edm4hep2json: All EDM4hep collections + ROOT legacy reader

[kjvbrt]

BEGINRELEASENOTES

• edm4hep2json now converts all EDM4hep collections, associations and Podio user data
• added ROOT legacy support for edm4hep2json

ENDRELEASENOTES

[tmadlener]

@kjvbrt should we aim to include this in the tag for the new key4hep release?

[kjvbrt]

Hi @tmadlener I would be glad If it is included. I'm a bit lost in the CI failures, can you hint what should I fix?

[tmadlener]

Are there any tests for this yet? That would make the small refactoring I propose below a bit easier to do, but if you don't have time to fix this now, I think we can also merge this as is and open an issue to keep track of that and address that ASAP after the tag, as the functionality doesn't change.

[tmadlener]

Also the failing CI workflow seems to have been ignored in the past and is most likely due to a newer version of HepMC in the stack that is used there.

[kjvbrt]

I will prepare test to check for all the collections in the current yaml file.

[kjvbrt]

I'm not sure what to do with Podio user data collections. For now they are ignored in the test.

[tmadlener]

Nice, thanks for the update.

I think for the user data collections we could cook something up with std::apply over the podio::SupportedUserDataTypes which would make it automatically correct, but I would postpone that to another PR as that might require a bit of refactoring around these and I think the better direction would actually be to add an abstract to_json to podio::CollectionBase which would get rid of the whole if-else chain entirely.