Fix incorrect internal error for very complicated back reference handling.

ChangeLog

@@ -223,6 +223,12 @@ followed by a caseful back reference, could lose the caselessness of the first
 repeated back reference (example: /(Z)(a)\2{1,2}?(?-i)\1X/i should match ZaAAZX
 but didn't).
 
+35. When a pattern is too complicated, PCRE2 gives up trying to find a minimum 
+matching length and just records zero. Typically this happens when there are
+too many nested or recursive back references. If the limit was reached in
+certain recursive cases it failed to be triggered and an internal error could 
+be the result.
+
 
 Version 10.22 29-July-2016
 --------------------------

src/pcre2_study.c

@@ -485,6 +485,7 @@ for (;;)
             this_recurse.prev = recurses;
             this_recurse.group = cs;
             dd = find_minlength(re, cs, startcode, utf, &this_recurse, countptr);
+            if (dd < 0) return dd;
             if (dd < d) d = dd;
             }
           }
@@ -525,6 +526,7 @@ for (;;)
           this_recurse.prev = recurses;
           this_recurse.group = cs;
           d = find_minlength(re, cs, startcode, utf, &this_recurse, countptr);
+          if (d < 0) return d;
           }
         }
       }
@@ -1551,7 +1553,8 @@ the minimum length is already known. */
 
 if ((re->flags & PCRE2_MATCH_EMPTY) == 0)
   {
-  switch(min = find_minlength(re, code, code, utf, NULL, &count))
+  min = find_minlength(re, code, code, utf, NULL, &count);
+  switch(min)
     {
     case -1:  /* \C in UTF mode or (*ACCEPT) or over-complex regex */
     break;    /* Leave minlength unchanged (will be zero) */

testdata/testinput2

@@ -4935,4 +4935,10 @@ a)"xI
 
 ".+\QX\E+"B,auto_callout,no_auto_possess
 
+# This one is here because Perl gives an 'unmatched )' error which goes away
+# if one of the \) sequences is removed - which is weird. PCRE finds it too
+# complicated to find a minimum matching length.
+
+"()X|((((((((()))))))((((())))))\2())((((((\2\2)))\2)(\22((((\2\2)2))\2)))(2\ZZZ)+:)Z^|91ZiZZnter(ZZ |91Z(ZZ ZZ(\r2Z( or#(\Z2(Z\Z(\2\2)2))\2Z)Z(\22Z((\Z2(Z\Z(\2\2)2))\2Z+:)Z|91Z(ZZ ZZ(\r2Z( or#(\Z2(Z\Z((Z*(\2(Z\':))\0)i|||||||||||||||loZ\2\2)2))\2Z)Z(\22Z((\Z2(Z\Z(\2\2)2))\2Z)))int \)\0nte!rnal errpr\2\\21r(2\ZZZ)+:)Z!|91Z(ZZ ZZ(\r2Z( or#(\Z2(Z\Z(\2\2)2))\2Z)Z(\22Z((\Z2(Z\Z(\2\2)2))\2Z)))int \)\0(2\ZZZ)+:)Z^|91ZiZZnter(ZZ |91Z(ZZ ZZ(\r2Z( or#(\Z2(Z\Z(\2\2)2))\2Z)Z(\22Z((\Z2(Z\Z(\2\2)2))\2Z)))int \)\0(2\ZZZ)+:)Z^)))int \)\0(2\ZZZ)+:)Z^|91ZiZZnter(ZZernZal ZZ(\r2Z( or#(\Z2(Z\Z(\2\2)2))\2Z)Z(\22Z((\Z2(Z\Z(\2\2)2))\2Z)))int \))\ZZ(\r2Z( or#(\Z2(Z\Z(\2\2)2))\2Z)Z(\22Z((\Z2(Z\Z(\2\2)))\2))))((((((\2\2))))))"I
+
 # End of testinput2 

testdata/testoutput2

@@ -15407,6 +15407,16 @@ Failed: error -33: bad offset value
         End
 ------------------------------------------------------------------
 
+# This one is here because Perl gives an 'unmatched )' error which goes away
+# if one of the \) sequences is removed - which is weird. PCRE finds it too
+# complicated to find a minimum matching length.
+
+"()X|((((((((()))))))((((())))))\2())((((((\2\2)))\2)(\22((((\2\2)2))\2)))(2\ZZZ)+:)Z^|91ZiZZnter(ZZ |91Z(ZZ ZZ(\r2Z( or#(\Z2(Z\Z(\2\2)2))\2Z)Z(\22Z((\Z2(Z\Z(\2\2)2))\2Z+:)Z|91Z(ZZ ZZ(\r2Z( or#(\Z2(Z\Z((Z*(\2(Z\':))\0)i|||||||||||||||loZ\2\2)2))\2Z)Z(\22Z((\Z2(Z\Z(\2\2)2))\2Z)))int \)\0nte!rnal errpr\2\\21r(2\ZZZ)+:)Z!|91Z(ZZ ZZ(\r2Z( or#(\Z2(Z\Z(\2\2)2))\2Z)Z(\22Z((\Z2(Z\Z(\2\2)2))\2Z)))int \)\0(2\ZZZ)+:)Z^|91ZiZZnter(ZZ |91Z(ZZ ZZ(\r2Z( or#(\Z2(Z\Z(\2\2)2))\2Z)Z(\22Z((\Z2(Z\Z(\2\2)2))\2Z)))int \)\0(2\ZZZ)+:)Z^)))int \)\0(2\ZZZ)+:)Z^|91ZiZZnter(ZZernZal ZZ(\r2Z( or#(\Z2(Z\Z(\2\2)2))\2Z)Z(\22Z((\Z2(Z\Z(\2\2)2))\2Z)))int \))\ZZ(\r2Z( or#(\Z2(Z\Z(\2\2)2))\2Z)Z(\22Z((\Z2(Z\Z(\2\2)))\2))))((((((\2\2))))))"I
+Capturing subpattern count = 108
+Max back reference = 22
+Contains explicit CR or LF match
+Subject length lower bound = 0
+
 # End of testinput2 
 Error -63: PCRE2_ERROR_BADDATA (unknown error number)
 Error -62: bad serialized data