Add support for tools on multiple diagram elements (group tool for example)

[sbegaudeau]

A couple of things to consider in a shape:

Let's consider the following pseudo-code of a diagram description:

DiagramDescription {
  name: 'Class Diagram'
  domainClass: 'code::Package'

  nodeDescriptions: [
    NodeDescription {
      name: 'Package Node Description'
      domainClass: 'code::Package',
      reusedChildNodeDescriptions: [
        'Package Node Description',
        'Class Node Description',
        'Interface Node Description'
      ]
    },
    NodeDescription {
      name: 'Class Node Description'
      domainClass: 'code::Class'
    },
    NodeDescription {
      name: 'Interface Node Description'
      domainClass 'code::Interface'
    }
  ]
  edgeDescriptions: [
    EdgeDescription {
      name: 'Relation Edge Description'
      from: ['Class Node Description', 'Interface Node Description']
      to: ['Class Node Description', 'Interface Node Description']
    },
    EdgeDescription {
      name: 'Extends Edge Description'
      from: ['Class Node Description']
      to: ['Class Node Description']
    },
    EdgeDescription {
      name: 'Implements Edge Description'
      from: ['Class Node Description']
      to: ['Interface Node Description']
    }
  ]
}

This description is for a class diagram like representation with packages, classes and interfaces on the background of the diagram. You can also have subpackages, classes and interfaces inside of packages. You can also have a class extending another class or implementing an interface. A very basic use case for a Sirius Web diagram.

We want to define tools that can act on multiple diagram elements. Here are a couple of use cases that we want to support:

• I want a tool to create a package from multiple classes at the same level. I select multiple Classes on the background of the diagram and create a new root package or I select multiple classes in a package and create a subpackage.
• I want a tool to create a package from multiple classes and interfaces at the same level. I can select classes and interfaces on the background of the diagram to create a new package. The tool has thus to consider diagram elements created from different descriptions.
• I want a tool to create relation edges instead of Extends / Implements by selecting multiple edges at once.
• I want a tool to be applied on both classes and implements edges.

Now that we have our use cases, here are a couple of questions that needs to be answered:

• Where can we define the tools in the View DSL?
• Where will the palette appear in case of multiple selection? (maybe on the last selected element when the user will Ctrl+click on various diagram elements)
• What should be displayed in the palette in case of a multiple selection? (probably only the tools relevant to the entire selection and the delete and show / hide tools)
• We would need various improvements to the GraphQL API with a SingleClickOnMultipleDiagramElementsTool / invoke SingleClickOnMultipleDiagramElementsTool

[pcdavid]

Also: how to tell the end-user which tools are not available just because his selection does not exactly match the tool's criterion. In the example above, assume we have 10 classes on the diagrams and one interface in the middle (that he may not notice). The user selected all the classes with a zone/rectangle selection tool, but just because there is a single interface in the selection, the tool he wanted to use (which only handles classes) is nowhere to be seen in the palette, with no feedback about why. That could be confusing.