GNU bug report logs -
#22316
font-lock corrupts `end' position in jit-lock after-change function.
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Reported by: Alan Mackenzie <acm <at> muc.de>
Date: Tue, 5 Jan 2016 21:46:01 UTC
Severity: normal
Done: Alan Mackenzie <acm <at> muc.de>
Bug is archived. No further changes may be made.
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Your bug report
#22316: font-lock corrupts `end' position in jit-lock after-change function.
which was filed against the emacs package, has been closed.
The explanation is attached below, along with your original report.
If you require more details, please reply to 22316 <at> debbugs.gnu.org.
--
22316: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=22316
GNU Bug Tracking System
Contact help-debbugs <at> gnu.org with problems
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Bug fixed.
--
Alan Mackenzie (Nuremberg, Germany).
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Hello, Emacs.
With the latest emacs-25 branch (committed 2016-01-05, ~21:15 +0000),
do emacs -Q, and load (or type in) the follow AWK Mode file (M-x
awk-mode, if required):
########################################################################
#!/usr/bin/gawk -f
BEGIN {
x = 4
}
#########################################################################
Notice the fontification of "BEGIN". Type a space anywhere on the first
line. The following happens:
(i) The fontification on the "B" of "BEGIN" is erased instantly.
(ii) Half a second (jit-lock-context-time) later, the fontification on
"EGIN" is erased.
The cause of the problem is in
font-lock-extend-jit-lock-region-after-change. The sequence is as
follows:
(i) In AWK Mode, font-lock-extend-after-change-region-function is
non-nil, and this function is called to set `beg' and `end', the
bounds of the region to fontify. In the above case, this region is
exactly line 1.
(ii) f-l-extend-j-l-r-a-change adds 1 to end. The region (beg end) now
covers line 1 and the "B" at the beginning of line 2.
(iii) After-change fontification fontifies this spurious region, (beg
end). Since "B" is "on its own", it appears to be an ordinary
variable use, hence is fontified without a face.
(iv) Half a second later, context fontification starts from `end', finds
"EGIN" and fontifies this as an ordinary variable, without a face.
The solution I propose is that should the region have been set by
font-lock-extend-after-change-region-function, the `end' position
should be accepted as is.
Here is a patch to implement this. I will commit it soon to emacs-25 if
I hear no objections.
diff --git a/lisp/font-lock.el b/lisp/font-lock.el
index 4a92069..3c1f01d 100644
--- a/lisp/font-lock.el
+++ b/lisp/font-lock.el
@@ -1302,15 +1302,18 @@ font-lock-extend-jit-lock-region-after-change
(point-min))))
(when (< end (point-max))
(setq end
- (if (get-text-property end 'font-lock-multiline)
- (or (text-property-any end (point-max)
- 'font-lock-multiline nil)
- (point-max))
+ (cond
+ ((get-text-property end 'font-lock-multiline)
+ (or (text-property-any end (point-max)
+ 'font-lock-multiline nil)
+ (point-max)))
+ ;; If `end' has been set by the function above, don't corrupt it.
+ (font-lock-extend-after-change-region-function end)
;; Rounding up to a whole number of lines should include the
;; line right after `end'. Typical case: the first char of
;; the line was deleted. Or a \n was inserted in the middle
;; of a line.
- (1+ end))))
+ (t (1+ end)))))
;; Finally, pre-enlarge the region to a whole number of lines, to try
;; and anticipate what font-lock-default-fontify-region will do, so as to
;; avoid double-redisplay.
--
Alan Mackenzie (Nuremberg, Germany).
This bug report was last modified 9 years and 194 days ago.
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