map :base attribute to '/data' source pointer if not used as an attribute

[gmkohler]

The specification for "/data" in a JSONAPI error object's source attribute and the suggested usage of :base in ActiveModel::Error seem aligned.

Wrote this such that any actual :base attribute would override this, but not sure what sort of tests need to be added or whether it's worth adding at all.

[JoeWoodward]

Might make sense to make this customizable too. I use form objects and attach exceptions to an attr_accessor :exception which should also be attached to /data if this interpretation of the spec is correct.

The only thing I think might be wrong here is that nested association errors shouldn't be on base but rather on a relationship instead. However, that's not in v1 of the spec so not sure

[gmkohler]

@JoeWoodward can you write an example of what you mean by:

The only thing I think might be wrong here is that nested association errors shouldn't be on base but rather on a relationship instead

?