[libcamera-devel] [RFC PATCH] libcamera: Disable automatic vcs versioning

[Tomi Valkeinen]

libcamera builds the git hash version into the libcamera library. This
makes ninja create the generated version.cpp on every build, and if the
git hash has changed, compilation of version.cpp and linking of
libcamera library.

This patch adds a meson option to disable this behavior and instead use
the meson project-version as the version built into the library, which
is only generated at meson configuration time.

With this change, ninja will nicely say "no work to do" if there's
nothing to compile, instead of starting the build and generating
version.cpp.

But, more importantly, it often reduces build time. For example, this
takes a particular git range compilation (~20 py bindings patches) from
43 seconds to 10 seconds. Obviously the improvement depends very much on
the patches in question. If every commit changes libcamera itself, there
is no difference.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen at ideasonboard.com>
---
 meson_options.txt         |  5 +++++
 src/libcamera/meson.build | 29 +++++++++++++++++++++--------
 2 files changed, 26 insertions(+), 8 deletions(-)

diff --git a/meson_options.txt b/meson_options.txt
index 7a9aecfc..6a0bd0be 100644
--- a/meson_options.txt
+++ b/meson_options.txt
@@ -63,3 +63,8 @@ option('pycamera',
         type : 'feature',
         value : 'disabled',
         description : 'Enable libcamera Python bindings (experimental)')
+
+option('disable-vcs-versioning',
+        type : 'boolean',
+        value : false,
+        description : 'Disable automatic libcamera library versioning with the git hash')
diff --git a/src/libcamera/meson.build b/src/libcamera/meson.build
index ce1f0f2f..6fd6f084 100644
--- a/src/libcamera/meson.build
+++ b/src/libcamera/meson.build
@@ -121,14 +121,27 @@ endforeach
 
 libcamera_sources += control_sources
 
-gen_version = meson.project_source_root() / 'utils' / 'gen-version.sh'
-
-# Use vcs_tag() and not configure_file() or run_command(), to ensure that the
-# version gets updated with every ninja build and not just at meson setup time.
-version_cpp = vcs_tag(command : [gen_version, meson.project_build_root(), meson.project_source_root()],
-                      input : 'version.cpp.in',
-                      output : 'version.cpp',
-                      fallback : meson.project_version())
+if get_option('disable-vcs-versioning')
+    cdata = configuration_data()
+    cdata.set('VCS_TAG', meson.project_version())
+
+    # For some reason using 'version.cpp' as output file works fine for generation
+    # but causes meson to delete the file before build. Any other file name
+    # seems to work.
+    version_cpp = configure_file(input : 'version.cpp.in',
+                                 output : 'version_static.cpp',
+                                 configuration : cdata)
+
+else
+    gen_version = meson.project_source_root() / 'utils' / 'gen-version.sh'
+
+    # Use vcs_tag() and not configure_file() or run_command(), to ensure that the
+    # version gets updated with every ninja build and not just at meson setup time.
+    version_cpp = vcs_tag(command : [gen_version, meson.project_build_root(), meson.project_source_root()],
+                          input : 'version.cpp.in',
+                          output : 'version.cpp',
+                          fallback : meson.project_version())
+endif
 
 libcamera_sources += version_cpp
 
-- 
2.34.1