Mypy improvements

src/attr/__init__.pyi

@@ -8,6 +8,7 @@ from typing import (
     List,
     Mapping,
     Optional,
+    Protocol,
     Sequence,
     Tuple,
     Type,
@@ -57,6 +58,10 @@ _CompareWithType = Callable[[Any, Any], bool]
 # _ValidatorType from working when passed in a list or tuple.
 _ValidatorArgType = Union[_ValidatorType[_T], Sequence[_ValidatorType[_T]]]
 
+# A protocol to be able to statically accept an attrs class.
+class AttrsClass(Protocol[_T]):
+    __attrs_attrs__: _T
+
 # _make --
 
 NOTHING: object
@@ -399,11 +404,7 @@ def define(
 mutable = define
 frozen = define  # they differ only in their defaults
 
-# TODO: add support for returning NamedTuple from the mypy plugin
-class _Fields(Tuple[Attribute[Any], ...]):
-    def __getattr__(self, name: str) -> Attribute[Any]: ...
-
-def fields(cls: type) -> _Fields: ...
+def fields(cls: type[AttrsClass[_T]]) -> _T: ...
 def fields_dict(cls: type) -> Dict[str, Attribute[Any]]: ...
 def validate(inst: Any) -> None: ...
 def resolve_types(

tests/test_mypy.yml

@@ -316,7 +316,6 @@
     class Confused:
        ...
 
-
 - case: testAttrsInheritance
   main: |
     import attr
@@ -1393,3 +1392,15 @@
         foo = x
 
     reveal_type(B)  # N: Revealed type is "def (foo: builtins.int) -> main.B"
+
+- case: testFields
+  main: |
+    from attr import define, fields
+
+    @define
+    class A:
+      a: int
+      b: str
+
+    reveal_type(fields(A))  # N: Revealed type is "Tuple[attr.Attribute[builtins.int], attr.Attribute[builtins.str]]"
+    fields(A).a