Empty --config-setting causing problems with meson-python build

[ianthomas23]

I am in the process of porting an existing Python/C++ project that uses cibuildwheel to the meson-python build backend (contourpy/contourpy#183). This is progressing well but there is one problem when using cibuildwheel.

The build verbosity flag passed to meson-python has a specific form of a config-setting that is compile-args=-v. This is easily achieved in cibuildwheel using CIBW_CONFIG_SETTINGS. Hence I do not need to use CIBW_BUILD_VERBOSITY and I leave it unspecified. But when I do this I end up with a build command of this form:

python -m build /project --wheel --config-setting=compile-args=-v --config-setting=

The problem is the empty --config-setting= at the end, which meson-python errors out on. The GHA run producing this is https://github.com/ianthomas23/contourpy/actions/runs/4715025410/jobs/8361738715 using cibuildwheel 2.12.1.

I figure that ideally cibuildwheel wouldn't emit the empty --config-setting. On naively looking at the cibuildwheel source code for the first time I think a possible fix is here

cibuildwheel/cibuildwheel/linux.py

Lines 263 to 265 in 7c9b837

	elif build_frontend == "build":
	verbosity_setting = " ".join(verbosity_flags)
	extra_flags += (f"--config-setting={verbosity_setting}",)

not appending to the extra_flags if the verbosity_setting is empty. But I assume there must be other places for a similar change for non-linux platforms.

Of course it could be argued that meson-python should tolerate the empty setting that is currently produced.

[henryiii]

That line (edit: two lines) looks suspect as is and I would not argue to make meson-python ignore empty settings. :)

[henryiii]

Also, is this really correct? This is not generic to all back ends, and is not the same thing as enabling verbose mode on pip. Build defaults to verbose mode, basically. I think it should probably be removed.

[joerick]

Agreed, this looks like a bug