Warn or fail when @HollowHashKey is used on unsupported types

[ghost]

The @HollowHashKey annotation is supported on Map and Set types only. However, it's possible to annotate any type and the client API generator will silently ignore it. As it seems reasonable from examples in the docs to, say, apply it to a List this can result in confusion or churn later than need be. At least generate a warning when detecting the annotation on a type other than Map or Set, perhaps with it being a hard failure as an optional config (or fail by default with a mechanism to opt-out).

[rpalcolea]

@toolbear,

isn't this for @HollowHashKey instead?

Also, how do you envision this? Something at the HollowObjectTypeMapper level to fail if present in a non valid type or a Java AbstractProcessor that works on compile time so people could see warnings at compile level on their IDEs? That would take more to get done.

[akhaku]

Yup, @HollowHashKey is indeed what he meant - updated. What we're going for here is the client code generation - if a data model object has eg a List member that is annotated with @HollowHashKey, the annotation is ignored silently, and a findElement isn't generated.