Fix `@typePolicy` on abstract types

[martinbonnin]

Currently, the key fields of the field's schema type are used in TypePolicyCacheKeyGenerator. For interfaces and unions to work as expected, the concrete type (as found in __typename) should be used instead.

[BoD]

Note this is now done in apollo-kotlin-normalized-cache. Keeping the issue open as we might want to try to backport it to the 'classic' cache here.

[simon-hogg]

Thanks for working on this. I have been following for a while and just want to enquire whether this could have manifest as strange behaviour with normalised entires keyed by interface parameters?
We are seeing some strange behaviour with
extend interface SomeInterface @typePolicy(keyFields: "id")
where a downstream watch() is failing to respond to a cached value change.
Could apollographql/apollo-kotlin-normalized-cache#156 possibly help with that?

[BoD]

@simon-hogg When you apply a type policy to an interface, TypePolicyCacheKeyGenerator should work as expected. The problematic case is when it's applied to types implementing the interface but not to the interface itself. So I think your issue may be something else, but it's hard to know for sure. Would it be possible to reproduce it in a simple project?

[simon-hogg]

Thanks for the reply 🙌
Sorry not to produce a good bug report here, this was one of those "ooh this sounds like it might be related". We have actually solved this temporarily by re-building the affected watch() calls in our view models for now when there are major changes. I need to carve out some time to reproduce in a project for you. I will add this to our ticket and start a new issue it it proves to be cache key related and reproducable.

[BoD]

After some discussion we don't think we'll want to backport the changes in apollographql/apollo-kotlin-normalized-cache#156 to this repo because it will have to introduce potentially confusing breaking changes. So closing this ticket for now.

@simon-hogg please don't hesitate to open a new ticket if you can get more details about your issue!