Fix non-diagnosis of syntax error for (?(?< when not followed by ! or =.

ChangeLog

@@ -45,6 +45,11 @@ discovered by the LLVM fuzzer.
 between a subroutine call and its quantifier was incorrectly compiled, leading
 to buffer overflow or other errors. This bug was discovered by the LLVM fuzzer.
 
+12. The illegal pattern /(?(?<E>.*!.*)?)/ was not being diagnosed as missing an 
+assertion after (?(. The code was failing to check the character after (?(?< 
+for the ! or = that would indicate a lookbehind assertion. This bug was
+discovered by the LLVM fuzzer.
+
 
 Version 10.10 06-March-2015
 ---------------------------

src/pcre2_compile.c

@@ -5272,7 +5272,9 @@ for (;; ptr++)
         if (tempptr[1] == CHAR_QUESTION_MARK &&
               (tempptr[2] == CHAR_EQUALS_SIGN ||
                tempptr[2] == CHAR_EXCLAMATION_MARK ||
-               tempptr[2] == CHAR_LESS_THAN_SIGN))
+                 (tempptr[2] == CHAR_LESS_THAN_SIGN &&
+                   (tempptr[3] == CHAR_EQUALS_SIGN ||
+                    tempptr[3] == CHAR_EXCLAMATION_MARK))))  
           {
           cb->iscondassert = TRUE;
           break;

testdata/testinput2

@@ -4241,4 +4241,8 @@ a random value. /Ix
 "(*NO_JIT)((?2)+)((?1)){"
     abcd{
 
+# Perl fails to diagnose the absence of an assertion
+
+"(?(?<E>.*!.*)?)"
+
 # End of testinput2 

testdata/testoutput2

@@ -573,7 +573,7 @@ Failed: error 128 at offset 3: assertion expected after (?( or (?(?C)
 Failed: error 115 at offset 7: reference to non-existent subpattern
 
 /(?(?<ab))/
-Failed: error 142 at offset 7: syntax error in subpattern name (missing terminator)
+Failed: error 128 at offset 3: assertion expected after (?( or (?(?C)
 
 /((?s)blah)\s+\1/I
 Capturing subpattern count = 1
@@ -14204,4 +14204,9 @@ No match
     abcd{
 Failed: error -52: nested recursion at the same subject position
 
+# Perl fails to diagnose the absence of an assertion
+
+"(?(?<E>.*!.*)?)"
+Failed: error 128 at offset 3: assertion expected after (?( or (?(?C)
+
 # End of testinput2