bug#42155: --with-source=PACKAGE=REPLACEMENT-SOURCE doesn't work recursively

[pkill9]

> I think what you're looking for is more of:
> 
> guix build --no-grafts mpv --with-input=youtube-dl=$(guix build
> --no-grafts youtube-dl
> --with-source=https://github.com/ytdl-org/youtube-dl/releases/download/2020.06.16/youtube-dl-2020.06.16.tar.gz)
> 
> This didn't work for me though, I got:
> guix build: error:
> /gnu/store/9ncacjhzwlchpr1y5fd8ahdq59dsya20-youtube-dl-2020.06.16:
> unknown package

Even if that worked, it doesn't fix the issue of the --with-source flag
not working on the specified package's inputs.

That command doesn't work because you're giving it a store path, not a
package specification.