new: can interpret ``bash-stdout`` tags in relations options

bin/compose-core

@@ -1512,34 +1512,60 @@ export -f setup_host_resources
 
 
 relation-get () {
-    local key="$1"
-    cat "$RELATION_DATA_FILE" | shyaml get-value "$key" 2>/dev/null
-    if [ "$?" != 0 ]; then
+    local key="$1" out
+    if ! out=$(cat "$RELATION_DATA_FILE" | shyaml get-value "$key" 2>/dev/null); then
         err "The key $WHITE$key$NORMAL was not found in relation's data."
         return 1
     fi
+    echo "$out" | yaml_get_interpret
 }
 export -f relation-get
 
 
+yaml_get_interpret() {
+    local content tag
+    content=$(cat -)
+    tag=$(echo "$content" | shyaml -y get-value) || return 1
+    tag="${tag%% *}"
+    content=$(echo "$content" | shyaml get-value) || return 1
+    if ! [ "${tag:0:1}" == "!" ]; then
+        echo "$content" || return 1
+        return 0
+    fi
+    case "$tag" in
+        "!bash-stdout")
+            echo "$content" | bash || {
+                err "shell code didn't end with errorlevel 0"
+                return 1
+            }
+            ;;
+        *)
+            err "Invalid object tag ${WHITE}$tag${NORMAL}"
+            return 1
+            ;;
+    esac
+}
+export -f yaml_get_interpret
+
+
 relation-base-compose-get () {
-    local key="$1"
-    echo "$RELATION_BASE_COMPOSE_DEF" | shyaml get-value "options.$key" 2>/dev/null
-    if [ "$?" != 0 ]; then
+    local key="$1" out
+    if ! out=$(echo "$RELATION_BASE_COMPOSE_DEF" | shyaml -y get-value "options.$key" 2>/dev/null); then
         err "The key $WHITE$key$NORMAL was not found in base service compose definition.."
         return 1
     fi
+    echo "$out" | yaml_get_interpret
 }
 export -f relation-base-compose-get
 
 
 relation-target-compose-get () {
-    local key="$1"
-    echo "$RELATION_BASE_COMPOSE_DEF" | shyaml get-value "options.$key" 2>/dev/null
-    if [ "$?" != 0 ]; then
+    local key="$1" out
+    if ! out=$(echo "$RELATION_TARGET_COMPOSE_DEF" | shyaml get-value "options.$key" 2>/dev/null); then
         err "The key $WHITE$key$NORMAL was not found in base service compose definition.."
         return 1
     fi
+    echo "$out" | yaml_get_interpret
 }
 export -f relation-target-compose-get