Ivan Serdiuk

External (xml) annotations are not supported for source code, only for assemblies. There is alternative way to adding dependencies to "JetBrains.Annotations" is to embed annotation's declarations in you source code,...

I think it is better to create feature request in ReSharper's youtrack ( https://youtrack.jetbrains.com ) to support xml external annotations for source code

Func does not support ItemNotNulll/ItemCanBeNull annotations. Request: https://youtrack.jetbrains.com/issue/RSRP-463008