Add Y037 code to check for possible usage of PEP 604 new syntax

CHANGELOG.md

@@ -4,6 +4,8 @@
 
 Features:
 * Introduce Y036 (check for badly defined `__exit__` and `__aexit__` methods).
+* Introduce Y037 (Use PEP 604 syntax instead of `typing.Union` and `typing.Optional`).
+  Contributed by Oleg Höfling.
 
 ## 22.3.0
 

README.md

@@ -68,6 +68,7 @@ currently emitted:
 | Y034 | Y034 detects common errors where certain methods are annotated as having a fixed return type, despite returning `self` at runtime. Such methods should be annotated with `_typeshed.Self`. This check looks for:<br><br>&nbsp;&nbsp;**1.**&nbsp;&nbsp;Any in-place BinOp dunder methods (`__iadd__`, `__ior__`, etc.) that do not return `Self`.<br>&nbsp;&nbsp;**2.**&nbsp;&nbsp;`__new__`, `__enter__` and `__aenter__` methods that return the class's name unparameterised.<br>&nbsp;&nbsp;**3.**&nbsp;&nbsp;`__iter__` methods that return `Iterator`, even if the class inherits directly from `Iterator`.<br>&nbsp;&nbsp;**4.**&nbsp;&nbsp;`__aiter__` methods that return `AsyncIterator`, even if the class inherits directly from `AsyncIterator`.<br><br>This check excludes methods decorated with `@overload` or `@abstractmethod`.
 | Y035 | `__all__` in a stub file should always have a value, as `__all__` in a `.pyi` file has identical semantics to `__all__` in a `.py` file. E.g. write `__all__ = ["foo", "bar"]` instead of `__all__: list[str]`.
 | Y036 | Y036 detects common errors in `__exit__` and `__aexit__` methods. For example, the first argument in an `__exit__` method should always be annotated with `type[Exception] | None`.
+| Y037 | Use PEP 604 syntax instead of `typing.Union` and `typing.Optional`. E.g. use `str \| int` instead of `Union[str, int]`, and use `str \| None` instead of `Optional[str]`.
 
 Many error codes enforce modern conventions, and some cannot yet be used in
 all cases:

pyi.py

@@ -625,6 +625,17 @@ def _check_import_or_attribute(
         elif fullname == "collections.namedtuple":
             error_message = Y024
 
+        # Y037 errors
+        elif fullname == "typing.Optional":
+            error_message = Y037.format(
+                old_syntax=fullname, example='"int | None" instead of "Optional[int]"'
+            )
+
+        elif fullname == "typing.Union":
+            error_message = Y037.format(
+                old_syntax=fullname, example='"int | str" instead of "Union[int, str]"'
+            )
+
         else:
             return
 
@@ -1480,3 +1491,4 @@ def parse_options(
 Y034 = 'Y034 {methods} usually return "self" at runtime. Consider using "_typeshed.Self" in "{method_name}", e.g. "{suggested_syntax}"'
 Y035 = 'Y035 "__all__" in a stub file must have a value, as it has the same semantics as "__all__" at runtime.'
 Y036 = "Y036 Badly defined {method_name} method: {details}"
+Y037 = "Y037 Use PEP 604 union types instead of {old_syntax} (e.g. {example})."

tests/del.pyi

@@ -1,3 +1,4 @@
+# flags: --ignore=Y037
 from typing import TypeAlias, Union
 
 ManyStr: TypeAlias = list[EitherStr]

tests/forward_refs.pyi

@@ -1,3 +1,4 @@
+# flags: --ignore=Y037
 from typing import Optional, TypeAlias, Union
 
 MaybeCStr: TypeAlias = Optional[CStr]

tests/forward_refs_annassign.pyi

@@ -1,3 +1,4 @@
+# flags: --ignore=Y037
 from typing import Optional, TypeAlias, Union
 
 MaybeCStr: TypeAlias = Optional[CStr]

tests/imports.pyi

@@ -1,3 +1,4 @@
+# flags: --extend-ignore=Y037
 # NOTE: F401 & F811 are ignored in this file in the .flake8 config file
 
 # GOOD IMPORTS

tests/pep604_union_types.pyi

@@ -0,0 +1,32 @@
+import typing
+from typing import (  # Y037 Use PEP 604 union types instead of typing.Optional (e.g. "int | None" instead of "Optional[int]"). # Y037 Use PEP 604 union types instead of typing.Union (e.g. "int | str" instead of "Union[int, str]").
+    Optional,
+    Union,
+)
+
+x1: Optional[str]
+x2: Optional
+x3: Union[str, int]
+x4: Union
+
+
+y1: typing.Optional[str]  # Y037 Use PEP 604 union types instead of typing.Optional (e.g. "int | None" instead of "Optional[int]").
+y2: typing.Optional  # Y037 Use PEP 604 union types instead of typing.Optional (e.g. "int | None" instead of "Optional[int]").
+y3: typing.Union[str, int]  # Y037 Use PEP 604 union types instead of typing.Union (e.g. "int | str" instead of "Union[int, str]").
+y4: typing.Union  # Y037 Use PEP 604 union types instead of typing.Union (e.g. "int | str" instead of "Union[int, str]").
+
+
+def f1(x: Optional[str] = ...) -> None: ...
+def f2() -> Optional[str]: ...
+def f3() -> Union[str, int]: ...
+def f4(x: Union[str, int] = ...) -> None: ...
+def f5(x: Optional) -> None: ...
+def f6(x: Union) -> None: ...
+
+
+def g1(x: typing.Optional[str] = ...) -> None: ...  # Y037 Use PEP 604 union types instead of typing.Optional (e.g. "int | None" instead of "Optional[int]").
+def g2() -> typing.Optional[str]: ...  # Y037 Use PEP 604 union types instead of typing.Optional (e.g. "int | None" instead of "Optional[int]").
+def g3() -> typing.Union[str, int]: ...  # Y037 Use PEP 604 union types instead of typing.Union (e.g. "int | str" instead of "Union[int, str]").
+def g4(x: typing.Union[str, int] = ...) -> None: ...  # Y037 Use PEP 604 union types instead of typing.Union (e.g. "int | str" instead of "Union[int, str]").
+def g5(x: typing.Optional) -> None: ...  # Y037 Use PEP 604 union types instead of typing.Optional (e.g. "int | None" instead of "Optional[int]").
+def g6(x: typing.Union) -> None: ...  # Y037 Use PEP 604 union types instead of typing.Union (e.g. "int | str" instead of "Union[int, str]").

tests/typevar.pyi

@@ -1,3 +1,4 @@
+# flags: --extend-ignore=Y037
 import typing
 from typing import Annotated, ParamSpec, TypeVar, TypeVarTuple, Union
 

tests/union_duplicates.pyi

@@ -1,3 +1,4 @@
+# flags: --extend-ignore=Y037
 import typing
 from typing import Union
 

tests/vanilla_flake8_not_clean_forward_refs.pyi

@@ -1,4 +1,4 @@
-# flags: --no-pyi-aware-file-checker
+# flags: --no-pyi-aware-file-checker --ignore=Y037
 from typing import TypeAlias, Union
 
 ManyStr: TypeAlias = list[EitherStr]  # F821 undefined name 'EitherStr'