Once we support registry configuration, allow specifying `--registry` in addition to `--index`

[carols10cents]

And then look up the index location in .cargo/config.

The configuration support is part of RFC 2141 and there's an implementation started by @withoutboats that will hopefully be merged in soon :)

That way, whenever you want to, say, publish to an alternative registry, if you've configured said registry in .cargo/config with a name of "myregistry" like so:

[registries.myregistry]
index = "https://github.com/myorg/crates-registry" 

you'd currently have to run:

cargo publish --index https://github.com/myorg/crates-registry

but we should be able to teach cargo to understand:

cargo publish --registry myregistry

and do the same thing.

[carols10cents]

This should have been closed, not sure why it wasn't!