Replace cargo login --host with cargo login --index.

[fa7ca7]

No description provided.

[rust-highfive]

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[bors]

☔ The latest upstream changes (presumably #4506) made this pull request unmergeable. Please resolve the merge conflicts.

[alexcrichton]

Thanks for the PR! I'm somewhat hesitant to do this as I think we'll probably want to deprecate and remove this flag entirely (both it and a possible --index flag). PRs like #4680 are working with a --registry flag for custom registries.

I'm somewhat hesitant to land a deprecation/rename just before we remove it, however, so perhaps it'd be best to just leave it until custom registries have stabilized?

[fa7ca7]

Hah, I was working last few days on stabilizing of #4206 which is a base for #4680. But seems like I am late)