vim-patch:7.4.497 #2295

Problem:    With some regexp patterns the NFA engine uses many states and
            becomes very slow.  To the user it looks like Vim freezes.
Solution:   When the number of states reaches a limit fall back to the old
            engine. (Christian Brabandt)

https://github.com/vim/vim/releases/tag/v7-4-497

Helped-by: David Bürgin <676c7473@gmail.com>
Helped-by: Justin M. Keyes <justinkz@gmail.com>
Helped-by: Scott Prager <splinterofchaos@gmail.com>

CMakeLists.txt

@@ -331,4 +331,16 @@ if(BUSTED_PRG)
       -DTEST_TYPE=functional
       -P ${PROJECT_SOURCE_DIR}/cmake/RunTests.cmake
     DEPENDS nvim tty-test)
+
+  add_custom_target(benchmark
+    COMMAND ${CMAKE_COMMAND}
+      -DBUSTED_PRG=${BUSTED_PRG}
+      -DNVIM_PRG=$<TARGET_FILE:nvim>
+      -DWORKING_DIR=${CMAKE_CURRENT_SOURCE_DIR}
+      -DBUSTED_OUTPUT_TYPE=${BUSTED_OUTPUT_TYPE}
+      -DTEST_DIR=${CMAKE_CURRENT_SOURCE_DIR}/test
+      -DBUILD_DIR=${CMAKE_BINARY_DIR}
+      -DTEST_TYPE=benchmark
+      -P ${PROJECT_SOURCE_DIR}/cmake/RunTests.cmake
+    DEPENDS nvim tty-test)
 endif()

Makefile

@@ -89,6 +89,9 @@ test: functionaltest
 unittest: | nvim
 	+$(BUILD_CMD) -C build unittest
 
+benchmark: | nvim
+	+$(BUILD_CMD) -C build benchmark
+
 clean:
 	+test -d build && $(BUILD_CMD) -C build clean || true
 	$(MAKE) -C src/nvim/testdir clean

runtime/doc/options.txt

@@ -5383,6 +5383,10 @@ A jump table for the options with a short description can be found at |Q_op|.
 	Note that when using the NFA engine and the pattern contains something
 	that is not supported the pattern will not match.  This is only useful
 	for debugging the regexp engine.
+	Using automatic selection enables Vim to switch the engine, if the
+	default engine becomes too costly.  E.g., when the NFA engine uses too
+	many states.  This should prevent Vim from hanging on a combination of
+	a complex pattern with long text.
 
 		*'relativenumber'* *'rnu'* *'norelativenumber'* *'nornu'*
 'relativenumber' 'rnu'	boolean	(default off)

src/nvim/regexp.c

@@ -6914,13 +6914,8 @@ static regengine_T bt_regengine =
   bt_regcomp,
   bt_regfree,
   bt_regexec_nl,
-  bt_regexec_multi
-#ifdef REGEXP_DEBUG
-  ,(char_u *)""
-#endif
-#ifdef DEBUG
-  ,NULL
-#endif
+  bt_regexec_multi,
+  (char_u *)""
 };
 
 
@@ -6934,21 +6929,14 @@ static regengine_T nfa_regengine =
   nfa_regcomp,
   nfa_regfree,
   nfa_regexec_nl,
-  nfa_regexec_multi
-#ifdef REGEXP_DEBUG
-  ,(char_u *)""
-#endif
-#ifdef DEBUG
-  , NULL
-#endif
+  nfa_regexec_multi,
+  (char_u *)""
 };
 
 /* Which regexp engine to use? Needed for vim_regcomp().
  * Must match with 'regexpengine'. */
 static int regexp_engine = 0;
-#define     AUTOMATIC_ENGINE    0
-#define     BACKTRACKING_ENGINE 1
-#define     NFA_ENGINE          2
+
 #ifdef REGEXP_DEBUG
 static char_u regname[][30] = {
   "AUTOMATIC Regexp Engine",
@@ -6990,10 +6978,8 @@ regprog_T *vim_regcomp(char_u *expr_arg, int re_flags)
       regexp_engine = AUTOMATIC_ENGINE;
     }
   }
-#ifdef REGEXP_DEBUG
   bt_regengine.expr = expr;
   nfa_regengine.expr = expr;
-#endif
 
