Make meson-python usage example more idiomatic

[rgommers]

• Use dependency('pybind11'), which is all that is needed since Meson 1.1.0,
• Don't define an unused py_mod Python module,
• Remove custom C++ compile flags that are not present in the scikit-build-core and Maturin examples (nor seem needed),
• Make indentation consistent,
• Use py.install_sources instead of a more complicated install_subdir call,

[henryiii]

Thanks! The example here is synced with the cookiecutter, so it needs to be changed there. I can move your changes there.

[rgommers]

Ah, thank you! I was also looking for the sources to be built, but I don't think they exist, right? Rather, it's a super simple hypothetical example? If there's an actual src/ tree somewhere, I missed it.

[henryiii]

The source is in {{cookiecutter.project_name}}/{% if cookiecutter.backend=='mesonpy' %}meson.build{% endif %}. We use cog to render the template (https://github.com/scientific-python/cookie/blob/main/helpers/cog_helpers.py, etc, are used to read in and render the examples as long as they are a full file example (I don't do this for partial file examples yet).

So those files are exactly what you get if you use cookiecutter/cruft/copier to render the template, are tested to work, and stay updated, etc.

[henryiii]

Hmmm,

../meson.build:22:3: ERROR: File src/__init__.py does not exist.

[henryiii]

Ahh, that one needs the package name, of course. The reason I went with install_subdir is it matched the other examples and installed the entire directory, rather than requiring (surprising?) the author to continuously update build.meson every time they add a file. While Meson recommends files listed explicitly, it's surprising to someone coming from Python where none of the other backends expect you to list every Python file.

[rgommers]

While Meson recommends files listed explicitly, it's surprising to someone coming from Python where none of the other backends expect you to list every Python file.

Sure, it's a toss-up. I think CMake also recommends against globbing? Happy to go back to install_subdir here if you prefer. The strip_directory part should go though - I'd write it as:

install_subdir('src/package', py.get_install_dir() / 'package')

[rgommers]

Note that since I didn't find the source files, I completely made up _main.py - it likely doesn't exist.

[henryiii]

Yes, and py.typed is missing. Let's do install_subdir. Someone can easily move to listing things if they prefer, but the template will work better this way.

CMake does discourage globbing (less-so now that CONFIGURE_DEPENDS exists), but we don't use globbing or even CMake at all for the Python files, those are picked up and installed by the scikit-build-core following the mechanism used in other Python backends, like hatchling.

[rgommers]

I'm not sure how that works exactly, but in meson-python it would be a little tricky to get that right. Installing all .py files is wrong, and the .gitattributes method doesn't quite work either because that would also exclude .py files from the sdist.

[henryiii]

We rip the procedure straight from hatchling. It's based on a "package" list. The default is ["<package_name>", "src/<package_name>", "python/<package_name>"] (last of which is unique to scikit-build-core). A user can specify their own custom list, including an empty list, which disables the process. Anything in these packages is included entirely (there is a wheel.exclude option too for filtering). Anything more exotic than packages needs to be copied around via CMake and won't work as well with editable installs (hatchling has a powerful force-include dict that we might also add a some point).

[rgommers]

Thanks for the context! I'll have to look into that, it does sound potentially useful.

[henryiii]

The strip_directory part should go though - I'd write it as:

That is invalid, the following produces an error saying only one argument is supported:

install_subdir('src/package', py.get_install_dir() / 'package')

../meson.build:22:0: ERROR: install_subdir takes exactly 1 arguments, but got 2.

This doesn't install packages correctly, it adds the "src" to the package directory:

install_subdir('src/package', install_dir: py.get_install_dir() / 'package')

E       AttributeError: module 'cookie_mesonpy' has no attribute '__version__'

It needs the directory strip to get rid of the leading "src".

[rgommers]

It needs the directory strip to get rid of the leading "src".

Ugh, you're right. I never work on packages with the src/ layout normally. Guess in a real package the meson.build file would not be at the top level, but inside src/.

[rgommers]

Thanks for the quick merge!