SYSML2 — validateTriggerInvocationExpressionWhenArgument constraint is wrong

The approved resolution to SYSML2-28 included adding the constraint validateTriggerInvocationExpressionWhenArgument, which requires:

If a TriggerInvocationExpression has kind = when, then it must have an argument Expression with a result that conforms to the type ScalarValues::Boolean.

However, the argument to a when trigger is not supposed to be an Expression with a Boolean result. Rather, it is an Expression whose result is the Evaluation of an Expression whose result is Boolean. That is, a trigger like when x > 0 is parsed as TriggerWhen({x > 0}), not as TriggerWhen(x > 0). So all properly parsed when triggers will violate validateTriggerInvocationExpressionWhenArgument as specified in the resolution to SYSML2-28.

Update the constraint

A TriggerInvocationExpression with kind=when is always parsed from the concrete syntax as having an argument that is a FeatureReferenceExpression whose referent is an Expression (per the resolution to SYSML2-495). In this context, it is sufficient to check that the referent Expression has a result that conforms to ScalarValues::Boolean.