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904339edbd
Introduce support for the Meson build system, a "modern" meta build
system that supports many different platforms, including Linux, macOS,
Windows and BSDs. Meson supports different backends, including Ninja,
Xcode and Microsoft Visual Studio. Several common IDEs provide an
integration with it.
The biggest contender compared to Meson is probably CMake as outlined in
our "Documentation/technical/build-systems.txt" file. Based on my own
personal experience from working with both build systems extensively I
strongly favor Meson over CMake. In my opinion, it feels significantly
easier to use with a syntax that feels more like a "real" programming
language. The second big reason is that Meson supports Rust natively,
which may prove to be important given that the project may pick up Rust
as another language eventually.
Using Meson is rather straight-forward. An example:
```
# Meson uses out-of-tree builds. You can set up multiple build
# directories, how you name them is completely up to you.
$ mkdir build
$ cd build
$ meson setup .. -Dprefix=/tmp/git-installation
# Build the project. This also provides several other targets like
e.g. `install` or `test`.
$ ninja
# Meson has been wired up to support execution of our test suites.
# Both our unit tests and our integration tests are supported.
# Running `meson test` without any arguments will execute all tests,
# but the syntax supports globbing to select only some tests.
$ meson test 't-*'
# Execute single test interactively to allow for debugging.
$ meson test 't0000-*' --interactive --test-args=-ix
```
The build instructions have been successfully tested on the following
systems, tests are passing:
- Apple macOS 10.15.
- FreeBSD 14.1.
- NixOS 24.11.
- OpenBSD 7.6.
- Ubuntu 24.04.
- Windows 10 with Cygwin.
- Windows 10 with MinGW64, except for t9700, which is also broken with
our Makefile.
- Windows 10 with Visual Studio 2022 toolchain, using the Native Tools
Command Prompt with `meson setup --vsenv`. Tests pass, except for
t9700.
- Windows 10 with Visual Studio 2022 solution, using the Native Tools
Command Prompt with `meson setup --backend vs2022`. Tests pass,
except for t9700.
- Windows 10 with VS Code, using the Meson plug-in.
It is expected that there will still be rough edges in the current
version. If this patch lands the expectation is that it will coexist
with our other build systems for a while. Like this, distributions can
slowly migrate over to Meson and report any findings they have to us
such that we can continue to iterate. A potential cutoff date for other
build systems may be Git 3.0.
Some notes:
- The installed distribution is structured somewhat differently than
how it used to be the case. All of our binaries are installed into
`$libexec/git-core`, while all binaries part of `$bindir` are now
symbolic links pointing to the former. This rule is consistent in
itself and thus easier to reason about.
- We do not install dashed binaries into `$libexec/git-core` anymore,
so there won't e.g. be a symlink for git-add(1). These are not
required by modern Git and there isn't really much of a use case for
those anymore. By not installing those symlinks we thus start the
deprecation of this layout.
- We're targeting Meson 1.3.0, which has been released relatively
recently November 2023. The only feature we use from that version is
`fs.relative_to()`, which we could replace if necessary. If so, we
could start to target Meson 1.0.0 and newer, released in December
2022.
- The whole build instructions count around 3300 lines, half of which
is listing all of our code and test files. Our Makefiles are around
5000 lines, autoconf adds another 1300 lines. CMake in comparison
has only 1200 linescode, but it avoids listing individual files and
does not wire up auto-configuration as extensively as the Meson
instructions do.
- We bundle a set of subproject wrappers for curl, expat, openssl,
pcre2 and zlib. This allows developers to build Git without these
dependencies preinstalled, and Meson will fetch and build them
automatically. This is especially helpful on Windows.
Helped-by: Eli Schwartz <eschwartz@gentoo.org>
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Contributed Software Although these pieces are available as part of the official git source tree, they are in somewhat different status. The intention is to keep interesting tools around git here, maybe even experimental ones, to give users an easier access to them, and to give tools wider exposure, so that they can be improved faster. I am not expecting to touch these myself that much. As far as my day-to-day operation is concerned, these subdirectories are owned by their respective primary authors. I am willing to help if users of these components and the contrib/ subtree "owners" have technical/design issues to resolve, but the initiative to fix and/or enhance things _must_ be on the side of the subtree owners. IOW, I won't be actively looking for bugs and rooms for enhancements in them as the git maintainer -- I may only do so just as one of the users when I want to scratch my own itch. If you have patches to things in contrib/ area, the patch should be first sent to the primary author, and then the primary author should ack and forward it to me (git pull request is nicer). This is the same way as how I have been treating gitk, and to a lesser degree various foreign SCM interfaces, so you know the drill. I expect things that start their life in the contrib/ area to graduate out of contrib/ once they mature, either by becoming projects on their own, or moving to the toplevel directory. On the other hand, I expect I'll be proposing removal of disused and inactive ones from time to time. If you have new things to add to this area, please first propose it on the git mailing list, and after a list discussion proves there is general interest (it does not have to be a list-wide consensus for a tool targeted to a relatively narrow audience -- for example I do not work with projects whose upstream is svn, so I have no use for git-svn myself, but it is of general interest for people who need to interoperate with SVN repositories in a way git-svn works better than git-svnimport), submit a patch to create a subdirectory of contrib/ and put your stuff there. -jc