vim-patch:8.0.0647: syntax highlighting can make cause a freeze

Problem:    Syntax highlighting can make cause a freeze.
Solution:   Apply 'redrawtime' to syntax highlighting, per window.
06f1ed2f78

runtime/doc/options.txt

@@ -4528,10 +4528,14 @@ A jump table for the options with a short description can be found at |Q_op|.
 'redrawtime' 'rdt'	number	(default 2000)
 			global
 	Time in milliseconds for redrawing the display.  Applies to
-	'hlsearch', 'inccommand' and |:match| highlighting.
+	'hlsearch', 'inccommand', |:match| highlighting and syntax
+	highlighting.
 	When redrawing takes more than this many milliseconds no further
-	matches will be highlighted.  This is used to avoid that Vim hangs
+	matches will be highlighted.
-	when using a very complicated pattern.
+	For syntax highlighting the time applies per window.  When over the
+	limit syntax highlighting is disabled until |CTRL-L| is used.
+	This is used to avoid that Vim hangs when using a very complicated
+	pattern.
 
 						*'regexpengine'* *'re'*
 'regexpengine' 're'	number	(default 0)

src/nvim/buffer_defs.h

@@ -391,6 +391,7 @@ typedef struct {
   hashtab_T b_keywtab;                  /* syntax keywords hash table */
   hashtab_T b_keywtab_ic;               /* idem, ignore case */
   int b_syn_error;                      /* TRUE when error occurred in HL */
+  bool b_syn_slow;                      // true when 'redrawtime' reached
   int b_syn_ic;                         /* ignore case for :syn cmds */
   int b_syn_spell;                      /* SYNSPL_ values */
   garray_T b_syn_patterns;              /* table for syntax patterns */

src/nvim/normal.c

@@ -4642,6 +4642,9 @@ static void nv_clear(cmdarg_T *cap)
   if (!checkclearop(cap->oap)) {
     /* Clear all syntax states to force resyncing. */
     syn_stack_free_all(curwin->w_s);
+    FOR_ALL_WINDOWS_IN_TAB(wp, curtab) {
+      wp->w_s->b_syn_slow = false;
+    }
     redraw_later(CLEAR);
   }
 }

src/nvim/regexp.c

@@ -5098,8 +5098,6 @@ static int regmatch(
         printf("Premature EOL\n");
 #endif
       }
-      if (status == RA_FAIL)
-        got_int = TRUE;
       return status == RA_MATCH;
     }
 
@@ -7226,7 +7224,7 @@ static void report_re_switch(char_u *pat)
 /// @param nl
 ///
 /// @return TRUE if there is a match, FALSE if not.
-static int vim_regexec_both(regmatch_T *rmp, char_u *line, colnr_T col, bool nl)
+static int vim_regexec_string(regmatch_T *rmp, char_u *line, colnr_T col, bool nl)
 {
   regexec_T rex_save;
   bool rex_in_use_save = rex_in_use;
@@ -7276,7 +7274,7 @@ int vim_regexec_prog(regprog_T **prog, bool ignore_case, char_u *line,
                       colnr_T col)
 {
   regmatch_T regmatch = {.regprog = *prog, .rm_ic = ignore_case};
-  int r = vim_regexec_both(&regmatch, line, col, false);
+  int r = vim_regexec_string(&regmatch, line, col, false);
   *prog = regmatch.regprog;
   return r;
 }
@@ -7285,7 +7283,7 @@ int vim_regexec_prog(regprog_T **prog, bool ignore_case, char_u *line,
 // Return TRUE if there is a match, FALSE if not.
 int vim_regexec(regmatch_T *rmp, char_u *line, colnr_T col)
 {
-  return vim_regexec_both(rmp, line, col, false);
+  return vim_regexec_string(rmp, line, col, false);
 }
 
 // Like vim_regexec(), but consider a "\n" in "line" to be a line break.
@@ -7293,7 +7291,7 @@ int vim_regexec(regmatch_T *rmp, char_u *line, colnr_T col)
 // Return TRUE if there is a match, FALSE if not.
 int vim_regexec_nl(regmatch_T *rmp, char_u *line, colnr_T col)
 {
-  return vim_regexec_both(rmp, line, col, true);
+  return vim_regexec_string(rmp, line, col, true);
 }
 
 /// Match a regexp against multiple lines.

