Union types don't automatically inherit Interface fields during code generation

[shawncruz]

The following spec is valid:

{
    "interfaces": {
        "shape": {
            "fields": [
                { "name": "sides", "type":  "integer", "description": "Indicates the number of sides a shape has"}
            ]
        }
    },
    "unions": {
        "shape": {
            "interfaces": ["shape"],
            "discriminator": "type",
            "types": [
                { "type": "shape_circle", "discriminator_value": "circle"},
                { "type": "shape_square", "discriminator_value": "square"},
                { "type": "shape_triangle", "discriminator_value": "triangle"},
            ]        
        }
    },
    "models": {
        "shape_circle": {
            "description": "This is a circle.",
            "fields": [
                { "name": "radius",  "type": "decimal" }
            ]
        },
        "shape_square": {
            "description": "This is a square.",
            "fields": [
                { "name": "length",  "type": "decimal" }
                { "name": "height",  "type": "decimal" }
            ]
        },
        "shape_triangle": {
            "description": "This is a triangle.",
            "fields": [
                { "name": "triangle_type",  "type": "TriangleTypeEnum" }
            ]
        },
    }
}

However, when running the apibuilder command on this spec, the generated classes will extend the trait Shape, but not generate the overridden field for sides. The example of this output would look something like:

class Circle needs to be abstract. Missing implementation for:
  def sides: Integer // inherited from trait Shape
final case class Circle(radius: Decimal) extends Shape

The workaround for this has been to explicitly add the interface fields to the models fields array, however we should most likely consider this spec json invalid before we even get to code generation.

[mbryzek]

@shawncruz this is by design. We introduced templates (experimental feature) which automatically adds the fields.