Mypy internal error with attrs frozen classes with property overrides attribute #7918

import attr

@attr.s(frozen=False)
class A:
    x: int = attr.ib(init=False)

@attr.s(frozen=True)
class B(A):
    @property
    def x(self) -> int:
        return 2

ignore_missing_imports = True
disallow_incomplete_defs = True
disallow_untyped_calls = True
disallow_untyped_defs = False

Traceback (most recent call last):
  File "mypy", line 10, in <module>
    sys.exit(console_entry())
  File "mypy/__main__.py", line 8, in console_entry
    main(None, sys.stdout, sys.stderr)
  File "mypy/main.py", line 93, in main
    res = build.build(sources, options, None, flush_errors, fscache, stdout, stderr)
  File "mypy/build.py", line 167, in build
    sources, options, alt_lib_path, flush_errors, fscache, stdout, stderr, extra_plugins
  File "mypy/build.py", line 235, in _build
    graph = dispatch(sources, manager, stdout)
  File "mypy/build.py", line 2620, in dispatch
    process_graph(graph, manager)
  File "mypy/build.py", line 2929, in process_graph
    process_stale_scc(graph, scc, manager)
  File "mypy/build.py", line 3022, in process_stale_scc
    mypy.semanal_main.semantic_analysis_for_scc(graph, scc, manager.errors)
  File "mypy/semanal_main.py", line 77, in semantic_analysis_for_scc
    process_top_levels(graph, scc, patches)
  File "mypy/semanal_main.py", line 202, in process_top_levels
    patches)
  File "mypy/semanal_main.py", line 330, in semantic_analyze_target
    active_type=active_type)
  File "mypy/semanal.py", line 378, in refresh_partial
    self.refresh_top_level(node)
  File "mypy/semanal.py", line 389, in refresh_top_level
    self.accept(d)
  File "mypy/semanal.py", line 4639, in accept
    node.accept(self)
  File "mypy/nodes.py", line 927, in accept
    return visitor.visit_class_def(self)
  File "mypy/semanal.py", line 1022, in visit_class_def
    self.analyze_class(defn)
  File "mypy/semanal.py", line 1099, in analyze_class
    self.analyze_class_body_common(defn)
  File "mypy/semanal.py", line 1108, in analyze_class_body_common
    self.apply_class_plugin_hooks(defn)
  File "mypy/semanal.py", line 1154, in apply_class_plugin_hooks
    hook(ClassDefContext(defn, decorator, self))
  File "mypy/plugins/attrs.py", line 295, in attr_class_maker_callback
    _make_frozen(ctx, attributes)
  File "mypy/plugins/attrs.py", line 627, in _make_frozen
    assert isinstance(node, Var)
AssertionError: