Assertion failure crash: assert isinstance(node.node, TypeVarLikeExpr)

Crash Report

The snippet below crashes mypy 1.18.2 and the latest code from master (96fac3a2e4).

Traceback

Traceback (most recent call last):
  File ".venv-mypy/bin/mypy", line 7, in <module>
    sys.exit(console_entry())
  File "mypy/mypy/__main__.py", line 15, in console_entry
    main()
  File "mypy/mypy/main.py", line 127, in main
    res, messages, blockers = run_build(sources, options, fscache, t0, stdout, stderr)
  File "mypy/mypy/main.py", line 211, in run_build
    res = build.build(sources, options, None, flush_errors, fscache, stdout, stderr)
  File "mypy/mypy/build.py", line 215, in build
    result = _build(
  File "mypy/mypy/build.py", line 294, in _build
    graph = dispatch(sources, manager, stdout)
  File "mypy/mypy/build.py", line 2945, in dispatch
    process_graph(graph, manager)
  File "mypy/mypy/build.py", line 3336, in process_graph
    done, still_working = manager.wait_for_done(graph)
  File "mypy/mypy/build.py", line 918, in wait_for_done
    process_stale_scc(graph, next_scc, self)
  File "mypy/mypy/build.py", line 3468, in process_stale_scc
    mypy.semanal_main.semantic_analysis_for_scc(graph, scc, manager.errors)
  File "mypy/mypy/semanal_main.py", line 95, in semantic_analysis_for_scc
    process_top_levels(graph, scc, patches)
  File "mypy/mypy/semanal_main.py", line 233, in process_top_levels
    deferred, incomplete, progress = semantic_analyze_target(
  File "mypy/mypy/semanal_main.py", line 410, in semantic_analyze_target
    analyzer.refresh_partial(
  File "mypy/mypy/semanal.py", line 701, in refresh_partial
    self.refresh_top_level(node)
  File "mypy/mypy/semanal.py", line 719, in refresh_top_level
    self.accept(d)
  File "mypy/mypy/semanal.py", line 7563, in accept
    node.accept(self)
  File "mypy/mypy/nodes.py", line 1478, in accept
    return visitor.visit_class_def(self)
  File "mypy/mypy/semanal.py", line 1827, in visit_class_def
    self.analyze_class(defn)
  File "mypy/mypy/semanal.py", line 2044, in analyze_class
    self.analyze_class_body_common(defn)
  File "mypy/mypy/semanal.py", line 2090, in analyze_class_body_common
    defn.defs.accept(self)
  File "mypy/mypy/nodes.py", line 1573, in accept
    return visitor.visit_block(self)
  File "mypy/mypy/semanal.py", line 5375, in visit_block
    self.accept(s)
  File "mypy/mypy/semanal.py", line 7563, in accept
    node.accept(self)
    ~~~~~~~~~~~^^^^^^
  File "mypy/mypy/nodes.py", line 1478, in accept
    return visitor.visit_class_def(self)
           ~~~~~~~~~~~~~~~~~~~~~~~^^^^^^
  File "mypy/mypy/semanal.py", line 1827, in visit_class_def
    self.analyze_class(defn)
    ~~~~~~~~~~~~~~~~~~^^^^^^
  File "mypy/mypy/semanal.py", line 1969, in analyze_class
    bases, tvar_defs, is_protocol = self.clean_up_bases_and_infer_type_variables(
                                    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^
        defn, bases, context=defn
        ^^^^^^^^^^^^^^^^^^^^^^^^^
    )
    ^
  File "mypy/mypy/semanal.py", line 2276, in clean_up_bases_and_infer_type_variables
    assert isinstance(node.node, TypeVarLikeExpr)
           ~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError: 

To Reproduce

class C:
    class Inner[T: C]:
        pass

    type T = c

Your Environment

• Mypy version used: 96fac3a2e45029 (and 1.18.2)
• Mypy command-line flags: N/A
• Mypy configuration options from mypy.ini (and other config files): N/A
• Python version used: 3.13.7
• Operating system and version: Arch Linux

assertion traceback で特定された clean_up_bases_and_infer_type_variables() の mypy/semanal.py から始め、提供されたネストしたジェネリッククラスと型エイリアスでクラッシュを再現します。その例の意味解析の経路を追跡し、mypy がその処理中に AssertionError を発生させなくなっていることを確認します。