Add signature for attr.evolve

mypy/plugins/attrs.py

@@ -883,3 +883,31 @@ def add_method(
         """
         self_type = self_type if self_type is not None else self.self_type
         add_method(self.ctx, method_name, args, ret_type, self_type, tvd)
+
+
+def evolve_callback(ctx: mypy.plugin.FunctionSigContext) -> FunctionLike:
+    """Callback to provide an accurate signature for attrs.evolve."""
+    if len(ctx.args[0]) < 1:
+        return ctx.default_signature
+
+    expr = ctx.args[0][0]
+    if not isinstance(expr, RefExpr):
+        # TODO: can't rely on expressions having a type!
+        return ctx.default_signature
+
+    node = expr.node
+    if node is None:
+        return ctx.default_signature
+
+    metadata = node.type.type.metadata
+
+    args = {
+        md_attribute["name"]: ctx.api.named_generic_type(md_attribute["init_type"], args=[])
+        for md_attribute in metadata.get("attrs", {}).get("attributes", [])
+    }
+
+    return ctx.default_signature.copy_modified(
+        arg_kinds=ctx.default_signature.arg_kinds[:1] + [ARG_NAMED_OPT] * len(args),
+        arg_names=ctx.default_signature.arg_names[:1] + list(args.keys()),
+        arg_types=ctx.default_signature.arg_types[:1] + list(args.values()),
+    )

mypy/plugins/default.py

@@ -9,6 +9,7 @@
     AttributeContext,
     ClassDefContext,
     FunctionContext,
+    FunctionSigContext,
     MethodContext,
     MethodSigContext,
     Plugin,
@@ -45,6 +46,15 @@ def get_function_hook(self, fullname: str) -> Callable[[FunctionContext], Type]
             return singledispatch.create_singledispatch_function_callback
         return None
 
+    def get_function_signature_hook(
+        self, fullname: str
+    ) -> Callable[[FunctionSigContext], FunctionLike] | None:
+        from mypy.plugins import attrs
+
+        if fullname in ("attr.evolve", "attr.assoc"):
+            return attrs.evolve_callback
+        return None
+
     def get_method_signature_hook(
         self, fullname: str
     ) -> Callable[[MethodSigContext], FunctionLike] | None:

test-data/unit/check-attr.test

@@ -1866,4 +1866,41 @@ reveal_type(D) # N: Revealed type is "def (a: builtins.int, b: builtins.str) ->
 D(1, "").a = 2 # E: Cannot assign to final attribute "a"
 D(1, "").b = "2" # E: Cannot assign to final attribute "b"
 
-[builtins fixtures/property.pyi]
+[builtins fixtures/property.pyi]
+
+[case testEvolve]
+import attr
+
+@attr.s(auto_attribs=True)
+class C:
+    name: str
+
+def q() -> C:
+    return C(name='foo')
+
+c = C(name='foo')
+attr.evolve()  # E: Missing positional argument "inst" in call to "evolve"
+attr.evolve(c)
+attr.evolve(c, name='bar')
+attr.evolve(
+    q(),
+    name=42,  # E: Argument "name" to "evolve" has incompatible type "int"; expected "str"
+)
+attr.evolve(
+    c,
+    age=42,  # type: ignore[call-arg]
+)
+
+# 'assoc' is deprecated equivalent of 'evolve'
+
+attr.assoc(
+    c,
+    name=42,  # E: Argument "name" to "assoc" has incompatible type "int"; expected "str"
+)
+attr.assoc(
+    c,
+    age=42,  # type: ignore[call-arg]
+)
+
+[builtins fixtures/dict.pyi]
+[typing fixtures/typing-medium.pyi]

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

@@ -244,3 +244,6 @@ def field(
     order: Optional[bool] = ...,
     on_setattr: Optional[object] = ...,
 ) -> Any: ...
+
+def evolve(inst: _T, **changes: Any) -> _T: ...
+def assoc(inst: _T, **changes: Any) -> _T: ...