Tracing context lost in actions/guards

[mrodal]

The tracing context is being lost when executing triggers in ReactiveStateMachineExecutor
I've uploaded a simple example project with this configuration:
https://github.com/mrodal/issue-context-propagation/blob/master/src/main/java/issues/context_propagation/Controller.java

As you can see the tracing is missing when inside the action:

Debugging I managed to find the part where it is getting lost, in this flatMap:

spring-statemachine/spring-statemachine-core/src/main/java/org/springframework/statemachine/support/ReactiveStateMachineExecutor.java

Line 119 in 4dcf6dc

triggerFlux = triggerSink.asFlux().flatMap(trigger -> handleTrigger(trigger), 1);

The example project has a controller with 2 endpoints

• /event which triggers the state machine
• /simple which executes a simplified code that reproduces the issue

The issue only happens when using Hooks.enableAutomaticContextPropagation() which we need to keep tracing in other parts of the code. I've reported the issue to the reactor team and you can see their response here: reactor/reactor-core#3887

Related issues:
micrometer-metrics/tracing#359
reactor/reactor-core#3887