Support factory= in attr plugin.

mypy/plugins/attrs.py

@@ -318,6 +318,12 @@ def _attribute_from_attrib_maker(ctx: 'mypy.plugin.ClassDefContext',
     init = _get_bool_argument(ctx, rvalue, 'init', True)
     # TODO: Check for attr.NOTHING
     attr_has_default = bool(_get_argument(rvalue, 'default'))
+    attr_has_factory = bool(_get_argument(rvalue, 'factory'))
+
+    if attr_has_default and attr_has_factory:
+        ctx.api.fail("Can't pass both `default` and `factory`.", rvalue)
+    elif attr_has_factory:
+        attr_has_default = True
 
     # If the type isn't set through annotation but is passed through `type=` use that.
     type_arg = _get_argument(rvalue, 'type')

test-data/unit/check-attr.test

@@ -771,3 +771,32 @@ class FFrozen(F):
     def bar(self) -> bool:
         return self._cb(5, 6)
 [builtins fixtures/callable.pyi]
+
+[case testAttrsWithFactory]
+from typing import List
+import attr
+def my_factory() -> int:
+    return 7
+@attr.s
+class A:
+    x: List[int] = attr.ib(factory=list)
+    y: int = attr.ib(factory=my_factory)
+A()
+[builtins fixtures/list.pyi]
+
+[case testAttrsFactoryAndDefault]
+import attr
+@attr.s
+class A:
+    x: int = attr.ib(factory=int, default=7)  # E: Can't pass both `default` and `factory`.
+[builtins fixtures/bool.pyi]
+
+[case testAttrsFactoryBadReturn]
+import attr
+def my_factory() -> int:
+    return 7
+@attr.s
+class A:
+    x: int = attr.ib(factory=list)  # E: Incompatible types in assignment (expression has type "List[T]", variable has type "int")
+    y: str = attr.ib(factory=my_factory) # E: Incompatible types in assignment (expression has type "int", variable has type "str")
+[builtins fixtures/list.pyi]

test-data/unit/lib-stub/attr.pyi

@@ -1,57 +1,97 @@
-from typing import TypeVar, overload, Callable, Any, Type, Optional
+from typing import TypeVar, overload, Callable, Any, Type, Optional, Union, Sequence, Mapping
 
 _T = TypeVar('_T')
 _C = TypeVar('_C', bound=type)
 
