diff --git a/mypy/plugins/attrs.py b/mypy/plugins/attrs.py
index e4328d764be6..4c96003ca326 100644
--- a/mypy/plugins/attrs.py
+++ b/mypy/plugins/attrs.py
@@ -69,6 +69,7 @@
TupleType,
Type,
TypeOfAny,
+ TypeType,
TypeVarType,
UninhabitedType,
UnionType,
@@ -935,7 +936,7 @@ def add_method(
def _get_attrs_init_type(typ: Instance) -> CallableType | None:
"""
- If `typ` refers to an attrs class, gets the type of its initializer method.
+ If `typ` refers to an attrs class, get the type of its initializer method.
"""
magic_attr = typ.type.get(MAGIC_ATTR_NAME)
if magic_attr is None or not magic_attr.plugin_generated:
@@ -1009,7 +1010,7 @@ def _get_expanded_attr_types(
def _meet_fields(types: list[Mapping[str, Type]]) -> Mapping[str, Type]:
"""
- "Meets" the fields of a list of attrs classes, i.e. for each field, its new type will be the lower bound.
+ "Meet" the fields of a list of attrs classes, i.e. for each field, its new type will be the lower bound.
"""
field_to_types = defaultdict(list)
for fields in types:
@@ -1026,7 +1027,7 @@ def _meet_fields(types: list[Mapping[str, Type]]) -> Mapping[str, Type]:
def evolve_function_sig_callback(ctx: mypy.plugin.FunctionSigContext) -> CallableType:
"""
- Generates a signature for the 'attr.evolve' function that's specific to the call site
+ Generate a signature for the 'attr.evolve' function that's specific to the call site
and dependent on the type of the first argument.
"""
if len(ctx.args) != 2:
@@ -1060,3 +1061,48 @@ def evolve_function_sig_callback(ctx: mypy.plugin.FunctionSigContext) -> Callabl
fallback=ctx.default_signature.fallback,
name=f"{ctx.default_signature.name} of {inst_type_str}",
)
+
+
+def fields_function_sig_callback(ctx: mypy.plugin.FunctionSigContext) -> CallableType:
+ """Provide the signature for `attrs.fields`."""
+ if not ctx.args or len(ctx.args) != 1 or not ctx.args[0] or not ctx.args[0][0]:
+ return ctx.default_signature
+
+ # <hack>
+ assert isinstance(ctx.api, TypeChecker)
+ inst_type = ctx.api.expr_checker.accept(ctx.args[0][0])
+ # </hack>
+ proper_type = get_proper_type(inst_type)
+
+ # fields(Any) -> Any, fields(type[Any]) -> Any
+ if (
+ isinstance(proper_type, AnyType)
+ or isinstance(proper_type, TypeType)
+ and isinstance(proper_type.item, AnyType)
+ ):
+ return ctx.default_signature
+
+ cls = None
+ arg_types = ctx.default_signature.arg_types
+
+ if isinstance(proper_type, TypeVarType):
+ inner = get_proper_type(proper_type.upper_bound)
+ if isinstance(inner, Instance):
+ # We need to work arg_types to compensate for the attrs stubs.
+ arg_types = [inst_type]
+ cls = inner.type
+ elif isinstance(proper_type, CallableType):
+ cls = proper_type.type_object()
+
+ if cls is not None and MAGIC_ATTR_NAME in cls.names:
+ # This is a proper attrs class.
