From: Alan Mackenzie <acm@muc.de>
To: emacs-devel@gnu.org, Gregory Heytings <gregory@heytings.org>
Subject: How the long-lines "optimisation" breaks font locking.
Date: Wed, 3 Aug 2022 18:39:16 +0000 [thread overview]
Message-ID: <YurA1CCzJseq26Ac@ACM> (raw)
Hello Gregory and Emacs.
In the current master,
(i) start emacs -Q
(ii) C-x C-f ~/long-line.cc
(iii) Enter the following into the buffer (3 lines):
char long_line[] = R"foo(
)foo"
(iv) Create a long line (> 10,000 characters) somehow and get it into
the kill ring.
(v) On the blank line 2 in long-line.cc, C-y inserting the long line.
(vi) Note that there is now a long valid raw string in the buffer,
correctly fontified.
(vii) Put point on a "o" in the foo on L3. Delete the o
(viii) Note that the opening delimiter of the raw string on L1 now has
warning-face. This is correct.
(ix) Undo this last change with C-_.
(x) Note that the opening delimiter falsely retains the warning-face,
although it is now the opener of a validly terminated raw string.
This is a bug.
(xi) Insert a LF (or several, if needed) into the long line, separating
it into two or more lines, none of which is "long".
(xii) Note that the raw string opener still has warning-face. A bug.
(xiii) Do M-x c++-mode. This fails to initialise the fontification
correctly, leaving the warning-face where it no longer belongs. This
is a bug.
(xiv) Note that in the foregoing operations, sometimes an error message
appears in the echo area about the lack of an expected syntax-table
text property. This is a bug.
I don't think it is improbable that a C++ hacker will create a long line
in a raw string. That this can cause permanent damage to the buffer's
fontification doesn't seem a good thing. That it is the recent
"optimisation" for long lines which causes it can be seen by repeating
the above steps, but with a line less than 10,000 characters long. The
fontification then behaves correctly.
--
Alan Mackenzie (Nuremberg, Germany).
next reply other threads:[~2022-08-03 18:39 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-03 18:39 Alan Mackenzie [this message]
2022-08-03 19:03 ` How the long-lines "optimisation" breaks font locking Lars Ingebrigtsen
2022-08-04 10:44 ` Alan Mackenzie
2022-08-04 12:54 ` Eli Zaretskii
2022-08-04 14:44 ` Alan Mackenzie
2022-08-04 14:52 ` Lars Ingebrigtsen
2022-08-04 15:22 ` Gregory Heytings
2022-08-05 1:23 ` Ihor Radchenko
2022-08-04 16:09 ` Eli Zaretskii
2022-08-05 10:56 ` Alan Mackenzie
2022-08-05 11:20 ` Eli Zaretskii
2022-08-05 13:04 ` Dmitry Gutov
2022-08-05 14:22 ` Eli Zaretskii
2022-08-05 14:29 ` Dmitry Gutov
2022-08-05 15:30 ` Eli Zaretskii
2022-08-05 19:50 ` Dmitry Gutov
2022-08-06 5:36 ` Eli Zaretskii
2022-08-06 10:54 ` Dmitry Gutov
2022-08-04 13:11 ` Eric S Fraga
2022-08-04 13:34 ` Po Lu
2022-08-04 14:38 ` Eric S Fraga
2022-08-04 16:16 ` SOLVED: " Eric S Fraga
2022-08-04 16:21 ` Eric S Fraga
2022-08-04 17:36 ` Stefan Kangas
2022-08-05 9:36 ` Eric S Fraga
2022-08-05 11:13 ` Eli Zaretskii
2022-08-05 12:28 ` Eric S Fraga
2022-08-05 13:40 ` Eric S Fraga
2022-08-05 23:11 ` Tim Cross
2022-08-05 23:23 ` Lars Ingebrigtsen
2022-08-08 11:51 ` Fraga, Eric
2022-08-03 19:15 ` Eli Zaretskii
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