Meson

Meson is a modern, open-source build system designed to be both fast and user-friendly. It aims to simplify the build process for developers. It does not execute the build itself but generates build files for a backend tool, most commonly Ninja, which then performs the actual compilation. Its build definitions are written in a simple, non-turing-complete DSL in files named meson.build.

Meson is a high-level build system that uses Ninja as its default, high-performance backend to carry out the actual build process

Using Meson instead of just Ninja provides a significant developer experience upgrade because Meson automates complex build logic, manages dependencies, and offers a cross-platform configuration layer. 

The relationship between Meson and Ninja

You can think of the relationship between Meson and Ninja as a division of labor between a “meta-build system” and a “low-level build tool”:

  • Meson is the “meta-build system”: A developer writes a simple, declarative meson.build file, which describes the project’s structure, dependencies, and build options in a human-readable, Python-like syntax. Meson’s job is to read this file and figure out the specific steps required to build the project.
  • Ninja is the “build tool”: Meson’s configuration step generates highly optimized, low-level build files for Ninja. When you run Ninja, it reads these files and executes the build commands as fast as possible, automatically detecting how to parallelize the work across your CPU cores. 

The standard workflow is

  1. Configure: Run meson setup <build_directory> once. Meson analyzes your project and system, then generates Ninja build files inside the specified directory.
  2. Build: Run ninja from the build directory. Ninja executes the build commands, such as compiling source files and linking libraries. 

Why use Meson and not just Ninja?

While Ninja is a powerful tool for executing builds quickly, it’s not designed to be written by hand. The build files it consumes are verbose, low-level, and painful to maintain directly. Meson solves this by generating the Ninja files for you, providing a higher-level abstraction with many advantages: 

Declarative and user-friendly syntax

  • Simplified builds: Meson’s Python-inspired language focuses on what you want to build (e.g., executable('myprogram', 'main.c')), not the specific compiler flags and commands needed to do so. This is far simpler than manually writing complex build scripts.
  • Cross-platform compatibility: Meson automatically handles the subtle differences between operating systems, compilers, and architectures, so a single meson.build file works everywhere. You don’t have to manage platform-specific logic manually. 

Automated features

  • Out-of-source builds: Meson enforces the separation of source code from generated build files. This keeps your project directory clean and allows you to create multiple build configurations (e.g., debug and release) from the same source tree.
  • Dependency management: Meson has built-in support for finding and using dependencies installed on the system via tools like pkg-config, or by automatically downloading and building them as subprojects. You don’t need to write custom logic for every library your project uses.
  • Best practices built-in: Features like unit testing, code coverage, and support for precompiled headers are integrated directly into Meson. This saves you from writing custom, ad-hoc shell scripts to get basic modern development features. 

Performance and correctness

  • Maximized speed: By letting Meson generate the Ninja files, you get the benefit of Ninja’s incredible build performance, which includes optimized parallel execution.
  • Correct incremental builds: The Meson and Ninja combination correctly detects when files are added or removed, ensuring that your incremental builds are always correct without needing a full rebuild. A bare Ninja file, especially one generated poorly, can be less robust.