A statement is executed even if one of its sub-expression produces an error

[echebbi]

Expected behavior

A statement is not executed if one of its sub-expression is invalid.

Current behavior

The statement is executed, eventually leading to unexpected results / subtle errors.

Reproducible example

Given:

open class State {

    @main
    def void run() {
        self.transiton.log();
    }

}

When: the transition attribute does not exist (typo)

Then: the interpreter still calls the log() service, leading the exception to be printed twice:

Why does it happen?

log() is called on the result of self.transiton which is... the no attribute called transiton error itself! The issue seems to come from the NotifyingEvaluationServices which, in case of error, returns a "placeholder" holding the exception:

ale-lang/plugins/org.eclipse.emf.ecoretools.ale.core/src/org/eclipse/emf/ecoretools/ale/core/interpreter/services/NotifyingEvaluationServices.java

Lines 88 to 96 in 9bf186e

	} catch (AcceleoQueryEvaluationException e) {
	Nothing placeHolder = new Nothing(e.getMessage(), e);
	if (e.getCause() instanceof AcceleoQueryEvaluationException) {
	addDiagnosticFor(diagnostic, Diagnostic.WARNING, placeHolder);
	} else {
	addDiagnosticFor(diagnostic, Diagnostic.ERROR, placeHolder);
	}
	return placeHolder;
	}

I tried to broadcast the exception instead but that resulted in the exception never being caught and crashing the whole interpreter. We have to be a bit more subtle here.