Handle escapes in string literals.

frog/leg/scanner/scanner.dart

Index: frog/leg/scanner/scanner.dart
diff --git a/frog/leg/scanner/scanner.dart b/frog/leg/scanner/scanner.dart
index bfce2342cb9597ab318b32124ef838c973f29a26..873fc0e76567129b90d084cc213b521d57c70517 100644
--- a/frog/leg/scanner/scanner.dart
+++ b/frog/leg/scanner/scanner.dart
@@ -629,16 +629,70 @@ class AbstractScanner<T> implements Scanner {
     }
   }
 
+  static bool isHexDigit(int character) {
+    if ($0 <= character && character <= $9) return true;
+    character |= 0x20;
+    return ($a <= character && character <= $f);
+  }
+
   int tokenizeSingleLineString(int next, int q1, int start) {
-    while (next !== $EOF) {
+    loop: while (next !== $EOF) {
       if (next === q1) {
         appendByteStringToken(STRING_INFO, utf8String(start, 0));
         return advance();
       } else if (next === $BACKSLASH) {
         next = advance();
-        if (next === $EOF) {
+        if (next === $EOF || next === $LF || next === $CR) {
           throw new MalformedInputException(charOffset);
         }
+        switch (next) {
+          case $u:
+            next = advance();
+            bool isBracketed = false;
+            int maxLength = 4;
+            if (next === $OPEN_CURLY_BRACKET) {
+              isBracketed = true;
+              maxLength = 7;
+              next = advance();
+            }
+            int startOffset = charOffset;
+            int unicodePoint = 0;
+            int length = 0;
+            while (length < maxLength && isHexDigit(next)) {
+              int digit = next <= $9 ? next - 0x30 : (next | 0x20) - ($a - 10);
+              unicodePoint = unicodePoint * 16 + digit;
+              length += 1;
+              next = advance();
+            }
+            if (isBracketed) {
+              if (length === 0) {
+                throw new MalformedInputException(startOffset);
+              }
+              if (next !== $CLOSE_CURLY_BRACKET) {
+                throw new MalformedInputException(charOffset);
+              }
+              next = advance();
+            } else if (length != 4) {
+              throw new MalformedInputException(startOffset + length);
+            }
+            if ((0xD800 <= unicodePoint && unicodePoint <= 0xDFFF) ||
+                unicodePoint > 0x10ffff) {
+              // Don't allow invalid code points in strings.
+              throw new MalformedInputException(startOffset);
+            }
+            // TODO(lrn): This should be just "continue", but the VM is bugged.
+            continue loop;
+          case $x:
+            for (int i = 0; i < 2; i++) {
+              next = advance();
+              if (!isHexDigit(next)) {
+                throw new MalformedInputException(charOffset);
+              }
+            }
+            break;
+          default:
+            // All other escapes are trivially valid.
+        }
       } else if (next === $$) {
         beginToken();
         next = advance();