Get drush pcomplete working in eshell

gistfile1.txt

(defun pcmpl-drush-commands ()
  "Return the most common drush commands by parsing the drush output."
  (with-temp-buffer
    (call-process-shell-command "drush" nil (current-buffer) nil "help")
    (goto-char 0)
    (search-forward "Core drush commands: (core)")
    ;; (search-forward "available drush commands in")
    (let (commands)
      (while (re-search-forward
              "^[[:blank:]]\\([[:word:]-.]+\\)"
              nil t)
        (push (match-string 1) commands)
        (when (match-string 2)
          (push (match-string 2) commands)))
      (sort commands #'string<))))

(pcmpl-drush-commands)

(defconst pcmpl-drush-commands (pcmpl-drush-commands)
  "List of `drush' commands.")

(defvar pcmpl-drush-ref-list-cmd "drush for-each-ref refs/ --format='%(refname)'"
  "The `drush' command to run to get a list of refs.")

(defun pcmpl-drush-get-refs (type)
  "Return a list of `drush' refs filtered by TYPE."
  (with-temp-buffer
    (insert (shell-command-to-string pcmpl-drush-ref-list-cmd))
    (goto-char (point-min))
    (let (refs)
      (while (re-search-forward (concat "^refs/" type "/\\(.+\\)$") nil t)
  (push (match-string 1) refs))
      (nreverse refs))))

(defun pcmpl-drush-remotes ()
  "Return a list of remote repositories."
  (split-string (shell-command-to-string "drush remote")))

(defun pcomplete/drush ()
  "Completion for `drush'."
  ;; Completion for the command argument.
  (pcomplete-here* pcmpl-drush-commands)
  (cond
   ((pcomplete-match "help" 1)
    (pcomplete-here* pcmpl-drush-commands))
   ((pcomplete-match (regexp-opt '("pull" "push")) 1)
    (pcomplete-here (pcmpl-drush-remotes)))
   ;; provide branch completion for the command `checkout'.
   ((pcomplete-match "checkout" 1)
    (pcomplete-here* (append (pcmpl-drush-get-refs "heads")
			     (pcmpl-drush-get-refs "tags"))))
   (t
    (while (pcomplete-here (pcomplete-entries))))))