How to debug meson-python?

[bruchar1]

Actually, the only way I know to invoke meson-python is to use pip or build module. How should I setup my environment to use a local version of meson-python, and to attach the debugger to it?

[rgommers]

Hi @bruchar1, that is indeed the only way to use it. The key thing to use a local install for debugging is to install meson-python into your active Python environment and then using that version of meson-python with your own package's build by disabling build isolation (e.g. pip install -e . --no-build-isolation or python -m build -wnx).

[dnicolodi]

I symlink the mesonpy directory from the meson-python repository into the Python project I want to build and I use

[build-system]
build-backend = 'mesonpy'
backend-path = ['.']

in pyproject.toml. Then I build the project as usual via pip or build.

I don't know how you can conveniently do the same on platforms that do not support symlinks.

[robtaylor]

I'm trying to debug an issue in meson-python. I've installed meson-python editable (pip install -e .) but when i (e.g.) try build the simple test with pip (pip wheel -w dist . -vvv --no-build-isolation) I get this error:

  Created temporary directory: /tmp/pip-modern-metadata-n5t09yun
  Running command Preparing metadata (pyproject.toml)
  Traceback (most recent call last):
    File "/home/robtaylor/.pyenv/versions/3.11.1/lib/python3.11/site-packages/pip/_vendor/pyproject_hooks/_in_process/_in_process.py", line 353, in <module>
      main()
    File "/home/robtaylor/.pyenv/versions/3.11.1/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/robtaylor/.pyenv/versions/3.11.1/lib/python3.11/site-packages/pip/_vendor/pyproject_hooks/_in_process/_in_process.py", line 142, in prepare_metadata_for_build_wheel
      backend = _build_backend()
                ^^^^^^^^^^^^^^^^
    File "/home/robtaylor/.pyenv/versions/3.11.1/lib/python3.11/site-packages/pip/_vendor/pyproject_hooks/_in_process/_in_process.py", line 77, in _build_backend
      obj = import_module(mod_path)
            ^^^^^^^^^^^^^^^^^^^^^^^
    File "/home/robtaylor/.pyenv/versions/3.11.1/lib/python3.11/importlib/__init__.py", line 126, in import_module
      return _bootstrap._gcd_import(name[level:], package, level)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    File "<frozen importlib._bootstrap>", line 1206, in _gcd_import
    File "<frozen importlib._bootstrap>", line 1178, in _find_and_load
    File "<frozen importlib._bootstrap>", line 1140, in _find_and_load_unlocked
    File "<frozen importlib._bootstrap>", line 1080, in _find_spec
    File "/home/robtaylor/.pyenv/versions/3.11.1/lib/python3.11/site-packages/_meson_python_editable_loader.py", line 268, in find_spec
      tree = self.rebuild()
             ^^^^^^^^^^^^^^
    File "/home/robtaylor/.pyenv/versions/3.11.1/lib/python3.11/site-packages/_meson_python_editable_loader.py", line 309, in rebuild
      subprocess.run(self._build_cmd, cwd=self._build_path, env=env, stdout=stdout, check=True)
    File "/home/robtaylor/.pyenv/versions/3.11.1/lib/python3.11/subprocess.py", line 548, in run
      with Popen(*popenargs, **kwargs) as process:
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^
    File "/home/robtaylor/.pyenv/versions/3.11.1/lib/python3.11/subprocess.py", line 1024, in __init__
      self._execute_child(args, executable, preexec_fn, close_fds,
    File "/home/robtaylor/.pyenv/versions/3.11.1/lib/python3.11/subprocess.py", line 1901, in _execute_child
      raise child_exception_type(errno_num, err_msg, err_filename)
  FileNotFoundError: [Errno 2] No such file or directory: '/tmp/pip-build-env-rtoj7uux/normal/bin/ninja'

same issue with python -m build -wnx.

Any ideas?!

[dnicolodi]

You installed meson-python in editable mode without disabling build isolation and you don't have ninja installed. pip set up an isolated build environment to build the editable wheel for meson-python and installed ninja there, but the environment got discarded once the editable wheel was installed.