chg: dev: do only one merging when computing docker-compose yaml from metadata.

bin/compose-core

@@ -2783,8 +2783,11 @@ export -f get_top_master_service_for_service
 ## docker-compose entry (thinking of subordinates). The result
 ## will be merge with master charms.
 _get_docker_compose_mixin_from_metadata_cached() {
-    local service="$1" charm="$2" metadata="$3" has_build_dir="$4" cache_file="$CACHEDIR/$FUNCNAME.cache.$(echo "$*" | md5_compat)" \
-          metadata_file metadata volumes docker_compose subordinate image
+    local service="$1" charm="$2" metadata="$3" \
+          has_build_dir="$4" \
+          cache_file="$CACHEDIR/$FUNCNAME.cache.$(echo "$*" | md5_compat)" \
+          metadata_file metadata volumes docker_compose subordinate image mixin mixins
+
     if [ -e "$cache_file" ]; then
         #debug "$FUNCNAME: STATIC cache hit $1"
         cat "$cache_file" &&
@@ -2792,7 +2795,7 @@ _get_docker_compose_mixin_from_metadata_cached() {
         return 0
     fi
 
-    mixin=$(echo -en "labels:\n- compose.charm=$charm")
+    mixins=("$(echo -en "labels:\n- compose.charm=$charm")")
     if [ "$metadata" ]; then
         ## resources to volumes
         volumes=$(
@@ -2813,7 +2816,7 @@ _get_docker_compose_mixin_from_metadata_cached() {
                 else
                     die "Invalid host-resource specified in 'metadata.yml'."
                 fi
-            done < <(echo "$metadata" | shyaml get-values-0 "host-resources" 2>/dev/null)
+            done < <(printf "%s" "$metadata" | shyaml get-values-0 "host-resources" 2>/dev/null)
             while read-0 resource; do
                 dest="$(charm.get_dir "$charm")/resources$resource"
                 if ! [ -e "$dest" ]; then
@@ -2823,20 +2826,12 @@ _get_docker_compose_mixin_from_metadata_cached() {
             done < <(echo "$metadata" | shyaml get-values-0 "charm-resources" 2>/dev/null)
                ) || return 1
         if [ "$volumes" ]; then
-            mixin=$(merge_yaml_str "$mixin" "$(echo -en "volumes:\n$volumes")") || {
-                err "Failed to merge mixin with ${WHITE}docker-compose${NORMAL} option" \
-                    "from charm ${DARKPINK}$charm$NORMAL."
-                return 1
-            }
+            mixins+=("volumes:"$'\n'"$volumes")
         fi
 
-        docker_compose=$(echo "$metadata" | shyaml get-value -y "docker-compose" 2>/dev/null)
+        docker_compose=$(printf "%s" "$metadata" | shyaml get-value -y "docker-compose" 2>/dev/null) || true
         if [ "$docker_compose" ]; then
-            mixin=$(merge_yaml_str "$mixin" "$docker_compose") || {
-                err "Failed to merge mixin with ${WHITE}docker-compose${NORMAL} option" \
-                    "from charm ${DARKPINK}$charm$NORMAL."
-                return 1
-            }
+            mixins+=("$docker_compose")
         fi
 
         if [ "$(echo "$metadata" | shyaml get-value "subordinate" 2>/dev/null)" == "True" ]; then
@@ -2846,26 +2841,23 @@ _get_docker_compose_mixin_from_metadata_cached() {
 
     image=$(echo "$metadata" | shyaml get-value "docker-image" 2>/dev/null)
     [ "$image" == "None" ] && image=""
-    image_or_build_statement=
     if [ "$image" ]; then
         if [ "$subordinate" ]; then
             err "Subordinate charm can not have a ${WHITE}docker-image${NORMAL} value."
             return 1
         fi
-        image_or_build_statement="image: $image"
+        mixins+=("image: $image")
     elif [ "$has_build_dir" ]; then
         if [ "$subordinate" ]; then
             err "Subordinate charm can not have a 'build' sub directory."
             return 1
         fi
-        image_or_build_statement="build: $(charm.get_dir "$charm")/build"
+        mixins+=("build: $(charm.get_dir "$charm")/build")
     fi
-    if [ "$image_or_build_statement" ]; then
-        mixin=$(merge_yaml_str "$mixin" "$image_or_build_statement") || {
-            err "Failed to merge yaml with image or build YAML statement."
+    mixin=$(merge_yaml_str "${mixins[@]}") || {
+        err "Failed to merge mixins from ${DARKPINK}${charm}${NORMAL} metadata."
         return 1
     }
-    fi
     echo "$mixin" | tee "$cache_file"
 }
 export -f _get_docker_compose_mixin_from_metadata_cached