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, 12 insertions, 0 deletions

diff --git a/src/editfns.c b/src/editfns.c
index 4587b1132b1..6dec2d468c0 100644
--- a/src/editfns.c
+++ b/src/editfns.c
@@ -2661,6 +2661,8 @@ DEFUN ("widen", Fwiden, Swiden, 0, 0, "",
 This allows the buffer's full text to be seen and edited.  */)
   (void)
 {
+  if (!NILP (Vinhibit_widen))
+    return Qnil;
   if (BEG != BEGV || Z != ZV)
     current_buffer->clip_changed = 1;
   BEGV = BEG;
@@ -4457,6 +4459,7 @@ syms_of_editfns (void)
   DEFSYM (Qbuffer_access_fontify_functions, "buffer-access-fontify-functions");
   DEFSYM (Qwall, "wall");
   DEFSYM (Qpropertize, "propertize");
+  DEFSYM (Qinhibit_widen, "inhibit-widen");
 
   DEFVAR_LISP ("inhibit-field-text-motion", Vinhibit_field_text_motion,
                doc: /* Non-nil means text motion commands don't notice fields.  */);
@@ -4517,6 +4520,15 @@ This variable is experimental; email 32252@debbugs.gnu.org if you need
 it to be non-nil.  */);
   binary_as_unsigned = false;
 
+  DEFVAR_LISP ("inhibit-widen", Vinhibit_widen,
+               doc: /* Non-nil inhibits the `widen' function.
+
+Do NOT set this globally to a non-nil value, as doing that will
+disable the `widen' function everywhere, including the \\[widen\]
+command.  This variable is intended to be let-bound around code
+that needs to disable `widen' temporarily.  */);
+  Vinhibit_widen = Qnil;
+
   defsubr (&Spropertize);
   defsubr (&Schar_equal);
   defsubr (&Sgoto_char);