We're contemplating whether to eventually replace our build systems with a build system that is easier to use. Add a comparison of build systems to our technical documentation as a baseline for discussion. Signed-off-by: Patrick Steinhardt <ps@xxxxxx> --- Documentation/Makefile | 1 + Documentation/technical/build-systems.txt | 224 ++++++++++++++++++++++ 2 files changed, 225 insertions(+) create mode 100644 Documentation/technical/build-systems.txt diff --git a/Documentation/Makefile b/Documentation/Makefile index e2ce98a751f..e1527c6d442 100644 --- a/Documentation/Makefile +++ b/Documentation/Makefile @@ -111,6 +111,7 @@ TECH_DOCS += MyFirstObjectWalk TECH_DOCS += SubmittingPatches TECH_DOCS += ToolsForGit TECH_DOCS += technical/bitmap-format +TECH_DOCS += technical/build-systems TECH_DOCS += technical/bundle-uri TECH_DOCS += technical/hash-function-transition TECH_DOCS += technical/long-running-process-protocol diff --git a/Documentation/technical/build-systems.txt b/Documentation/technical/build-systems.txt new file mode 100644 index 00000000000..d9dafb407c4 --- /dev/null +++ b/Documentation/technical/build-systems.txt @@ -0,0 +1,224 @@ += Build Systems + +The build system is the primary way for both developers and system integrators +to interact with the Git project. As such, being easy to use and extend for +those who are not directly developing Git itself is just as important as other +requirements we have on any potential build system. + +This document outlines the different requirements that we have for the build +system and then compares available build systems using these criteria. + +== Requirements + +The following subsections present a list of requirements that we have for any +potential build system. Sections are sorted by decreasing priority. + +=== Platform support + +The build system must have support for all of our platforms that we continually +test against as outlined by our platform support policy. These platforms are: + + - Linux + - Windows + - macOS + +Furthermore, the build system should have support for the following platforms +that generally have somebody running test pipelines against regularly: + + - AIX + - FreeBSD + - NetBSD + - NonStop + - OpenBSD + +The platforms which must be supported by the tool should be aligned with our +[platform support policy](platform-support.txt). + +=== Auto-detection of supported features + +The build system must support auto-detection of features which are or aren't +available on the current platform. Platform maintainers should not be required +to manually configure the complete build. + +Auto-detection of the following items is considered to be important: + + - Check for the existence of headers. + - Check for the existence of libraries. + - Check for the existence of exectuables. + - Check for the runtime behavior of specific functions. + - Check for specific link order requirements when multiple libraries are + involved. + +=== Ease of use + +The build system should be both easy to use and easy to extend. While this is +naturally a subjective metric it is likely not controversial to say that some +build systems are considerably harder to use than others. + +=== IDE support + +The build system should integrate with well-known IDEs. Well-known IDEs include: + + - Microsoft Visual Studio + - Visual Studio Code + - Xcode + +There are four levels of support: + + - Native integration into the IDE. + - Integration into the IDE via a plugin. + - Integration into the IDE via generating a project description with the build + system. + - No integration. + +Native integration is preferable, but integration via either a plugin or by +generating a project description via the build system are considered feasible +alternatives. + +Another important distinction is the level of integration. There are two +features that one generally wants to have: + + - Integration of build targets. + - Automatic setup of features like code completion with detected build + dependencies. + +The first bullet point is the bare minimum, but is not sufficient to be +considered proper integration. + +=== Out-of-tree builds + +The build system should support out-of-tree builds. Out-of-tree builds allow a +developer to configure multiple different build directories with different +configuration, e.g. one "debug" build and one "release" build. + +=== Cross-platform builds + +The build system should support cross-platform builds, e.g. building for arm on +an x86-64 host. + +=== Language support + +The following languages and toolchains are of relevance and should be supported +by the build system: + + - C: the primary compiled