[fix] add ynh_install_app_dependencies into _common.sh

scripts/_common.sh

@@ -302,4 +302,37 @@ ynh_exit_properly () {
 ynh_abort_if_errors () {
   set -eu # Exit if a command fail, and if a variable is used unset.
   trap ynh_exit_properly EXIT # Capturing exit signals on shell script
+}
+
+# Define and install dependencies with a equivs control file
+# This helper can/should only be called once per app
+#
+# usage: ynh_install_app_dependencies dep [dep [...]]
+# | arg: dep - the package name to install in dependence
+ynh_install_app_dependencies () {
+    dependencies=$@
+    manifest_path="../manifest.json"
+    if [ ! -e "$manifest_path" ]; then
+      manifest_path="../settings/manifest.json" # Into the restore script, the manifest is not at the same place
+    fi
+    version=$(sudo python3 -c "import sys, json;print(json.load(open(\"$manifest_path\"))['version'])") # Retrieve the version number in the manifest file.
+    dep_app=${app//_/-} # Replace all '_' by '-'
+
+    if ynh_package_is_installed "${dep_app}-ynh-deps"; then
+    echo "A package named ${dep_app}-ynh-deps is already installed" >&2
+    else
+        cat > ./${dep_app}-ynh-deps.control << EOF  # Make a control file for equivs-build
+Section: misc
+Priority: optional
+Package: ${dep_app}-ynh-deps
+Version: ${version}
+Depends: ${dependencies// /, }
+Architecture: all
+Description: Fake package for ${app} (YunoHost app) dependencies
+ This meta-package is only responsible of installing its dependencies.
+EOF
+        ynh_package_install_from_equivs ./${dep_app}-ynh-deps.control \
+            || ynh_die "Unable to install dependencies" # Install the fake package and its dependencies
+        ynh_app_setting_set $app apt_dependencies $dependencies
+    fi
 }