Fix mishandling of typing.Self in attrs generated inits

mypy/checker.py

@@ -2492,9 +2492,9 @@ class C(B, A[int]): ...  # this is unsafe because...
                 ok = is_subtype(first_sig, second_sig, ignore_pos_arg_names=True)
         elif first_type and second_type:
             if isinstance(first.node, Var):
-                first_type = expand_self_type(first.node, first_type, fill_typevars(ctx))
+                first_type = expand_self_type(first_type, first.node.info, fill_typevars(ctx))
             if isinstance(second.node, Var):
-                second_type = expand_self_type(second.node, second_type, fill_typevars(ctx))
+                second_type = expand_self_type(second_type, second.node.info, fill_typevars(ctx))
             ok = is_equivalent(first_type, second_type)
             if not ok:
                 second_node = base2[name].node
@@ -3062,7 +3062,9 @@ def lvalue_type_from_base(
             base_node = base_var.node
             base_type = base_var.type
             if isinstance(base_node, Var) and base_type is not None:
-                base_type = expand_self_type(base_node, base_type, fill_typevars(expr_node.info))
+                base_type = expand_self_type(
+                    base_type, base_node.info, fill_typevars(expr_node.info)
+                )
             if isinstance(base_node, Decorator):
                 base_node = base_node.func
                 base_type = base_node.type

mypy/checkmember.py

@@ -737,7 +737,7 @@ def analyze_var(
         if not (mx.is_self or mx.is_super) or supported_self_type(
             get_proper_type(mx.original_type)
         ):
-            t = expand_self_type(var, t, mx.original_type)
+            t = expand_self_type(t, var.info, mx.original_type)
         t = get_proper_type(expand_type_by_instance(t, itype))
         freeze_all_type_vars(t)
         result: Type = t
@@ -768,7 +768,7 @@ def analyze_var(
                 # and similarly for B1 when checking against B
                 dispatched_type = meet.meet_types(mx.original_type, itype)
                 signature = freshen_all_functions_type_vars(functype)
-                bound = get_proper_type(expand_self_type(var, signature, mx.original_type))
+                bound = get_proper_type(expand_self_type(signature, var.info, mx.original_type))
                 assert isinstance(bound, FunctionLike)
                 signature = bound
                 signature = check_self_arg(
@@ -986,7 +986,7 @@ def analyze_class_attribute_access(
             # In the above example this means that we infer following types:
             #     C.x -> Any
             #     C[int].x -> int
-            t = get_proper_type(expand_self_type(node.node, t, itype))
+            t = get_proper_type(expand_self_type(t, node.node.info, itype))
             t = erase_typevars(expand_type_by_instance(t, isuper), {tv.id for tv in def_vars})
 
         is_classmethod = (is_decorated and cast(Decorator, node.node).func.is_class) or (

mypy/expandtype.py

@@ -3,7 +3,7 @@
 from typing import Iterable, Mapping, Sequence, TypeVar, cast, overload
 from typing_extensions import Final
 
-from mypy.nodes import ARG_POS, ARG_STAR, ArgKind, Var
+from mypy.nodes import ARG_POS, ARG_STAR, ArgKind, TypeInfo
 from mypy.type_visitor import TypeTranslator
 from mypy.types import (
     ANY_STRATEGY,
@@ -508,17 +508,23 @@ def expand_unpack_with_variables(
 
 
 @overload
-def expand_self_type(var: Var, typ: ProperType, replacement: ProperType) -> ProperType:
+def expand_self_type(typ: ProperType, info: TypeInfo, replacement: ProperType) -> ProperType:
     ...
 
 
 @overload
-def expand_self_type(var: Var, typ: Type, replacement: Type) -> Type:
+def expand_self_type(typ: Type, info: TypeInfo, replacement: Type) -> Type:
     ...
 
