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, 34 insertions, 1 deletions

diff --git a/src/buffer.c b/src/buffer.c
index d948aaa2662..ef7e6f18340 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -5882,7 +5882,40 @@ this threshold.
 If nil, these display shortcuts will always remain disabled.
 
 There is no reason to change that value except for debugging purposes.  */);
-  XSETFASTINT (Vlong_line_threshold, 10000);
+  XSETFASTINT (Vlong_line_threshold, 50000);
+
+  DEFVAR_INT ("long-line-locked-narrowing-region-size",
+              long_line_locked_narrowing_region_size,
+              doc: /* Region size for locked narrowing in buffers with long lines.
+
+This variable has effect only in buffers which contain one or more
+lines whose length is above `long-line-threshold', which see.  For
+performance reasons, in such buffers, low-level hooks such as
+`fontification-functions' or `post-command-hook' are executed on a
+narrowed buffer, with a narrowing locked with `narrowing-lock'.  This
+variable specifies the size of the narrowed region around point.
+
+To disable that narrowing, set this variable to 0.
+
+There is no reason to change that value except for debugging purposes.  */);
+  long_line_locked_narrowing_region_size = 500000;
+
+  DEFVAR_INT ("long-line-locked-narrowing-bol-search-limit",
+              long_line_locked_narrowing_bol_search_limit,
+              doc: /* Limit for beginning of line search in buffers with long lines.
+
+This variable has effect only in buffers which contain one or more
+lines whose length is above `long-line-threshold', which see.  For
+performance reasons, in such buffers, low-level hooks such as
+`fontification-functions' or `post-command-hook' are executed on a
+narrowed buffer, with a narrowing locked with `narrowing-lock'.  The
+variable `long-line-locked-narrowing-region-size' specifies the size
+of the narrowed region around point.  This variable, which should be a
+small integer, specifies the number of characters by which that region
+can be extended backwards to start it at the beginning of a line.
+
+There is no reason to change that value except for debugging purposes.  */);
+  long_line_locked_narrowing_bol_search_limit = 128;
 
   DEFVAR_INT ("large-hscroll-threshold", large_hscroll_threshold,
     doc: /* Horizontal scroll of truncated lines above which to use redisplay shortcuts.