Improve font locking in buffers with long lines (bug#56682).

* src/dispextern.h (struct it): New 'narrowed_zv' field.

* src/xdisp.c (init_iterator): Set the field.
(get_narrowed_zv): New function to set the field.
(handle_fontified_prop): Use the field, together with 'narrowed_begv',
to narrow the portion of the buffer that 'Vfontification_functions'
will see.  Also bind 'inhibit-widen'.
(get_narrowed_len): New function, factored out of 'get_narrowed_begv'.
(unwind_narrowed_zv): New function.

* src/editfns.c (syms_of_editfns): New variable and symbol 'inhibit-widen'.
(Fwiden): Do nothing when 'inhibit-widen' is non-nil.

1 files changed, 5 insertions, 0 deletions

diff --git a/src/dispextern.h b/src/dispextern.h
index 1cdfdca74c0..bafa98161d0 100644
--- a/src/dispextern.h
+++ b/src/dispextern.h
@@ -2336,6 +2336,10 @@ struct it
      optimize display (see the SET_WITH_NARROWED_BEGV macro).  */
   ptrdiff_t narrowed_begv;
 
+  /* Alternate end position of the buffer that may be used to
+     optimize display.  */
+  ptrdiff_t narrowed_zv;
+
   /* C string to iterate over.  Non-null means get characters from
      this string, otherwise characters are read from current_buffer
      or it->string.  */
@@ -3401,6 +3405,7 @@ void redisplay_preserve_echo_area (int);
 void init_iterator (struct it *, struct window *, ptrdiff_t,
                     ptrdiff_t, struct glyph_row *, enum face_id);
 ptrdiff_t get_narrowed_begv (struct window *w);
+ptrdiff_t get_narrowed_zv (struct window *w);
 void init_iterator_to_row_start (struct it *, struct window *,
                                  struct glyph_row *);
 void start_display (struct it *, struct window *, struct text_pos);