language used by Git, must be supported. Relevant + toolchains are GCC, Clang and MSVC. + - Rust: candidate as a second compiled lanugage, should be supported. Relevant + toolchains is the LLVM-based rustc. + +Built-in support for the respective languages is preferred over support that +needs to be wired up manually to avoid unnecessary complexity. Native support +includes the following features: + + - Compiling objects. + - Dependency tracking. + - Detection of available features. + - Discovery of relevant toolchains. + - Linking libraries and executables. + - Templating placeholders in scripts. + +=== Test integration + +It should be possible to integrate tests into the build system such that it is +possible to build and test Git within the build system. Features which are nice +to have: + + - Track build-time dependencies for respective tests. Unit tests have + different requirements than integration tests. + - Allow filtering of which tests to run. + - Allow running tests such that utilities like `test_pause` or `debug` work. + +== Comparison + +The following list of build systems are considered: + +- GNU Make +- autoconf +- CMake +- Meson + +=== GNU Make + +- Platform support: ubitquitous on all platforms, but not well-integrated into Windows. +- Auto-detection: no built-in support for auto-detection of features. +- Ease of use: easy to use, but discovering available options is hard. Makefile + rules can quickly get out of hand once reaching a certain scope. +- IDE support: execution of Makefile targets is supported by many IDEs +- Out-of-tree builds: supported in theory, not wired up in practice. +- Cross-platform builds: supported in theory, not wired up in practice. +- Language support: + - C: Limited built-in support, many parts need to be wired up manually. + - Rust: No built-in support, needs to be wired up manually. +- Test integration: partially supported, many parts need to be wired up + manually. + +=== autoconf + +- Platform support: ubiquitous on all platforms, but not well-integrated into Windows. +- Auto-detection: supported. +- Ease of use: easy to use, discovering available options is comparatively + easy. The autoconf syntax is prohibitively hard to extend though due to its + complex set of interacting files and the hard-to-understand M4 language. +- IDE support: no integration into IDEs at generation time. The generated + Makefiles have the same level of support as GNU Make. +- Out-of-tree builds: supported in theory, not wired up in practice. +- Cross-platform builds: supported. +- Language support: + - C: Limited built-in support, many parts need to be wired up manually. + - Rust: No built-in support, needs to be wired up manually. +- Test integration: partially supported, many parts need to be wired up + manually. + +=== CMake + +- Platform support: not as extensive as GNU Make or autoconf, but all major + platforms are supported. + - AIX + - Cygwin + - FreeBSD + - Linux + - OpenBSD + - Solaris + - Windows + - macOS +- Ease of use: easy to use, discovering available options is not always + trivial. The scripting language used by CMake is somewhat cumbersome to use, + but extending CMake build instructions is doable. +- IDE support: natively integrated into Microsoft Visual Studio. Can generate + project descriptions for Xcode. An extension is available for Visual Studio + Code. Many other IDEs have plugins for CMake. +- Out-of-tree builds: supported. +- Cross-platform builds: supported. +- Language support: + - C: Supported for GCC, Clang, MSVC and other toolchains. + - Rust: No built-in support, needs to be wired up manually. +- Test integration: supported, even though test dependencies are a bit + cumbersome to use via "test fixtures". Interactive test runs are not + supported. + +=== Meson + +- Platform: not as extensive as GNU Make or autoconf, but all major platforms + and some smaller ones are supported. + - AIX + - Cygwin + - DragonflyBSD + - FreeBSD + - Haiku + - Linux + - NetBSD + - OpenBSD + - Solaris + - Windows + - macOS +- Ease of use: easy to use, discovering available options is easy. The + scripting language is straight-forward to use. +- IDE support: Supports generating build instructions for Xcode and Microsoft + Visual Studio, a plugin exists for Visual Studio Code. +- Out-of-tree builds: supported. +- Cross-platform builds: supported. +- Language support: + - C: Supported for GCC, Clang, MSVC and other toolchains. + - Rust: Supported for rustc. +- Test integration: supported. Interactive tests are supported starting with + Meson 1.5.0 via the `--interactive` flag. -- 2.47.0.229.g8f8d6eee53.dirty
