Add syntastic integration

[Limeth]

This PR adds support for Syntastic linting for C via Meson/Ninja.

In my .vimrc, I additionally have the following, to enable this syntastic plugin only when there's a meson.build in the current directory.

autocmd FileType c call ConsiderMesonForLinting()
function ConsiderMesonForLinting()
    silent !test -f meson.build > /dev/null 2>&1
    if v:shell_error == 0
        let g:syntastic_c_checkers = ['meson']
    endif
endfunction

[igankevich]

Jakub, thank you for the PR!

Overall, it looks nice, but there are two things I'm not easy with.

1. There are far too many non-portable shell invocations. Could you, please, use filereadable() and isdirectory() functions to check for file/directory availability? They are much faster and portable alternatives to shell functions.

2. Please, replace hard-coded 'meson' and 'ninja' with g:meson_command and g:meson_ninja_command. These variables are already used by the plugin as mentioned in README. Mixing hard-coded commands and custom commands from variables may confuse users.

[Limeth]

I just tried using the g:meson_command and g:meson_ninja_command, but they seem to be undefined. As far as I can tell, these are the possible solutions:

• Change the visibility of s:MesonCommand and s:NinjaCommand to g:MesonCommand and g:NinjaCommand respectively, and then use these commands from within the syntax checker; or
• Keep the visibility and copy the functions to the syntax checker

Regarding the (test -d build > /dev/null 2>&1 || meson build) && ninja -C build command; I've done some research into Syntastic and I believe there isn't a way to register a function instead of a command to be called when highlighting is supposed to be updated. So I propose the following:

• Keep the command as it is (According to ShellCheck, the command should be fine for POSIX systems, but I'm not sure about Windows. Is it possible to install Vim on Windows without a POSIX-compliant shell?);
• Remove the conditional call to meson build in order to get rid of "special" syntax. This would require the user to have run :MesonInit before opening a C file, otherwise the syntax checker wouldn't be available.

[igankevich]

OK. Let's change visibility of MesonCommand and NinjaCommand functions and call them from the syntax checker. It would be better to move both to plugin/meson.vim then.

As for the makeprgBuild, I would rather remove the whole exe_before part: Syntastic documentation says that these parts can be redefined by the user. Anyway, you provide error format for C errors only, and errors produced by running meson will not be detected. As far as I understand Syntastic, you would need another checker to catch and parse them.

[Limeth]

Anyway, you provide error format for C errors only, and errors produced by running meson will not be detected.

Yes, this script provides highlighting for C files. From my experience with Meson (I've only just begun using it), I haven't yet encountered any Meson warnings that should be displayed as syntax highlighting within C files. It may be possible to add highlighting for the meson.build file, but that would most likely fall under a different syntax checker plugin (possibly syntax_checkers/build/meson.vim).

[igankevich]

I haven't yet encountered any Meson warnings that should be displayed as syntax highlighting within C files.

There are no such warnings. Meson emit errors for meson.build files only. They look like this: https://github.com/igankevich/mesonic/blob/master/compiler/meson.vim#L62

It may be possible to add highlighting for the meson.build file, but that would most likely fall under a different syntax checker plugin (possibly syntax_checkers/build/meson.vim).

As far as I understand, this is the only clean way of checking meson.build errors with Syntastic. If you want, you may add this syntax checker plugin, and I will merge it in in one pull request.

The rest of the code is good enough to merge, I will do it as soon as you reply!

[Limeth]

I honestly don't know how I'd make a syntax checker for a file named meson.build instead of for all files with the .build extension. I think this functionality should fall under a separate PR anyway. I don't currently need it either, as my meson.build currently consists of 3 lines only.