pyproject.toml requires mypy 1.4.0-1.5.0 + mypycify in setup.py: failure (AssertionError)

[mr-c]

Bug Report

When upgrading a mypycify-using Python project from mypy 1.3.0 to a newer version, a pip install of my project fails where it does not with mypy 1.3.0

To Reproduce

git clone https://github.com/common-workflow-language/cwltool
cd cwltool
sed  -i 's/mypy==1.3.0/mypy==1.4.0/' pyproject.toml  # or to 1.4.1, or 1.5.0
MYPYPATH=mypy-stubs CWLTOOL_USE_MYPYC=1 pip install  .

Expected Behavior

$ MYPYPATH=mypy-stubs CWLTOOL_USE_MYPYC=1 pip install .
Processing /home/michael/cwltool
  Installing build dependencies ... done
  Getting requirements to build wheel ... done
  Installing backend dependencies ... done
  Preparing metadata (pyproject.toml) ... done
Requirement already satisfied: setuptools in ./env3.11/lib/python3.11/site-packages (from cwltool==3.1) (66.1.1)

[snip]

Building wheels for collected packages: cwltool
  Building wheel for cwltool (pyproject.toml) ... done
  Created wheel for cwltool: filename=cwltool-3.1-cp311-cp311-linux_x86_64.whl size=3672349 sha256=c467454417b08ede66d0832b6a17e7b00cded2d7e6073be12100d83746bb04ae
  Stored in directory: /tmp/pip-ephem-wheel-cache-z0z1cpyr/wheels/ee/cd/42/595fc105979e9f4d5af86398d7a0f9de9008e61383a87ccdb1
Successfully built cwltool

Actual Behavior

(passing --no-binary mypy to pip install to get a more interesting stacktrace, the same error occurs without it)

$ MYPYPATH=mypy-stubs CWLTOOL_USE_MYPYC=1 pip install  . --no-binary mypy
Processing /home/michael/cwltool
  Installing build dependencies ... done
  Getting requirements to build wheel ... error
  error: subprocess-exited-with-error
  
  × Getting requirements to build wheel did not run successfully.
  │ exit code: 1
  ╰─> [35 lines of output]
      Traceback (most recent call last):
        File "/home/michael/cwltool/env3.11/lib/python3.11/site-packages/pip/_vendor/pyproject_hooks/_in_process/_in_process.py", line 353, in <module>
          main()
        File "/home/michael/cwltool/env3.11/lib/python3.11/site-packages/pip/_vendor/pyproject_hooks/_in_process/_in_process.py", line 335, in main
          json_out['return_val'] = hook(**hook_input['kwargs'])
                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
        File "/home/michael/cwltool/env3.11/lib/python3.11/site-packages/pip/_vendor/pyproject_hooks/_in_process/_in_process.py", line 118, in get_requires_for_build_wheel
          return hook(config_settings)
                 ^^^^^^^^^^^^^^^^^^^^^
        File "/tmp/pip-build-env-rnls4s4_/overlay/lib/python3.11/site-packages/setuptools/build_meta.py", line 341, in get_requires_for_build_wheel
          return self._get_build_requires(config_settings, requirements=['wheel'])
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
        File "/tmp/pip-build-env-rnls4s4_/overlay/lib/python3.11/site-packages/setuptools/build_meta.py", line 323, in _get_build_requires
          self.run_setup()
        File "/tmp/pip-build-env-rnls4s4_/overlay/lib/python3.11/site-packages/setuptools/build_meta.py", line 338, in run_setup
          exec(code, locals())
        File "<string>", line 91, in <module>
        File "/tmp/pip-build-env-rnls4s4_/overlay/lib/python3.11/site-packages/mypyc/build.py", line 511, in mypycify
          groups, group_cfilenames = mypyc_build(
                                     ^^^^^^^^^^^^
        File "/tmp/pip-build-env-rnls4s4_/overlay/lib/python3.11/site-packages/mypyc/build.py", line 421, in mypyc_build
          group_cfiles, ops_text = generate_c(
                                   ^^^^^^^^^^^
        File "/tmp/pip-build-env-rnls4s4_/overlay/lib/python3.11/site-packages/mypyc/build.py", line 233, in generate_c
          emit_messages(options, errors.new_messages(), t2 - t1)
                                 ^^^^^^^^^^^^^^^^^^^^^
        File "/tmp/pip-build-env-rnls4s4_/overlay/lib/python3.11/site-packages/mypyc/errors.py", line 25, in new_messages
          return self._errors.new_messages()
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
        File "/tmp/pip-build-env-rnls4s4_/overlay/lib/python3.11/site-packages/mypy/errors.py", line 871, in new_messages
          msgs.extend(self.file_messages(path))
                      ^^^^^^^^^^^^^^^^^^^^^^^^
        File "/tmp/pip-build-env-rnls4s4_/overlay/lib/python3.11/site-packages/mypy/errors.py", line 857, in file_messages
          assert self.read_source
      AssertionError
      [end of output]
  
  note: This error originates from a subprocess, and is likely not a problem with pip.
error: subprocess-exited-with-error

× Getting requirements to build wheel did not run successfully.
│ exit code: 1
╰─> See above for output.

note: This error originates from a subprocess, and is likely not a problem with pip.

Same for mypy 1.4.1 and 1.5.0

Your Environment

• Mypy version used: 1.4.0+
• Python version used: 3.11.2

[mr-c]

I've git bisected this error down to 768ba66 by @koogoro from #15070
(using its parent commit 3d9661c I don't get an error).

Therefore the topic-mypyc label should probably be removed

[mr-c]

Ping