bug#24057: 25.1.50; ffap interprets comments beginning with "//" as file path

[Eli Zaretskii]

> From: Kaushal Modi <kaushal.modi@gmail.com>
> Date: Mon, 25 Jul 2016 17:13:51 +0000
> Cc: 24057@debbugs.gnu.org, npostavs@users.sourceforge.net
> 
>  So if you disagree with my suggestion to skip comment-start instead of
>  using comment-search-forward, the behavior you propose should IMO be
>  off by default.
> 
> If that's the only way forward, I will add a defcustom in the next patch. But 
> it doesn't feel right. A defcustom is
> being created for a very corner case. Even if I agree with that, it does not 
> feel right to set its default value so
> that the buggy behavior is retained by default just to backward compatibility 
> sake.

Not sure which behavior you call "buggy".  I'm okay with
unconditionally skipping the comment leader string, such as "//" in
C/C++ case.  If you want to skip more than that, I think skipping the
rest should be optional, defaulting to off.  How's that "buggy"?

> How about we add the defcustom and set the default value so that this bug is 
> fixed. And we wait for people
> using the master branch to report any issues caused by this. Also we let 
> emacs-devel know that this
> defcustom is going in. 

I don't want us to introduce backward-incompatible behavior, except
when strictly necessary.  In this case, skipping the initial "//" is
necessary, but skipping more slashes is not.

Thanks.