   /*
    * First try the NFA engine, unless backtracking was requested.
@@ -7003,11 +6989,12 @@ regprog_T *vim_regcomp(char_u *expr_arg, int re_flags)
   else
     prog = bt_regengine.regcomp(expr, re_flags);
 
-  if (prog == NULL) {       /* error compiling regexp with initial engine */
+  // Check for error compiling regexp with initial engine.
+  if (prog == NULL) {
 #ifdef BT_REGEXP_DEBUG_LOG
-    if (regexp_engine != BACKTRACKING_ENGINE) {     /* debugging log for NFA */
-      FILE *f;
-      f = fopen(BT_REGEXP_DEBUG_LOG_NAME, "a");
+    // Debugging log for NFA.
+    if (regexp_engine != BACKTRACKING_ENGINE) {
+      FILE *f = fopen(BT_REGEXP_DEBUG_LOG_NAME, "a");
       if (f) {
         fprintf(f, "Syntax error in \"%s\"\n", expr);
         fclose(f);
@@ -7016,12 +7003,22 @@ regprog_T *vim_regcomp(char_u *expr_arg, int re_flags)
             BT_REGEXP_DEBUG_LOG_NAME);
     }
 #endif
-    /*
-     * If the NFA engine failed, the backtracking engine won't work either.
-     *
-       if (regexp_engine == AUTOMATIC_ENGINE)
-        prog = bt_regengine.regcomp(expr, re_flags);
-     */
+    // If the NFA engine failed, try the backtracking engine.
+    // Disabled for now, both engines fail on the same patterns.
+    // Re-enable when regcomp() fails when the pattern would work better
+    // with the other engine.
+    //
+    // if (regexp_engine == AUTOMATIC_ENGINE) {
+    //   prog = bt_regengine.regcomp(expr, re_flags);
+    //   regexp_engine = BACKTRACKING_ENGINE;
+    // }
+  }
+
+  if (prog != NULL) {
+    // Store the info needed to call regcomp() again when the engine turns out
+    // to be very slow when executing it.
+    prog->re_engine = regexp_engine;
+    prog->re_flags = re_flags;
   }
 
   return prog;
@@ -7036,29 +7033,62 @@ void vim_regfree(regprog_T *prog)
     prog->engine->regfree(prog);
 }
 
-/*
- * Match a regexp against a string.
- * "rmp->regprog" is a compiled regexp as returned by vim_regcomp().
- * Uses curbuf for line count and 'iskeyword'.
- *
- * Return TRUE if there is a match, FALSE if not.
- */
-int 
-vim_regexec (
-    regmatch_T *rmp,
-    char_u *line,      /* string to match against */
-    colnr_T col            /* column to start looking for match */
-)
+static void report_re_switch(char_u *pat)
 {
-  return rmp->regprog->engine->regexec_nl(rmp, line, col, false);
+  if (p_verbose > 0) {
+    verbose_enter();
+    MSG_PUTS(_("Switching to backtracking RE engine for pattern: "));
+    MSG_PUTS(pat);
+    verbose_leave();
+  }
 }
 
-/*
- * Like vim_regexec(), but consider a "\n" in "line" to be a line break.
- */
+/// Matches a regexp against a string.
+/// "rmp->regprog" is a compiled regexp as returned by vim_regcomp().
+/// Uses curbuf for line count and 'iskeyword'.
+/// When "nl" is true consider a "\n" in "line" to be a line break.
+///
+/// @param rmp
+/// @param line the string to match against
+/// @param col  the column to start looking for match
+/// @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)
+{
+  int result = rmp->regprog->engine->regexec_nl(rmp, line, col, nl);
+
+  // NFA engine aborted because it's very slow, use backtracking engine instead.
+  if (rmp->regprog->re_engine == AUTOMATIC_ENGINE
+      && result == NFA_TOO_EXPENSIVE) {
+    int save_p_re = p_re;
+    int re_flags = rmp->regprog->re_flags;
+    char_u *pat = vim_strsave(((nfa_regprog_T *)rmp->regprog)->pattern);
+
+    p_re = BACKTRACKING_ENGINE;
+    vim_regfree(rmp->regprog);
+    report_re_switch(pat);
+    rmp->regprog = vim_regcomp(pat, re_flags);
+    if (rmp->regprog != NULL) {
+      result = rmp->regprog->engine->regexec_nl(rmp, line, col, nl);
+    }
+
+    free(pat);
+    p_re = save_p_re;
+  }
+
+  return result;
+}
+
+int vim_regexec(regmatch_T *rmp, char_u *line, colnr_T col)
+{
+  return vim_regexec_both(rmp, line, col, false);
+}
+
+// Like vim_regexec(), but consider a "\n" in "line" to be a line break.
 int vim_regexec_nl(regmatch_T *rmp, char_u *line, colnr_T col)
 {
-  return rmp->regprog->engine->regexec_nl(rmp, line, col, true);
+  return vim_regexec_both(rmp, line, col, true);
 }
 
