[PATCH v2 0/5] rust: generate bindings via cbindgen

Hi,

this small patch series introduces support for cbindgen(1). This tool is used to generate C headers from `extern "C"` blocks so that Rust code can easily be called from C code.

For now, the only use case is to verify that our varint reimplementation matches the C implementation. But later on this can and will be used to call Rust-specific features from C, as well.

The topic is built on top of c54a18ef67 (The twenty-second batch, 2025-10-22) with ps/ci-rust at e509b5b8be (rust: support for Windows, 2025-10-15) merged into it.

Changes in v2:
  - Take some of the pieces from Ezekiel's "cbindgen.toml" file. I have
    not yet taken `usize_is_size_t`, as that option requires cbindgen
    v0.16.0, which is not available on Ubuntu 20.04.
  - Backfill missing jobs for GitLab CI.
  - Fix CI failures on Alma Linux 8 because cbindgen isn't available
    there.
  - Link to v1: https://lore.kernel.org/r/20251023-b4-pks-rust-cbindgen-v1-0-c19b61b03127@pks.im

Thanks!

Patrick

---
Patrick Steinhardt (5):
      gitlab-ci: reorder Linux job matrix to match GitHub's order
      gitlab-ci: backfill missing Linux jobs
      ci: use Debian instead of deprecated i386/ubuntu
      meson: rename Rust library target
      rust: generate bindings via cbindgen

 .github/workflows/main.yml |  3 +--
 .gitignore                 |  1 +
 .gitlab-ci.yml             | 22 ++++++++++++++--------
 Makefile                   | 14 +++++++++++---
 cbindgen.toml              | 13 +++++++++++++
 ci/install-dependencies.sh | 16 +++++++++++-----
 ci/lib.sh                  |  2 +-
 meson.build                | 25 ++++++++++++++++++++-----
 shared.mak                 |  1 +
 src/meson.build            |  2 +-
 varint.c                   |  9 +++++++++
 11 files changed, 83 insertions(+), 25 deletions(-)

Range-diff versus v1:

-:  ---------- > 1:  81e7677f3a gitlab-ci: reorder Linux job matrix to match GitHub's order
-:  ---------- > 2:  c367154007 gitlab-ci: backfill missing Linux jobs
1:  740702529c ! 3:  a1d7260326 ci: use Debian instead of deprecated i386/ubuntu
    @@ .gitlab-ci.yml: test:linux:
            - jobname: linux32
     -        image: i386/ubuntu:20.04
     +        image: i386/debian:latest
    -       - jobname: linux-meson
    -         image: ubuntu:rolling
    -         CC: gcc
    +       # A RHEL 8 compatible distro.  Supported until 2029-05-31.
    +       - jobname: almalinux-8
    +         image: almalinux:8
     
      ## ci/install-dependencies.sh ##
     @@ ci/install-dependencies.sh: fedora-*|almalinux-*)
    @@ ci/lib.sh: then
      		CI_OS_NAME=osx
      		JOBS=$(nproc)
      		;;
    --	*,alpine:*|*,fedora:*|*,ubuntu:*|*,i386/ubuntu:*)
    -+	*,alpine:*|*,fedora:*|*,ubuntu:*|*,i386/debian:*)
    +-	*,almalinux:*|*,alpine:*|*,debian:*|*,fedora:*|*,ubuntu:*|*,i386/ubuntu:*)
    ++	*,almalinux:*|*,alpine:*|*,debian:*|*,fedora:*|*,ubuntu:*|*,i386/debian:*)
      		CI_OS_NAME=linux
      		JOBS=$(nproc)
      		;;
2:  ff696cfb2e = 4:  490c8a4d45 meson: rename Rust library target
3:  67a9f353df ! 5:  8b7a2469b2 rust: generate bindings via cbindgen
    @@ cbindgen.toml (new)
     @@
     +language = "C"
     +
    ++# Write a warning into the generated file.
    ++autogen_warning = "/* Warning, this file is autogenerated by cbindgen. Don't modify this manually. */"
    ++
     +# Don't include standard C headers. These are managed by "git-compat-util.h".
     +no_includes = true
     +
     +# Use plain structs instead of using typedefs.
     +style = "tag"
    ++
    ++# Match our coding style more closely.
    ++tab_width = 8
     
      ## ci/install-dependencies.sh ##
    -@@ ci/install-dependencies.sh: fedora-*|almalinux-*)
    +@@ ci/install-dependencies.sh: alpine-*)
    + 		bash cvs gnupg perl-cgi perl-dbd-sqlite perl-io-tty >/dev/null
    + 	;;
    + fedora-*|almalinux-*)
    ++	RUST_DEPS="cargo cbindgen"
    + 	case "$jobname" in
    ++	almalinux-8)
    ++		# AlmaLinux 8 does not have cbindgen, it was only added in version 9.
    ++		RUST_DEPS=;;
    + 	*-meson)
      		MESON_DEPS="meson ninja";;
      	esac
    ++
      	dnf -yq update >/dev/null &&
     -	dnf -yq install shadow-utils sudo make pkg-config gcc findutils diffutils perl python3 gawk gettext zlib-devel expat-devel openssl-devel curl-devel pcre2-devel $MESON_DEPS cargo >/dev/null
    -+	dnf -yq install shadow-utils sudo make pkg-config gcc findutils diffutils perl python3 gawk gettext zlib-devel expat-devel openssl-devel curl-devel pcre2-devel $MESON_DEPS cargo cbindgen >/dev/null
    ++	dnf -yq install shadow-utils sudo make pkg-config gcc findutils diffutils perl python3 gawk gettext \
    ++		zlib-devel expat-devel openssl-devel curl-devel pcre2-devel $MESON_DEPS $RUST_DEPS >/dev/null
      	;;
      ubuntu-*|i386/debian-*|debian-*)
      	# Required so that apt doesn't wait for user input on certain packages.

--- base-commit: 8654b230d9afe1326340989dd7082997c672472e change-id: 20251009-b4-pks-rust-cbindgen-d80779ed2269