Warn about missing BPMN Shape

[korthout]

Problem you would like to solve

I was not warned by Modeler that the diagram was missing a BPMN Shape for a process element.

Specifically, there was no <bpmndi:BPMNShape> for this:

<bpmn:sequenceFlow id="Flow_1d8avtw" sourceRef="Activity_1ipwzk8" targetRef="Activity_0ll9m9k" />

Proposed solution

Warn the user with a problem stating that the process model has an item not visible in the diagram, and which item.

Alternatives considered

Pay really good attention to the XML :)

In all honesty, another option is for Zeebe to reject models where the visual diagram does not provide a shape for each element in the process. There are several issues with this:

• breaks backward compatibility
• less interoperability with models produced by third parties
• I like doing less

Additional context

I investigated a process instance that unexpectedly had an extra token after a parallel gateway. This made us think we had a bug in the engine.

After detailed root causing, I discovered that Zeebe executed the process instance correctly. There was a rogue Sequence Flow by passing the Parallel Gateway in the bpmn process (XML), but the visual diagram did not contain a BPMNShape for this item.

• incident channel with analysis: #inc-unexpected-token-in-process-instance
• applied fix of process after encountering issue https://github.com/zeebe-io/zeebe-engineering-processes/pull/389

[barmac]

We could get this for free if we enable bpmnlint:recommended ruleset per default.

Otherwise this can be achieved via a plugin: https://github.com/camunda/camunda-modeler-custom-linter-rules-plugin

[nikku]

@barmac Lightweight alternative to be considered: Add only the no-bpmndi rule. I think it is an important safeguard; at best it will save our users a bunch of time to root cause bugs.

[nikku]

Moving to ready to discuss with the team.