Add PEP 714 support for JSON API client

[charliermarsh]

Summary

Closes #3689.

Test Plan

Manually verified we pick up core-metadata from PyPI if I remove the aliases.

[charliermarsh]

Oh interesting, Serde does not treat aliases as fallbacks. They're mutually exclusive.

[charliermarsh]

Repeating like this is the only way I could figure out to support multiple aliases under different names, where multiple values can be present. (PyPI serves both core-metadata and data-dist-info-metadata; serde's alias feature errors if multiple values are present.)

[charliermarsh]

Per PEP 714, we could omit data_dist_info_metadata... But there may be registries that only serve that in practice, since that's what pip did for a while.

[BurntSushi]

I would define a separate wire type with what you want to support, and then implement From<FileWire> for File (or TryFrom if needed). Then use #[serde(from = "FileWire")]. That way, you can resolve the aliases down to one field at deserialization time, and avoid spreading that complexity outward to anyone consuming File.

[charliermarsh]

Hmm, but we already have a separate File type that we use in our own abstractions.

[charliermarsh]

So in a sense this is FileWire. And we have a From elsewhere.

[BurntSushi]

Ah I was confused because I wouldn't normally expect a wire type to have pub fields and otherwise be exported. Basically, my suggestion boils down to "encapsulate the aliases at the deserialization boundary." But if the point of File is to be the boundary and be exposed to the world, then yeah, I think what you have is fine.

[charliermarsh]

Yeah this is meant to be roughly "the exact JSON we get from the API", so I suppose this is ok.