In case anyone else is having compilation issues, adding

'-XXLanguage:+NewInference'

does not work with google’s custom compiler

1.3.70-dev-withExperimentalGoogleExtensions-20200424

That is correct. FYI, we are working to make it work with the new inference, and hopefully will have everything compatible before kotlin 1.4 https://android-review.googlesource.com/c/platform/frameworks/support/+/1297834