[parser] implement error reporting for Scanner errors

src/messages.h

Index: src/messages.h
diff --git a/src/messages.h b/src/messages.h
index e7af4fb43a05f927ac85b0b8e54c48d97f4e506f..2f9538f05c1b51b631c239bd06baa7097ecd7dd0 100644
--- a/src/messages.h
+++ b/src/messages.h
@@ -462,6 +462,11 @@ class CallSite {
   T(UnterminatedTemplateExpr, "Missing } in template expression")              \
   T(FoundNonCallableHasInstance, "Found non-callable @@hasInstance")           \
   T(NonObjectInInstanceOfCheck, "Expecting an object in instanceof check")     \
+  T(InvalidHexEscapeSequence, "Invalid hexadecimal escape sequence")           \
+  T(InvalidUnicodeEscapeSequence, "Invalid Unicode escape sequence")           \
+  T(UndefinedUnicodeCodePoint, "Undefined Unicode code-point")                 \
+  T(UnclosedUnicodeEscapeSequence,                                             \
+    "Unclosed Unicode escape sequence --- Expected `}`")                       \

[adamk, 2016/03/18 18:21:55]

This one is weird in a couple ways:

- More traditional formatting would be "[...] sequence: expected '}'" (note
forward-single quotes, lower case, and colon instead of "---").
- In the example message test, the error doesn't actually seem all that helpful,
since there _is_ a '}', it's just too late. But maybe that's ok?

[caitp (gmail), 2016/03/21 16:15:03]

I rewrote the message to match similar-ish messages in ToT. Some of the Proxy
invariant check messages have the (expected ...) stuff in parentheses, lower
cased.
Maybe once there's more of a reason to, it could march ahead up to a set number
of characters to look for a  `}`, and choose a better error message if it finds
one? But I'm not really sure it matters that much ---- Either way it's still
more information than "Unexpected or illegal token"

   /* EvalError */                                                              \
   T(CodeGenFromStrings, "%")                                                   \
   /* URIError */                                                               \