emacs-27 89740e9: Prevent redisplay from moving point behind user's back

[Eli Zaretskii]

branch: emacs-27
commit 89740e9cb59ec05f3eef5a53dc39845d7d9fb638
Author: Eli Zaretskii <eliz@gnu.org>
Commit: Eli Zaretskii <eliz@gnu.org>

    Prevent redisplay from moving point behind user's back
    
    * src/bidi.c (bidi_at_paragraph_end, bidi_find_paragraph_start):
    Bind inhibit-quit to a non-nil value around calls to
    fast_looking_at, to prevent breaking out of redisplay_window,
    which temporarily moves point in buffers shown in non-selected
    windows.  (Bug#44448)
---
 src/bidi.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/src/bidi.c b/src/bidi.c
index 3abde7f..77e92c3 100644
--- a/src/bidi.c
+++ b/src/bidi.c
@@ -1458,6 +1458,11 @@ bidi_at_paragraph_end (ptrdiff_t charpos, ptrdiff_t 
bytepos)
   else
     start_re = paragraph_start_re;
 
+  /* Prevent quitting inside re_match_2, as redisplay_window could
+     have temporarily moved point.  */
+  ptrdiff_t count = SPECPDL_INDEX ();
+  specbind (Qinhibit_quit, Qt);
+
   val = fast_looking_at (sep_re, charpos, bytepos, ZV, ZV_BYTE, Qnil);
   if (val < 0)
     {
@@ -1467,6 +1472,7 @@ bidi_at_paragraph_end (ptrdiff_t charpos, ptrdiff_t 
bytepos)
        val = -2;
     }
 
+  unbind_to (count, Qnil);
   return val;
 }
 
@@ -1542,6 +1548,11 @@ bidi_find_paragraph_start (ptrdiff_t pos, ptrdiff_t 
pos_byte)
   if (cache_buffer->base_buffer)
     cache_buffer = cache_buffer->base_buffer;
 
+  /* Prevent quitting inside re_match_2, as redisplay_window could
+     have temporarily moved point.  */
+  ptrdiff_t count = SPECPDL_INDEX ();
+  specbind (Qinhibit_quit, Qt);
+
   while (pos_byte > BEGV_BYTE
         && n++ < MAX_PARAGRAPH_SEARCH
         && fast_looking_at (re, pos, pos_byte, limit, limit_byte, Qnil) < 0)
@@ -1559,6 +1570,7 @@ bidi_find_paragraph_start (ptrdiff_t pos, ptrdiff_t 
pos_byte)
       else
        pos = find_newline_no_quit (pos, pos_byte, -1, &pos_byte);
     }
+  unbind_to (count, Qnil);
   if (n >= MAX_PARAGRAPH_SEARCH)
     pos = BEGV, pos_byte = BEGV_BYTE;
   if (bpc)