[PATCH RFC 1/3] meson: add infrastructure to build internal Rust library

From: Patrick Steinhardt <ps@pks.im>
Date: Sep 4, 2025, 14:26 UTC
Message-ID: <20250904-b4-pks-rust-breaking-change-v1-1-3af1d25e0be9@pks.im>
In-Reply-To: <20250904-b4-pks-rust-breaking-change-v1-0-3af1d25e0be9@pks.im>

Add the infrastructure into Meson to build an internal Rust library. Building the Rust parts of Git are for now entirely optional, as they are mostly intended as a test balloon for both Git developers, but also for distributors of Git. So for now, they may contain:

  - New features that are not mission critical to Git and that users can
    easily live without.

  - Alternative implementations of small subsystems.

If these test balloons are successful, we will eventually make Rust a mandatory dependency for our build process in Git 3.0.

The availability of a Rust toolchain will be auto-detected by Meson at setup time. This behaviour can be tweaked via the `-Drust=` feature toggle.

Next to the linkable Rust library, also wire up tests that can be executed via `meson test`. This allows us to use the native unit testing capabilities of Rust.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 meson.build       | 16 +++++++++++++++-
 meson_options.txt |  2 ++
 src/lib.rs        |  0
 src/meson.build   | 12 ++++++++++++
 4 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/meson.build b/meson.build
index e8ec0eca165..1c0e98bbc14 100644
--- a/meson.build
+++ b/meson.build
@@ -1702,8 +1702,21 @@ version_def_h = custom_target(
 )
 libgit_sources += version_def_h
 
+libgit_libraries = [ ]
+
+if meson.version().version_compare('>=1.9.0')
+  rust_available = add_languages('rust', native: false, required: get_option('rust'))
+else
+  rust_available = false
+endif
+rust_option = get_option('rust').disable_auto_if(not rust_available)
+
+if rust_option.allowed() and meson.version().version_compare('>=1.9.0')
+  subdir('src')
+endif
+
 libgit = declare_dependency(
-  link_with: static_library('git',
+  link_with: libgit_libraries + static_library('git',
     sources: libgit_sources,
     c_args: libgit_c_args + [
       '-DGIT_VERSION_H="' + version_def_h.full_path() + '"',
@@ -2239,6 +2252,7 @@ summary({
   'pcre2': pcre2,
   'perl': perl_features_enabled,
   'python': target_python.found(),
+  'rust': rust_option.allowed(),
 }, section: 'Auto-detected features', bool_yn: true)
 
 summary({
diff --git a/meson_options.txt b/meson_options.txt
index 1668f260a18..143dee9237c 100644
--- a/meson_options.txt
+++ b/meson_options.txt
@@ -71,6 +71,8 @@ option('zlib_backend', type: 'combo', choices: ['auto', 'zlib', 'zlib-ng'], valu
 # Build tweaks.
 option('breaking_changes', type: 'boolean', value: false,
   description: 'Enable upcoming breaking changes.')
+option('rust', type: 'feature', value: 'auto',
+  description: 'Enable building with Rust.')
 option('macos_use_homebrew_gettext', type: 'boolean', value: true,
   description: 'Use gettext from Homebrew instead of the slightly-broken system-provided one.')
 
diff --git a/src/lib.rs b/src/lib.rs
new file mode 100644
index 00000000000..e69de29bb2d
diff --git a/src/meson.build b/src/meson.build
new file mode 100644
index 00000000000..2bd2045a8ab
--- /dev/null
+++ b/src/meson.build
@@ -0,0 +1,12 @@
+rustmod = import('rust')
+
+libgit_rs = static_library('git_rs',
+  sources: [
+    'lib.rs',
+  ],
+  rust_abi: 'c',
+)
+
+rustmod.test('git-rs', libgit_rs)
+
+libgit_libraries += libgit_rs

-- 
2.51.0.417.g1ba7204a04.dirty