Support customize built-in expressions for LG and AdaptiveExpression

[luhan2017]

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

Describe the solution you'd like

https://github.com/microsoft/BotBuilder-Samples/blob/master/samples/csharp_dotnetcore/language-generation/20.extending-with-custom-functions/Bots/CustomFunctionBot.cs
In this sample, we support user to add a custom expression function in code. But if we add this in composer runtime, we can't use it in composer UX, since the function is not registered in the LSP.

Here is the piece of code I add in composer runtime:

           const string mySqrtFnName = "contoso.sqrt";
           // Add custom sqrt function
            Expression.Functions.Add(mySqrtFnName, (args) =>
            {
                object retValue = null;
                if (args[0] != null)
                {
                    double dblValue;
                    if (double.TryParse(args[0], out dblValue))
                    {
                        retValue = System.Math.Sqrt(dblValue);
                    }
                }
                return retValue;
            });

But I will see this error in the UX:

The easy way might be we add those custom functions as a white list in composer?

Describe alternatives you've considered

Additional context

[didaskein]

Hi,
Also a question linked to the custom Function, Could it be possible to have natively access to the locale of the user inside the code of the function ?

I would like to avoid to add a parameter in the function (not very user friendly ;))

Thank you.

[didaskein]

Also 2 features evolutions request linked to custom function :

• Be able to Call Async code inside a custom function
• Be able to return Activity (Speak,Event...) not only text

Thanks.

[cwhitten]

Closing this workitem as complete - see #3656 for continued investment in this area.