) -> T: ...
 
 class C(Generic[T]): ...
 reveal_type(test(C))  # N: Revealed type is "__main__.C[Any]"
+
+[case testGenericSpecialFormAsType]
+from typing import Generic
+
+g: type[Generic] = Generic
+
+def f(t: type[Generic]) -> None: ...
+f(Generic)

test-data/unit/check-protocols.test

@@ -4809,3 +4809,23 @@ bad_rep(t)  # E: Argument 1 to "bad_rep" has incompatible type "C"; expected "P[
             # N:     Got: \
             # N:         def rep(self) -> C
 [builtins fixtures/tuple.pyi]
+
+[case testProtocolSpecialFormAsType]
+from typing import Protocol
+
+x: type[Protocol] = Protocol
+
+def f(t: type[Protocol]) -> None: ...
+f(Protocol)
+
+ts: tuple[type[Protocol], ...] = (Protocol,)
+[builtins fixtures/bool.pyi]
+
+[case testTypingExtensionsProtocolSpecialFormAsType]
+from typing_extensions import Protocol
+
+x: type[Protocol] = Protocol
+
+def f(t: type[Protocol]) -> None: ...
+f(Protocol)
+[builtins fixtures/dict.pyi]

test-data/unit/fixtures/typing-async.pyi

@@ -14,8 +14,10 @@ Any = object()
 Union = 0
 Optional = 0
 TypeVar = 0
-Generic = 0
-Protocol = 0
+class _Generic: ...
+Generic: type[_Generic]
+class _Protocol: ...
+Protocol: type[_Protocol]
 Tuple = 0
 Callable = 0
 NamedTuple = 0

test-data/unit/fixtures/typing-full.pyi

@@ -25,8 +25,10 @@ def assert_type(o, t): ...
 overload = 0
 Any = object()
 Optional = 0
-Generic = 0
-Protocol = 0
+class _Generic: ...
+Generic: type[_Generic]
+class _Protocol: ...
+Protocol: type[_Protocol]
 Tuple = 0
 _promote = 0
 Type = 0

test-data/unit/fixtures/typing-medium.pyi

@@ -12,8 +12,10 @@ Any = object()
 Union = 0
 Optional = 0
 TypeVar = 0
-Generic = 0
-Protocol = 0
+class _Generic: ...
+Generic: type[_Generic]
+class _Protocol: ...
+Protocol: type[_Protocol]
 Tuple = 0
 Callable = 0
 _promote = 0

test-data/unit/fixtures/typing-namedtuple.pyi

@@ -1,5 +1,6 @@
 TypeVar = 0
-Generic = 0
+class _Generic: ...
+Generic: type[_Generic]
 Any = object()
 overload = 0
 Type = 0

test-data/unit/fixtures/typing-override.pyi

@@ -1,5 +1,6 @@
 TypeVar = 0
-Generic = 0
+class _Generic: ...
+Generic: type[_Generic]
 Any = object()
 overload = 0
 Type = 0

test-data/unit/fixtures/typing-typeddict-iror.pyi

@@ -16,8 +16,10 @@ Any = object()
 Union = 0
 Optional = 0
 TypeVar = 0
-Generic = 0
-Protocol = 0
+class _Generic: ...
+Generic: type[_Generic]
+class _Protocol: ...
+Protocol: type[_Protocol]
 Tuple = 0
 Callable = 0
 NamedTuple = 0

test-data/unit/fixtures/typing-typeddict.pyi

@@ -15,8 +15,10 @@ Any = object()
 Union = 0
 Optional = 0
 TypeVar = 0
-Generic = 0
-Protocol = 0
+class _Generic: ...
+Generic: type[_Generic]
+class _Protocol: ...
+Protocol: type[_Protocol]
 Tuple = 0
 Callable = 0
 NamedTuple = 0

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

@@ -15,8 +15,10 @@ Any = object()
 Union = 0
 Optional = 0
 TypeVar = 0
-Generic = 0
-Protocol = 0
+class _Generic: ...
+Generic: type[_Generic]
+class _Protocol: ...
+Protocol: type[_Protocol]
 Tuple = 0
 Callable = 0
 NamedTuple = 0

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

@@ -18,7 +18,8 @@ class _SpecialForm:
         pass
 
 NamedTuple = 0
-Protocol: _SpecialForm = ...
+class _Protocol: ...
+Protocol: type[_Protocol]
 def runtime_checkable(x: _T) -> _T: pass
 runtime = runtime_checkable