Questions regarding `registry-index`.

[ehuss]

The ability to specify an alternate registry via URL with registry-index in a dependency was added in #4957. I had some questions about this:

• Should this be documented?
• Why was it chosen to use a different key instead of reusing the registry field as suggested in the RFC?
• How is it supposed to work? cargo publish doesn't seem to handle it properly. There are almost no tests for it.

cc @sfackler

[sfackler]

registry is elaborated into registry-index by cargo package so that the published crate doesn't depend on what the user decided the name of the registry should be. It's basically an implementation detail and shouldn't be used by people directly.

[sfackler]

The linked issue goes into more detail: #4880

[ehuss]

When is that rewritten registry-index used? AFAICT, Cargo always uses the index data for dependencies, and ignores the Cargo.toml in the crate file.

[sfackler]

#4880 (comment)

[sfackler]

The registry name is resolved to a URL at manifest parse time. We definitely parse the manifest, or there'd be no reason to go through all the effort of canonicalizing it in the first place.

[ehuss]

Ah, yea, I understand now. I'm working on a PR at #6500, and I updated it with some fixes related to this. If you have some time to look at it and provide feedback, I'd appreciate it.