Re: jit-lock doesn't honor font-lock-lines-before

[martin rudalics <rudalics@gmx.at>]

 >     Because this means that every time I insert one character, redisplay
 >     would refontify `font-lock-lines-before' in addition to the current
 >     line.
 >
 > Would that be bad?

It would slow down editing long lines.  jit-lock is supposed to make
editing faster.

 >
 >       Whether and when these lines are refontified
 >     would be _also_ decided by the redisplay engine.  And the latter doesn't
 >     know about `font-lock-lines-before'.  For example, editing the first
 >     line in a window would not "include the line before in refontification".
 >
 > This is a good point.  However, it can probably be fixed by a change in
 > the fontification function--when it is called, it should extend the starting
 > point for refontification upward by the specified number of lines.
 > (This might be the only fix needed.)
 >
 >

In `font-lock-default-fontify-region', immediately before the comment

           ;; check to see if we should expand the beg/end area for
           ;; proper multiline matches

insert either

           (setq beg (line-beginning-position (1- font-lock-lines-before)))

or - but this would have to be mentioned in the doc-string of
`font-lock-lines-before' -

           (when font-lock-multiline
             (setq beg (line-beginning-position (1- font-lock-lines-before))))

remove the corresponding line from `font-lock-after-change-function' and
wait what happens?  I'm still sceptical, though ... fontifications would
always overlap by `font-lock-lines-before' lines.