Meson

Much like Autotools and CMake, Meson is a build system. But it is meant to be both fast and as user friendly as possible. GNOME’s goal is to port modules to use the Meson build system.

Phases

The MesonBuilder and MesonPackage base classes come with the following phases:

meson - generate ninja files
build - build the project
install - install the project

By default, these phases run:

$ mkdir spack-build
$ cd spack-build
$ meson .. --prefix=/path/to/installation/prefix
$ ninja
$ ninja test  # optional
$ ninja install

Any of these phases can be overridden in your package as necessary. There is also a check method that looks for a test target in the build file. If a test target exists and the user runs:

$ spack install --test=root <meson-package>

Spack will run ninja test after the build phase.

Important files

Packages that use the Meson build system can be identified by the presence of a meson.build file. This file declares things like build instructions and dependencies.

One thing to look for is the meson_version key that gets passed to the project function:

project('gtk+', 'c',
     version: '3.94.0',
     default_options: [
       'buildtype=debugoptimized',
       'warning_level=1',
       # We only need c99, but glib needs GNU-specific features
       # https://github.com/mesonbuild/meson/issues/2289
       'c_std=gnu99',
     ],
     meson_version: '>= 0.43.0',
     license: 'LGPLv2.1+')

This means that Meson 0.43.0 is the earliest release that will work. You should specify this in a depends_on statement.

Build system dependencies

At the bare minimum, packages that use the Meson build system need meson and `ninja` dependencies. Since this is always the case, the MesonPackage base class already contains:

depends_on("meson", type="build")
depends_on("ninja", type="build")

If you need to specify a particular version requirement, you can override this in your package:

depends_on("meson@0.43.0:", type="build")
depends_on("ninja", type="build")

Finding meson flags

To get a list of valid flags that can be passed to meson, run the following command in the directory that contains meson.build:

$ meson setup --help

Passing arguments to meson

If you need to pass any arguments to the meson call, you can override the meson_args method like so:

def meson_args(self):
    return ["--warnlevel=3"]

This method can be used to pass flags as well as variables.

Note that the MesonPackage base class already defines variants for buildtype, default_library and strip, which are mapped to default Meson arguments, meaning that you don’t have to specify these.

External documentation

For more information on the Meson build system, see: https://mesonbuild.com/index.html