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Typecheck crashes with mypy.types.TypeVarId object expected; got int #19857

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Closed as duplicate
Typecheck crashes with mypy.types.TypeVarId object expected; got int#19857
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crash

Description

@fjarri
fjarri
opened on Sep 15, 2025

I am still working on an MRE, the problem is kind of hard to isolate, but perhaps it's already a known issue.

The failure can be seen in this CI run: https://github.com/fjarri-eth/pons/actions/runs/17743317902/job/50422375174?pr=82

Locally, with traceback enabled (Python 3.10.10, mypy 1.18.1, trio 0.31.0, trio-typing 0.10.0):

> mypy pons --show-traceback
/Users/bogdan/.pyenv/versions/3.10.10/envs/pons/lib/python3.10/site-packages/trio-stubs/__init__.pyi:135: error: INTERNAL ERROR -- Please try using mypy master on GitHub:
https://mypy.readthedocs.io/en/stable/common_issues.html#using-a-development-mypy-build
Please report a bug at https://github.com/python/mypy/issues
version: 1.18.1
Traceback (most recent call last):
  File "mypy/checker.py", line 641, in accept
  File "mypy/nodes.py", line 1122, in accept
  File "mypy/checker.py", line 5414, in visit_decorator
  File "mypy/checker.py", line 5450, in visit_decorator_inner
  File "mypy/checkexpr.py", line 1605, in check_call
  File "mypy/checkexpr.py", line 1848, in check_callable_call
  File "mypy/checkexpr.py", line 1286, in apply_function_plugin
  File "/Users/bogdan/.pyenv/versions/3.10.10/envs/pons/lib/python3.10/site-packages/trio_typing/plugin.py", line 464, in takes_callable_and_args_callback
    TypeVarType(
  File "mypy/types.py", line 658, in __init__
TypeError: mypy.types.TypeVarId object expected; got int
/Users/bogdan/.pyenv/versions/3.10.10/envs/pons/lib/python3.10/site-packages/trio-stubs/__init__.pyi:135: : note: use --pdb to drop into pdb

(pons library doesn't even use trio, only the tests do, so I'm still figuring out how to isolate this)

With mypy trunk (mypy-1.19.0+dev.73affc0c60aa8d9a7fdc43c8d57fd65c9ea870f1) the traceback is longer, but the issue seems to be the same:

Traceback (most recent call last):
  File "/Users/bogdan/.pyenv/versions/pons/bin/mypy", line 8, in <module>
    sys.exit(console_entry())
  File "/Users/bogdan/.pyenv/versions/3.10.10/envs/pons/lib/python3.10/site-packages/mypy/__main__.py", line 15, in console_entry
    main()
  File "/Users/bogdan/.pyenv/versions/3.10.10/envs/pons/lib/python3.10/site-packages/mypy/main.py", line 127, in main
    res, messages, blockers = run_build(sources, options, fscache, t0, stdout, stderr)
  File "/Users/bogdan/.pyenv/versions/3.10.10/envs/pons/lib/python3.10/site-packages/mypy/main.py", line 211, in run_build
    res = build.build(sources, options, None, flush_errors, fscache, stdout, stderr)
  File "/Users/bogdan/.pyenv/versions/3.10.10/envs/pons/lib/python3.10/site-packages/mypy/build.py", line 196, in build
    result = _build(
  File "/Users/bogdan/.pyenv/versions/3.10.10/envs/pons/lib/python3.10/site-packages/mypy/build.py", line 272, in _build
    graph = dispatch(sources, manager, stdout)
  File "/Users/bogdan/.pyenv/versions/3.10.10/envs/pons/lib/python3.10/site-packages/mypy/build.py", line 2946, in dispatch
    process_graph(graph, manager)
  File "/Users/bogdan/.pyenv/versions/3.10.10/envs/pons/lib/python3.10/site-packages/mypy/build.py", line 3346, in process_graph
    process_stale_scc(graph, scc, manager)
  File "/Users/bogdan/.pyenv/versions/3.10.10/envs/pons/lib/python3.10/site-packages/mypy/build.py", line 3475, in process_stale_scc
    meta_tuples[id] = graph[id].write_cache()
  File "/Users/bogdan/.pyenv/versions/3.10.10/envs/pons/lib/python3.10/site-packages/mypy/build.py", line 2507, in write_cache
    new_interface_hash, meta_tuple = write_cache(
  File "/Users/bogdan/.pyenv/versions/3.10.10/envs/pons/lib/python3.10/site-packages/mypy/build.py", line 1595, in write_cache
    data = tree.serialize()
  File "/Users/bogdan/.pyenv/versions/3.10.10/envs/pons/lib/python3.10/site-packages/mypy/nodes.py", line 407, in serialize
    "names": self.names.serialize(self._fullname),
  File "/Users/bogdan/.pyenv/versions/3.10.10/envs/pons/lib/python3.10/site-packages/mypy/nodes.py", line 4652, in serialize
    data[key] = value.serialize(fullname, key)
  File "/Users/bogdan/.pyenv/versions/3.10.10/envs/pons/lib/python3.10/site-packages/mypy/nodes.py", line 4545, in serialize
    data["node"] = self.node.serialize()
  File "/Users/bogdan/.pyenv/versions/3.10.10/envs/pons/lib/python3.10/site-packages/mypy/nodes.py", line 3819, in serialize
    "names": self.names.serialize(self.fullname),
  File "/Users/bogdan/.pyenv/versions/3.10.10/envs/pons/lib/python3.10/site-packages/mypy/nodes.py", line 4652, in serialize
    data[key] = value.serialize(fullname, key)
  File "/Users/bogdan/.pyenv/versions/3.10.10/envs/pons/lib/python3.10/site-packages/mypy/nodes.py", line 4545, in serialize
    data["node"] = self.node.serialize()
  File "/Users/bogdan/.pyenv/versions/3.10.10/envs/pons/lib/python3.10/site-packages/mypy/nodes.py", line 1133, in serialize
    "var": self.var.serialize(),
  File "/Users/bogdan/.pyenv/versions/3.10.10/envs/pons/lib/python3.10/site-packages/mypy/nodes.py", line 1305, in serialize
    "type": None if self.type is None else self.type.serialize(),
  File "/Users/bogdan/.pyenv/versions/3.10.10/envs/pons/lib/python3.10/site-packages/mypy/types.py", line 2685, in serialize
    return {".class": "Overloaded", "items": [t.serialize() for t in self.items]}
  File "/Users/bogdan/.pyenv/versions/3.10.10/envs/pons/lib/python3.10/site-packages/mypy/types.py", line 2685, in <listcomp>
    return {".class": "Overloaded", "items": [t.serialize() for t in self.items]}
  File "/Users/bogdan/.pyenv/versions/3.10.10/envs/pons/lib/python3.10/site-packages/mypy/types.py", line 2535, in serialize
    "arg_types": [t.serialize() for t in self.arg_types],
  File "/Users/bogdan/.pyenv/versions/3.10.10/envs/pons/lib/python3.10/site-packages/mypy/types.py", line 2535, in <listcomp>
    "arg_types": [t.serialize() for t in self.arg_types],
  File "/Users/bogdan/.pyenv/versions/3.10.10/envs/pons/lib/python3.10/site-packages/mypy/types.py", line 2535, in serialize
    "arg_types": [t.serialize() for t in self.arg_types],
  File "/Users/bogdan/.pyenv/versions/3.10.10/envs/pons/lib/python3.10/site-packages/mypy/types.py", line 2535, in <listcomp>
    "arg_types": [t.serialize() for t in self.arg_types],
  File "/Users/bogdan/.pyenv/versions/3.10.10/envs/pons/lib/python3.10/site-packages/mypy/types.py", line 691, in serialize
    assert not self.id.is_meta_var()
AttributeError: 'int' object has no attribute 'is_meta_var'