+_ValidatorType = Callable[[Any, Any, _T], Any]
+_ConverterType = Callable[[Any], _T]
+_FilterType = Callable[[Any, Any], bool]
+_ValidatorArgType = Union[_ValidatorType[_T], Sequence[_ValidatorType[_T]]]
+
+# This form catches an explicit None or no default and infers the type from the other arguments.
+@overload
+def attrib(default: None = ...,
+           validator: Optional[_ValidatorArgType[_T]] = ...,
+           repr: bool = ...,
+           cmp: bool = ...,
+           hash: Optional[bool] = ...,
+           init: bool = ...,
+           convert: Optional[_ConverterType[_T]] = ...,
+           metadata: Optional[Mapping[Any, Any]] = ...,
+           type: Optional[Type[_T]] = ...,
+           converter: Optional[_ConverterType[_T]] = ...,
+           factory: Optional[Callable[[], _T]] = ...,
+           ) -> _T: ...
+# This form catches an explicit default argument.
 @overload
-def attr(default: Optional[_T] = ...,
-         validator: Optional[Any] = ...,
-         repr: bool = ...,
-         cmp: bool = ...,
-         hash: Optional[bool] = ...,
-         init: bool = ...,
-         convert: Optional[Callable[[Any], _T]] = ...,
-         metadata: Any = ...,
-         type: Optional[Type[_T]] = ...,
-         converter: Optional[Callable[[Any], _T]] = ...) -> _T: ...
+def attrib(default: _T,
+           validator: Optional[_ValidatorArgType[_T]] = ...,
+           repr: bool = ...,
+           cmp: bool = ...,
+           hash: Optional[bool] = ...,
+           init: bool = ...,
+           convert: Optional[_ConverterType[_T]] = ...,
+           metadata: Optional[Mapping[Any, Any]] = ...,
+           type: Optional[Type[_T]] = ...,
+           converter: Optional[_ConverterType[_T]] = ...,
+           factory: Optional[Callable[[], _T]] = ...,
+           ) -> _T: ...
+# This form catches explicit None or no default but with no other arguments returns Any.
 @overload
-def attr(default: None = ...,
-         validator: None = ...,
-         repr: bool = ...,
-         cmp: bool = ...,
-         hash: Optional[bool] = ...,
-         init: bool = ...,
-         convert: Optional[Callable[[Any], _T]] = ...,
-         metadata: Any = ...,
-         type: None = ...,
-         converter: None = ...) -> Any: ...
+def attrib(default: None = ...,
+           validator: None = ...,
+           repr: bool = ...,
+           cmp: bool = ...,
+           hash: Optional[bool] = ...,
+           init: bool = ...,
+           convert: None = ...,
+           metadata: Optional[Mapping[Any, Any]] = ...,
+           type: None = ...,
+           converter: None = ...,
+           factory: None = ...,
+           ) -> Any: ...
+# This form covers type=non-Type: e.g. forward references (str), Any
+@overload
+def attrib(default: Optional[_T] = ...,
+           validator: Optional[_ValidatorArgType[_T]] = ...,
+           repr: bool = ...,
+           cmp: bool = ...,
+           hash: Optional[bool] = ...,
+           init: bool = ...,
+           convert: Optional[_ConverterType[_T]] = ...,
+           metadata: Optional[Mapping[Any, Any]] = ...,
+           type: object = ...,
+           converter: Optional[_ConverterType[_T]] = ...,
+           factory: Optional[Callable[[], _T]] = ...,
+           ) -> Any: ...
 
 @overload
-def attributes(maybe_cls: _C,
-               these: Optional[Any] = ...,
-               repr_ns: Optional[str] = ...,
-               repr: bool = ...,
-               cmp: bool = ...,
-               hash: Optional[bool] = ...,
-               init: bool = ...,
-               slots: bool = ...,
-               frozen: bool = ...,
-               str: bool = ...,
-               auto_attribs: bool = ...) -> _C: ...
+def attrs(maybe_cls: _C,
+          these: Optional[Mapping[str, Any]] = ...,
+          repr_ns: Optional[str] = ...,
+          repr: bool = ...,
+          cmp: bool = ...,
+          hash: Optional[bool] = ...,
+          init: bool = ...,
+          slots: bool = ...,
+          frozen: bool = ...,
+          str: bool = ...,
+          auto_attribs: bool = ...) -> _C: ...
 @overload
-def attributes(maybe_cls: None = ...,
-               these: Optional[Any] = ...,
-               repr_ns: Optional[str] = ...,
-               repr: bool = ...,
-               cmp: bool = ...,
-               hash: Optional[bool] = ...,
-               init: bool = ...,
-               slots: bool = ...,
-               frozen: bool = ...,
-               str: bool = ...,
-               auto_attribs: bool = ...) -> Callable[[_C], _C]: ...
+def attrs(maybe_cls: None = ...,
+          these: Optional[Mapping[str, Any]] = ...,
+          repr_ns: Optional[str] = ...,
+          repr: bool = ...,
+          cmp: bool = ...,
+          hash: Optional[bool] = ...,
+          init: bool = ...,
+          slots: bool = ...,
+          frozen: bool = ...,
+          str: bool = ...,
+          auto_attribs: bool = ...) -> Callable[[_C], _C]: ...
+
 
 # aliases
-s = attrs = attributes
-ib = attrib = attr
+s = attributes = attrs
+ib = attr = attrib
 dataclass = attrs # Technically, partial(attrs, auto_attribs=True) ;)