Ignore qualifiers on lookaheads within lookbehinds when checking for a fixed

length.

ChangeLog

@@ -100,6 +100,10 @@ a pattern. Because \G is in a lookbehind assertion, there has to be a
 "bumpalong" before there can be a match. The automatic "advance by one 
 character after an empty string match" rule is therefore inappropriate. A more 
 complicated algorithm has now been implemented.
+
+22. When checking to see if a lookbehind is of fixed length, lookaheads were 
+correctly ignored, but qualifiers on lookaheads were not being ignored, leading 
+to an incorrect "lookbehind assertion is not fixed length" error.
       
 
 Version 10.31 12-February-2018

src/pcre2_compile.c

@@ -8572,6 +8572,32 @@ for (;; pptr++)
     case META_LOOKAHEADNOT:
     pptr = parsed_skip(pptr + 1, PSKIP_KET);
     if (pptr == NULL) goto PARSED_SKIP_FAILED;
+    
+    /* Also ignore any qualifiers that follow a lookahead assertion. */
+    
+    switch (pptr[1])
+      {
+      case META_ASTERISK:
+      case META_ASTERISK_PLUS:
+      case META_ASTERISK_QUERY:   
+      case META_PLUS:
+      case META_PLUS_PLUS: 
+      case META_PLUS_QUERY:
+      case META_QUERY:
+      case META_QUERY_PLUS:
+      case META_QUERY_QUERY:       
+      pptr++;
+      break;
+      
+      case META_MINMAX:
+      case META_MINMAX_PLUS:
+      case META_MINMAX_QUERY:
+      pptr += 3;
+      break;
+      
+      default:
+      break;      
+      }
     break;
 
     /* Lookbehinds can be ignored, but must themselves be checked. */

testdata/testinput1

@@ -6192,4 +6192,14 @@ ef) x/x,mark
 /(?<=\G.)/g,aftertext
     abc
 
+/(?<=(?=.)?)/
+
+/(?<=(?=.)?+)/
+
+/(?<=(?=.)*)/
+
+/(?<=(?=.){4,5})/
+
+/(?<=(?=.){4,5}x)/
+
 # End of testinput1 

testdata/testinput2

@@ -5435,4 +5435,6 @@ a)"xI
 
 /(?=a+)a(a+)++b/B
 
+/(?<=(?=.){4,5}x)/B
+
 # End of testinput2

testdata/testoutput1

@@ -9831,4 +9831,14 @@ No match
  0: 
  0+ 
 
+/(?<=(?=.)?)/
+
+/(?<=(?=.)?+)/
+
+/(?<=(?=.)*)/
+
+/(?<=(?=.){4,5})/
+
+/(?<=(?=.){4,5}x)/
+
 # End of testinput1 

testdata/testoutput2

@@ -16583,6 +16583,20 @@ No match
         End
 ------------------------------------------------------------------
 
+/(?<=(?=.){4,5}x)/B
+------------------------------------------------------------------
+        Bra
+        AssertB
+        Reverse
+        Assert
+        Any
+        Ket
+        x
+        Ket
+        Ket
+        End
+------------------------------------------------------------------
+
 # End of testinput2
 Error -70: PCRE2_ERROR_BADDATA (unknown error number)
 Error -62: bad serialized data