bug#3269: 23.0.93; C-mode text highlighting

On Wed, May 13, 2009 at 08:39:47AM +0200, Thomas Christensen wrote:

> In c-mode type:
> #define FOO "\
> foo\n\
> bar\n\
> "

> Then place the cursor after foo\n\ and press RETURN for a new line.

> The highlighting is now broken, and I can only restore it by reverting
> the buffer.

That's a bit vague, so let me fill it out for you.  ;-)

When you press RETURN as described, the new line you've just made lacks a
backslash, hence terminates the macro.  (Yes, I know you knew that.)

    #define FOO "\
    foo\n\

    bar\n\
    "

The "foo" line has lost its fontification, and this is the bug.  I know
what's causing it, and it _might_ be easily fixable.  What's more, I
don't this bug was in Emacs 22, so Chong Yidong would allow it to be
fixed.  :-)

The "bar" line and what follows (which is no longer part of the macro)
is so remote from being valid C syntax that no compaint about its
fontification is reasonable.  

If you insert a backslash in the blank line, the bottom bit becomes
correctly fontified again.  The top bit needs you to type M-o M-o, as
Andreas said, to restore its colour.  This is because font lock, when
triggered by a buffer change, only refontifies the current line and those
below it.  This is a longstanding problem with font lock which is
difficult (though not impossible) to fix.

Thanks for taking the trouble to report this bug.

-- 
Alan Mackenzie (Nuremberg, Germany).