Define a base DSC Resource interface

[michaeltlombardi]

As an engineer developing and maintaining DSC Resources, I want to be able to ensure my implementation of a DSC Resource is valid and matches the expectations of the contract the platform guarantees. This ensures write-time validation as PowerShell classes which declare themselves to inherit from an interface and does not implement the members of that interface errors at parse time.

While this functionality is at least partially covered by the DscResource attribute, that attribute is widely used for prior versions of DSC and is (at least conceptually) non-idiomatic for implementing a class; given that classes can (and are documented as being able to) specifying interfaces and that any new interface definition would not break older implementations, I think this might be a step forward which also makes the documentation of a DSC Resource's required implementation more clear/discoverable.

Further, other interfaces could be built from this one, extending the expected implementation surface of a DSC Resource to match known-good patterns (which we could also leverage).

Proposal

I propose the creation of an IDscResource interface that defines a basic DSC Resource's surface.

At a minimum, this interface should require:

• A Get method which takes no input and returns an instance of the implementing class
• A Test method, which takes no input and returns a Boolean
• A Set method, which does not return anything

To expand on the idea of inherited interfaces, an IGuestConfigDscResource interface might inherit from IDscResource and also require the Reasons property.