Keep original IDs, if unused in target diagram

[nikku]

Is your feature request related to a problem? Please describe.

As a user I'd like to paste contents from another diagram without loosing the original IDs.

Use case: Merge diagrams by pasting conflicting parts from one diagram to the other.

Describe the solution you'd like

• Keep IDs when inserting copied contents, if the IDs are not taken yet in the target diagram

Describe alternatives you've considered

None.

---

Related to SUPPORT-4777

[barmac]

IDs are explicitly removed via https://github.com/bpmn-io/bpmn-js/blob/develop/lib/features/copy-paste/ModdleCopy.js#L219

[MaxTru]

We will not be able to deliver this for milestone M50 - I will get in touch with the CSM responsible to inform the customer

[MaxTru]

Great job @barmac! <3 that we have this

[nikku]

There exists an issue with the way we implemented this bug fix via bpmn-io/bpmn-js@1253326.

In the Camunda Modeler paste into another diagram only works for the first time. The second time I do it, it blows up:

[barmac]

That's confusing :/ Thanks for reporting!

[barmac]

I was able to reproduce it. It seems that the ID of a copied element is not reserved in the moddle.ids. The ID appears then as unassigned.

[nikku]

I suggest that we create an end-to-end integration test in ModelerSpec (testing with two modeler instances) to assert this is actually fixed for good.

[nikku]

As discussed I created a failing end-to-end test case here: bpmn-js#copy-paste-failing.

[barmac]

OK I was able to find the root cause of the problem. Let me try to explain it.

In the BpmnFactory, we _ensureId when an element is created. This assigns a new id if it's not already provided in the properties passed to BpmnFactory#create. Such ID is at the same time claimed in the moddle.ids object.

However, if the properties passed to BpmnFactory#create already include ID, it will never be claimed in the moddle.ids object unless the caller assigns it themself. Nevertheless, the element added on a diagram is also added to the ElementRegistry, and this is where the error thrown in the test case originates from.

I just debugged it and it seems a bit more complicated.