src/vs/workbench/api/common/extHostLanguageFeatures.ts/SignatureHelpAdapter/provideSignatureHelp
class SignatureHelpAdapter:	async provideSignatureHelp(resource: URI, position: IPosition, context: extHostProtocol.ISignatureHelpContextDto, token: CancellationToken): Promise<extHostProtocol.ISignatureHelpDto | undefined> {
		const doc = this._documents.getDocument(resource);
		const pos = typeConvert.Position.to(position);
		const vscodeContext = this.reviveContext(context);

		const value = await this._provider.provideSignatureHelp(doc, pos, token, vscodeContext);
		if (value) {
			const id = this._cache.add([value]);
			return { ...typeConvert.SignatureHelp.from(value), id };
		}
		return undefined;
	}