Re: Patch: goto-address -vs- font-lock-mode

[Stefan Monnier <monnier@iro.umontreal.ca>]

>     This patch adds a new minor mode that acts like `goto-address'.
>     Unlike goto-address, it uses font-lock to add properties to text in
>     the buffer.  This means that changes to the buffer which add URLs or
>     email address will automatically be detected.

> Would it be more appropriate to use overlays for this?
> You wouldn't want to copy those properties ever, and it is better
> if adding them does not modify the buffer.

Unless there are many URLs in the buffer, overlays do seem better suited.

> Is it feasible to use the font-lock mechanism to add overlays?

Of course, since font-lock provides the hooks to plug any piece of
elisp code.   You could do something like:

(defun g-a-f-l-add-overlay (type)
  (let ((ol (make-overlay (match-beginning 0) (match-end 0))))
    (overlay-put ol 'goto-address t)
    (case type
      (url ...)
      (mail ...))
    ...))
    

(defun g-a-f-l-remove-overlays (b e)
  (remove-overlays b e 'goto-address t))

(define-minor-mode goto-address-font-lock-mode
  "A minor mode that adds `goto-address' functionality via `font-lock-mode'.
Allows user to use mouse/keyboard command to click to go to a URL
or to send e-mail.
Enables `font-lock-mode' in the current buffer if not already enabled."
  nil nil nil
  (let ((keywords
	 `((,goto-address-mail-regexp . (0 (g-a-f-l-add-overlay 'mail)))
	   (,goto-address-url-regexp  . (0 (g-a-f-l-add-overlay 'url))))))
    (font-lock-remove-keywords nil keywords)
    (remove-hook 'font-lock-unfontify-region-function
                 'g-a-f-l-remove-overlays t)
    (when goto-address-font-lock-mode
      (font-lock-mode 1)
      (font-lock-add-keywords nil keywords)
      (add-hook 'font-lock-unfontify-region-function
                'g-a-f-l-remove-overlays nil t)))
  (font-lock-fontify-buffer))


But then you could also hook into jit-lock rather than font-lock, which
would have the advantage of not depending on (on infringing on) the user's
choice to use font-lock or not.


        Stefan