Oct 6, 2025 · Sep 22, 2025 · Sep 22, 2025 · Sep 22, 2025 · Sep 23, 2025 · Sep 23, 2025
diff --git a/docs/source/error_code_list2.rst b/docs/source/error_code_list2.rst
                print("red")
            case _:
                print("other")

 .. _code-untyped-decorator:

 Error if an untyped decorator makes a typed function effectively untyped [untyped-decorator]
 --------------------------------------------------------------------------------------------

 If enabled with :option:`--disallow-untyped-decorators <mypy --disallow-untyped-decorators>`
 mypy generates an error if a typed function is wrapped by an untyped decorator
 (as this would effectively remove the benefits of typing the function).

 Example:

 .. code-block:: python

        def printing_decorator(func):
            def wrapper(*args, **kwds):
                print("Calling", func)
                return func(*args, **kwds)
            return wrapper
        # A decorated function.
        @printing_decorator  # E: Untyped decorator makes function "add_forty_two" untyped  [untyped-decorator]
        def add_forty_two(value: int) -> int:
            return value + 42
diff --git a/mypy/errorcodes.py b/mypy/errorcodes.py
    sub_code_of=MISC,
 )

 UNTYPED_DECORATOR: Final = ErrorCode(
    "untyped-decorator", "Error if an untyped decorator makes a typed function untyped", "General"
 )

 NARROWED_TYPE_NOT_SUBTYPE: Final = ErrorCode(
    "narrowed-type-not-subtype",
    "Warn if a TypeIs function's narrowed type is not a subtype of the original type",
diff --git a/mypy/messages.py b/mypy/messages.py
            )

    def typed_function_untyped_decorator(self, func_name: str, context: Context) -> None:
        self.fail(f'Untyped decorator makes function "{func_name}" untyped', context)
        self.fail(
            f'Untyped decorator makes function "{func_name}" untyped',
            context,
            code=codes.UNTYPED_DECORATOR,
        )

    def bad_proto_variance(
        self, actual: int, tvar_name: str, expected: int, context: Context
diff --git a/test-data/unit/check-errorcodes.test b/test-data/unit/check-errorcodes.test
 def g():
    pass

 [case testErrorCodeUntypedDecorator]
 # flags: --disallow-untyped-decorators --warn-unused-ignores
 def d(f): return f

 @d  # E: Untyped decorator makes function "x" untyped  [untyped-decorator]
 def x() -> int: return 1
 @d  # type: ignore
 def y() -> int: return 2
 @d  # type: ignore[untyped-decorator]
 def best() -> int: return 3
 @d  # type: ignore[misc]  # E: Unused "type: ignore" comment  [unused-ignore] \
                          # E: Untyped decorator makes function "z" untyped  [untyped-decorator] \
                          # N: Error code "untyped-decorator" not covered by "type: ignore" comment
 def z() -> int: return 4

 [case testErrorCodeIndexing]
 from typing import Dict
 x: Dict[int, int]
Original file line number	Diff line number	Diff line change
Expand Up		@@ -676,3 +676,26 @@ Example:
		print("red")
		case _:
		print("other")

		.. _code-untyped-decorator:

		Error if an untyped decorator makes a typed function effectively untyped [untyped-decorator]
		--------------------------------------------------------------------------------------------

		If enabled with :option:`--disallow-untyped-decorators <mypy --disallow-untyped-decorators>`
		mypy generates an error if a typed function is wrapped by an untyped decorator
		(as this would effectively remove the benefits of typing the function).

		Example:

		.. code-block:: python

		def printing_decorator(func):
		def wrapper(args, *kwds):
		print("Calling", func)
		return func(args, *kwds)
		return wrapper
		# A decorated function.
		@printing_decorator # E: Untyped decorator makes function "add_forty_two" untyped [untyped-decorator]
		def add_forty_two(value: int) -> int:
		return value + 42
Original file line number	Diff line number	Diff line change
Expand Up		@@ -302,6 +302,10 @@ def __hash__(self) -> int:
		sub_code_of=MISC,
		)

		UNTYPED_DECORATOR: Final = ErrorCode(
		"untyped-decorator", "Error if an untyped decorator makes a typed function untyped", "General"
		)

		NARROWED_TYPE_NOT_SUBTYPE: Final = ErrorCode(
		"narrowed-type-not-subtype",
		"Warn if a TypeIs function's narrowed type is not a subtype of the original type",
Expand Down
Original file line number	Diff line number	Diff line change
Expand Up		@@ -2008,7 +2008,11 @@ def untyped_decorated_function(self, typ: Type, context: Context) -> None:
		)

		def typed_function_untyped_decorator(self, func_name: str, context: Context) -> None:
		self.fail(f'Untyped decorator makes function "{func_name}" untyped', context)
		self.fail(
		f'Untyped decorator makes function "{func_name}" untyped',
		context,
		code=codes.UNTYPED_DECORATOR,
		)

		def bad_proto_variance(
		self, actual: int, tvar_name: str, expected: int, context: Context
Expand Down
Original file line number	Diff line number	Diff line change
Expand Up		@@ -394,6 +394,21 @@ def f() -> None:
		def g():
		pass

		[case testErrorCodeUntypedDecorator]
		# flags: --disallow-untyped-decorators --warn-unused-ignores
		def d(f): return f

		@d # E: Untyped decorator makes function "x" untyped [untyped-decorator]
		def x() -> int: return 1
		@d # type: ignore
		def y() -> int: return 2
		@d # type: ignore[untyped-decorator]
		def best() -> int: return 3
		@d # type: ignore[misc] # E: Unused "type: ignore" comment [unused-ignore] \
		# E: Untyped decorator makes function "z" untyped [untyped-decorator] \
		# N: Error code "untyped-decorator" not covered by "type: ignore" comment
		def z() -> int: return 4

		[case testErrorCodeIndexing]
		from typing import Dict
		x: Dict[int, int]
Expand Down