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short-description: Overview of the Meson build system
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# Overview

Meson is a build system that is designed to be as user-friendly as possible without sacrificing performance. The main tool for this is a custom language that the user uses to describe the structure of his build. The main design goals of this language has been simplicity, clarity and conciseness. Much inspiration was drawn from the Python programming language, which is considered very readable, even to people who have not programmed in Python before.

Another main idea has been to provide first class support for modern programming tools and best practices. These include features as varied as unit testing, code coverage reporting, precompiled headers and the like. All of these features should be immediately available to any project using Meson. The user should not need to hunt for third party macros or write shell scripts to get these features. They just just work out of the box.

This power should not come at the expense of limited usability. Many software builds require unorthodox steps. A common example is that you first need to build a custom tool and then use that tool to generate more source code to build. This functionality needs to be supported and be as easy to use as other parts of the system.

Terminology
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Meson follows the overall structure of other popular build systems, such as CMake and GNU Autotools. This means that the build is divided into two discrete steps: *configure step* and *build step*. The first step inspects the system, checks for dependencies and does all other steps necessary to configure the build. It then generates the actual build system. The second step is simply executing this generated build system. The end result is a bunch of *build targets*, which are usually executables and shared and static libraries.

The directory that contains the source code is called the *source directory*. Correspondingly the directory where the output is written is called the *build directory*. In other build systems it is common to have these two be the same directory. This is called an *in-source build*. The case where the build directory is separate is called an *out-of-source build*.

What sets Meson apart from most build systems is that it enforces a separate build directory. All files created by the build system are put in the build directory. It is actually impossible to do an in-source build. For people used to building inside their source tree, this may seem like a needless complication. However there are several benefits to doing only out-of-source builds. These will be explained in the next chapter.

When the source code is built, a set of *unit tests* is usually run. They ensure that the program is working as it should. If it does, the build result can be *installed* after which it is ready for use.