Why does the following program write the message 'Foo' twice?

[Gary Willoughby]

On Wednesday, 19 March 2014 at 10:10:18 UTC, Vladimir Panteleev 
wrote:
> If you use rdmd, it will be printed twice, because rdmd invokes 
> dmd once to gather the program's dependencies, and a second 
> time to actually build the program.

Yes i'm using rdmd. Thanks.