fix unicode in identifiers

Author: Protryon

src/main/java/com/shapesecurity/shift/es2017/parser/PatternAcceptor.java

@@ -248,20 +248,16 @@ private Maybe<String> eatUnicodeOrCharacter() {
                 return Maybe.empty();
             }
             return this.backtrackOnFailureMaybe(state -> {
-                int characterValue;
                 if (state.match("\\u")) {
                     state.skipCodePoint();
                     Maybe<Integer> maybeCharacterValue = acceptUnicodeEscape(state);
-                    if (!maybeCharacterValue.isJust()) {
-                        return Maybe.empty();
-                    }
-                    characterValue = maybeCharacterValue.fromJust();
-                } else {
-                    characterValue = pattern.codePointAt(state.index);
-                    state.index += Character.toChars(characterValue).length;
+                    return maybeCharacterValue.map(value -> new String(Character.toChars(value)));
+                }
+                Maybe<String> character = state.nextCodePoint();
+                if (character.isJust()) {
+                    state.skipCodePoint();
                 }
-                String character = new String(Character.toChars(characterValue));
-                return Maybe.of(character);
+                return character;
             });
         }
 
@@ -663,7 +659,7 @@ private Maybe<Integer> acceptUnicodeEscape(State superState) {
             }
             int value = Integer.parseInt(hex, 16);
 
-            if (value >= 0xD800 && value <= 0xDBFF) {
+            if (this.unicode && value >= 0xD800 && value <= 0xDBFF) {
                 Maybe<Integer> surrogatePairValue = state.backtrackOnFailureMaybe(subState -> {
                     if (!subState.eat("\\u")) {
                         return Maybe.empty();