ci: Make fringe meson-install arguments optional

Both the subdir and prepare arguments are very specific to
building the extensions-tool subproject stand-alone. In order
to make the script more generic, turn those required arguments
into optional --subdir and --prepare ones.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2712>

.gitlab-ci.yml

@@ -68,11 +68,11 @@ workflow:
                  'C Development Tools and Libraries' &&
 
       ./.gitlab-ci/install-meson-project.sh \
+        --subdir subprojects/extensions-tool/ \
+        --prepare ./generate-translations.sh \
         -Dman=false \
         https://gitlab.gnome.org/GNOME/gnome-shell.git \
-        main \
-        subprojects/extensions-tool/ \
-        ./generate-translations.sh &&
+        main &&
 
       dnf clean all
 

.gitlab-ci/install-meson-project.sh

@@ -4,12 +4,14 @@ set -e
 
 usage() {
   cat <<-EOF
-	Usage: $(basename $0) [OPTION…] REPO_URL COMMIT SUBDIR PREPARE
+	Usage: $(basename $0) [OPTION…] REPO_URL COMMIT
 
 	Check out and install a meson project
 
 	Options:
 	  -Dkey=val      Option to pass on to meson
+	  --subdir       Build subdirectory instead of whole project
+	  --prepare      Script to run before build
 
 	  -h, --help     Display this help
 
@@ -19,6 +21,8 @@ usage() {
 TEMP=$(getopt \
   --name=$(basename $0) \
   --options='D:h' \
+  --longoptions='subdir:' \
+  --longoptions='prepare:' \
   --longoptions='help' \
   -- "$@")
 
@@ -26,6 +30,8 @@ eval set -- "$TEMP"
 unset TEMP
 
 MESON_OPTIONS=()
+SUBDIR=.
+PREPARE=:
 
 while true; do
   case "$1" in
@@ -34,6 +40,16 @@ while true; do
       shift 2
     ;;
 
+    --subdir)
+      SUBDIR=$2
+      shift 2
+    ;;
+
+    --prepare)
+      PREPARE=$2
+      shift 2
+    ;;
+
     -h|--help)
       usage
       exit 0
@@ -46,15 +62,13 @@ while true; do
   esac
 done
 
-if [[ $# -lt 4 ]]; then
+if [[ $# -lt 2 ]]; then
   usage
   exit 1
 fi
 
 REPO_URL="$1"
 COMMIT="$2"
-SUBDIR="$3"
-PREPARE="$4"
 
 CHECKOUT_DIR=$(mktemp --directory)
 trap "rm -rf $CHECKOUT_DIR" EXIT