[libcamera-devel] [RFC 1/1] build: Preserve upstream git versioning using meson dist

[Naushir Patuck]

When distributions build and package libcamera libraries, they may not
necessarily run the build in the upstream source tree. In these cases, the git
SHA1 versioning information will be lost.

This change addresses that problem by requiring package managers to run
'meson dist' to create a tarball of the source files and build from there.
On runing 'meson dist', the utils/run-dist.sh script will create a version.gen
file in the release tarball with the version string generated from the existing
utils/gen-version.sh script.

The build system has been updated to check for the presence of this version.gen
file and read the version string from it. If the file is not present, the
version string is generated by running utils/gen-version.sh as it currently
does.

Signed-off-by: Naushir Patuck <naush at raspberrypi.com>
---
 meson.build               | 30 ++++++++++++++++++++----------
 src/libcamera/meson.build | 11 +++++------
 utils/run-dist.sh         |  9 +++++++++
 3 files changed, 34 insertions(+), 16 deletions(-)
 create mode 100644 utils/run-dist.sh

diff --git a/meson.build b/meson.build
index a49c484fe64e..f27bfd479a5c 100644
--- a/meson.build
+++ b/meson.build
@@ -10,20 +10,30 @@ project('libcamera', 'c', 'cpp',
     ],
     license : 'LGPL 2.1+')
 
-# Generate version information. The libcamera_git_version variable contains the
-# full version with git patch count and SHA1 (e.g. 1.2.3+211-c94a24f4), while
-# the libcamera_version variable contains the major.minor.patch (e.g. 1.2.3)
-# only. If the source tree isn't under git control, or if it matches the last
-# git version tag, the build metadata (e.g. +211-c94a24f4) is omitted from
-# libcamera_git_version.
-libcamera_git_version = run_command('utils/gen-version.sh',
-                                    meson.build_root()).stdout().strip()
-if libcamera_git_version == ''
-    libcamera_git_version = meson.project_version()
+fs_mod = import('fs')
+if not fs_mod.is_file('version.gen')
+    # Generate version information. The libcamera_git_version variable contains the
+    # the full version with git patch count and SHA1 (e.g. 1.2.3+211-c94a24f4), while
+    # the libcamera_version variable contains the major.minor.patch (e.g. 1.2.3)
+    # only. If the source tree isn't under git control, or if it matches the last
+    # git version tag, the build metadata (e.g. +211-c94a24f4) is omitted from
+    # libcamera_git_version.
+    libcamera_git_version = run_command('utils/gen-version.sh',
+                                        meson.build_root()).stdout().strip()
+    if libcamera_git_version == ''
+        libcamera_git_version = meson.project_version()
+    endif
+else
+    # Read the version information from the file generated by the utils/run-dist.sh
+    # script on a 'meson dist' command.
+    libcamera_git_version = run_command(['cat', 'version.gen']).stdout().strip()
 endif
 
 libcamera_version = libcamera_git_version.split('+')[0]
 
+# This script gererates the version.gen file on a 'meson dist' command.
+meson.add_dist_script('utils/run-dist.sh')
+
 # Configure the build environment.
 cc = meson.get_compiler('c')
 cxx = meson.get_compiler('cpp')
diff --git a/src/libcamera/meson.build b/src/libcamera/meson.build
index 243dd3c180eb..360eaf80ecf1 100644
--- a/src/libcamera/meson.build
+++ b/src/libcamera/meson.build
@@ -93,12 +93,11 @@ endforeach
 
 libcamera_sources += control_sources
 
-gen_version = meson.source_root() / 'utils' / 'gen-version.sh'
-
-version_cpp = vcs_tag(command : [gen_version, meson.build_root()],
-                      input : 'version.cpp.in',
-                      output : 'version.cpp',
-                      fallback : meson.project_version())
+version_data = configuration_data()
+version_data.set('VCS_TAG', libcamera_git_version)
+version_cpp = configure_file(input : 'version.cpp.in',
+                             output : 'version.cpp',
+                             configuration : version_data)
 
 libcamera_sources += version_cpp
 
diff --git a/utils/run-dist.sh b/utils/run-dist.sh
new file mode 100644
index 000000000000..1b2a6348c6bc
--- /dev/null
+++ b/utils/run-dist.sh
@@ -0,0 +1,9 @@
+#!/bin/sh
+
+# SPDX-License-Identifier: GPL-2.0-or-later
+#
+# On a meson dist run, generate the version string and store it in a file.
+# This will late be picked up by the build system and used in place of running
+# the utils/gen-version.sh script again since we may not be running in the
+# upstream git source tree, and so version information would be lost.
+"$MESON_DIST_ROOT"/utils/gen-version.sh > "$MESON_DIST_ROOT"/version.gen
-- 
2.25.1