Use TypeGuard for has in Python 3.10 and above (#997)

* Use `TypeGuard` for `has` in Python 3.10 and above

* fixup! Use `TypeGuard` for `has` in Python 3.10 and above

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Test the negative case

* Add type guard example

Co-authored-by: Hynek Schlawack <hs@ox.cx>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

src/attr/__init__.pyi

@@ -27,6 +27,11 @@ from . import validators as validators
 from ._cmp import cmp_using as cmp_using
 from ._version_info import VersionInfo
 
+if sys.version_info >= (3, 10):
+    from typing import TypeGuard
+else:
+    from typing_extensions import TypeGuard
+
 __version__: str
 __version_info__: VersionInfo
 __title__: str
@@ -470,7 +475,7 @@ def astuple(
     tuple_factory: Type[Sequence[Any]] = ...,
     retain_collection_types: bool = ...,
 ) -> Tuple[Any, ...]: ...
-def has(cls: type) -> bool: ...
+def has(cls: type) -> TypeGuard[Type[AttrsInstance]]: ...
 def assoc(inst: _T, **changes: Any) -> _T: ...
 def evolve(inst: _T, **changes: Any) -> _T: ...
 

tests/test_mypy.yml

@@ -1371,3 +1371,15 @@
       b: str
 
     fields(A)  # E: Argument 1 to "fields" has incompatible type "Type[A]"; expected "Type[AttrsInstance]"
+
+- case: testHasTypeGuard
+  main: |
+    from attrs import define, has
+
+    @define
+    class A:
+        pass
+
+    reveal_type(A)  # N: Revealed type is "def () -> main.A"
+    if has(A):
+        reveal_type(A)  # N: Revealed type is "Type[attr.AttrsInstance]"

tests/typing_example.py

@@ -416,3 +416,9 @@ def accessing_from_attrs() -> None:
     attrs.setters.frozen
     attrs.validators.and_
     attrs.cmp_using
+
+
+def has_typeguard() -> None:
+    foo = object
+    if attrs.has(foo):
+        foo.__attrs_attrs__