mypy settings in the project file:

[tool.mypy]
plugins = "trio_typing.plugin"
strict = true
warn_unreachable = true
implicit_reexport = true

Activity

  1. fjarri
    added
    bugmypy got something wrong
    on Sep 15, 2025

  2. fjarri commented on Sep 15, 2025

    @fjarri
    fjarri
    on Sep 15, 2025
    Author

    Ah, actually the MRE turned out to be simple.

    pyproject.toml:

    [project]
name = "mypy-test"
version = "0.0.0"
requires-python = ">=3.10"

[tool.mypy]
plugins = "trio_typing.plugin"
strict = true
warn_unreachable = true
implicit_reexport = true

    t.py:

    import trio

    mypy t.py:

    /Users/bogdan/.pyenv/versions/3.10.10/envs/mypy-test/lib/python3.10/site-packages/trio-stubs/__init__.pyi:135: error: INTERNAL ERROR -- Please try using mypy master on GitHub:
https://mypy.readthedocs.io/en/stable/common_issues.html#using-a-development-mypy-build
If this issue continues with mypy master, please report a bug at https://github.com/python/mypy/issues
version: 1.18.1
/Users/bogdan/.pyenv/versions/3.10.10/envs/mypy-test/lib/python3.10/site-packages/trio-stubs/__init__.pyi:135: : note: please use --show-traceback to print a traceback when reporting a bug

    pip list:

    Package            Version
------------------ -----------
async-generator    1.10
attrs              25.3.0
exceptiongroup     1.3.0
idna               3.10
importlib_metadata 8.7.0
mypy               1.18.1
mypy_extensions    1.1.0
outcome            1.3.0.post0
packaging          25.0
pathspec           0.12.1
pip                22.3.1
setuptools         65.5.0
sniffio            1.3.1
sortedcontainers   2.4.0
tomli              2.2.1
trio               0.31.0
trio-typing        0.10.0
typing_extensions  4.15.0
zipp               3.23.0

  3. brianschubert commented on Sep 15, 2025

    @brianschubert
    brianschubert
    on Sep 15, 2025
    Collaborator

    Thanks for the report. Note that the exception is coming from inside the trio_typing plugin. You'll need to report this to trio-typing. You can point them to the discussion in #17671. I'm afraid there isn't anything for us to do on the mypy side.

    Closing as duplicate of #17671 (different plugin, but same issue)

  4. brianschubert
    closed this as a duplicateof Mypy crashes with 1.11.1 version and Pydantic 1.10.11 #17671 on Sep 15, 2025
  5. brianschubert
    added
    crash
    and removed
    bugmypy got something wrong
    on Sep 15, 2025
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