 /*
@@ -7078,5 +7108,28 @@ long vim_regexec_multi(
   proftime_T  *tm                 /* timeout limit or NULL */
 )
 {
-  return rmp->regprog->engine->regexec_multi(rmp, win, buf, lnum, col, tm);
+  int result = rmp->regprog->engine->regexec_multi(rmp, win, buf, lnum, col,
+                                                   tm);
+
+  // NFA engine aborted because it's very slow, use backtracking engine instead.
+  if (rmp->regprog->re_engine == AUTOMATIC_ENGINE
+      && result == NFA_TOO_EXPENSIVE) {
+    int save_p_re = p_re;
+    int re_flags = rmp->regprog->re_flags;
+    char_u *pat = vim_strsave(((nfa_regprog_T *)rmp->regprog)->pattern);
+
+    p_re = BACKTRACKING_ENGINE;
+    vim_regfree(rmp->regprog);
+    report_re_switch(pat);
+    rmp->regprog = vim_regcomp(pat, re_flags);
+    if (rmp->regprog != NULL) {
+      result = rmp->regprog->engine->regexec_multi(rmp, win, buf, lnum, col,
+                                                   tm);
+    }
+
+    free(pat);
+    p_re = save_p_re;
+  }
+
+  return result;
 }

src/nvim/regexp_defs.h

@@ -30,6 +30,16 @@
  */
 #define NFA_MAX_BRACES 20
 
+// In the NFA engine: how many states are allowed.
+#define NFA_MAX_STATES 100000
+#define NFA_TOO_EXPENSIVE -1
+
+// Which regexp engine to use? Needed for vim_regcomp().
+// Must match with 'regexpengine'.
+#define AUTOMATIC_ENGINE    0
+#define BACKTRACKING_ENGINE 1
+#define NFA_ENGINE          2
+
 typedef struct regengine regengine_T;
 
 /*
@@ -40,6 +50,8 @@ typedef struct regengine regengine_T;
 typedef struct regprog {
   regengine_T *engine;
   unsigned regflags;
+  unsigned re_engine;  ///< Automatic, backtracking or NFA engine.
+  unsigned re_flags;   ///< Second argument for vim_regcomp().
 } regprog_T;
 
 /*
@@ -48,9 +60,11 @@ typedef struct regprog {
  * See regexp.c for an explanation.
  */
 typedef struct {
-  /* These two members implement regprog_T */
+  // These four members implement regprog_T.
   regengine_T *engine;
   unsigned regflags;
+  unsigned re_engine;
+  unsigned re_flags;  ///< Second argument for vim_regcomp().
 
   int regstart;
   char_u reganch;
@@ -78,9 +92,11 @@ struct nfa_state {
  * Structure used by the NFA matcher.
  */
 typedef struct {
-  /* These two members implement regprog_T */
+  // These four members implement regprog_T.
   regengine_T *engine;
   unsigned regflags;
+  unsigned re_engine;
+  unsigned re_flags;  ///< Second argument for vim_regcomp().
 
