Add scaffolding for assigning alpha-numeric codes to rustc diagnostics

src/libsyntax/parse/lexer/mod.rs

@@ -1308,7 +1308,7 @@ mod test {
     use std::io::util;
 
     fn mk_sh() -> diagnostic::SpanHandler {
-        let emitter = diagnostic::EmitterWriter::new(box util::NullWriter);
+        let emitter = diagnostic::EmitterWriter::new(box util::NullWriter, None);
         let handler = diagnostic::mk_handler(box emitter);
         diagnostic::mk_span_handler(handler, CodeMap::new())
     }