 
-def expand_self_type(var: Var, typ: Type, replacement: Type) -> Type:
+@overload
+def expand_self_type(typ: None, info: TypeInfo, replacement: Type) -> None:
+    ...
+
+
+def expand_self_type(typ: Type | None, info: TypeInfo, replacement: Type) -> Type | None:
     """Expand appearances of Self type in a variable type."""
-    if var.info.self_type is not None and not var.is_property:
-        return expand_type(typ, {var.info.self_type.id: replacement})
+    if typ is not None and info.self_type is not None:
+        return expand_type(typ, {info.self_type.id: replacement})
+
     return typ

mypy/plugins/attrs.py

@@ -6,6 +6,7 @@
 from typing_extensions import Final, Literal
 
 import mypy.plugin  # To avoid circular imports.
+from mypy.expandtype import expand_self_type
 from mypy.exprtotype import TypeTranslationError, expr_to_unanalyzed_type
 from mypy.nodes import (
     ARG_NAMED,
@@ -46,6 +47,7 @@
     deserialize_and_fixup_type,
 )
 from mypy.server.trigger import make_wildcard_trigger
+from mypy.state import state
 from mypy.typeops import make_simplified_union, map_type_from_supertype
 from mypy.types import (
     AnyType,
@@ -112,7 +114,7 @@ def argument(self, ctx: mypy.plugin.ClassDefContext) -> Argument:
         """Return this attribute as an argument to __init__."""
         assert self.init
 
-        init_type: Type | None = None
+        init_type: Type | None
         if self.converter:
             if self.converter.init_type:
                 init_type = self.converter.init_type
@@ -147,6 +149,9 @@ def argument(self, ctx: mypy.plugin.ClassDefContext) -> Argument:
         else:
             arg_kind = ARG_OPT if self.has_default else ARG_POS
 
+        with state.strict_optional_set(ctx.api.options.strict_optional):
+            init_type = expand_self_type(init_type, self.info, fill_typevars(self.info))
+
         # Attrs removes leading underscores when creating the __init__ arguments.
         return Argument(Var(self.name.lstrip("_"), init_type), init_type, None, arg_kind)
 

mypy/plugins/dataclasses.py

@@ -2,10 +2,9 @@
 
 from __future__ import annotations
 
-from typing import Optional
 from typing_extensions import Final
 
-from mypy.expandtype import expand_type
+from mypy.expandtype import expand_self_type
 from mypy.nodes import (
     ARG_NAMED,
     ARG_NAMED_OPT,
@@ -106,22 +105,13 @@ def to_argument(self, current_info: TypeInfo) -> Argument:
             arg_kind = ARG_OPT
         return Argument(
             variable=self.to_var(current_info),
-            type_annotation=self.expand_type(current_info),
+            type_annotation=expand_self_type(self.type, self.info, fill_typevars(current_info)),
             initializer=None,
             kind=arg_kind,
         )
 
-    def expand_type(self, current_info: TypeInfo) -> Optional[Type]:
-        if self.type is not None and self.info.self_type is not None:
-            # In general, it is not safe to call `expand_type()` during semantic analyzis,
-            # however this plugin is called very late, so all types should be fully ready.
-            # Also, it is tricky to avoid eager expansion of Self types here (e.g. because
-            # we serialize attributes).
-            return expand_type(self.type, {self.info.self_type.id: fill_typevars(current_info)})
-        return self.type
-
     def to_var(self, current_info: TypeInfo) -> Var:
-        return Var(self.name, self.expand_type(current_info))
+        return Var(self.name, expand_self_type(self.type, self.info, fill_typevars(current_info)))
 
     def serialize(self) -> JsonDict:
         assert self.type

mypy/subtypes.py

@@ -1249,7 +1249,7 @@ def find_node_type(
     else:
         typ = node.type
         if typ is not None:
-            typ = expand_self_type(node, typ, subtype)
+            typ = expand_self_type(typ, node.info, subtype)
     p_typ = get_proper_type(typ)
     if typ is None:
         return AnyType(TypeOfAny.from_error)

test-data/unit/check-attr.test

@@ -1866,4 +1866,19 @@ 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 testSelfInClassInit]
+# flags: --strict-optional
+from attrs import define
+from typing import Union, Self
+
+@define
+class C:
+    a: Union[Self, None] = None
+
+reveal_type(C) # N: Revealed type is "def (a: Union[__main__.C, None] =) -> __main__.C"
+C(C())
+C(None)
+
+[builtins fixtures/property.pyi]