Inconsistent JSONAPI serialization when missing related serializer

[beauby]

Suppose we have a Post class with has_many :comments, along with a PostSerializer. If we forget to define a CommentSerializer, rendering a Post with the JSONAPI adapter leads to the confusing following result (the comments are actually embedded in the relationship, which breaks JSONAPI spec):

{
  data: {
    type: 'posts',
    id: 1,
    attributes: { title: 'Title', body: 'Body' }
    relationships: {
      comments: {
        { 
          data: [{ id: 1, contents: 'Contents', author_id: 1, post_id: 1 },
                 { id: 2, contents: 'Contents', author_id: 2, post_id: 1 }]
        }
      }
    }
  }
}

It might be helpful to either have a way to warn the user that a given model does not have a corresponding serializer defined (as suggested in #1068), or have a default behavior of serializing stuff as Resource Identifiers.

[joaomdmoura]

Check #1068 (comment)

[beauby]

After giving more thoughts to this, I really think there should at least be a warning when a related serializer does not exist, because in the current situation gets very confusing when you misspel a serializer name in its definition (like class PotsSerializer).

[remear]

@beauby This is still an issue, yes?

[beauby]

@remear Yes, I believe so.

[beauby]

This was never fixed, was it?

[NullVoxPopuli]

Related: #1949 ?