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Meson Build System

repository·master·Indexed 27 days ago

https://github.com/mesonbuild/meson

Meson is a next-generation build system designed for speed and usability, utilizing a Python-based configuration language and Ninja as its backend. It provides specialized modules for Qt (including compile_resources, compile_ui, compile_moc, and compile_translations), tools for managing compiler arguments via add_global_arguments and add_project_arguments, and integration with WrapDB for dependency management.

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What's inside Meson

  1. Overview of the Meson Build system

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    Meson is an open source build system designed for speed and user-friendliness. It aims to minimize the time developers spend writing or debugging build definitions and the time spent waiting for compilation.

    Key Features

    • Multiplatform Support: Works on Linux, macOS, Windows, and supports compilers like GCC, Clang, and Visual Studio.
    • Language Support: Supports C, C++, C#, D, Fortran, Java, and Rust.
    • Readable DSL: Uses a non-Turing complete Domain Specific Language for build definitions.
    • Cross Compilation: Supports many operating systems and bare metal targets.
    • Performance: Optimized for fast full and incremental builds.
    • Dependency Management: Includes a built-in multiplatform dependency provider that integrates with distro packages.

  2. Adhere to Meson's non-Turing complete design principle

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    The Meson definition language is intentionally not Turing complete. To maintain this, the following are strictly prohibited:

    • Defining custom functions inside meson.build files.
    • Implementing generalized loops within the language.

    Any change that would introduce Turing completeness is automatically rejected.

  4. Understand Meson's Python dependency requirements

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    Meson is implemented in Python and follows a strict rule to avoid 'dependency hell': it is not allowed to have any dependencies outside of the Python standard library. To use Meson, you only need to ensure that Python 3 is installed on your system. Depending on your build target, you may also need Ninja.

  5. Understand Meson language syntax and types

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    Meson uses a strongly typed, dynamically typed (duck typed) specification language. The main building blocks are variables, numbers, booleans, strings, arrays, function calls, method calls, if statements, and includes.

    Key Syntax Rules:

    • One statement per line. Multiple statements on a single line are not supported.
    • Function and method argument lists can be split over multiple lines.
    • Since version 0.50, you can use a backslash (\) at the end of a line to create multi-line statements.
    • All objects in Meson are immutable. Operations that appear to mutate an object actually create a new object and reassign it to the variable name.

  6. Core Design Principles of Meson

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    Meson is designed as a declarative, high-level build system that focuses on simplicity, speed, and enforcing best practices. Key architectural decisions include:

    • Declarative DSL: Uses a domain-specific language to declare build targets rather than writing imperative scripts. This allows the system to handle complex tasks like flag propagation automatically.
    • Separation of Source and Build Directories: Meson strictly enforces that all build artifacts are stored in a separate build directory. This prevents stray files from polluting the source tree and enables reliable features like precompiled headers.
    • High-Level Abstractions: Instead of manually managing compiler and linker flags for dependencies, users declare dependencies, and Meson handles the 'plumbing'.
    • Fast Backends: On Unix-like systems, Meson defaults to using Ninja instead of Make to ensure high-speed configuration and compilation.
    • Developer-Centric Defaults: Defaults are optimized for development, such as building objects without optimization and including debug information by default.

  7. Understand the Meson build workflow

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    Meson operates using a two-step process similar to CMake or GNU Autotools:

    1. Configure step: Meson inspects your system, checks for required dependencies, and performs necessary configuration tasks. This step generates the actual backend build system (e.g., Ninja files).
    2. Build step: This step executes the generated build system to produce build targets, which are typically executables, shared libraries, or static libraries.

    After a successful build, you can run unit tests to verify the program and then install the results to make them ready for use.

  8. Use the External Project module to build non-Meson projects

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    The unstable-external_project module allows Meson to build code using other build systems (like Autotools). This is typically used for subprojects where a system dependency is missing.

    Requirements for the external project:

    • Must support out-of-tree builds (the configure script is invoked inside Meson's build directory).
    • The configure script must generate a Makefile in the current workdir.
    • The configure script must accept common directories (prefix, libdir, etc.) as command line arguments.
    • The configure script must support common environment variables like CFLAGS and CC.
    • The compilation step must detect and handle reconfigure needs transparently.

    Note: This is an experimental module and its API may change.

  9. Understand Meson's policy on mixing build systems

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    Meson is designed around the principle that dependencies should either be provided by the platform (e.g., via Pkg-Config) or built as Meson subprojects.

    "Build system mixing" refers to any mechanism where one build system uses build artifacts from a different build system's build directory. This includes having one build system call another to build dependencies within the same build directory.

    Important Limitations:

    • Meson only provides functionality for simple mixing cases.
    • Complex mixed-build setups are not guaranteed to work and may break in future versions.
    • Meson will not provide maintenance or support for complex mixed-build scenarios.
    • Breakages caused by changes in other build systems are not considered Meson bugs.
    • Issues requiring Meson to work around broken functionality in another build system are not supported; such issues must be addressed upstream in the other build system.

  10. Compare Meson with other build systems

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    When choosing a build system, consider the following trade-offs between Meson and other common tools:

    GNU Autotools

    • Pros: Excellent support for legacy Unix platforms and a large selection of existing modules.
    • Cons: Slow, complicated, hard to use correctly, unreliable, difficult to debug, and poor support for non-Unix platforms (especially Windows).

    CMake

    • Pros: Great support for multiple backends like Visual Studio and XCode.
    • Cons: The scripting language is cumbersome and some simple tasks are unnecessarily complicated.

    SCons

    • Pros: Provides the full power of Python for build definitions.
    • Cons: Slow. Unlike most other build systems, SCons requires you to pass configuration settings on every invocation (e.g., if you run scons OPT1 OPT2, a subsequent run of just scons will reconfigure without those options).

    Bazel

    • Pros: Proven to scale to very large projects.
    • Cons: Implemented in Java, has poor Windows support, is heavily focused on Google's specific workflows, and requires signing a CLA to contribute code.

    Meson

    • Pros: High performance, user-friendly, and designed to be 'invisible' to the developer. It offers native support for modern tools (precompiled headers, coverage, Valgrind, etc.) and uses a non-Turing complete language for build definitions, making them easy to read and understand.
    • Cons: Relatively new with a smaller user base compared to legacy systems; Visual Studio and XCode backends may not match the quality of the Ninja backend.

  11. Generate uninstalled pkg-config files

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    Since version 0.54.0, Meson generates uninstalled pkg-config files located in <build dir>/meson-uninstalled/.

    To build an application against these uninstalled libraries without installing them to a prefix, set the PKG_CONFIG_PATH environment variable to point to the uninstalled directory:

    PKG_CONFIG_PATH=<builddir>/meson-uninstalled <command>
    PKG_CONFIG_PATH=<builddir>/meson-uninstalled

  12. Use Clang-CL with Visual Studio

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    To use clang-cl with Visual Studio (supported in VS 2017 and 2019), follow these steps:

    1. Install llvm+clang for Windows.
    2. Install the llvm toolset extension for visual studio.
    3. Configure Meson to use the compilers by either using a native file or by setting environment variables in your shell before running Meson:
    set CC=clang-cl
set CXX=clang-cl
    set CC=clang-cl
set CXX=clang-cl
meson setup builddir