libcamera: skip auto version generation when building for Chromium OS

Commit b817bcec6b ("libcamera: Auto generate version information")
causes the build to fail in the Chromium OS build environment, because
git update-index tries to take a lock (ie. write) in the git repo that
is outside of the build directory.

The solution is to simply skip git update-index if we are building in
the Chromium OS build environment, and this decision is made if the
build directory is not a subdirectory of the source directory.

Signed-off-by: Paul Elder <paul.elder@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

meson.build

@@ -15,7 +15,7 @@ project('libcamera', 'c', 'cpp',
 # 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.source_root()).stdout().strip()
+                                    meson.build_root()).stdout().strip()
 if libcamera_git_version == ''
     libcamera_git_version = meson.project_version()
 endif

src/libcamera/meson.build

@@ -81,7 +81,7 @@ libcamera_sources += control_types_cpp
 
 gen_version = join_paths(meson.source_root(), 'utils', 'gen-version.sh')
 
-version_cpp = vcs_tag(command : [gen_version, meson.source_root()],
+version_cpp = vcs_tag(command : [gen_version, meson.build_root()],
                       input : 'version.cpp.in',
                       output : 'version.cpp',
                       fallback : meson.project_version())

utils/gen-version.sh

@@ -3,13 +3,11 @@
 # SPDX-License-Identifier: GPL-2.0-or-later
 # Generate a version string using git describe
 
-if [ -n "$1" ]
-then
-	cd "$1" 2>/dev/null || exit 1
-fi
+build_dir="$1"
 
 # Bail out if the directory isn't under git control
-git rev-parse --git-dir >/dev/null 2>&1 || exit 1
+src_dir=$(git rev-parse --git-dir 2>&1) || exit 1
+src_dir=$(readlink -f "$src_dir/..")
 
 # Get a short description from the tree.
 version=$(git describe --abbrev=8 --match "v[0-9]*" 2>/dev/null)
@@ -24,7 +22,10 @@ fi
 
 # Append a '-dirty' suffix if the working tree is dirty. Prevent false
 # positives due to changed timestamps by running git update-index.
+if [ -z "$build_dir" ] || (echo "$build_dir" | grep -q "$src_dir")
+then
 	git update-index --refresh > /dev/null 2>&1
+fi
 git diff-index --quiet HEAD || version="$version-dirty"
 
 # Replace first '-' with a '+' to denote build metadata, strip the 'g' in from