code: private JCDiagnostic createBadClassFileDiagnostic(JavaFileObject file, JCDiagnostic diag) {
          String key = (file.getKind() == JavaFileObject.Kind.SOURCE
                      ? "bad.source.file.header" : "bad.class.file.header");
          return diagFactory.fragment(key, file, diag);
      }
docs: where