Plugins cannot define jump-to-definition handlers (responses are not combined)

[jvanbruegge]

As can be seen here https://github.com/haskell/haskell-language-server/blob/master/hls-plugin-api/src/Ide/Types.hs#L555 HLS always returns the first response for jump-to-definition, which happens to be ghcide. Multiple responses could be combined into one, by turning LocationLink into a Location

[michaelpj]

In fact, I think Location can be turned into LocationLink, which is the richer type:

• uri -> targetUri
• range -> targetRange
• range -> targetSelectionRange
• don't provide originSelectionRange

And the other direction:

• targetRange -> range
• targetUri -> uri

So I think what we would want to do is check the client capability for LocationLink support, and depending on whether it's set translate Locations to LocationLinks or vice versa.

[michaelpj]

... and then just concatenate the results

[joyfulmantis]

Currently the type the plugins provide for is the same as the ones lsp sends on to the client. I was thinking it would be nice to have a type the plugins need to provide that is separate from the actual method type the client accepts, specifically by being more specific. In this case only accepting locationlink for example, and then refactor the combine responses to convert that type into the client accepted type (ideally by querying capabilities) before combining. Separate types would allow us to enforce that the plugin is only returning our preferred type.

[michaelpj]

Yeah, I agree that that would be nice, might be a bit of a pain to implement. But we could almost certainly provide types that are e.g. easier to combine.

[jvanbruegge]

This was fixed by #3846