Feature: Download link for revised packages

[andreasabel]

Hackage provides download URLs for uploaded packages, but these do not include the revisions.
It would be good to also have download URLs for specific revisions of a package, which would deliver the patched package tarball.

There seems to be interest from the Arch community in such a feature see a discussion with @Vekhir at this PR:

• Allow text>=2.1, include GHC 9.8.1 in CI audreyt/string-qq#6 (comment)

[geekosaur]

This would have to be generated on the fly, because hackage-server doesn't store updated package tarballs; rather, it appends the updated revision to the index, and cabal get overwrites the original tarball's cabal file with the revised one. This is done to preserve immutability of the Hackage store. (@hasufell complains about this somewhat regularly.)

[hasufell]

There seems to be interest from the Arch community in such a feature see a discussion with @Vekhir at this PR

Hackage does provide API though to get the latest (or any) cabal file revision for a package.

Using that you can easily circumvent this restriction. But it does make it more annoying for distributors, mirrors, etc.

@hasufell complains about this somewhat regularly.

It is indeed a mis-feature, for many reasons.

The strongest argument is that a tarball should be a self-contained entity.