Improve locked narrowing around low-level hooks.

* src/buffer.c (syms_of_buffer): Two new variables,
'long-line-locked-narrowing-region-size' and
'long-line-locked-narrowing-bol-search-limit', to make the locked
narrowing around low-level hooks configurable.

Increase the default value of 'long-line-threshold'.  After
carefully considering the (few) bug reports about long line
optimizations, I concluded that the previous default value was too
low.

* src/xdisp.c (get_locked_narrowing_begv)
(get_locked_narrowing_zv): Two new functions.
(handle_fontified_prop, reseat): Use them.

* src/keyboard.c (safe_run_hooks_maybe_narrowed): Use them.

* src/dispextern.h (struct it): Add two new fields to store the
values returned by these functions.
Make them externally visible.

* src/editfns.c: (Fsave_restriction): Update docstring.

1 files changed, 40 insertions, 4 deletions

diff --git a/src/xdisp.c b/src/xdisp.c
index 658ce57b7ea..430201874c3 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -3533,6 +3533,34 @@ get_closer_narrowed_begv (struct window *w, ptrdiff_t pos)
   return max ((pos / len - 1) * len, BEGV);
 }
 
+ptrdiff_t
+get_locked_narrowing_begv (ptrdiff_t pos)
+{
+  if (long_line_locked_narrowing_region_size == 0)
+    return BEGV;
+  int begv;
+  int len = long_line_locked_narrowing_region_size / 2;
+  begv = max (pos - len, BEGV);
+  int limit = long_line_locked_narrowing_bol_search_limit;
+  while (limit)
+    {
+      if (begv == BEGV || FETCH_BYTE (CHAR_TO_BYTE (begv) - 1) == '\n')
+	return begv;
+      begv--;
+      limit--;
+    }
+  return begv;
+}
+
+ptrdiff_t
+get_locked_narrowing_zv (ptrdiff_t pos)
+{
+  if (long_line_locked_narrowing_region_size == 0)
+    return ZV;
+  int len = long_line_locked_narrowing_region_size / 2;
+  return min (pos + len, ZV);
+}
+
 static void
 unwind_narrowed_begv (Lisp_Object point_min)
 {
@@ -4368,13 +4396,13 @@ handle_fontified_prop (struct it *it)
 
       if (current_buffer->long_line_optimizations_p)
 	{
-	  ptrdiff_t begv = it->narrowed_begv;
-	  ptrdiff_t zv = it->narrowed_zv;
+	  ptrdiff_t begv = it->locked_narrowing_begv;
+	  ptrdiff_t zv = it->locked_narrowing_zv;
 	  ptrdiff_t charpos = IT_CHARPOS (*it);
 	  if (charpos < begv || charpos > zv)
 	    {
-	      begv = get_narrowed_begv (it->w, charpos);
-	      zv = get_narrowed_zv (it->w, charpos);
+	      begv = get_locked_narrowing_begv (charpos);
+	      zv = get_locked_narrowing_zv (charpos);
 	    }
 	  narrow_to_region_locked (make_fixnum (begv), make_fixnum (zv),
 				   Qfontification_functions);
@@ -7435,12 +7463,20 @@ reseat (struct it *it, struct text_pos pos, bool force_p)
 	{
 	  it->narrowed_begv = get_narrowed_begv (it->w, window_point (it->w));
 	  it->narrowed_zv = get_narrowed_zv (it->w, window_point (it->w));
+	  it->locked_narrowing_begv
+	    = get_locked_narrowing_begv (window_point (it->w));
+	  it->locked_narrowing_zv
+	    = get_locked_narrowing_zv (window_point (it->w));
 	}
       else if ((pos.charpos < it->narrowed_begv || pos.charpos > it->narrowed_zv)
 		&& (!redisplaying_p || it->line_wrap == TRUNCATE))
 	{
 	  it->narrowed_begv = get_narrowed_begv (it->w, pos.charpos);
 	  it->narrowed_zv = get_narrowed_zv (it->w, pos.charpos);
+	  it->locked_narrowing_begv
+	    = get_locked_narrowing_begv (window_point (it->w));
+	  it->locked_narrowing_zv
+	    = get_locked_narrowing_zv (window_point (it->w));
 	}
     }