Client should report current value of activeSignature to signatureHelpProvider

[KamasamaK]

• VSCode Version: 1.15.1
• OS Version: Windows 10 Pro, version 1703 (x64)

Steps to Reproduce:

1. Trigger signature help with multiple signatures
2. Manually change active signature
3. Type a non-separator character
4. Watch it revert to previously active signature

Reproduces without extensions: N/A

With the current value of activeSignature in the request, the signatureHelpProvider could more intelligently decide what the activeSignature value should be in its response. This is especially the case when both arguments are not reasonably distinct enough for the provider to otherwise determine the active signature and must make it arbitrary.

Ref: #16256

[MofX]

I also really like to see this feature:
Not only from a language extension developer's perspective, but also from a user's perspective:
If i manually select one overload, I'd like it to stick, until I'm finished typing the call.
When looking at a complete function call, it is no problem to not have this, because then the overload should be deducible, but while I'm typing in, I might like to see the overload I am about to use.

This is especially true for the language I am working on (some internal markup language), where only the final number of parameters allows deduction of the used overload.

For all scenarios that I could think about, to be satisfy-able, the SignatureHelpProvider needs to know, if the user manually selected an overload and the number of this overload

[KamasamaK]

This could be made part of the new SignatureHelpContext proposed in #51731

[jrieken]

Yeah, we can think of that. What exactly do you need @KamasamaK?

[KamasamaK]

@jrieken I would like the activeSignature value in the SignatureHelpContext. As described in the opening comment, the provider must return activeSignature but currently has to do so without knowing what the current value is in the client (if it has one).

[mjbvz]

One complication is the case where there are multiple active signature help providers. In this case, the activeParameter /activeSignature alone likely isn't enough, since the provider needs a way to know if it was the one that returned the previous signature help

We could pass back the entire SignatureHelp object to support this

[jrieken]

One complication is the case where there are multiple active signature help providers.

Not sure I understand that. Don't we always take the first provider that has a result?

https://github.com/Microsoft/vscode/blob/6bbf94c2f16a6c2150dd9789f97f44f6f17cff35/src/vs/editor/contrib/parameterHints/provideSignatureHelp.ts#L20-L27

[mjbvz]

Fixed by #65440 which introduces a new activeSignatureHelp field on the SignatureHelpContext object. This new field is proposed API for December/January

Please share any feedback or concerns about the current api proposal