add TRUNCATE_TO_UNIQUE shortening dir strategy

This creates the shortest unique path elements that can be unambiguously expanded to the original path.

README.md

@@ -313,6 +313,7 @@ Customizations available are:
 |`truncate_from_right`|Just leaves the beginning of a folder name untouched. E.g. your folders will be truncated like so: "/ro../Pr../office". How many characters will be untouched is controlled by `POWERLEVEL9K_SHORTEN_DIR_LENGTH`.|
 |`truncate_with_package_name`|Search for a `package.json` or `composer.json` and prints the `name` field to abbreviate the directory path. The precedence and/or files could be set by `POWERLEVEL9K_DIR_PACKAGE_FILES=(package.json composer.json)`. If you have [jq](https://stedolan.github.io/jq/) installed, it will dramatically improve the speed of this strategy.|
 |`truncate_with_folder_marker`|Search for a file that is specified by `POWERLEVEL9K_SHORTEN_FOLDER_MARKER` and truncate everything before that (if found, otherwise stop on $HOME and ROOT).|
+|`truncate_to_unique`|Parse all parent path components and truncate them to the shortest unique length. If you copy&paste the result to a shell, after hitting TAB it should expand to the original path unambiguously.|
 
 For example, if you wanted the truncation behavior of the `fish` shell, which
 truncates `/usr/share/plasma` to `/u/s/plasma`, you would use the following:

powerlevel9k.zsh-theme

@@ -709,6 +709,27 @@ prompt_dir() {
         # the current path.
         current_path=$current_path${PWD#${last_marked_folder}*}
       ;;
+      truncate_to_unique)
+        # for each parent path component find the shortest unique beginning
+        # characters sequence
+        paths=(${(s:/:)PWD})
+        cur_path='/'
+        cur_short_path='/'
+        for directory in ${paths[@]}
+        do
+          cur_dir=''
+          for (( i=0; i<${#directory}; i++ )); do
+            cur_dir+="${directory:$i:1}"
+            matching=("$cur_path"/"$cur_dir"*/)
+            if [[ ${#matching[@]} -eq 1 ]]; then
+              break
+            fi
+          done
+          cur_short_path+="$cur_dir/"
+          cur_path+="$directory/"
+        done
+        current_path="${cur_short_path: : -1}"
+      ;;
       *)
         current_path="$(print -P "%$((POWERLEVEL9K_SHORTEN_DIR_LENGTH+1))(c:$POWERLEVEL9K_SHORTEN_DELIMITER/:)%${POWERLEVEL9K_SHORTEN_DIR_LENGTH}c")"
       ;;

test/segments/dir.spec

@@ -381,4 +381,25 @@ function testOmittingFirstCharacterWorksWithChangingPathSeparatorAndRightTruncat
   unset POWERLEVEL9K_SHORTEN_STRATEGY
 }
 
+function testTruncateToUniqueWorks() {
+  POWERLEVEL9K_DIR_OMIT_FIRST_CHARACTER=true
+  POWERLEVEL9K_DIR_PATH_SEPARATOR='xXx'
+  POWERLEVEL9K_SHORTEN_DIR_LENGTH=2
+  POWERLEVEL9K_SHORTEN_STRATEGY='truncate_to_unique'
+  mkdir -p /tmp/powerlevel9k-test/adam/devl
+  mkdir -p /tmp/powerlevel9k-test/alice/devl
+  mkdir -p /tmp/powerlevel9k-test/alice/docs
+  mkdir -p /tmp/powerlevel9k-test/bob/docs
+  cd /tmp/powerlevel9k-test/alice/devl
+
+  assertEquals "%K{blue} %F{black}txXxpxXxalxXxde %k%F{blue}%f " "$(build_left_prompt)"
+
+  cd -
+  rm -fr /tmp/powerlevel9k-test
+  unset POWERLEVEL9K_DIR_PATH_SEPARATOR
+  unset POWERLEVEL9K_DIR_OMIT_FIRST_CHARACTER
+  unset POWERLEVEL9K_SHORTEN_DIR_LENGTH
+  unset POWERLEVEL9K_SHORTEN_STRATEGY
+}
+
 source shunit2/source/2.1/src/shunit2