src/nvim/screen.c

@@ -1135,6 +1135,8 @@ static void win_update(win_T *wp)
   /* reset got_int, otherwise regexp won't work */
   save_got_int = got_int;
   got_int = 0;
+  // Set the time limit to 'redrawtime'.
+  proftime_T syntax_tm = profile_setlimit(p_rdt);
   win_foldinfo.fi_level = 0;
 
   /*
@@ -1362,7 +1364,7 @@ static void win_update(win_T *wp)
         /*
          * Display one line.
          */
-        row = win_line(wp, lnum, srow, wp->w_grid.Rows, mod_top == 0, false);
+        row = win_line(wp, lnum, srow, wp->w_grid.Rows, mod_top == 0, false, &syntax_tm);
 
         wp->w_lines[idx].wl_folded = FALSE;
         wp->w_lines[idx].wl_lastlnum = lnum;
@@ -1393,7 +1395,7 @@ static void win_update(win_T *wp)
         if (fold_count != 0) {
           fold_line(wp, fold_count, &win_foldinfo, lnum, row);
         } else {
-          (void)win_line(wp, lnum, srow, wp->w_grid.Rows, true, true);
+          (void)win_line(wp, lnum, srow, wp->w_grid.Rows, true, true, &syntax_tm);
         }
       }
 
@@ -2041,7 +2043,8 @@ win_line (
     int startrow,
     int endrow,
     bool nochange,                    // not updating for changed text
-    bool number_only                  // only update the number column
+    bool number_only,                 // only update the number column
+    proftime_T *syntax_tm
 )
 {
   int c = 0;                          // init for GCC
@@ -2189,18 +2192,20 @@ win_line (
     // To speed up the loop below, set extra_check when there is linebreak,
     // trailing white space and/or syntax processing to be done.
     extra_check = wp->w_p_lbr;
-    if (syntax_present(wp) && !wp->w_s->b_syn_error) {
+    if (syntax_present(wp) && !wp->w_s->b_syn_error && !wp->w_s->b_syn_slow) {
       // Prepare for syntax highlighting in this line.  When there is an
       // error, stop syntax highlighting.
       save_did_emsg = did_emsg;
       did_emsg = false;
-      syntax_start(wp, lnum);
+      syntax_start(wp, lnum, syntax_tm);
       if (did_emsg) {
         wp->w_s->b_syn_error = true;
       } else {
         did_emsg = save_did_emsg;
-        has_syntax = true;
+        if (!wp->w_s->b_syn_slow) {
-        extra_check = true;
+          has_syntax = true;
+          extra_check = true;
+        }
       }
     }
 
@@ -2540,8 +2545,9 @@ win_line (
       wp->w_cursor = pos;
 
       /* Need to restart syntax highlighting for this line. */
-      if (has_syntax)
+      if (has_syntax) {
-        syntax_start(wp, lnum);
+        syntax_start(wp, lnum, syntax_tm);
+      }
     }
   }
 
@@ -2587,6 +2593,9 @@ win_line (
     }
     next_search_hl(wp, shl, lnum, (colnr_T)v,
                    shl == &search_hl ? NULL : cur);
+    if (wp->w_s->b_syn_slow) {
+      has_syntax = false;
+    }
 
     // Need to get the line again, a multi-line regexp may have made it
     // invalid.

src/nvim/syntax.c

@@ -359,6 +359,7 @@ static reg_extmatch_T *next_match_extmatch = NULL;
 static win_T    *syn_win;               /* current window for highlighting */
 static buf_T    *syn_buf;               /* current buffer for highlighting */
 static synblock_T *syn_block;           /* current buffer for highlighting */
+static proftime_T *syn_tm;
 static linenr_T current_lnum = 0;       /* lnum of current state */
 static colnr_T current_col = 0;         /* column of current state */
 static int current_state_stored = 0;      /* TRUE if stored current state
@@ -384,7 +385,7 @@ static int syn_time_on = FALSE;
  * it.	Careful: curbuf and curwin are likely to point to another buffer and
  * window.
  */
-void syntax_start(win_T *wp, linenr_T lnum)
+void syntax_start(win_T *wp, linenr_T lnum, proftime_T *syntax_tm)
 {
   synstate_T  *p;
   synstate_T  *last_valid = NULL;
@@ -411,6 +412,7 @@ void syntax_start(win_T *wp, linenr_T lnum)
   }
   changedtick = buf_get_changedtick(syn_buf);
   syn_win = wp;
+  syn_tm = syntax_tm;
 
