bug#25362: 26.0.50; comment-region goes into an infinite loop

[Dima Kogan <dima@secretsauce.net>]

Alan Mackenzie <acm@muc.de> writes:

> Hello again, Dima.
>
> As already observed, this bug happens simply in C Mode by attempting to
> comment out the four lines inside the function, doing this by marking
> the lines then C-c C-c.
>
> The cause was a rather nasty situation where a "syntactic whitespace
> cache", designed to facilitate moving rapidly over large areas of WS
> (particularly long comments at the beginning of files) got screwed up by
> the insertion of "// " onto a line already containing a "//" later on.
>
> Here is a patch.  It is not yet in its final form (the comments need
> fixing).  Would you please try it out and let me know how well/how badly
> it works:

Hi. I'm now running with this patch, and some cursory testing says that
it works. I briefly ran into an issue where I

1. highlighted a problematic region
2. hit M-; (this worked correctly)
3. Hit M-/ to undo

This undo restored the text correctly, but the whole region remained
highlighted as a comment, even after the undo removed the comment
characters. I hit this once, but cannot reproduce it anymore. If this
description means something to you, feel free to act on it :)


> Thanks for this rather obscure bug report.  :-)

Heh. I just report issues that pop up during the course of the day. We
owe you hugely for responding to these bugs and maintaining cc-mode.
Thanks!