Add worktree {add,remove} <branch> command

Wrap `git worktree {add,remove} <path> <branch>` to streamline working
with multiple worktrees.

worktree/_worktree

@@ -0,0 +1,50 @@
+#compdef worktree
+
+__worktree_branches() {
+  local -a branches
+  branches=(
+    ${(fo)"$(git branch --format='%(refname:short)' 2>/dev/null)"}
+    ${${${${(fo)"$(git for-each-ref --format='%(refname)' refs/remotes 2>/dev/null)"}#refs/remotes/}#*/}:#HEAD}
+  )
+  _describe 'branch' branches
+}
+
+__worktree_active_branches() {
+  local -a branches
+  branches=(${(fo)"$(git worktree list --porcelain 2>/dev/null | \
+    awk '/^worktree /{ wt++ } wt>1 && /^branch refs\/heads\//{ sub(/^branch refs\/heads\//, ""); print }')"})
+  _describe 'branch' branches
+}
+
+_worktree() {
+  local context curcontext="$curcontext" state line
+  typeset -A opt_args
+
+  _arguments -C \
+    '1: :->cmd' \
+    '*:: :->args'
+
+  case $state in
+    (cmd)
+      local commands; commands=(
+        'add:Create a worktree for a branch'
+        'remove:Remove a worktree by branch'
+        'rm:Remove a worktree by branch'
+      )
+      _describe -t commands 'worktree command' commands "$@"
+      ;;
+    (args)
+      curcontext="${curcontext%:*:*}:worktree-cmd-$words[1]:"
+      case $line[1] in
+        (add)
+          _arguments '1:: :__worktree_branches'
+          ;;
+        (rm|remove)
+          _arguments '1:: :__worktree_active_branches'
+          ;;
+      esac
+      ;;
+  esac
+}
+
+_worktree "$@"