Increment the next arg id on named arguments to allow adding positional arguments after named arguments.

[calebkiage]

Increment the next arg id on named arguments to allow adding positional arguments after named arguments.

Closes #3817

[vitaut]

Fixed in 4c5b4af but thanks for the PR.

[calebkiage]

This PR handles the case instead of throwing an exception. Isn't that a better developer experience?

[calebkiage]

I thought this intuition could be used for the arguments: if an automatic arg is used, advance the next argument, if a manual is used, set the next argument index. That way, they can be mixed together.

[vitaut]

Named arguments are conceptually similar to positional ones. Mixing them with automatic indexing is very confusing which is why it is better to ban them as we already do elsewhere.

[calebkiage]

That's fair enough. What I've seen other libraries do to mix them is to give the behavior of a moving index that is reset by manual indexing. So, format("{} {} {0} {}") is the same as format("{0} {1} {0} {1}").