ST6RI-939 Fix StackOverflow when loading a ResourceSet

[AxelRICHARD]

Fix a StackOverflowError when loading a ResourceSet containing TransitionUsage elements.

Context

Loading a SysML-XMI ResourceSet can trigger a StackOverflowError when derived properties are evaluated on TransitionUsage elements.

The recursion involves the derived transition properties and the implicit member computation performed by TransitionUsageAdapter, especially around:

• TransitionUsage::source
• TransitionUsage::sourceFeature()
• TransitionUsage::succession
• Implicit transition members and binding connectors

Observed Behavior

The application fails with a recursive stack similar to:

java.lang.StackOverflowError
  at org.omg.sysml.delegate.setting.TransitionUsage_source_SettingDelegate.basicGet(...)
  at org.omg.sysml.lang.sysml.impl.TransitionUsageImpl.getSource(...)
  at org.omg.sysml.adapter.TransitionUsageAdapter.computeTransitionLinkConnectors(...)
  at org.omg.sysml.adapter.TransitionUsageAdapter.addAdditionalMembers(...)
  at org.omg.sysml.util.NamespaceUtil.addAdditionalMembersTo(...)
  at org.omg.sysml.util.UsageUtil.getSourceFeatureOf(...)
  at org.omg.sysml.lang.sysml.impl.TransitionUsageImpl.sourceFeature(...)
  at org.omg.sysml.delegate.setting.TransitionUsage_source_SettingDelegate.basicGet(...)
  ...

SysML-Level Explanation

In SysML, TransitionUsage::source is a derived property. It is computed from sourceFeature(), which identifies the feature used as the source of the transition succession.

At the same time, TransitionUsageAdapter may add implicit members required by transition semantics, such as:

• the implicit source member;
• transition link connectors;
• binding connectors between the succession, the transition link, and parameters.

The issue is that this implicit member computation is not reentrant-safe.

Recursion Cycle

The problematic cycle is:

1. Code reads transition.getSource().
2. This evaluates the derived property TransitionUsage::source.
3. The derived property calls transition.sourceFeature().
4. sourceFeature() delegates to UsageUtil.getSourceFeatureOf(transition).
5. UsageUtil.getSourceFeatureOf(...) calls NamespaceUtil.addAdditionalMembersTo(transition).
6. TransitionUsageAdapter.addAdditionalMembers() calls computeTransitionLinkConnectors().
7. computeTransitionLinkConnectors() reads transition.getSource().
8. The same cycle starts again.

This leads to unbounded recursion and eventually a StackOverflowError.

Typical Trigger

The issue can occur when a TransitionUsage has parameters, but its succession-related implicit members are not fully available at the time source is evaluated.

In that state, computeTransitionLinkConnectors() attempts to compute source-related binding connectors and reads transition.getSource(), which re-enters the same implicit member computation.

Changes

Added a Boolean isComputingTransitionLinkConnectors that is set to true during the computation of transition link connectors and reset to false when the computation is done. However, if computeTransitionLinkConnectors ends up being recursively called, it returns without calling TransitionUsage.getSource().

[AxelRICHARD]

Hello @seidewitz do you need something else for this pull request? If no, can I set it as "Ready for review"?

[seidewitz]

Really, this computation needs to be revised so the adding of additional members can be eliminated. For now, though, the simple change proposed in this PR is sufficient.