What's wrong with this alias?

[Dr.No via Digitalmars-d-learn]

consider this:

module report;

// output an error message on stderr
void error(A...)(string fmt, A args)
{
        import colorize : fg, color, cwriteln, cwritefln, cwrite;
        stderr.cwrite("error: ".color(fg.yellow));
        cwritefln(fmt.color(fg.yellow), args);
}

void warning(A...)(string fmt, A args)
{
        import colorize : fg, color, cwriteln, cwritefln, cwrite;
        cwrite("warning: ".color(fg.blue));
        cwritefln(fmt.color(fg.blue), args);
}

then

class C
{

        void error(A...)(string fmt, A args)
        {
                import report : error;
                reportedAnyError = true;
                error(fmt, args);
        }
        alias warning = report.warning;
}


I got this:

Error: undefined identifier report.warning

but this works:

        void warning(A...)(string fmt, A args)
        {
                import report : warning;
                warning(fmt, args);
        }

why alias cannot find my symbol there?