Experimental parser: handle hex escapes in strings

src/lexer/lexer_py.re

 # Copyright 2013 the V8 project authors. All rights reserved.
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 #       notice, this list of conditions and the following disclaimer.
 #     * Redistributions in binary form must reproduce the above
 #       copyright notice, this list of conditions and the following
 #       disclaimer in the documentation and/or other materials provided
@@ skipping 182 matching lines @@
     goto default_action;
   }
 }|push_token(IDENTIFIER)|Identifier>
 
 eof             <|terminate|>
 default_action  <push_token(ILLEGAL)>
 
 <<DoubleQuoteString>>
 /\\\n\r?/ <||continue>
 /\\\r\n?/ <||continue>
-/\\./     <||continue>
+/\\[xX][:hex_digit:]{2}/ <||continue>
+/\\[^xX\r\n]/     <||continue>
 /\n|\r/   <|push_token(ILLEGAL)|>
 "\""      <|push_token(STRING)|>
 eof       <|terminate_illegal|>
 catch_all <||continue>
 
 <<SingleQuoteString>>
 /\\\n\r?/ <||continue>
 /\\\r\n?/ <||continue>
-/\\./     <||continue>
+/\\[xX][:hex_digit:]{2}/ <||continue>
+/\\[^xX\r\n]/     <||continue>
 /\n|\r/   <|push_token(ILLEGAL)|>
 "'"       <|push_token(STRING)|>
 eof       <|terminate_illegal|>
 catch_all <||continue>
 
 <<Identifier>>
 identifier_char <|push_token(IDENTIFIER)|continue>
 /\\u[0-9a-fA-F]{4}/ <{
   if (V8_UNLIKELY(!ValidIdentifierPart())) {
     goto default_action;
   }
 }|push_token(IDENTIFIER)|continue>
 
 <<SingleLineComment>>
 line_terminator  <|push_line_terminator|>
 eof <|skip_and_terminate|>
 catch_all <||continue>
 
 <<MultiLineComment>>
 /\*+\//             <|skip|>
 # TODO find a way to generate the below rule
 /\*+[^\/*]/       <||continue>
 line_terminator  <push_line_terminator||continue>
 eof <|skip_and_terminate|>
 catch_all        <||continue>