   nfa_state_T         *start;           /* points into state[] */
 
@@ -91,9 +107,7 @@ typedef struct {
   int has_zend;                         /* pattern contains \ze */
   int has_backref;                      /* pattern contains \1 .. \9 */
   int reghasz;
-#ifdef DEBUG
   char_u              *pattern;
-#endif
   int nsubexp;                          /* number of () */
   int nstate;
   nfa_state_T state[1];                 /* actually longer.. */
@@ -143,9 +157,7 @@ struct regengine {
   int (*regexec_nl)(regmatch_T*, char_u*, colnr_T, bool);
   long (*regexec_multi)(regmmatch_T*, win_T*, buf_T*, linenr_T, colnr_T,
       proftime_T*);
-#ifdef DEBUG
   char_u      *expr;
-#endif
 };
 
 #endif  // NVIM_REGEXP_DEFS_H

src/nvim/regexp_nfa.c

@@ -2347,7 +2347,6 @@ static void nfa_set_code(int c)
 
 }
 
-#ifdef REGEXP_DEBUG
 static FILE *log_fd;
 
 /*
@@ -2468,7 +2467,6 @@ static void nfa_dump(nfa_regprog_T *prog)
   }
 }
 #endif      /* REGEXP_DEBUG */
-#endif      /* REGEXP_DEBUG */
 
 /*
  * Parse r.e. @expr and convert it into postfix form.
@@ -4908,6 +4906,12 @@ static int nfa_regmatch(nfa_regprog_T *prog, nfa_state_T *start, regsubs_T *subm
     nextlist->n = 0;                /* clear nextlist */
     nextlist->has_pim = FALSE;
     ++nfa_listid;
+    if (prog->re_engine == AUTOMATIC_ENGINE && nfa_listid >= NFA_MAX_STATES) {
+      // Too many states, retry with old engine.
+      nfa_match = NFA_TOO_EXPENSIVE;
+      goto theend;
+    }
+
     thislist->id = nfa_listid;
     nextlist->id = nfa_listid + 1;
 
@@ -5082,6 +5086,10 @@ static int nfa_regmatch(nfa_regprog_T *prog, nfa_state_T *start, regsubs_T *subm
            */
           result = recursive_regmatch(t->state, NULL, prog,
               submatch, m, &listids);
+          if (result == NFA_TOO_EXPENSIVE) {
+            nfa_match = result;
+            goto theend;
+          }
 
           /* for \@! and \@<! it is a match when the result is
            * FALSE */
@@ -5180,6 +5188,10 @@ static int nfa_regmatch(nfa_regprog_T *prog, nfa_state_T *start, regsubs_T *subm
         /* First try matching the pattern. */
         result = recursive_regmatch(t->state, NULL, prog,
             submatch, m, &listids);
+        if (result == NFA_TOO_EXPENSIVE) {
+          nfa_match = result;
+          goto theend;
+        }
         if (result) {
           int bytelen;
 
@@ -6019,6 +6031,7 @@ nextchar:
   log_fd = NULL;
 #endif
 
+theend:
   /* Free memory */
   free(list[0].t);
   free(list[1].t);
@@ -6068,8 +6081,12 @@ static long nfa_regtry(nfa_regprog_T *prog, colnr_T col)
   clear_sub(&subs.synt);
   clear_sub(&m.synt);
 
-  if (nfa_regmatch(prog, start, &subs, &m) == FALSE)
+  int result = nfa_regmatch(prog, start, &subs, &m);
+  if (result == FALSE) {
     return 0;
+  } else if (result == NFA_TOO_EXPENSIVE) {
+    return result;
+  }
 
   cleanup_subexpr();
   if (REG_MULTI) {
@@ -6186,9 +6203,7 @@ nfa_regexec_both (
   nfa_nsubexpr = prog->nsubexp;
   nfa_listid = 1;
   nfa_alt_listid = 2;
-#ifdef REGEXP_DEBUG
   nfa_regengine.expr = prog->pattern;
-#endif
 
   if (prog->reganch && col > 0)
     return 0L;
@@ -6228,9 +6243,7 @@ nfa_regexec_both (
 
   retval = nfa_regtry(prog, col);
 
-#ifdef REGEXP_DEBUG
   nfa_regengine.expr = NULL;
-#endif
 
 theend:
   return retval;
@@ -6248,9 +6261,7 @@ static regprog_T *nfa_regcomp(char_u *expr, int re_flags)
   if (expr == NULL)
     return NULL;
 
