type-safety

Author: ikonst

mypy/plugins/attrs.py

@@ -929,17 +929,19 @@ def add_method(
         add_method(self.ctx, method_name, args, ret_type, self_type, tvd)
 
 
-def _get_attrs_init_type(typ: Instance) -> CallableType | None:
+def _get_attrs_init_type(typ: Type) -> tuple[Instance, CallableType] | tuple[None, None]:
     """
     If `typ` refers to an attrs class, gets the type of its initializer method.
     """
+    if not isinstance(typ, Instance):
+        return None, None
     magic_attr = typ.type.get(MAGIC_ATTR_NAME)
     if magic_attr is None or not magic_attr.plugin_generated:
-        return None
+        return None, None
     init_method = typ.type.get_method("__init__") or typ.type.get_method(ATTRS_INIT_NAME)
     if not isinstance(init_method, FuncDef) or not isinstance(init_method.type, CallableType):
-        return None
-    return init_method.type
+        return None, None
+    return typ, init_method.type
 
 
 def evolve_function_sig_callback(ctx: mypy.plugin.FunctionSigContext) -> CallableType:
@@ -965,13 +967,11 @@ def evolve_function_sig_callback(ctx: mypy.plugin.FunctionSigContext) -> Callabl
     inst_type = get_proper_type(inst_type)
     if isinstance(inst_type, AnyType):
         return ctx.default_signature  # evolve(Any, ....) -> Any
-    # We stringify it first, so that TypeVars maintain their name.
     inst_type_str = format_type_bare(inst_type)
     attrs_type = inst_type.upper_bound if isinstance(inst_type, TypeVarType) else inst_type
-    attrs_init_type = None
-    if isinstance(attrs_type, Instance):
-        attrs_init_type = _get_attrs_init_type(attrs_type)
-    if attrs_init_type is None:
+
+    attrs_type, attrs_init_type = _get_attrs_init_type(attrs_type)
+    if attrs_type is None or attrs_init_type is None:
         ctx.api.fail(
             f'Argument 1 to "evolve" has a variable type "{inst_type_str}" not bound to an attrs class'
             if isinstance(inst_type, TypeVarType)