Serialization crash on `pandera` with `pandas-stubs`

[sterliakov]

Crash Report

Running mypy on pandera with pandas-stubs installed results in a crash.

Traceback

pandera/api/function_dispatch.py:12: note: By default the bodies of untyped functions are not checked, consider using --check-untyped-defs  [annotation-unchecked]
Traceback (most recent call last):
  File "/tmp/tmp.KoqC85pWUZ/pandera/.venv/bin/mypy", line 10, in <module>
    sys.exit(console_entry())
             ^^^^^^^^^^^^^^^
  File "/tmp/tmp.KoqC85pWUZ/pandera/.venv/lib/python3.12/site-packages/mypy/__main__.py", line 15, in console_entry
    main()
  File "mypy/main.py", line 109, in main
  File "mypy/main.py", line 193, in run_build
  File "mypy/build.py", line 194, in build
  File "mypy/build.py", line 269, in _build
  File "mypy/build.py", line 2940, in dispatch
  File "mypy/build.py", line 3338, in process_graph
  File "mypy/build.py", line 3465, in process_stale_scc
  File "mypy/build.py", line 2502, in write_cache
  File "mypy/build.py", line 1562, in write_cache
  File "mypy/nodes.py", line 390, in serialize
  File "mypy/nodes.py", line 4049, in serialize
  File "mypy/nodes.py", line 3986, in serialize
  File "mypy/nodes.py", line 3408, in serialize
  File "mypy/types.py", line 678, in serialize
  File "mypy/types.py", line 2467, in serialize
  File "mypy/types.py", line 1495, in serialize
  File "mypy/types.py", line 678, in serialize
  File "mypy/types.py", line 3173, in serialize
AssertionError: Internal error: unresolved placeholder type None

To Reproduce

I'll try to narrow this down later, but now a repro script:

cd $(mktemp -d)
git clone https://github.com/pandera-dev/pandera
cd pandera
git checkout 33fe68b7d0c7c3a760469b9898acf286334fe34f  # Head as of now
python -m venv .venv
. ./.venv/bin/activate
pip install . 'mypy==1.14.1' 'pandas-stubs==2.2.3.241126'
hash -r
mypy pandera --show-traceback

Your Environment

• Mypy version used: 1.14.1 and current master
• Mypy command-line flags: n/a
• Mypy configuration options from mypy.ini (and other config files): as specified in pandera's setup.cfg
• Python version used: 3.12 and 3.13 tested
• Operating system and version: Ubuntu 22.04.5 LTS (Linux pc 5.15.0-130-generic #140-Ubuntu SMP Wed Dec 18 17:59:53 UTC 2024 x86_64 x86_64 x86_64 GNU/Linux)

[hauntsaninja]

Likely related to #17396 (comment)
I had a hacky fix for it, but regressed type checking in some normal cases. If you see a better fix that would be cool!