+ ret_type = cls.names[MAGIC_ATTR_NAME].type
+ assert ret_type is not None
+ return ctx.default_signature.copy_modified(arg_types=arg_types, ret_type=ret_type)
+
+ ctx.api.fail(
+ f'Argument 1 to "fields" has incompatible type "{format_type_bare(proper_type, ctx.api.options)}"; expected an attrs class',
+ ctx.context,
+ )
+
+ return ctx.default_signature
diff --git a/mypy/plugins/default.py b/mypy/plugins/default.py
index 1edc91a1183c..500eef76a9d9 100644
--- a/mypy/plugins/default.py
+++ b/mypy/plugins/default.py
@@ -45,6 +45,7 @@ def get_function_hook(self, fullname: str) -> Callable[[FunctionContext], Type]
return ctypes.array_constructor_callback
elif fullname == "functools.singledispatch":
return singledispatch.create_singledispatch_function_callback
+
return None
def get_function_signature_hook(
@@ -54,6 +55,8 @@ def get_function_signature_hook(
if fullname in ("attr.evolve", "attrs.evolve", "attr.assoc", "attrs.assoc"):
return attrs.evolve_function_sig_callback
+ elif fullname in ("attr.fields", "attrs.fields"):
+ return attrs.fields_function_sig_callback
return None
def get_method_signature_hook(
diff --git a/test-data/unit/check-plugin-attrs.test b/test-data/unit/check-plugin-attrs.test
index ce1d670431c7..e34408454a83 100644
--- a/test-data/unit/check-plugin-attrs.test
+++ b/test-data/unit/check-plugin-attrs.test
@@ -1548,6 +1548,59 @@ takes_attrs_cls(A(1, "")) # E: Argument 1 to "takes_attrs_cls" has incompatible
takes_attrs_instance(A) # E: Argument 1 to "takes_attrs_instance" has incompatible type "Type[A]"; expected "AttrsInstance" # N: ClassVar protocol member AttrsInstance.__attrs_attrs__ can never be matched by a class object
[builtins fixtures/plugin_attrs.pyi]
+[case testAttrsFields]
+import attr
+from attrs import fields as f # Common usage.
+
+@attr.define
+class A:
+ b: int
+ c: str
+
+reveal_type(f(A)) # N: Revealed type is "Tuple[attr.Attribute[builtins.int], attr.Attribute[builtins.str], fallback=__main__.A.____main___A_AttrsAttributes__]"
+reveal_type(f(A)[0]) # N: Revealed type is "attr.Attribute[builtins.int]"
+reveal_type(f(A).b) # N: Revealed type is "attr.Attribute[builtins.int]"
+f(A).x # E: "____main___A_AttrsAttributes__" has no attribute "x"
+
+[builtins fixtures/plugin_attrs.pyi]
+
+[case testAttrsGenericFields]
+from typing import TypeVar
+
+import attr
+from attrs import fields
+
+@attr.define
+class A:
+ b: int
+ c: str
+
+TA = TypeVar('TA', bound=A)
+
+def f(t: TA) -> None:
+ reveal_type(fields(t)) # N: Revealed type is "Tuple[attr.Attribute[builtins.int], attr.Attribute[builtins.str], fallback=__main__.A.____main___A_AttrsAttributes__]"
+ reveal_type(fields(t)[0]) # N: Revealed type is "attr.Attribute[builtins.int]"
+ reveal_type(fields(t).b) # N: Revealed type is "attr.Attribute[builtins.int]"
+ fields(t).x # E: "____main___A_AttrsAttributes__" has no attribute "x"
+
+
+[builtins fixtures/plugin_attrs.pyi]
+
+[case testNonattrsFields]
+from typing import Any, cast, Type
+from attrs import fields
+
+class A:
+ b: int
+ c: str
+
+fields(A) # E: Argument 1 to "fields" has incompatible type "Type[A]"; expected an attrs class
+fields(None) # E: Argument 1 to "fields" has incompatible type "None"; expected an attrs class
+fields(cast(Any, 42))
+fields(cast(Type[Any], 43))
+
+[builtins fixtures/plugin_attrs.pyi]
+
[case testAttrsInitMethodAlwaysGenerates]
from typing import Tuple
import attr
diff --git a/test-data/unit/lib-stub/attr/__init__.pyi b/test-data/unit/lib-stub/attr/__init__.pyi
index 1a3838aa3ab1..24ffc0f3f275 100644
--- a/test-data/unit/lib-stub/attr/__init__.pyi
+++ b/test-data/unit/lib-stub/attr/__init__.pyi
@@ -247,3 +247,5 @@ def field(
def evolve(inst: _T, **changes: Any) -> _T: ...
def assoc(inst: _T, **changes: Any) -> _T: ...
+
+def fields(cls: type) -> Any: ...
diff --git a/test-data/unit/lib-stub/attrs/__init__.pyi b/test-data/unit/lib-stub/attrs/__init__.pyi
index 8e9aa1fdced5..cc09ce9b0b49 100644
--- a/test-data/unit/lib-stub/attrs/__init__.pyi
+++ b/test-data/unit/lib-stub/attrs/__init__.pyi
@@ -129,3 +129,5 @@ def field(
def evolve(inst: _T, **changes: Any) -> _T: ...
def assoc(inst: _T, **changes: Any) -> _T: ...
+
+def fields(cls: type) -> Any: ...