ST6RI-921 Invalid feature references are allowed in filter expressions

[seidewitz]

This PR removes an exception made in the Pilot Implementation that allowed invalid feature references in filter expressions.

Background

Both the KerML Specification (in 7.4.14 Packages) and the SysML Specification (in 7.5.4 Import Filtering) show examples of referencing features using a qualified name notation. For example:

filter @Annotations::ApprovalAnnotation and
    Annotations::ApprovalAnnotation::approved and
    Annotations::ApprovalAnnotation::level > 1;

This example has subexpressions that are feature reference expressions for non-package-level features, such as Annotations::Approval::approved. However, filter expressions are at package level (have no featuring type), and therefore do not have access to non-package-level features.

This should have caused a checkConnectorTypeFeaturing error on the implied binding connector between the referent feature and the expression result. But the Pilot Implementation had an explicit check coded in FeatureReferenceExpressionAdapter::addReferenceConnector to not add the binding connector if the expression was in a filter, so no error was reported. There is no such exception in the normative metamodel, despite the examples given in Clause 7 of the specifications (see also KERML11-183 on the specification inconsistency).

Changes

Updated FeatureReferenceExpressionAdapter::addReferenceConnector to remove the exception for filter expressions.

Feature expressions such as in the example above now cause errors. The corrected version of the example is:

filter @Annotations::ApprovalAnnotation and
    (as Annotations::ApprovalAnnotation).approved and
    (as Annotations::ApprovalAnnotation).level > 1;

[hpdekoning]

Looks good to merge.