Proposal: Support for Embedding in Mock

[frozenbonito]

Certain interfaces may have a mechanism to guarantee that a specific type is embedded.

For example, the <ServiceName>Server interface generated by protoc-gen-go-grpc contains an unexported mustEmbedUnimplemented<ServiceName>Server method, which can be implemented by embedding the Unimplemented<ServiceName>Server from the same package.

You can find more information here:
https://github.com/grpc/grpc-go/tree/master/cmd/protoc-gen-go-grpc#future-proofing-services

Real examples can be seen in the helloworld example of grpc-go:

• https://github.com/grpc/grpc-go/blob/941102b7811f/examples/helloworld/helloworld/helloworld_grpc.pb.go#L72-L76
• https://github.com/grpc/grpc-go/blob/941102b7811f/examples/helloworld/helloworld/helloworld_grpc.pb.go#L83-L88

To support this pattern, I propose a feature that allows specified types to be embedded in mocks. For instance, how about running moq -out mocks_test.go . MyInterface{Type1,Type2} (or MyInterface:MyMock{Type1,Type2}) to embed Type1 and Type2 in MyInterface mock?