meson: fix version generation from git

run_command() was only run at configure time, meaning the generated
version (that was passed on to the sources via -DYAMBAR_VERSION)
became stale.

Fix by implementing a shell script that generates a header file, and
wrap this in a custom target that is run every time (but the generated
file is only updated when the version changes)

doc/meson.build

@@ -1,3 +1,5 @@
+sh = find_program('sh', native: true)
+
 scdoc = dependency('scdoc', native: true)
 scdoc_prog = find_program(scdoc.get_pkgconfig_variable('scdoc'), native: true)
 

generate-version.sh

@@ -0,0 +1,32 @@
+#!/usr/bin/bash
+
+set -e
+
+default_version=${1}
+src_dir=${2}
+out_file=${3}
+
+# echo "default version:  ${default_version}"
+# echo "source directory: ${src_dir}"
+# echo "output file:      ${out_file}"
+
+if [[ $(command -v git) ]]; then
+    new_version="$(git describe --always --tags) ($(env LC_TIME=C date "+%b %d %Y"), branch '$(git rev-parse --abbrev-ref HEAD)')"
+else
+    new_version="${default_version}"
+fi
+
+new_version="#define YAMBAR_VERSION \"${new_version}\""
+
+if [[ -f "${out_file}" ]]; then
+    old_version=$(<"${out_file}")
+else
+    old_version=""
+fi
+
+# echo "old version: ${old_version}"
+# echo "new version: ${new_version}"
+
+if [[ "${old_version}" != "${new_version}" ]]; then
+    echo "${new_version}" > "${out_file}"
+fi

main.c

@@ -22,6 +22,7 @@
 
 #define LOG_MODULE "main"
 #include "log.h"
+#include "version.h"
 
 static volatile sig_atomic_t aborted = 0;
 

meson.build

@@ -10,28 +10,6 @@ project('yambar', 'c',
 is_debug_build = get_option('buildtype').startswith('debug')
 plugs_as_libs = get_option('core-plugins-as-shared-libraries')
 
-version = '"@0@"'.format(meson.project_version())
-
-sh = find_program('sh', native: true)
-git = find_program('git', required: false, native: true)
-
-if git.found()
-  commit_hash = run_command(
-    [sh.path(), '-c',
-     '@0@ --git-dir="$MESON_SOURCE_ROOT/.git" describe --always --tags'.format(
-       git.path())])
-
-  branch = run_command(
-    [sh.path(), '-c',
-     '@0@ "--git-dir=$MESON_SOURCE_ROOT/.git" rev-parse --abbrev-ref HEAD'.format(
-       git.path())])
-
-  if commit_hash.returncode() == 0 and branch.returncode() == 0
-    version = '"@0@ (" __DATE__ ", branch \'@1@\')"'.format(
-      commit_hash.stdout().strip(), branch.stdout().strip())
-  endif
-endif
-
 # Common dependencies
 cc = meson.get_compiler('c')
 dl = cc.find_library('dl')
@@ -59,8 +37,7 @@ wlroots = dependency('wlroots', required: get_option('backend-wayland'))
 backend_wayland = wayland_client.found() and wayland_cursor.found() and wlroots.found()
 
 add_project_arguments(
-  ['-D_GNU_SOURCE',
+  ['-D_GNU_SOURCE'] +
-   '-DYAMBAR_VERSION=@0@'.format(version)] +
   (is_debug_build ? ['-D_DEBUG'] : []) +
   (backend_x11 ? ['-DENABLE_X11'] : []) +
   (backend_wayland ? ['-DENABLE_WAYLAND'] : []) +
@@ -87,6 +64,13 @@ subdir('decorations')
 subdir('particles')
 subdir('modules')
 
+generate_version_sh = files('generate-version.sh')
+version = custom_target(
+  'generate_version',
+  build_always_stale: true,
+  output: 'version.h',
+  command: [generate_version_sh, meson.project_version(), '@SOURCE_DIR@', '@OUTPUT@'])
+
 yambar = executable(
   'yambar',
   'color.h',
@@ -102,6 +86,7 @@ yambar = executable(
   'tag.c', 'tag.h',
   'tllist.h',
   'yml.c', 'yml.h',
+  version,
   dependencies: [bar, freetype, fontconfig, pixman, yaml, threads, dl] +
                 decorations + particles + modules,
   build_rpath: '$ORIGIN/modules:$ORIGIN/decorations:$ORIGIN/particles',