Meson: Vala projects should automatically add 'c' to project languages

[meghprkh]

The current code is broken (maybe worked with a past version). Here is the new code:

project('valaprog', ['c', 'vala'])

glib = dependency('glib-2.0')
gobject = dependency('gobject-2.0')

executable('valaprog', 'prog.vala',
           dependencies: [glib, gobject])

[meghprkh]

Referencing this page: https://github.com/mesonbuild/meson/wiki/Vala

[nirbheek]

Fixed, thanks!

[meghprkh]

@nirbheek looks like it is not fixed. Maybe you forgot to push =)

[nirbheek]

I pushed it to the wrong repository. Fixed now. ;)

I didn't add ['c'] to the list of project languages. I don't think that should be needed for a vala-only project. If it is, that's a bug and should be fixed. I can't test that, so please tell me if that's broken too.

[meghprkh]

Yes I needed to add 'c' to the project languages otherwise it threw the following error.

(I think that is because first meson pre-compiles to C and then compiles the C files)

$ ninja-build 
[1/1] Regenerating build files
The Meson build system
Version: 0.31.0
Source dir: /home/megh/projects/gnome/mesonbuild/vala-sample
Build dir: /home/megh/projects/gnome/mesonbuild/vala-sample/build
Build type: native build
Build machine cpu family: x86_64
Build machine cpu: x86_64
Project name: valaprog
Native vala compiler: valac (unknown 0.32.1)
Build targets in project: 1
Traceback (most recent call last):
  File "/usr/lib/python3.5/site-packages/mesonbuild/mesonmain.py", line 254, in run
    app.generate()
  File "/usr/lib/python3.5/site-packages/mesonbuild/mesonmain.py", line 158, in generate
    g.generate(intr)
  File "/usr/lib/python3.5/site-packages/mesonbuild/backend/ninjabackend.py", line 178, in generate
    [self.generate_target(t, outfile) for t in self.build.get_targets().values()]
  File "/usr/lib/python3.5/site-packages/mesonbuild/backend/ninjabackend.py", line 178, in <listcomp>
    [self.generate_target(t, outfile) for t in self.build.get_targets().values()]
  File "/usr/lib/python3.5/site-packages/mesonbuild/backend/ninjabackend.py", line 313, in generate_target
    obj_list.append(self.generate_single_compile(target, outfile, src, True, [], header_deps))
  File "/usr/lib/python3.5/site-packages/mesonbuild/backend/ninjabackend.py", line 1436, in generate_single_compile
    compiler = self.get_compiler_for_source(src)
  File "/usr/lib/python3.5/site-packages/mesonbuild/backend/backends.py", line 80, in get_compiler_for_source
    raise RuntimeError('No specified compiler can handle file ' + src)
RuntimeError: No specified compiler can handle file valaprog@exe/prog.c
FAILED: '/usr/bin/python3' '/usr/bin/meson' --internal regenerate '/home/megh/projects/gnome/mesonbuild/vala-sample' '/home/megh/projects/gnome/mesonbuild/vala-sample/build' --backend ninja
ninja: error: rebuilding 'build.ninja': subcommand failed

[nirbheek]

I can see why this would happen, but Meson should automatically add 'c' to the list of languages. I'm re-purposing this bug for this issue.

[meghprkh]

IMHO temporarily you should add 'c' to the wiki page. But it may not matter much as the error is quite expressive

[meghprkh]

Also currently if you run meson build (the initial command) it gives a super-clear error:

The Meson build system
Version: 0.31.0
Source dir: /home/megh/projects/gnome/mesonbuild/vala-sample
Build dir: /home/megh/projects/gnome/mesonbuild/vala-sample/build
Build type: native build
Build machine cpu family: x86_64
Build machine cpu: x86_64
Project name: valaprog
Native vala compiler: valac (unknown 0.32.1)

Meson encountered an error in file meson.build, line 1, column 0:
Compiling Vala requires C. Add C to your project languages and rerun Meson.

[nirbheek]

I'll leave the decision to @jpakkane, but I don't see why an error should be thrown for this. If C is always needed for compiling Vala, why not always add it when 'vala' is in languages? :)

[arteymix]

@nirbheek I guess that since Meson is very explicit by nature, it's a better thing to state that. Especially since a Vala build is typically mixed with C-specific directives.

Eventually, it could be possible to support standalone Vala build (exclusively with valac) and resolve dependencies from VAPIs.

[jpakkane]

This is not just a question of Vala + C but of adding languages automatically in general. Meson aims to be explicit and non-surprising. Adding a language to a project is a big thing with implications, we should not do that behing the user's backs.