mypy failing in PyPy with "no module named librt"

[jaraco]

As observed in https://github.com/python/importlib_metadata/actions/runs/20407220899, every skeleton project is failing on PyPy.

=========================== short test summary info ============================
FAILED conftest.py::mypy - ModuleNotFoundError: No module named 'librt'
FAILED docs/__init__.py::mypy - ModuleNotFoundError: No module named 'librt'
FAILED docs/conf.py::mypy - ModuleNotFoundError: No module named 'librt'
FAILED exercises.py::mypy - ModuleNotFoundError: No module named 'librt'
FAILED importlib_metadata/__init__.py::mypy - ModuleNotFoundError: No module named 'librt'
FAILED importlib_metadata/_adapters.py::mypy - ModuleNotFoundError: No module named 'librt'
FAILED importlib_metadata/_collections.py::mypy - ModuleNotFoundError: No module named 'librt'
FAILED importlib_metadata/_compat.py::mypy - ModuleNotFoundError: No module named 'librt'
FAILED importlib_metadata/_functools.py::mypy - ModuleNotFoundError: No module named 'librt'
FAILED importlib_metadata/_itertools.py::mypy - ModuleNotFoundError: No module named 'librt'
FAILED importlib_metadata/_meta.py::mypy - ModuleNotFoundError: No module named 'librt'
FAILED importlib_metadata/_text.py::mypy - ModuleNotFoundError: No module named 'librt'
FAILED importlib_metadata/_typing.py::mypy - ModuleNotFoundError: No module named 'librt'
FAILED importlib_metadata/compat/__init__.py::mypy - ModuleNotFoundError: No module named 'librt'
FAILED importlib_metadata/compat/py311.py::mypy - ModuleNotFoundError: No module named 'librt'
FAILED importlib_metadata/compat/py39.py::mypy - ModuleNotFoundError: No module named 'librt'
FAILED importlib_metadata/diagnose.py::mypy - ModuleNotFoundError: No module named 'librt'
FAILED tests/__init__.py::mypy - ModuleNotFoundError: No module named 'librt'
FAILED tests/_context.py::mypy - ModuleNotFoundError: No module named 'librt'
FAILED tests/_path.py::mypy - ModuleNotFoundError: No module named 'librt'
FAILED tests/compat/__init__.py::mypy - ModuleNotFoundError: No module named 'librt'
FAILED tests/compat/py312.py::mypy - ModuleNotFoundError: No module named 'librt'
FAILED tests/compat/py39.py::mypy - ModuleNotFoundError: No module named 'librt'
FAILED tests/compat/test_py39_compat.py::mypy - ModuleNotFoundError: No module named 'librt'
FAILED tests/data/__init__.py::mypy - ModuleNotFoundError: No module named 'librt'
/opt/hostedtoolcache/PyPy/3.10.16/x64/lib/pypy3.10/tempfile.py:869: ResourceWarning: Implicitly cleaning up <TemporaryDirectory '/tmp/pip-run-x2ksoee1'>
  _warnings.warn(warn_message, ResourceWarning)
/opt/hostedtoolcache/PyPy/3.10.16/x64/lib/pypy3.10/tempfile.py:869: ResourceWarning: Implicitly cleaning up <TemporaryDirectory '/tmp/pip-run-gnr44azb'>
  _warnings.warn(warn_message, ResourceWarning)
/opt/hostedtoolcache/PyPy/3.10.16/x64/lib/pypy3.10/tempfile.py:869: ResourceWarning: Implicitly cleaning up <TemporaryDirectory '/tmp/pip-run-ftnu9ymc'>
  _warnings.warn(warn_message, ResourceWarning)
/opt/hostedtoolcache/PyPy/3.10.16/x64/lib/pypy3.10/tempfile.py:869: ResourceWarning: Implicitly cleaning up <TemporaryDirectory '/tmp/pip-run-spv2qguk'>
  _warnings.warn(warn_message, ResourceWarning)
FAILED tests/data/sources/example/example/__init__.py::mypy - ModuleNotFoundError: No module named 'librt'
FAILED tests/data/sources/example2/example2/__init__.py::mypy - ModuleNotFoundError: No module named 'librt'
FAILED tests/fixtures.py::mypy - ModuleNotFoundError: No module named 'librt'
FAILED tests/test_api.py::mypy - ModuleNotFoundError: No module named 'librt'
FAILED tests/test_integration.py::mypy - ModuleNotFoundError: No module named 'librt'
FAILED tests/test_main.py::mypy - ModuleNotFoundError: No module named 'librt'
FAILED tests/test_zip.py::mypy - ModuleNotFoundError: No module named 'librt'

I've observed the same locally and on other projects.

[jaraco]

The issue occurs when running mypy directly:

 tempora main 🐚 .tox/pypy/bin/mypy .
Traceback (most recent call last):
  File "/Users/jaraco/code/jaraco/tempora/.tox/pypy/bin/mypy", line 5, in <module>
    from mypy.__main__ import console_entry
  File "/Users/jaraco/code/jaraco/tempora/.tox/pypy/lib/pypy3.10/site-packages/mypy/__main__.py", line 9, in <module>
    from mypy.main import main, process_options
  File "/Users/jaraco/code/jaraco/tempora/.tox/pypy/lib/pypy3.10/site-packages/mypy/main.py", line 17, in <module>
    from mypy import build, defaults, state, util
  File "<frozen importlib._bootstrap>", line 1078, in _handle_fromlist
  File "<frozen importlib._bootstrap>", line 241, in _call_with_frames_removed
  File "/Users/jaraco/code/jaraco/tempora/.tox/pypy/lib/pypy3.10/site-packages/mypy/build.py", line 31, in <module>
    from librt.internal import cache_version
ModuleNotFoundError: No module named 'librt'

[Avasam]

I'd like to suggest skipping mypy on PyPy entirely: #187

Whilst the symptom is currently quelled, this is an issue that has happened in the past, is likely to come up again in the future, and may lock everything on a lower mypy version for quite a while.

Locking mypy to a lower version for one test but not the others is also fragile and can lead to differing, unreconcilable results. For example if 1 environment requires a type: ignore, but on the other that results in an unused ignore error.

Even when it works, I don't think running mypy on PyPy brings any value, and is actively wasting time. Both from the CI runtime, and from playing cat-and-mouse with a test that brings no value.