Bus-branch export produces an invalid XIIDM file

[sylvlecl]

• Do you want to request a feature or report a bug?

Bug

• What is the current behavior?

See unit test in https://github.com/powsybl/powsybl-core/pull/2386

When exporting to an XIIDM file in bus-branch topology, elements may have no associated connectable bus. It causes the XIIDM file to be invalid (impossible to import).

• What is the expected behavior?

To be decided:

• do not export those elements ? but it can be difficult to handle if it is referenced elsewhere
• try harder to find a connectable bus ?

[sylvlecl]

@annetill @miovd @geofjamg @EtienneLt After discussion: it appears it is "known" that the bus-branch export is not supported

--> we should remove completely the support for that export parameter

Is it agreed ? Of course it's a breaking change. We can document that it could be replaced by the bus-breaker export where the retained switches are configured according to the needs.

[miovd]

@annetill @miovd @geofjamg @EtienneLt After discussion: it appears it is "known" that the bus-branch export is not supported

--> we should remove completely the support for that export parameter

Is it agreed ? Of course it's a breaking change. We can document that it could be replaced by the bus-breaker export where the retained switches are configured according to the needs.

Please note before taking a decision that there are users of the feature (dynawo project and ELM for example use the bus-branch export to run their calculations).