bug#12196: 24.1.50; setting cache-long-line-scans to non-nil freezes Emacs

[Eli Zaretskii <eliz@gnu.org>]

> From: Christopher Schmidt <christopher@ch.ristopher.com>
> Cc: bug-gnu-emacs@gnu.org
> Date: Mon, 10 Sep 2012 11:28:35 +0100 (BST)
> 
> Emacs loops here:
> 
>     #0  scan_buffer (target=10, start=6730, end=6749, count=1, shortage=0x7fff171cbbf0, allow_quit=1) at search.c:742
>     #1  0x000000000059844f in find_before_next_newline (from=6730, to=0, cnt=1) at search.c:945
>     #2  0x00000000005c8c1f in Fline_end_position (n=4) at editfns.c:808
>     #3  0x000000000058cdcb in Fend_of_line (n=4) at cmds.c:201
> 
>     p start_byte
>     $11 = 6750
>     p cursor
>     $12 = (unsigned char *) 0x3ddc6ad ");\n\n\treturn 0;\n}\n\n\n"
>     p base
>     $13 = (unsigned char *) 0x3ddc6ad ");\n\n\treturn 0;\n}\n\n\n"
> 
> These values do not change.
> 
> At the beginning of loop (search.c:669):
> 
>     p start
>     $14 = 6730
>     p end
>     $15 = 6749
> 
> target is '\n' of course.  Ultimately the problem boils down to
> region_cache_forward (search.c:686) always returning 0 from the first
> invocation, thus start_byte (search.c:688) is not modified throughout
> the loop.
> 
>     #0  region_cache_forward (buf=0x4f1db30, c=0x4bae990, pos=6750, next=0x7fff171cbb38) at region-cache.c:706
>     #1  0x0000000000597995 in scan_buffer (target=10, start=6730, end=6749, count=1, shortage=0x7fff171cbbf0, allow_quit=1) at search.c:687
> 
>     p buf->text->z
>     $21 = 6749

Thanks.  Does the patch below help?

=== modified file 'src/search.c'
--- src/search.c	2012-09-04 17:34:54 +0000
+++ src/search.c	2012-09-10 11:07:13 +0000
@@ -681,10 +681,11 @@ scan_buffer (register int target, ptrdif
            to see where we can avoid some scanning.  */
         if (target == '\n' && newline_cache)
           {
-            ptrdiff_t next_change;
+            ptrdiff_t next_change = 0;
             immediate_quit = 0;
             while (region_cache_forward
-                   (current_buffer, newline_cache, start_byte, &next_change))
+                   (current_buffer, newline_cache, start_byte, &next_change)
+		   || next_change == Z)
               start_byte = next_change;
             immediate_quit = allow_quit;