provideSignatureHelp doesn't seem to render anything despite being called and returning data

[DanTup]

• VSCode Version: 1.4
• OS Version: Windows 10

I'm trying to implement a signatureHelpProvider (which I believe is the thing that gives me parameter hints when I type ( or , when calling a method/signature/etc.).

My code seems to be called; I see "running" in the console whenever I type a ( but nothing ever appears in the editor! Here's my code:

provideSignatureHelp(document: TextDocument, position: Position, token: CancellationToken): SignatureHelp {
    console.log("running...");
    return {
        activeParameter: 0,
        activeSignature: 0,
        signatures: [{
            label: "test",
            documentation: "test2",
            parameters: [
                {
                    label: "test3",
                    documentation: "test4",
                }
            ]
        }]
    };
}

There are no errors shown anywhere, but also no popup. I've tried 1-based indexes for activeParameter/activeSignature but no difference.

Any ideas what might be causing this or how I could debug further?

[jrieken]

I'll investigate

[jrieken]

Ok, the problem is that we spec vscode.SignatureHelp as a class and the method above returns an object literal which fails the instanceof check. It's an ongoing debate whether TypeScript should flag this as compile error or not - both things are structurally equal but instanceof is nominal check.

When you return something like new vscode.SignatureHelp it will work

[DanTup]

Aha; gotcha! I will change it over and give it a whirl today. Thank you! 😄

[jrieken]

and for reference: microsoft/TypeScript#8168

[DanTup]

By the way, I've implemented most of my providers this way and they all seemed to work, I presume this is something specific to signatures that the others don't do?

[jrieken]

You might just be lucky ;-) Often we only check if something is an array but not the array types... Tho there are plans to accept both - class instances and look-alike literals

[DanTup]

Btw, in some sample code in the issue you linked, you warn on bad stuff:

            } else {
                // warn about everything else
                console.warn('INVALID result from completion provider. expected CompletionItem-array or CompletionList but got:', value);
                return;
            }

But for this one, you don't. If easy to add, a warning might make it easier for understand what's happening.