bug#7089: 23.2; slow ansi-color-apply

[Leo]

I have found ansi-color-apply very expensive and slow.

To test this, do the following

  (remove-hook 'eshell-output-filter-functions 'eshell-handle-ansi-color)
  (add-hook 'eshell-preoutput-filter-functions 'ansi-color-apply)

and do something in eshell that can output a large coloured text such
as:

  cd /usr/include; ack time

where ack is a single file perl script from http://betterthangrep.com/.
The CPU usage should shoot up to very high.

The following version (after brief testing) seems to be noticeably
faster.

(defun ansi-color-apply* (string)
  "A more efficient implementation of `ansi-color-apply' (which see)."
  (let ((face (car ansi-color-context))
        start end fragment escape-sequence)
    ;; If context was saved and is a string, prepend it.
    (if (cadr ansi-color-context)
        (setq string (concat (cadr ansi-color-context) string)
              ansi-color-context nil))
    (with-temp-buffer
      (insert string)
      (setq start (point-min-marker))
      (goto-char start)
      (while (re-search-forward ansi-color-drop-regexp nil t)
        (replace-match ""))
      (goto-char start)
      ;; Find the next escape sequence.
      (while (re-search-forward ansi-color-regexp nil t)
        (setq end (match-beginning 0))
        (when face
          (put-text-property start end 'ansi-color t)
          (put-text-property start end 'face face))
        (setq start (copy-marker (match-end 0)))
        (setq escape-sequence (match-string 1))
        (replace-match "")
        (setq face (ansi-color-apply-sequence escape-sequence face)))
      ;; search for the possible start of a new escape sequence
      (if (re-search-forward "\033" nil t)
          (setq end (match-beginning 0)
                fragment (buffer-substring end (point-max)))
        (setq end (point-max)))
      ;; if the rest of the string should have a face, put it there
      (when face
        (put-text-property start end 'ansi-color t)
        (put-text-property start end 'face face))
      ;; save context
      (if (or face fragment)
          (setq ansi-color-context (list face fragment))
        (setq ansi-color-context nil))
      (buffer-string))))

Leo