-#ifdef REGEXP_DEBUG
   nfa_regengine.expr = expr;
-#endif
 
   init_class_tab();
 
@@ -6325,10 +6336,8 @@ static regprog_T *nfa_regcomp(char_u *expr, int re_flags)
 #endif
   /* Remember whether this pattern has any \z specials in it. */
   prog->reghasz = re_has_z;
-#ifdef REGEXP_DEBUG
   prog->pattern = vim_strsave(expr);
   nfa_regengine.expr = NULL;
-#endif
 
 out:
   free(post_start);
@@ -6342,9 +6351,7 @@ fail:
 #ifdef REGEXP_DEBUG
   nfa_postfix_dump(expr, FAIL);
 #endif
-#ifdef REGEXP_DEBUG
   nfa_regengine.expr = NULL;
-#endif
   goto out;
 }
 
@@ -6355,9 +6362,7 @@ static void nfa_regfree(regprog_T *prog)
 {
   if (prog != NULL) {
     free(((nfa_regprog_T *)prog)->match_text);
-#ifdef REGEXP_DEBUG
     free(((nfa_regprog_T *)prog)->pattern);
-#endif
     free(prog);
   }
 }

src/nvim/version.c

@@ -243,7 +243,7 @@ static int included_patches[] = {
   500,
   499,
   //498 NA
-  //497,
+  497,
   //496 NA
   //495 NA
   494,

test/benchmark/bench_re_freeze_spec.lua

@@ -0,0 +1,67 @@
+-- Test for benchmarking RE engine.
+
+local helpers = require('test.functional.helpers')
+local feed, insert, source = helpers.feed, helpers.insert, helpers.source
+local clear, execute, wait = helpers.clear, helpers.execute, helpers.wait
+
+-- Temporary file for gathering benchmarking results for each regexp engine.
+local result_file = 'benchmark.out'
+-- Fixture containing an HTML fragment that can make a search appear to freeze.
+local sample_file = 'test/benchmark/samples/re.freeze.txt'
+
+-- Vim script code that does both the work and the benchmarking of that work.
+local measure_cmd =
+    [[call Measure(%d, ']] .. sample_file .. [[', '\s\+\%%#\@<!$', '+5')]]
+local measure_script = [[
+    func! Measure(re, file, pattern, arg)
+      let sstart=reltime()
+    
+      execute 'set re=' . a:re
+      execute 'split' a:arg a:file
+      call search(a:pattern, '', '', 10000)
+      q!
+    
+      $put =printf('file: %s, re: %d, time: %s', a:file, a:re, reltimestr(reltime(sstart)))
+    endfunc]]
+
+describe('regexp search', function()
+  -- The test cases rely on a small Vim script, which we source here, and also
+  -- on a temporary result file, which we prepare and write to disk.
+  setup(function()
+    clear()
+    source(measure_script)
+    insert('" Benchmark_results:')
+    execute('write! ' .. result_file)
+  end)
+
+  -- At the end of the test run we just print the contents of the result file
+  -- for human inspection and promptly delete the file.
+  teardown(function()
+    print ''
+    for line in io.lines(result_file) do
+      print(line)
+    end
+    os.remove(result_file)
+  end)
+
+  it('is working with regexpengine=0', function()
+    local regexpengine = 0
+    execute(string.format(measure_cmd, regexpengine))
+    execute('write')
+    wait()
+  end)
+
+  it('is working with regexpengine=1', function()
+    local regexpengine = 1
+    execute(string.format(measure_cmd, regexpengine))
+    execute('write')
+    wait()
+  end)
+
+  it('is working with regexpengine=2', function()
+    local regexpengine = 2
+    execute(string.format(measure_cmd, regexpengine))
+    execute('write')
+    wait()
+  end)
+end)

test/benchmark/preload.lua

@@ -0,0 +1,4 @@
+-- Modules loaded here will not be cleared and reloaded by Busted.
+-- Busted started doing this to help provide more isolation.  See issue #62
+-- for more information about this.
+local helpers = require('test.functional.helpers')