This is a proposal PR to generate mocks without error for following cases:

type Water[R any, C UnsignedInteger] interface {
	Fish(R) []C
}

type UnsignedInteger interface {
	~uint | ~uint32 | ~uint64
}

Go types package seems to wrap interfaces that contain type constraints by checking a type set literal of the form ~T and A|B.
https://github.com/golang/go/blob/master/src/go/types/decl.go#L668

So gomock can just ignore that pattern to generate mocks safely without don't know how to mock method of type errors. I think this can be a better solution for custom type constraints than -exclude flag.