x/pkgsite: show interfaces/implementations

[adonovan]

A Go user is confused as to how to find implementations of interfaces: https://bsky.app/profile/sszuecs.bsky.social/post/3lis5o4nv322u.

Google's internal package index relates each interface type to its concrete implementations (and vice versa), and each interface method to it corresponding method. This would be useful information to display in pkgsite too.

It requires a global index of methods, similar to what we build in gopls and Google's internal package index, but the ideas are familiar at this point.

[seankhliao]

maybe a dupe of #20131 ?
though that was changed from godoc to pkgsite

[adonovan]

maybe a dupe of #20131 ?

Thanks, yeah, it is essentially a dupe.

though that was changed from godoc to pkgsite

This feature has a long history. I implemented it in x/tools/cmd/godoc over a decade ago but it never made it to pkgsite. I suspect that it may be trickier to implement fully in pkgsite because (a) unlike godoc, pkgsite doesn't type-check anything and (b) pkgsite doesn't currently show any cross-package derived data, which would requirea global index.

[zigo101]

Will this be implemented in the global space for all Go packages in the world?
If yes, then some popular interface types might have tens of thousands implementations
which will make some std package pages bloat.

Golds implements this in a project scope.

[adonovan]

Will this be implemented in the global space for all Go packages in the world?

Ranking is clearly a part of the solution. I would expect to see implementations in the same package before those in dependencies in the same module, before non-dependency packages in the same module, before arbitrary dependencies in other modules, before arbitrary unrelated packages in the ecosystem. The last could be behind a "more..." button.

[jba]

This is a large feature. Don't expect it anytime soon.
Also, it would have to be syntax-based, thus inaccurate.