Show function signature while providing the arguments

[mfronczyk]

Is your feature request related to a problem? Please describe.

When adding a function call, the extension suggests a list of functions with signatures, but when a function is selected and you start providing the parameters, the signature is not visible anymore and you need to bring the signature back sometimes for more complex functions.

Describe the solution you'd like

It'd be nice to keep the tooltip with the function signature open till you finish the call and make the current parameter bold there. It seems that the VS code extension for Idris has such feature, so maybe it'd be possible to add it here also?

Please see the Idris solution here - swr1bm86/vscode-idris@fd42429

[michaelpj]

Looks like this is textDocument/signatureHelp, which we indeed don't have an implementation for.

[alexnaspo]

I would be interested in working on this. I started hacking something together in ghcide but I'm wondering if this should be done within a HLS plugin?

[fendor]

It could be a plugin, but also part of ghcide directly, but let's see how the implementation looks like. If you require a slew of new dependencies, likely we want it in a plugin. If it basically can be done with the existing infrastructure, it is fine.

[michaelpj]

Also, sorry, forgot to link to the pre-existing issue that has some discussion: #2348

[michaelpj]

Hmm, possibly that is slightly different. I think that might be asking to show the argument doc in the main doc for an identifier? But we definitely also want them in signature help

[michaelpj]

No, I think that issue is different. Signature help is triggered by the user writing a character, i.e. while they're writing the function application. If we want argument haddock to be visible afterwards then we need it to be in the hover as well.

[samuel-williams-da]

@alexnaspo I see you have a WIP branch, are you still working on this?

[alexnaspo]

@samuel-williams-da I was having some trouble and got a bit busy so please don't let it hold up anyone else's work