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IndexError: list index out of range in visit_list_comprehension #20530

@correctmost

Description

@correctmost

Crash Report

The (fuzzed) snippet below crashes mypy 1.19.1 and master (c41dbd0).

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 135, in main
    res, messages, blockers = run_build(sources, options, fscache, t0, stdout, stderr)
  File "mypy/mypy/main.py", line 219, in run_build
    res = build.build(sources, options, None, flush_errors, fscache, stdout, stderr)
  File "mypy/mypy/build.py", line 320, in build
    result = build_inner(
  File "mypy/mypy/build.py", line 417, in build_inner
    graph = dispatch(sources, manager, stdout)
  File "mypy/mypy/build.py", line 3178, in dispatch
    process_graph(graph, manager)
  File "mypy/mypy/build.py", line 3588, in process_graph
    done, still_working, results = manager.wait_for_done(graph)
  File "mypy/mypy/build.py", line 1070, in wait_for_done
    process_stale_scc(graph, next_scc, self)
  File "mypy/mypy/build.py", line 3745, in process_stale_scc
    mypy.semanal_main.semantic_analysis_for_scc(graph, scc, manager.errors)
  File "mypy/mypy/semanal_main.py", line 94, in semantic_analysis_for_scc
    process_top_levels(graph, scc, patches)
  File "mypy/mypy/semanal_main.py", line 232, in process_top_levels
    deferred, incomplete, progress = semantic_analyze_target(
  File "mypy/mypy/semanal_main.py", line 409, in semantic_analyze_target
    analyzer.refresh_partial(
  File "mypy/mypy/semanal.py", line 703, in refresh_partial
    self.refresh_top_level(node)
  File "mypy/mypy/semanal.py", line 721, in refresh_top_level
    self.accept(d)
  File "mypy/mypy/semanal.py", line 7598, in accept
    node.accept(self)
    ~~~~~~~~~~~^^^^^^
  File "mypy/mypy/nodes.py", line 1602, in accept
    return visitor.visit_expression_stmt(self)
           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^
  File "mypy/mypy/semanal.py", line 5408, in visit_expression_stmt
    s.expr.accept(self)
    ~~~~~~~~~~~~~^^^^^^
  File "mypy/mypy/nodes.py", line 2764, in accept
    return visitor.visit_list_comprehension(self)
           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^
  File "mypy/mypy/semanal.py", line 6303, in visit_list_comprehension
    expr.generator.accept(self)
    ~~~~~~~~~~~~~~~~~~~~~^^^^^^
  File "mypy/mypy/nodes.py", line 2747, in accept
    return visitor.visit_generator_expr(self)
           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^
  File "mypy/mypy/semanal.py", line 6326, in visit_generator_expr
    expr.left_expr.accept(self)
    ~~~~~~~~~~~~~~~~~~~~~^^^^^^
  File "mypy/mypy/nodes.py", line 2764, in accept
    return visitor.visit_list_comprehension(self)
           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^
  File "mypy/mypy/semanal.py", line 6300, in visit_list_comprehension
    if not self.is_func_scope() or not self.function_stack[-1].is_coroutine:
                                       ~~~~~~~~~~~~~~~~~~~^^^^
IndexError: list index out of range

To Reproduce

[[x async for x in x] for y in y]

Your Environment

  • Mypy version used: c41dbd0 (and 1.19.1)
  • Mypy command-line flags: N/A
  • Mypy configuration options from mypy.ini (and other config files): N/A
  • Python version used: 3.13.11
  • Operating system and version: Arch Linux

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