speed up truncate_to_unique

internal/p10k.zsh

@@ -1138,16 +1138,25 @@ prompt_dir() {
     truncate_to_unique)
       expand=1
       delim=${POWERLEVEL9K_SHORTEN_DELIMITER-'*'}
-      _p9k_prompt_length $delim
-      local -i real_delim_len=_P9K_RETVAL i=2 n=1 q=0
+      local -i i=2
       [[ $p[1] == / ]] && (( ++i ))
+      local parent="${PWD%/${(pj./.)parts[i,-1]}}"
+      if (( i <= $#parts )); then
+        local mtime=()
+        zstat -A mtime +mtime -- ${(@)${:-{$i..$#parts}}/(#b)(*)/$parent/${(pj./.)parts[i,$match[1]]}} 2>/dev/null || mtime=()
+        mtime="${(pj:\1:)mtime}"
+      else
+        local mtime='good'
+      fi
+      if ! _p9k_cache_get $0 "${parts[@]}" || [[ -z $mtime || $mtime != $_P9K_CACHE_VAL[1] ]] ; then
+        _p9k_prompt_length $delim
+        local -i real_delim_len=_P9K_RETVAL n=1 q=0
         [[ -n $parts[i-1] ]] && parts[i-1]="\${(Q)\${:-${(qqq)${(q)parts[i-1]}}}}"$'\2'
         [[ $p[i,-1] == *["~!#\$^&*()\\\"'<>?{}[]"]* ]] && q=1
         local -i d=${POWERLEVEL9K_SHORTEN_DELIMITER_LENGTH:--1}
         (( d >= 0 )) || d=real_delim_len
         shortenlen=${POWERLEVEL9K_SHORTEN_DIR_LENGTH:-1}
         (( shortenlen >= 0 )) && n=shortenlen
-      local parent="${PWD%/${(pj./.)parts[i,-1]}}"
         for (( ; i <= $#parts - n; ++i )); do
           local dir=$parts[i]
           if [[ -n $POWERLEVEL9K_SHORTEN_FOLDER_MARKER &&
@@ -1179,6 +1188,9 @@ prompt_dir() {
           (( q )) && parts[i]='${(Q)${:-'${(qqq)${(q)parts[i]}}'}}'
           parts[i]+=$'\2'
         done
+        _p9k_cache_set "$mtime" "${parts[@]}"
+      fi
+      parts=("${(@)_P9K_CACHE_VAL[2,-1]}")
     ;;
     truncate_with_folder_marker)
       if [[ -n $POWERLEVEL9K_SHORTEN_FOLDER_MARKER ]]; then