Bug#400771: vim-gtk loops in syntax_start()

[Carlo Wood]

Package: vim-gtk
Version: 7.0-122+1

vim uses 100% cpu while scrolling up (starting in a given state)
the attached file.

How to reproduce:

Open a gnome-terminal with a height of 24 lines and a width of
126 characters (maximized horizontally on a 1024x768 screen using
courier 11 font (default)).

In this gnome-terminal run:

$ /usr/bin/vim.gtk Makefile.am

Go to the top of the file if not already there.
Press and hold 'j', scrolling down until you hit the bottom.
Then press and hold 'k', scrolling up until vim freezes and
starts to use 100% cpu. If it doesn't freeze the first time,
try doing it again (go always completely to the bottom and
completely to the top - use scrolling, not 'G' to jump).

Once looping, it loops inside syntax_start where current_lnum
loops over the values 27 to 31, jumping back to 27 after
having had value 31 in the last line of load_current_state.
At that moment we have the following backtrace:

#0  load_current_state (from=0x827a154) at syntax.c:1504
#1  0x0817167f in syntax_start (wp=0x81e5a38, lnum=37) at syntax.c:593
#2  0x08142c85 in win_update (wp=0x81e5a38) at screen.c:2694
#3  0x0814565f in update_screen (type=0) at screen.c:535
#4  0x080d2bb5 in main_loop (cmdwin=0, noexmode=0) at main.c:1083
#5  0x080d5c86 in main (argc=Cannot access memory at address 0x3) at main.c:934

It never leaves syntax_start(), in fact, it never leaves the
while loop in this function:

559         while (current_lnum < lnum)
560         {
561             syn_start_line();
562             (void)syn_finish_line(FALSE);
563             ++current_lnum;
564
565             /* If we parsed at least "minlines" lines or started at a valid
566              * state, the current state is considered valid. */
567             if (current_lnum >= first_stored)
568             {
569                 /* Check if the saved state entry is for the current line and is
570                  * equal to the current state.  If so, then validate all saved
571                  * states that depended on a change before the parsed line. */
572                 if (prev == NULL)
573                     sp = syn_buf->b_sst_first;
574                 else
575                     sp = prev->sst_next;
576                 if (sp != NULL
577                         && sp->sst_lnum == current_lnum
578                         && syn_stack_equal(sp))
579                 {
580                     parsed_lnum = current_lnum;
581                     prev = sp;
582                     while (sp != NULL && sp->sst_change_lnum <= parsed_lnum)
583                     {
584                         if (sp->sst_lnum <= lnum)
585                             /* valid state before desired line, use this one */
586                             prev = sp;
587                         else if (sp->sst_change_lnum == 0)
588                             /* past saved states depending on change, break here. */
589                             break;
590                         sp->sst_change_lnum = 0;
591                         sp = sp->sst_next;
592                     }
593                     load_current_state(prev);
594                 }
595                 /* Store the state at this line when it's the first one, the line
596                  * where we start parsing, or some distance from the previously
597                  * saved state.  But only when parsed at least 'minlines'. */
598                 else if (prev == NULL
599                             || current_lnum == lnum
600                             || current_lnum >= prev->sst_lnum + dist)
601                     prev = store_current_state(prev);
602             }

Attached: 'Makefile.am.gz', please gunzip before opening ;).

Output of ":filetype"
filetype detection:ON  plugin:ON  indent:OFF

Output of ":set filetype"
  filetype=automake  

-- 
Carlo Wood <carlo at alinoe.com>

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