Allow go-to-definition to show references when invoked on a declaration

[tothambrus11]

Description

When the definition request is sent at a site of a declaration (e.g. when somebody ctrl+clicks a function declaration's name), we currently return an empty list (or maybe nil?). At least VSCode and Zed have a feature when after a definition request whose result includes the cursor, they realize that we would just jumpt back to ourselves, so they issue a references request and show all the usages of our symbol, which has quite a nice UX.

To enable this, we would need to pattern match the node under cursor, and if it's not a name but a declaration, just return the span of that declaration. I tested this in Hylo's LSP, and this strategy is confirmed to work in VSCode:

References for the support:

• Zed: Fall back to FindAllReferences if cmd-click did not preform GoToDefinition elsewhere zed-industries/zed#9243
• VSCode: Feature Request: open Peek References when Ctrl-click is on the symbol in its declaration microsoft/vscode#73081

[Pradyumn-cloud]

Hello, I tried to work on this issue and found- SourceKitLSPServer.swift:2128-2136 returns declaration for Swift symbols that have both bestLocalDeclaration + a USR (symbol.usr?.hasPrefix("s:")).
We can add a fallback that also handles cases where SourceKit does not provide a USR. Would you like me to implement it?

[ahoppen]

If we don’t have a USR, we wouldn’t be able to find references, so I don’t think there’s no point in fixing anything for the case.

@tothambrus11 I just tried reproducing it and was able to see the jump-to-references behavior for SourceKit-LSP. Do you have an example project where you don’t see it?

[tothambrus11]

I will check again with the latest version. The last time I checked, the LSP seemed to bring me to the start of the declaration, which is the expected behavior. Maybe the VSCode extension has something misconfigured.