bug#12792: 24.2.50; shell-mode renders all its output in a yellow face

[Wolfgang Jenkner <wjenkner@inode.at>]

On Sat, Nov 03 2012, Wolfgang Jenkner wrote:

> On Sat, Nov 03 2012, Eli Zaretskii wrote:

>> SGR parameter 39 means go back to the default foreground color.  How
>> can ansi-color not support it and still be useful?

> I'll fix this omission if nobody beats me to it.

Here's a rewrite of `ansi-color-apply-sequence' which implements SGR
codes 39 and 49.  It's straightforward but, sadly, uses side-effects all
over the place.  At this point, however, I'd just like to know if its
behaviour meets everybody's expectations, so please test it a bit.

Wolfgang

(defun ansi-color-apply-sequence (escape-sequence codes)
  "Apply ESCAPE-SEQ to CODES and return the new list of codes.

ESCAPE-SEQ is an escape sequence parsed by `ansi-color-parse-sequence'.

For each new code, the following happens: if it is 1-7, add it to
the list of codes; if it is 21-25 or 27, delete appropriate
parameters from the list of codes; if it is 30-37 resp. 39, the
foreground color code is replaced or added resp. deleted; if it
is 40-47 resp. 49, the background color code is replaced or added
resp. deleted; any other code is discarded together with the old
codes.  Finally, the so changed list of codes is returned."
  (let ((new-codes (ansi-color-parse-sequence escape-sequence))
	(fg (and codes (>= (car codes) 30) (<= (car codes) 37)
		 (pop codes)))
	(bg (and codes (>= (car codes) 40) (<= (car codes) 47)
		 (pop codes))))
    (while new-codes
      (let ((new (pop new-codes)))
	(cond ((and (>= new 1) (<= new 7))
	       (unless (memq new codes)
		 (push new codes)))
	      ((and (= new 22)
		    (setq codes (remq 1 codes))
		    nil))
	      ((and (= new 25)
		    (setq codes (remq 6 codes))
		    nil))
	      ;; The standard says `21 doubly underlined' while
	      ;; http://en.wikipedia.org/wiki/ANSI_escape_code claims
	      ;; `21 Bright/Bold: off or Underline: Double'.
	      ((and (>= new 21) (<= new 27) (/= new 26))
	       (setq codes (remq (- new 20) codes)))
	      ((and (>= new 30) (<= new 37))
	       (setq fg new))
	      ((= new 39)
	       (setq fg nil))
	      ((and (>= new 40) (<= new 47))
	       (setq bg new))
	      ((= new 49)
	       (setq bg nil))
	      (t
	       (setq codes nil fg nil bg nil)))))
    (when bg
      (push bg codes))
    (when fg
      (push fg codes))
    codes))