fix: dependency calculation has numerous issues.

Loop were not supported, and many bug crippled the order of the
calculation. Added also some caching to avoid recalculating this each
time.

bin/compose

@@ -648,25 +648,37 @@ export -f get_service_deps
 
 
 _rec_get_depth() {
-    local elt=$1
-
-    #debug "Asking for $DARKYELLOW$elt$NORMAL dependencies"
-    if [ "${depths[$elt]}" ]; then
+    local elt=$1 dep deps max cache_file="$state_tmpdir/$FUNCNAME.cache.$1"
+    [ "${depths[$elt]}" ] && return 0
+    if [ -e "$cache_file" ]; then
+        # debug "$FUNCNAME: cache hit ($*)"
+        depths[$elt]=$(cat "$cache_file")
         return 0
     fi
-    deps=$(get_service_deps "$elt") || return 1
-    if [ -z "$deps" ]; then
-        depths[$elt]=0
-    fi
 
+    visited[$elt]=1
+    #debug "Setting visited[$elt]"
+    #debug "Asking for $DARKYELLOW$elt$NORMAL dependencies"
+    deps=$(get_service_deps "$elt") || {
+        debug "Failed get_service_deps $elt"
+        return 1
+    }
+    # debug "$elt deps are:" $deps
     max=0
     for dep in $deps; do
+        [ "${visited[$dep]}" ] && {
+            #debug "Already computing $dep"
+            continue
+        }
         _rec_get_depth "$dep" || return 1
-        if (( "${depths[$dep]}" > "$max" )); then
+        #debug "Requesting depth[$dep]"
+        if (( ${depths[$dep]} > max )); then
             max="${depths[$dep]}"
-        fi
+        fi 
     done
+    # debug "Setting depth[$elt] to $((max + 1))"
     depths[$elt]=$((max + 1))
+    echo "${depths[$elt]}" > $cache_file
 }
 export -f _rec_get_depth
 
@@ -685,11 +697,10 @@ get_ordered_service_dependencies() {
     fi
 
     declare -A depths
-    visited=()
+    declare -A visited
     heads=("${services[@]}")
     while [ "${#heads[@]}" != 0 ]; do
         array_pop heads head
-        visited+=("$head")
         _rec_get_depth "$head" || return 1
     done