Earlier quoted context omitted.
...and ensure _all_ package metadata required to perform dependency resolution can be retrieved through an API (in other words without downloading wheels).
Yeah, that’s sort of what I meant by my suggestion. Requirements that can only be resolved by downloading and executing code is a huge burden on tooling
For comparison, pacman (the Arch Linux package manager) packages have fairly similar ".PKGINFO" file in them; but in order to support resolving dependencies without downloading the packages, the server's repository index includes not just a listing of the (name, version) tuple for each package, it also includes each package's full .PKGINFO.
Enhancing the PyPA "Simple repository API" to allow fetching the METADATA independently of the wheel would be a relatively simple enhancement that would make a big difference.
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As I was writing this comment, I discovered that PyPA did this; they adopted PEP 658 in March of this year! https://github.com/pypa/packaging.python.org/commit/1ebb57b7...