C++ runtime: Incorrect token string inserted for missing token

[nyh]

The ScyllaDB project uses Antlr3 with the C++ runtime.
In scylladb/scylladb#1703 it was noted that ugly error messages are reported. Particularly strange is:

line 1:20 missing K_VIEW at '<missing '

Forget for a moment why ScyllaDB even tries to print this token (it shouldn't!) but the fact that any token is being printed as <missing appears to be a simple Antlr3 bug:
/usr/include/antlr3parser.inl has in Parser<ImplTraits>::getMissingSymbol() the following code:

        // Create the token text that shows it has been inserted
        //
        token->setText("<missing ");
        text = token->getText();

        if      (!text.empty())
        {
                text.append((const char *) this->get_rec()->get_state()->get_tokenName(expectedTokenType) );
                text.append(">");
        }

Note how this code modifies the variable "text", which is a copy of the text in the token, and not the text in the token... Unfortunately, this isn't Java - when getText() returns a string (see /usr/include/antlr3commontoken.hpp) it is a copy, not a reference, and modifying it doesn't modify the token object.

Correct code would probably look something like this (untested):

StringType text("< missing");
text.append((const char *) this->get_rec()->get_state()->get_tokenName(expectedTokenType) );
text.append(">");
token->setText(text);