Re: cc-mode fontification feels random

[Stefan Monnier]

> Because of the order various jit-lock chunks are fontified.  If the
> chunk which establishes foo as a type is fontified first, subsequent
> fontifications of foo will use font-lock-type-face.  Otherwise, not.

The way this is handled in other modes is to keep a highwater mark of
the buffer position up to which the text has been scanned for type
definitions and then in the font-lock-keywords you start by scanning the
text between this mark and the text that needs to be fontified (and
then moving the mark, of course).

Of course, this presumes that text later in the buffer can't affect
highlighting of earlier text (e.g. a type definition has to come before
its first use).  And it can have other downsides (e.g. if you already do
the scan for highlighting itself, it means you now have to do the scan
twice (once to collect and once to highlight), and it also means that if
the user jumps to the end of the buffer you'll have to scan the whole
buffer before you can start highlighting the last screenful of text).

> Maybe an improvement might come from scanning the buffer for occurrences
> of foo after foo has been recognised as a type and entered into the CC
> Mode table.  That way, the lack of fontification on foo would be
> temporary, at least provided your Emacs is configured to fontify
> non-displayed bits of the buffer in the background (which it is by
> default).

Not since:

    commit d0483d25c034c38a8c6f0d718e9780c50e6ba03a
    Author: David Kastrup <dak@gnu.org>
    Date:   Sun Mar 4 08:41:08 2007 +0000
    
        * NEWS (fontification): Mention that the new default for
        jit-lock-stealth-time is now nil.
        
        * jit-lock.el (jit-lock-stealth-time): Change default to nil.
        Preserve 16 as default value for "seconds" when customizing.
    
    diff --git a/lisp/jit-lock.el b/lisp/jit-lock.el
    --- a/lisp/jit-lock.el
    +++ b/lisp/jit-lock.el
    @@ -77,9 +77,9 @@
    -(defcustom jit-lock-stealth-time 16
    +(defcustom jit-lock-stealth-time nil
       "*Time in seconds to wait before beginning stealth fontification.
     Stealth fontification occurs if there is no input within this time.
     If nil, stealth fontification is never performed.

> This might need enhanced support from jit-lock, such as some sort of
> signal indicating a buffer has been completly fontified.

Indeed, there's no way currently for font-lock to tell jit-lock that it
has decided to fontify a particular chunk without being requested to do
so (Eli suggests setting the `fontified` property, but this means that
all the clients of jit-lock have done their work, so it's only correct
to set it from font-lock if you run the other `jit-lock-functions` (or
if there are currently no other `jit-lock-functions`)),

The closest related functionality is that a jit-lock function
(e.g. `font-lock-fontify-region`) can return a value of the form
(jit-lock-bounds BEG . END) to indicate the region it actually
fontified (which should cover the region they were asked to fontify).


        Stefan