Re: [Emacs-diffs] emacs-24 d69e9f1: CC Mode: Stop Font Lock forcing fontification from BOL. Fixes debbugs#19669.

[Stefan Monnier]

> OK.  I think I've got it now.  jit-lock-fontify-now is expanding
> backwards into a region which is already fontified,

Whether it's already fontified is not the important point.
The important point is that it's already been *rendered* (i.e. the
buffer's content has already been read and turned into data in the
glyph matrices used to draw on the screen).

> but for which it doesn't "have permission",

It has permission alright, but whatever it does will only affect that
next redisplay (i.e. usually at the next command).

> The abstract cause of all these difficulties seems to be Font Lock's not
> distinguishing between a beginning of region to be used for analysis, and
> the beginning of region to which face properties will be applied.

Font lock indeed doesn't have a notion of "beginning of region to be
used for analysis" at all, so it can't distinguish it from the notion of
"beginning of region to which face properties will be applied".  If your
keyword rules need to look at some earlier text to get context, they're
free to do so.

> this understanding.  Perhaps if "any part of the buffer prior to that"
> had been "the initial part of the first line before `orig-start'", I
> would have got it sooner.

But that's very specific to your case.  Usually the problem occurs when
orig-start is at a BOL, but start is at an earlier line.


        Stefan