Implemented java identity escapes, replacing syntax escapes.

Author: lmasroca

core/src/main/antlr4/org/evomaster/core/parser/RegexJava.g4

@@ -129,7 +129,6 @@ quoteChar
  | E
 ;
 
-//TODO
 CharacterEscape
  : SLASH ControlEscape
  | SLASH 'c' ControlLetter
@@ -138,8 +137,7 @@ CharacterEscape
  | SLASH OctalEscapeSequence
  | SLASH ('p' | 'P') BRACE_open PCharacterClassEscapeLabel BRACE_close // this is only implemented in Java at the moment
                                                         // as on JS this is allowed only while certain flags are enabled
-
- //| IdentityEscape
+ | SLASH ~[a-zA-Z0-9] // identity escape
  ;
 
 // Instead of listing all unicode scripts, blocks, etc. the parser allows anything
@@ -164,13 +162,6 @@ fragment ControlLetter
  : [?-_a-z]
  ;
 
-
-//TODO
-//fragment IdentityEscape ::
-//SourceCharacter but not IdentifierPart
-//<ZWJ>
-//<ZWNJ>
-
 //TODO
 //DecimalEscape
 // //[lookahead ∉ DecimalDigit]
@@ -261,7 +252,6 @@ classEscape
 atomEscape
  : CharacterClassEscape
  | CharacterEscape
- | SyntaxEscapes
  | BackReference
  | NamedBackReference
  ;
@@ -284,11 +274,6 @@ CharacterClassEscape
   : SLASH [dDsSwWvVhH]
  ;
 
-
-SyntaxEscapes
- : SLASH [^$\\.*+?()[\]{}|/\-,:<>=!]
- ;
-
 CARET                      : '^';
 DOLLAR                     : '$';
 SLASH                      : '\\';

core/src/main/kotlin/org/evomaster/core/parser/GeneRegexJavaVisitor.kt

@@ -28,13 +28,9 @@ class GeneRegexJavaVisitor(externalRegexFlags: RegexFlags = RegexFlags()) : Rege
     )
 
     /**
-     * These are the Java regex syntax characters, all of these can be escaped to be treated as literals.
+     * None of these can be escaped to be treated as literals. Some may be part of legal escape sequences.
      */
-    private val allowedSyntaxEscapes = setOf(
-        '^', '$', '\\', '.', '*', '+', '?',
-        '(', ')', '[', ']', '{', '}', '|',
-        '/', '-', ',' ,':', '<', '>', '=', '!'
-    )
+    private val notIdentityEscapes = ('a'..'z').toList() + ('A'..'Z').toList() + ('0'..'9').toList()
 
     /**
      * Capture groups in order of appearance (1-based index -> list index 0).
@@ -470,7 +466,7 @@ class GeneRegexJavaVisitor(externalRegexFlags: RegexFlags = RegexFlags()) : Rege
             } else {
                 // This case handles the escaped syntax characters, like "\." and "\+", etc. cases
                 // where '.' and '+', etc. should be treated as regular chars
-                assert(startText[0] == '\\' && startText[1] in allowedSyntaxEscapes)
+                assert(startText[0] == '\\' && startText[1] !in notIdentityEscapes)
                 start = startText[1]
                 end = start
             }
@@ -647,7 +643,7 @@ class GeneRegexJavaVisitor(externalRegexFlags: RegexFlags = RegexFlags()) : Rege
                         currentFlags
                 )
             }
-            in allowedSyntaxEscapes -> PatternCharacterBlockGene(txt, txt.substring(1), currentFlags)
+            !in notIdentityEscapes -> PatternCharacterBlockGene(txt, txt.substring(1), currentFlags)
             else -> CharacterClassEscapeRxGene(txt.substring(1), currentFlags)
         })
     }