   /*
    * Allocate syntax stack when needed.
@@ -2887,6 +2889,7 @@ static char_u *syn_getcurline(void)
 static int syn_regexec(regmmatch_T *rmp, linenr_T lnum, colnr_T col, syn_time_T *st)
 {
   int r;
+  int timed_out = 0;
   proftime_T pt;
   const int l_syn_time_on = syn_time_on;
 
@@ -2902,7 +2905,8 @@ static int syn_regexec(regmmatch_T *rmp, linenr_T lnum, colnr_T col, syn_time_T
   }
 
   rmp->rmm_maxcol = syn_buf->b_p_smc;
-  r = vim_regexec_multi(rmp, syn_win, syn_buf, lnum, col, NULL, NULL);
+  r = vim_regexec_multi(rmp, syn_win, syn_buf, lnum, col,
+                        syn_tm, &timed_out);
 
   if (l_syn_time_on) {
     pt = profile_end(pt);
@@ -2914,6 +2918,9 @@ static int syn_regexec(regmmatch_T *rmp, linenr_T lnum, colnr_T col, syn_time_T
     if (r > 0)
       ++st->match;
   }
+  if (timed_out) {
+    syn_win->w_s->b_syn_slow = true;
+  }
 
   if (r > 0) {
     rmp->startpos[0].lnum += lnum;
@@ -3144,6 +3151,7 @@ static void syn_cmd_iskeyword(exarg_T *eap, int syncing)
 void syntax_clear(synblock_T *block)
 {
   block->b_syn_error = false;           // clear previous error
+  block->b_syn_slow = false;            // clear previous timeout
   block->b_syn_ic = false;              // Use case, by default
   block->b_syn_spell = SYNSPL_DEFAULT;  // default spell checking
   block->b_syn_containedin = false;
@@ -5682,7 +5690,7 @@ int syn_get_id(
   // When the position is not after the current position and in the same
   // line of the same buffer, need to restart parsing.
   if (wp->w_buffer != syn_buf || lnum != current_lnum || col < current_col) {
-    syntax_start(wp, lnum);
+    syntax_start(wp, lnum, NULL);
   } else if (col > current_col) {
       // next_match may not be correct when moving around, e.g. with the
       // "skip" expression in searchpair()
@@ -5757,8 +5765,10 @@ int syn_get_foldlevel(win_T *wp, long lnum)
   int level = 0;
 
   /* Return quickly when there are no fold items at all. */
-  if (wp->w_s->b_syn_folditems != 0) {
+  if (wp->w_s->b_syn_folditems != 0
-    syntax_start(wp, lnum);
+      && !wp->w_s->b_syn_error
+      && !wp->w_s->b_syn_slow) {
+    syntax_start(wp, lnum, NULL);
 
     for (int i = 0; i < current_state.ga_len; ++i) {
       if (CUR_STATE(i).si_flags & HL_FOLD) {

src/nvim/testdir/test_syntax.vim

@@ -503,3 +503,37 @@ func Test_syn_wrong_z_one()
   " call test_override("ALL", 0)
   bwipe!
 endfunc
+
+func Test_syntax_hangs()
+  if !has('reltime') || !has('float') || !has('syntax')
+    return
+  endif
+
+  " This pattern takes a long time to match, it should timeout.
+  new
+  call setline(1, ['aaa', repeat('abc ', 1000), 'ccc'])
+  let start = reltime()
+  set nolazyredraw redrawtime=101
+  syn match Error /\%#=1a*.*X\@<=b*/
+  redraw
+  let elapsed = reltimefloat(reltime(start))
+  call assert_true(elapsed > 0.1)
+  call assert_true(elapsed < 1.0)
+
+  " second time syntax HL is disabled
+  let start = reltime()
+  redraw
+  let elapsed = reltimefloat(reltime(start))
+  call assert_true(elapsed < 0.1)
+
+  " after CTRL-L the timeout flag is reset
+  let start = reltime()
+  exe "normal \<C-L>"
+  redraw
+  let elapsed = reltimefloat(reltime(start))
+  call assert_true(elapsed > 0.1)
+  call assert_true(elapsed < 1.0)
+
+  set redrawtime&
+  bwipe!
+endfunc