To be fair, if you leave out the git+ at the start that is “standard git URL format” for ssh-based repositories. The <user>@<domain>:<path> form is just shorthand syntax copied from scp that git also happens to support. But I assume that since it is not a canonical URL, nix does not support it.
Yeah that’s also fair. Btw I forgot that nix used to support URLs in that format, so when you’re used to that it’s extra annoying that suddenly it gives an “invalid URL” error.
Ha, and (just a small heads-up) indeed the quotes are very necessary, because of the ?, otherwise one often gets away with unquoted URLs, but this had me scratching my head a bit due to the funky error message (go figure, as a 25+years linux veteran )