Add failing test for a calculation with a :struct return type

[skanderm]

Types don't seem to get pulled in when using a :struct return type in a calculation with an instance_of constraint. I ran into this as a more complicated circumstance (a calculation -> struct with instance_of constraint (another resource) -> calculation -> union NewType -> array -> struct), but this might be the core of it!

# 1
%{
  errors: [
    %{message: "Field \"structCalc\" must not have a selection since type \"JsonString\" has no subfields.", locations: [%{line: 3, column: 5}]},
    %{message: "Cannot query field \"some\" on type \"JsonString\".", locations: [%{line: 4, column: 7}]}
  ]
}

[zachdaniel]

Thanks for the test! I don't have time to investigate this right now. The issue will likely arise from somewhere in AshGraphql.all_attributes_and_arguments not traversing struct types, would you have a chance to look into it?

[skanderm]

Just getting back to this. It's looking like there's no logic for traversing the combination of :struct return type and :instance_of constraints (for both single and {:array, :struct}.

The calculation shows up in AshGraphql.all_attributes_and_arguments but there needs to be an extra step to pull SomeStructType.subtype_constraints.

[skanderm]

I can take a crack at adding the traversal around lib/ash_graphql.ex:747 in nested_attrs/4 unless you'd prefer to do it yourself!

Edit: that might actually not be the right place to change things, but either way happy to try.