Y068: Don't use @OverRide (#528)

Author: srittau

CHANGELOG.md

@@ -1,5 +1,8 @@
 # Change Log
 
+New error codes:
+* Introduce Y068: Don't use `@override` in stub files.
+
 ## 5.5.0
 
 New error codes:

ERRORCODES.md

@@ -80,8 +80,8 @@ The following warnings are currently emitted by default:
 | <a id="Y064" href="#Y064">Y064</a> | Use simpler syntax to define final literal types. For example, use `x: Final = 42` instead of `x: Final[Literal[42]]`. | Style
 | <a id="Y065" href="#Y065">Y065</a> | Don't use bare `Incomplete` in argument and return annotations. Instead, leave them unannotated. Omitting an annotation entirely from a function will cause some type checkers to view the parameter or return type as "untyped"; this may result in stricter type-checking on code that makes use of the stubbed function. | Style
 | <a id="Y066" href="#Y066">Y066</a> | When using if/else with `sys.version_info`, put the code for new Python versions first. | Style
-| <a id="Y067" href="#Y067">Y067</a> | Don't use `Incomplete | None = None` in
-argument annotations. Instead, just use `=None`. | Style
+| <a id="Y067" href="#Y067">Y067</a> | Don't use `Incomplete \| None = None` in argument annotations. Instead, just use `=None`. | Style
+| <a id="Y068" href="#Y068">Y068</a> | Don't use `@override` in stub files. Problems with a function signature deviating from its superclass are inherited from the implementation, and other tools such as stubtest are better placed to recognize deviations between stubs and the implementation. | Understanding stubs
 
 ## Warnings disabled by default
 

flake8_pyi/errors.py

@@ -127,6 +127,8 @@ class Error(NamedTuple):
     'put the code for new Python versions first, e.g. "{new_syntax}"'
 )
 Y067 = 'Y067 Use "=None" instead of "Incomplete | None = None"'
+Y068 = 'Y068 Do not use "@override" in stub files.'
+
 Y090 = (
     'Y090 "{original}" means '
     '"a tuple of length 1, in which the sole element is of type {typ!r}". '

flake8_pyi/visitor.py

@@ -226,6 +226,7 @@ def _is_object(node: ast.AST | None, name: str, *, from_: Container[str]) -> boo
 )
 _is_Generic = partial(_is_object, name="Generic", from_=_TYPING_MODULES)
 _is_Unpack = partial(_is_object, name="Unpack", from_=_TYPING_MODULES)
+_is_override = partial(_is_object, name="override", from_=_TYPING_MODULES)
 
 
 def _is_union(node: ast.expr | None) -> TypeIs[ast.BinOp]:
@@ -2032,6 +2033,12 @@ def check_protocol_param_kinds(
                 pos_or_kw, errors.Y091.format(arg=pos_or_kw.arg, method=node.name)
             )
 
+    def check_for_override(self, node: ast.FunctionDef | ast.AsyncFunctionDef) -> None:
+        for deco in node.decorator_list:
+            if _is_override(deco):
+                self.error(deco, errors.Y068)
+                return
+
     @staticmethod
     def _is_positional_pre_570_argname(name: str) -> bool:
         # https://peps.python.org/pep-0484/#positional-only-arguments
@@ -2094,6 +2101,7 @@ def _visit_function(self, node: ast.FunctionDef | ast.AsyncFunctionDef) -> None:
             self.check_self_typevars(node, decorator_names)
             if self.enclosing_class_ctx.is_protocol_class:
                 self.check_protocol_param_kinds(node, decorator_names)
+            self.check_for_override(node)
 
     def visit_arg(self, node: ast.arg) -> None:
         if _is_NoReturn(node.annotation):

tests/override.pyi

@@ -0,0 +1,24 @@
+import typing
+import typing as t
+from typing import override, override as over
+
+import typing_extensions
+
+class Foo:
+    def f(self) -> None: ...
+    def g(self) -> None: ...
+    def h(self) -> None: ...
+    def j(self) -> None: ...
+    def k(self) -> None: ...
+
+class Bar(Foo):
+    @override  # Y068 Do not use "@override" in stub files.
+    def f(self) -> None: ...
+    @typing.override  # Y068 Do not use "@override" in stub files.
+    def g(self) -> None: ...
+    @t.override  # Ideally we'd catch this too, but the infrastructure is not in place.
+    def h(self) -> None: ...
+    @over  # Ideally we'd catch this too, but the infrastructure is not in place.
+    def j(self) -> None: ...
+    @typing_extensions.override  # Y068 Do not use "@override" in stub files.
+    def k(self) -> None: ...