Container Drop tools defined in Diagram Extensions are limited

[flatombe]

When specifying a 'Container Drop' tool, there is a mandatory field 'Containers' which specifies for which mappings the drop needs to be evaluated.
Editing this field does not actually edit the ContainerDropDescription, but instead edits the specified mapping.

This is fine in most cases, as the ContainerDropDescription is specified in the same odesign file as the 'Containers' mappings it applies to.

In the context of a Diagram Extension however, one usually cannot edit the referenced 'Containers' mappings.

This issue can be solved in two very different ways, depending on what 'Diagram Extensions' is supposed to support:

• If Diagram Extensions should support this scenario, then the field 'Containers' of ContainerDropDescription should be mapped to an EReference that belongs to ContainerDropDescription. At runtime, when evaluating a drop, Sirius should look both in the mapping's Drop Descriptions and also search in all 'ContainerDropDescription' to determine all applicable drop tools.
• If Diagram Extensions should not support this scenario, then editing the field 'Containers' of ContainerDropDescription should restrict the scope of selectable mappings to those which are actually editable, and the validation should return an error in case referenced mappings are not actually editable.

(Sirius 6.3.3)