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Subject: |
Fforward-comment: Incorrect recognition of end of comment in C++ |
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Date: |
Thu, 16 Apr 2020 12:44:26 +0000 |
Hello, Emacs.
C++ comments can be continued onto the next line by an escaped NL. This
is configured in Emacs with the variable comment-end-can-be-escaped.
However, Fforward_comment (in the backward direction) doesn't take this
into account. A BOL following an escaped NL cannot be at the end of a
C++ line comment:
// C++ comment first line \
Second line of comment
^
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point
Point here is in the middle of a comment.
It is therefore wrong in Fforward_comment not to check
comment-end-can-be-escaped when immediately after an Sendcomment. This
can be fixed thusly:
diff --git a/src/syntax.c b/src/syntax.c
index e24b98da32..ff125b137c 100644
--- a/src/syntax.c
+++ b/src/syntax.c
@@ -2572,8 +2572,9 @@ between them, return t; otherwise return nil. */)
}
else if (code == Sendcomment)
{
- found = back_comment (from, from_byte, stop, comnested, comstyle,
- &out_charpos, &out_bytepos);
+ found = (!quoted || !Vcomment_end_can_be_escaped)
+ && back_comment (from, from_byte, stop, comnested, comstyle,
+ &out_charpos, &out_bytepos);
if (!found)
{
if (c == '\n')
This should clearly go into the master branch. I think it should also go
into the emacs-27 release branch, since it is relevant for a nasty bug,
bug #40052. There, scrolling in a C++ include file, which consists of a
#define macro ~2,400 lines long is deadly slow. With the above fix in
place, scrolling is over 4 times as fast, although still too slow.
--
Alan Mackenzie (Nuremberg, Germany).
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