x/tools/gopls: codelens to show implementations of interfaces

[trivial-zero]

Since go does not have an explicit declaration of which interfaces one implements, it is hard to follow someone's code. I know that there is a command to show all the interfaces, but it is not very intuitive nor efficient.

Goland has the feature of showing a gutter when a function implements an interface. It would be nice to show maybe a codelens over the implementation and the type, or a similar solution as Goland.

Codelens:

Goland:

I found an extension that does kinda the opposite which is not very helpful in most scenario: galkowskit/go-interface-annotations

[2opremio]

That's exactly how rust-analyzer handles traits

[icearith]

this feature seems exactly what I want.

[Shawn-Huang-Tron]

This feature is very useful and we use it frequently. A lot of my friends doesn't like vscode-go just because of the leak of this feature.So they change to goland.Hope to add such a feature.

[tony-sol]

+1
this would be an extremely usefull

[hyangah]

cc @golang/tools-team This can be expensive depending on the size of the search space, but given that there are already similar functionalities (Find All Implementations, or LSP textDocument/implementation), I guess gopls has sufficient information to package this info as a codelens. Is there any concern?

[findleyr]

We have this in our long-term roadmap for gopls (along with a references codelens), most likely once we build out indexes that can satisfy these queries cheaply. Moving to the gopls issue tracker.