Implement generate-index-metadata command

[synek317]

It solves the issue #4497

[rust-highfive]

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[alexcrichton]

Thanks for the PR! Unfortunately now though there's a soft feature freeze in Cargo so it may be some time before the cargo team has bandwidth to review this

[Eh2406]

As someone without much of the background context, I would like to see more documentation. What dose it do? How can it be used? How can it be configured?

If my guess about what this does, I'd love to see an extenuation that let us take a resolution bug report and tern it into a reproducible test case.

[bors]

☔ The latest upstream changes (presumably #6347) made this pull request unmergeable. Please resolve the merge conflicts.

[synek317]

@alexcrichton was it freeze until rust 2018 release or is it freeze to the end of the year?
I've rebased my branch so it is mergeable again.

[Eh2406]

cc @ehuss

[ehuss]

At this time I think we'd like to experiment with index-related commands out of tree. I'm putting together a new subcommand which provides several options for managing an index, which I'll be posting soon. Do you have interest in running a registry? If so, feedback and testing would be helpful to figure out what features are needed.

[synek317]

This is my subcommand to create registry in a git repository: https://github.com/synek317/cargo-git-registry

It is very much work in progress but with generate-index-metadata it worked well and I've successfully created registry. Maybe the last issue was copy-paste the code from crates.io to create registry directories (e.g. ca/rg/cargo), but this is really small.

With generate-index-metadata in master cargo branch I'm going to go back to this project. It would really help me at work.

[ehuss]

@synek317 Nice! I'm trying to make it possible to implement this separately just using cargo metadata because linking against Cargo is a pain. I hit a bit of a roadblock due to some implementation issues, but I hope to have it resolved soon.

[dwijnand]

Closing in favour of the conversation in #4497 and the out-of-tree experimentation in https://github.com/ehuss/cargo-index.