[feature] Add support for meson subproject

[fnadeau]

What is your suggestion?

Add support for meson subproject.

Context: I'm planning, still in developpement, to open a PR for gstreamer-full (gstreamer build fully in static mode, see commit ) but it requires support for subproject in meson.

Proposed syntax looks like this:

tc.subproject_lists["gstreamer"] = [{'coretracers': 'enabled' if self.options.with_coretracers else 'disabled'}]
tc.subproject_lists["gst-plugins-base"] = [{'adder': 'enabled' if self.options.with_adder else 'disabled'}]

This is still in development. I'm not particularly found of the naming, especially subproject_list, so any suggestion that would make this more readable and/or understandable is more than welcom.

I would like to know the interrest in such feature. I currently have this commit. I would like to have input/ help for unit tests (unit testing the whole project has been... challanging and not really 100% pass, to say the least) and also with logic.

I have two point where I need help:

• Unit test: How can I unit test this in the most isolated way possible. So far, unit testing has been far from straight forward for my level of knowledge. I understant that there are many pitfalls (various versions of python and OS), but still... I failed to run anything that would be of any significant help, at least to me. Running on my machine yeld more failure than expected (missing compiler version, python 3.11 support lacking, etc..)
• The generated conan_meson_native.ini I have has some unwanted carriage return in it. It doesn't prevent it from working, just looks weird. In the [gst-plugins-base:project options] section, each element has an empty line. Here is a sample:

  
  [properties]

[constants] preprocessor_definitions = []

[project options] wrap_mode = 'nofallback' bindir = 'bin' sbindir = 'bin' libexecdir = 'bin' includedir = 'include' libdir = 'lib' auto_features = 'disabled' default_library = 'static' gst-full-target-type = 'static_library' base = 'enabled' good = 'disabled' ugly = 'disabled' bad = 'disabled' libav = 'disabled' build-tools-source = 'system' orc-source = 'subproject' introspection = 'disabled' orc = 'enabled' gst-full-plugins = '*'

[gstreamer:project options] coretracers = 'enabled'

[gst-plugins-base:project options] gio-typefinder = 'enabled'

gio = 'enabled'

adder = 'enabled'

audiomixer = 'enabled'

audioresample = 'enabled'

encoding = 'enabled'

rawparse = 'enabled'

volume = 'enabled'

videoconvertscale = 'enabled'

dsd = 'enabled'

videorate = 'enabled'

app = 'enabled'

playback = 'enabled'

audiorate = 'enabled'

audiotestsrc = 'enabled'

overlaycomposition = 'enabled'

subparse = 'enabled'

debugutils = 'enabled'

tcp = 'enabled'

drm = 'enabled'

pbtypes = 'enabled'

audioconvert = 'enabled'

typefind = 'enabled'

videotestsrc = 'enabled'

compositor = 'enabled'

[binaries] c = 'gcc' cpp = 'g++'

This is related to a closed ticket: #12774

Your input is greatly appreciated. 

### Have you read the CONTRIBUTING guide?

- [x] I've read the CONTRIBUTING guide

[memsharded]

Hi @fnadeau

Thanks for your suggestion.

I am not an expert in Meson, if I understood it correctly, the requested Conan feature would be to be able to pass options to subprojects defined in the meson.build files, isn't it? Wouldn't the syntax subproject_options be more directly mapped to that, specially given that we already have the MesonToolchain.project_options?

I think this feature can be added, thanks for offering to contribute.

For the test, it would be good enough do add something very similar to test_check_pkg_config_paths() in conans/test/integration/toolchains/meson/test_mesontoolchain.py, that checks the generated files, no need for a full functional compiling test.

[fnadeau]

I added this commit to my branch with suggestion from @memsharded, thanks for those.

I'm still working on gstreamer-full, I'll open a PR as soon as I'm certain the feature can be frozen. In the meanwhile, any input on this feature is appreciated.

[memsharded]

I have seen the commit, and I think it is good. It has little risk, it can be documented as experimental and moved forward, but sounds great until you further validate it with the gstreamer.

[franramirez688]

Hi @fnadeau

It looks good that branch! 👏 What I'd suggest is to add another functional test to check that it's doing what we expect for those subprojects. I can help with that for sure! 😁 We have some examples here conans/test/functional/toolchains/meson/.

[fnadeau]

Should this be also done for Conan v1?

[memsharded]

Not necessary to backport to Conan 1, thanks!