Re-factor handling of whole-pattern recursion in the interpreter

Author: PhilipHazel

ChangeLog

@@ -170,6 +170,11 @@ undefined behaviour.
 
 46. Fix backref iterators when PCRE2_MATCH_UNSET_BACKREF is set in JIT.
 
+47. Refactor the handling of whole-pattern recursion (?0) in pcre2_match() so
+that its end is handled similarly to other recursions. This has altered the
+behaviour of   /|(?0)./endanchored   which was previously not right. However,
+it still differs from JIT.
+
 
 Version 10.42 11-December-2022
 ------------------------------

src/pcre2_match.c

@@ -838,17 +838,15 @@ fprintf(stderr, "++ %2ld op=%3d %s\n", Fecode - mb->start_code, *Fecode,
     assert_accept_frame = F;
     RRETURN(MATCH_ACCEPT);
 
-    /* If recursing, we have to find the most recent recursion. */
+    /* For ACCEPT within a recursion, we have to find the most recent
+    recursion. If not in a recursion, fall through to code that is common with
+    OP_END. */
 
     case OP_ACCEPT:
-    case OP_END:
-
-    /* Handle end of a recursion. */
-
     if (Fcurrent_recurse != RECURSE_UNSET)
       {
 #ifdef DEBUG_SHOW_OPS
-      fprintf(stderr, "++ End within recursion\n");
+      fprintf(stderr, "++ Accept within recursion\n");
 #endif
       offset = Flast_group_offset;
       for(;;)
@@ -857,7 +855,6 @@ fprintf(stderr, "++ %2ld op=%3d %s\n", Fecode - mb->start_code, *Fecode,
         N = (heapframe *)((char *)match_data->heapframes + offset);
         P = (heapframe *)((char *)N - frame_size);
         if (GF_IDMASK(N->group_frame_type) == GF_RECURSE) break;
-
         offset = P->last_group_offset;
         }
 
@@ -873,11 +870,17 @@ fprintf(stderr, "++ %2ld op=%3d %s\n", Fecode - mb->start_code, *Fecode,
       Fecode += 1 + LINK_SIZE;
       continue;
       }
+    /* Fall through */
 
-    /* Not a recursion. Fail for an empty string match if either PCRE2_NOTEMPTY
-    is set, or if PCRE2_NOTEMPTY_ATSTART is set and we have matched at the
-    start of the subject. In both cases, backtracking will then try other
-    alternatives, if any. */
+    /* OP_END itself can never be reached within a recursion because that is
+    picked up when the OP_KET that always precedes OP_END is reached. */
+
+    case OP_END:
+
+    /* Fail for an empty string match if either PCRE2_NOTEMPTY is set, or if
+    PCRE2_NOTEMPTY_ATSTART is set and we have matched at the start of the
+    subject. In both cases, backtracking will then try other alternatives, if
+    any. */
 
     if (Feptr == Fstart_match &&
          ((mb->moptions & PCRE2_NOTEMPTY) != 0 ||
@@ -5856,7 +5859,8 @@ fprintf(stderr, "++ %2ld op=%3d %s\n", Fecode - mb->start_code, *Fecode,
     /* ===================================================================== */
     /* The end of a parenthesized group. For all but OP_BRA and OP_COND, the
     starting frame was added to the chained frames in order to remember the
-    starting subject position for the group. */
+    starting subject position for the group. (Not true for OP_BRA when it's a
+    whole pattern recursion, but that is handled separately below.)*/
 
     case OP_KET:
     case OP_KETRMIN:
@@ -5908,8 +5912,37 @@ fprintf(stderr, "++ %2ld op=%3d %s\n", Fecode - mb->start_code, *Fecode,
 
     switch (*bracode)
       {
-      case OP_BRA:    /* No need to do anything for these */
-      case OP_COND:
+      /* Whole pattern recursion is handled as a recursion into group 0, but
+      the entire pattern is wrapped in OP_BRA/OP_KET rather than a capturing
+      group - a design mistake: it should perhaps have been capture group 0.
+      Anyway, that means the end of such recursion must be handled here. It is
+      detected by checking for an immediately following OP_END when we are
+      recursing in group 0. If this is not the end of a whole-pattern
+      recursion, there is nothing to be done. */
+
+      case OP_BRA:
+      if (Fcurrent_recurse != 0 || Fecode[1+LINK_SIZE] != OP_END) break;
+
+      /* It is the end of whole-pattern recursion. */
+
+      offset = Flast_group_offset;
+      if (offset == PCRE2_UNSET) return PCRE2_ERROR_INTERNAL;
+      N = (heapframe *)((char *)match_data->heapframes + offset);
+      P = (heapframe *)((char *)N - frame_size);
+      Flast_group_offset = P->last_group_offset;
+
+      /* Reinstate the previous set of captures and then carry on after the
+      recursion call. */
+
+      memcpy((char *)F + offsetof(heapframe, ovector), P->ovector,
+        Foffset_top * sizeof(PCRE2_SIZE));
+      Foffset_top = P->offset_top;
+      Fcapture_last = P->capture_last;
+      Fcurrent_recurse = P->current_recurse;
+      Fecode = P->ecode + 1 + LINK_SIZE;
+      continue;  /* With next opcode */
+
+      case OP_COND:     /* No need to do anything for these */
       case OP_SCOND:
       break;
 
@@ -5976,9 +6009,8 @@ fprintf(stderr, "++ %2ld op=%3d %s\n", Fecode - mb->start_code, *Fecode,
       if (!PRIV(script_run)(P->eptr, Feptr, utf)) RRETURN(MATCH_NOMATCH);
       break;
 
-      /* Whole-pattern recursion is coded as a recurse into group 0, so it
-      won't be picked up here. Instead, we catch it when the OP_END is reached.
-      Other recursion is handled here. */
+      /* Whole-pattern recursion is coded as a recurse into group 0, and is
+      handled with OP_BRA above. Other recursion is handled here. */
 
       case OP_CBRA:
       case OP_CBRAPOS:

testdata/testinput2

@@ -6066,4 +6066,19 @@ a)"xI
 /\G(?:(?=(\1.|)(.))){1,13}?(?!.*\2.*\2)\1\K\2/g
     aaabcccdeee
 
+# This currently doesn't match JIT
+
+/|(?0)./endanchored,aftertext
+\= Expect error
+    abcd\=no_jit
+
+/|a(?0)/endanchored
+    aaaa
+
+# This currently doesn't match JIT
+
+/(?:|(?0).)(?(R)|\z)/
+\= Expect error
+    abcd\=no_jit
+
 # End of testinput2

testdata/testoutput2

@@ -17965,6 +17965,24 @@ No match
  1: ccc
  2: d
 
+# This currently doesn't match JIT
+
+/|(?0)./endanchored,aftertext
+\= Expect error
+    abcd\=no_jit
+Failed: error -52: nested recursion at the same subject position
+
+/|a(?0)/endanchored
+    aaaa
+ 0: aaaa
+
+# This currently doesn't match JIT
+
+/(?:|(?0).)(?(R)|\z)/
+\= Expect error
+    abcd\=no_jit
+Failed: error -52: nested recursion at the same subject position
+
 # End of testinput2
 Error -70: PCRE2_ERROR_BADDATA (unknown error number)
 Error -62: bad serialized data