When attempting to apply the System.AttributeUsage attribute to a class, Visual Studio will show the error "Attribute 'AttributeUsage' is only valid on classes derived from System.Attribute". Is it possible to specify such a requirement for a custom attribute?
Imagine an attribute class CommandAttribute, which would specify the name of a command. It should only be present on classes which implement ICommand so that we can guarantee that methods like ExecuteCommand(...) exist on the class.
I can of course use reflection to check that the applied classes implement the interface at run time, but ideally we could enforce this at compile time.
Unfortunately, this is not directly supported by the C# language.
However, you can write your own code analysis rule using the .NET Compiler Platform (aka Roslyn) and enforce that condition yourself.