improve: extend SecondaryToPrimaryMapper so it also gets the old resource

[csviri]

This might needed in some corner cases where might help with optimizations to which resource to trigger.

TBD: add more details here

Signed-off-by: Attila Mészáros a_meszaros@apple.com

[csviri]

see also discussio here: https://discord.com/channels/723455000604573736/723455000604573739/1508830486913482913

[csviri]

as discussed with @dvob , he will created a detailed issue for this.

[dvob]

@csviri thank you for implementing this so quickly. I also created issue #3401 for reference which we can more or less close right away if this is merged.

I updated my reproducer to use two different types (MyThing and MyThingConfig), in the hope that it is more understandable. I also updated it to use this PR and it did work (test does no longer fail) https://github.com/dvob/java-operator-sdk-repo-example/tree/csviri-secondary-to-primary-improve

However, when updating my reproducer, I ran into a different challenge. In my initial reproducer I used only one CRD (Repo) which referenced itself. But now I have to two different CRDs and in withPrimaryToSecondaryMapper I basically want to access the MyThingConfig informer which I'm building which is not easily possible. For now I did some dirty hack. But you might have a better idea to achieve this: https://github.com/dvob/java-operator-sdk-repo-example/blob/4b9e01c3099ae580036aa81cbe1558c0d422f0b0/src/main/java/com/example/MyThingReconciler.java#L53 ?

One thing which also came to my mind is, that if you not specify withPrimaryToSecondaryMapper it will use the DefaultPrimaryToSecondaryIndex which most likely will behave wrong in such a scenario. This is not really a problem, as you just can set withPrimaryToSecondaryMapper, but I'm just no sure how obvious this is for users of the API.