Crash during cache serialization when checking select projects in mypy_primer

[brianschubert]

Crash Report

I haven't been able to reproduce this locally yet, but it seems to be occurring consistently when running mypy_primer in the CI. Examples: #19832 (comment), #19073 (comment), #19486 (comment)

Common factors:

• Occurs when checking the projects scipy-stubs and AutoSplit
• Traceback ending with Error serializing zipimport.

See brianschubert#4 for the full output from a primer run.

Traceback

Traceback (most recent call last):
  File "/tmp/mypy_primer/mypy_old/venv/bin/mypy", line 7, in <module>
    sys.exit(console_entry())
             ~~~~~~~~~~~~~^^
  File "/tmp/mypy_primer/mypy_old/venv/lib/python3.13/site-packages/mypy/__main__.py", line 15, in console_entry
    main()
    ~~~~^^
  File "/tmp/mypy_primer/mypy_old/venv/lib/python3.13/site-packages/mypy/main.py", line 127, in main
    res, messages, blockers = run_build(sources, options, fscache, t0, stdout, stderr)
                              ~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/tmp/mypy_primer/mypy_old/venv/lib/python3.13/site-packages/mypy/main.py", line 211, in run_build
    res = build.build(sources, options, None, flush_errors, fscache, stdout, stderr)
  File "/tmp/mypy_primer/mypy_old/venv/lib/python3.13/site-packages/mypy/build.py", line 196, in build
    result = _build(
        sources, options, alt_lib_path, flush_errors, fscache, stdout, stderr, extra_plugins
    )
  File "/tmp/mypy_primer/mypy_old/venv/lib/python3.13/site-packages/mypy/build.py", line 272, in _build
    graph = dispatch(sources, manager, stdout)
  File "/tmp/mypy_primer/mypy_old/venv/lib/python3.13/site-packages/mypy/build.py", line 2946, in dispatch
    process_graph(graph, manager)
    ~~~~~~~~~~~~~^^^^^^^^^^^^^^^^
  File "/tmp/mypy_primer/mypy_old/venv/lib/python3.13/site-packages/mypy/build.py", line 3346, in process_graph
    process_stale_scc(graph, scc, manager)
    ~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^
  File "/tmp/mypy_primer/mypy_old/venv/lib/python3.13/site-packages/mypy/build.py", line 3475, in process_stale_scc
    meta_tuples[id] = graph[id].write_cache()
                      ~~~~~~~~~~~~~~~~~~~~~^^
  File "/tmp/mypy_primer/mypy_old/venv/lib/python3.13/site-packages/mypy/build.py", line 2493, in write_cache
    data = Buffer()
  File "/tmp/mypy_primer/mypy_old/venv/lib/python3.13/site-packages/mypy/cache.py", line 28, in __init__
    raise NotImplementedError
NotImplementedError
Error serializing zipimport

[brianschubert]

cc @ilevkivskyi

[ilevkivskyi]

--fixed-format-cache is not officially supported for interpreted mypy yet (see release notes). If you really want to use it you can run pip install -U mypyc/lib-rt (from mypy repo root).

[ilevkivskyi]

Oh I guess this is because those projects are using --fixed-format-cache. I guess @hauntsaninja you will need to add that command to mypy_primer. It may actually be beneficial in general, since this will detect effects of changes in lib-rt by a PR.

[ilevkivskyi]

(to clear this needs to be run only once per venv)

[brianschubert]

Reopening for now for visibility until there’s a workaround for mypy_primer