`AssertionError: Must not defer during final iteration` with recursive class definition

Crash Report

mypy 2.1.0 and master (938dbe2f) crash on the snippet below.

Traceback

Traceback (most recent call last):
  File ".venv-mypy/bin/mypy", line 6, in <module>
    sys.exit(console_entry())
  File "mypy/mypy/__main__.py", line 16, in console_entry
    main()
  File "mypy/mypy/main.py", line 154, in main
    res, messages, blockers = run_build(sources, options, fscache, t0, stdout, stderr)
  File "mypy/mypy/main.py", line 244, in run_build
    res = build.build(sources, options, None, flush_errors, fscache, stdout, stderr)
  File "mypy/mypy/build.py", line 422, in build
    result = build_inner(
  File "mypy/mypy/build.py", line 537, in build_inner
    graph = dispatch(sources, manager, stdout, connect_threads)
  File "mypy/mypy/build.py", line 4134, in dispatch
    process_graph(graph, manager)
  File "mypy/mypy/build.py", line 4602, in process_graph
    done, still_working, results = manager.wait_for_done(graph)
  File "mypy/mypy/build.py", line 1478, in wait_for_done
    process_stale_scc(graph, next_scc, self)
  File "mypy/mypy/build.py", line 4769, in process_stale_scc
    mypy.semanal_main.semantic_analysis_for_scc(graph, scc, manager.errors)
  File "mypy/mypy/semanal_main.py", line 91, in semantic_analysis_for_scc
    process_top_levels(graph, scc, patches)
  File "mypy/mypy/semanal_main.py", line 200, in process_top_levels
    deferred, incomplete, progress = semantic_analyze_target(
  File "mypy/mypy/semanal_main.py", line 380, 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 728, in refresh_top_level
    self.accept(d)
  File "mypy/mypy/semanal.py", line 7695, in accept
    node.accept(self)
    ~~~~~~~~~~~^^^^^^
  File "mypy/mypy/nodes.py", line 1727, in accept
    return visitor.visit_class_def(self)
           ~~~~~~~~~~~~~~~~~~~~~~~^^^^^^
  File "mypy/mypy/semanal.py", line 1840, in visit_class_def
    self.analyze_class(defn)
    ~~~~~~~~~~~~~~~~~~^^^^^^
  File "mypy/mypy/semanal.py", line 1991, in analyze_class
    self.clean_up_bases_and_infer_type_variables(defn, bases, context=defn)
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "mypy/mypy/semanal.py", line 2329, in clean_up_bases_and_infer_type_variables
    result = self.analyze_class_typevar_declaration(base, has_type_var_tuple)
  File "mypy/mypy/semanal.py", line 2409, in analyze_class_typevar_declaration
    tvar = self.analyze_unbound_tvar(arg)
  File "mypy/mypy/semanal.py", line 2435, in analyze_unbound_tvar
    return self.analyze_unbound_tvar_impl(t)
           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^
  File "mypy/mypy/semanal.py", line 2444, in analyze_unbound_tvar_impl
    self.record_incomplete_ref()
    ~~~~~~~~~~~~~~~~~~~~~~~~~~^^
  File "mypy/mypy/semanal.py", line 7321, in record_incomplete_ref
    self.defer()
    ~~~~~~~~~~^^
  File "mypy/mypy/semanal.py", line 7296, in defer
    assert not self.final_iteration, "Must not defer during final iteration"
           ^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError: Must not defer during final iteration

To Reproduce

from typing import Generic

class C(Generic[C]):
    pass

Your Environment

• Mypy version used: 2.1.0 and 938dbe2f
• Mypy command-line flags: N/A
• Mypy configuration options from mypy.ini (and other config files): N/A
• Python version used: 3.14.5
• Operating system and version: Arch Linux

Reproduziere den Absturz mit dem bereitgestellten rekursiven Generic-Beispiel und verfolge dann den Pfad der semantischen Analyse durch mypy/semanal.py, insbesondere analyze_unbound_tvar_impl und defer. Erledigt bedeutet, dass das Snippet nicht mehr den AssertionError der letzten Iteration auslöst; im Report wird keine Datei für Regressionstests genannt, also finde die vorhandenen Tests der semantischen Analyse, bevor du Abdeckung hinzufügst.