Make scanner handle invalid unicode escapes in identifiers correctly.

test/mjsunit/regress/regress-1620.js

+// Copyright 2011 the V8 project authors. All rights reserved.
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+
+// Don't allow malformed unicode escape sequences in identifiers.
+// In strings and regexps we currently allow malformed unicode escape
+// sequences without throwing a SyntaxError. Instead "\u22gk" would
+// treat the "\u" as an identity escape, and evaluate to "u22gk".
+// Due to code sharing, we did the same in identifiers. This should
+// no longer be the case.
+// See: http://code.google.com/p/v8/issues/detail?id=1620
+
+assertThrows("var \\u\\u\\u = 42;");
+assertThrows("var \\u41 = 42;");
+assertThrows("var \\u123 = 42;");
+eval("var \\u1234 = 42;");
+assertEquals(42, eval("\u1234"));
+assertThrows("var uuu = 42; var x = \\u\\u\\u");
+
+// Regressions introduced and fixed again while fixing the above.
+
+// Handle 0xFFFD correctly (it's a valid value, and shouldn't be used
+// to mark an error).
+assertEquals(0xFFFD, "\uFFFD".charCodeAt(0));
+
+// Handle unicode escapes in regexp flags correctly.
+assertThrows("/x/g\\uim", SyntaxError);
+assertThrows("/x/g\\u2im", SyntaxError);
+assertThrows("/x/g\\u22im", SyntaxError);
+assertThrows("/x/g\\u222im", SyntaxError);
+assertThrows("/x/g\\\\u2222im", SyntaxError);