Better support for Meson editable installs

[paugier]

PDM could be improved for packages using Meson and meson-python. Note that Meson is nowadays quite important. It is used in particular for Numpy, Scipy and Scikit-image.

For these packages, the editable install (https://meson-python.readthedocs.io/en/latest/how-to-guides/editable-installs.html) has to be made with:

python -m pip install --no-build-isolation --editable .

and therefore the build dependencies have to be installed in the main virtual environment.

Currently, I have a build dev group:

[build-system]
requires = ["meson-python", "numpy", "transonic>=0.6.1", "pythran>=0.9.7"]
build-backend = 'mesonpy'

[tool.pdm.dev-dependencies]
build = ["meson-python", "ninja", "numpy", "transonic>=0.6.1", "pythran>=0.9.7"]

And I install with:

pdm sync --clean --no-self
pdm run pip install -e . --no-deps --no-build-isolation -v

This is complicated and not optimal. PDM could detect that the project uses mesonpy, install the build requirements in the main env and install in editable mode with the correct option (--no-build-isolation).

Note that there is the same problem for subpackages in the repository also using Meson. For example, I'd like to have:

[project.optional-dependencies]
# so that users can run `pip install fluidfft[fftw]`
# However, it should not be included in the lock file because for development 
# we want to install fluidfft-fftw from source
fftw = ["fluidfft-fftw"]

[tool.pdm.dev-dependencies]
# we want to have this one in the lock file
# fluidfft-fftw uses Meson and should be installed in editable mode with `--no-build-isolation`
plugins = [
    "-e fluidfft-fftw @ file:///${PROJECT_ROOT}/plugins/fluidfft-fftw",
]

Related question: is it possible to tell PDM that some optional dependency groups should not be included by default in the lock file?

[pawamoy]

I think you could this:

pdm sync --clean --no-isolation

...instead of pdm sync ... then pdm run pip ....

There's also the PDM_BUILD_ISOLATION=0 environment variable. This will affect all source builds, not just the project itself.

[amolenaar]

I'm testing PDM for PyGObject, which is also meson-python based.

I added

[tool.pdm.options]
install = ["--no-isolation"]

to pyproject.toml. This seems to do the trick for me.

[paugier]

Thanks for the advice. @amolenaar What about installation of the build dependencies? Do you also repeat them in a dev group?

[amolenaar]

Yes, there's a dev group containing meson-python and friends. I linked the PR.