GNU bug report logs - #56848
CC Mode fontification bug

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Gregory Heytings <gregory <at> heytings.org>
Subject: bug#56848: closed (Re: bug#56848: CC Mode fontification bug)
Date: Sat, 14 Jan 2023 21:29:01 +0000

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Your bug report

#56848: CC Mode fontification bug

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 56848 <at> debbugs.gnu.org.

-- 
56848: https://debbugs.gnu.org/cgi/bugreport.cgi?bug=56848
GNU Bug Tracking System
Contact help-debbugs <at> gnu.org with problems

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From: Gregory Heytings <gregory <at> heytings.org>
To: 56848-done <at> debbugs.gnu.org
Cc: Alan Mackenzie <acm <at> muc.de>
Subject: Re: bug#56848: CC Mode fontification bug
Date: Sat, 14 Jan 2023 21:28:24 +0000

Closing this bug.  The proposed patch has been included in commits 
4bd8ad2bc5 and 1cbc22b9c7.

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From: Gregory Heytings <gregory <at> heytings.org>
To: bug-gnu-emacs <at> gnu.org
Subject: CC Mode fontification bug
Date: Sun, 31 Jul 2022 00:16:37 +0000

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Recipe:

emacs -Q
C-x C-f src/xdisp.c RET
M-g c 28 RET
;; take note of the word there: "window"
M-: (get-char-property 28 'fontified) RET
;; observe that this returns t
M-g g 800 RET
C-v
M-: (get-char-property 28 'fontified) RET
;; observe that this returns nil, because "struct window" is now visible

This is a BUG.

When font locking has put a fontified property and one of the 
font-lock-*-faces on characters in the buffer, a mode should not undo that 
unless it has a very good reason to do so.  Otherwise scrolling again 
through an already fontified buffer calls fontification functions again 
without reason.

Patch attached.

With the patch, scrolling again through an already fontified buffer is 
~25% faster.

[Be-conservative-with-occurrences-of-newly-found-types.patch (text/x-diff, attachment)]

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