What is Meson?

I have discovered Meson a couple of years back and since then use it for most of my projects written in Vala. This post is an attempt at describing the good, bad and ugly of the build system.

So, what is Meson?

a build system
portable (see Python portability)
a Ninja generator
use case oriented
fast
opiniated

What it’s not?

a general purpose build system
a Turing-complete language
extensible (only in Python)

It handle 80% of the cases nicely and elegantly.

Since it is use case oriented, features are introduced on need. It keeps a tight balance between conciseness, generality and features.

It mixes configure and build step so that the build essentially become one big tree. Then, the build system determine what goes into the configuration and what goes into the build.

The cognitive load is very low, which means it’s very easy to learn the basics and make actual usage of it. This is critical, because all the time spent on setting the build hardly contribute to the project goal.

The following is a basic build that check for dependencies (using pkg-config) and build an executable:

project('Meson Example', 'c', 'vala')

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

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

Building becomes a piece of cake:

mkdir build && cd build
meson ..
ninja

Only a few keywords are sufficient for most builds:

executable
library with shared_library and static_library
dependency
declare_dependency

Built-in benchmarks and tests, just pass the executable to either benchmark or test.

The main downside is that if what you want to do is not supported, you either have to hack things or wait until the feature gets into the build system.

The system is very opiniated. It’s both a good and bad thing. Good since you don’t need to write a lot to get most jobs done. Bad because you might hit a wall eventually.

There’s also the Python question. It requires at least 3.4. This is becoming less an problematic as old distributions progressively die out, but still can prevent you now. Here’s a few ideas to remedy this problem:

build a dependency-free zipball (see issue #588)
backport Meson to older Python version

Meson is getting better over time and so far has managed to become the best build system for Vala. This is why I highly recommend it.