Fix/add error messages

[mikaelweiss]

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Resolves #365

[zachdaniel]

Very nice! I think we'll need to do a few more things on this one.

Firstly, we'll need to make sure that the callbacks defined in the EctoType module for a given type still follow Ecto's expectations:

https://github.com/elixir-ecto/ecto/blob/v3.13.5/lib/ecto/type.ex#L294

And to really vet that, we'll want to make sure to test ash_postgres against these changes. A good way to do that will be to clone down ash_postgres, set export ASH_VERSION=local and then run the tests (typically mix test --exclude migration).

[mikaelweiss]

The load/3 and dump/3 functions in the EctoType module (lib/ash/type/type.ex:1731 and lib/ash/type/type.ex:1744) both swallow errors with catch-all clauses, which follows Ecto's expectations:

@impl true
def load(term, _, params) do
  parent = @parent

  case parent.cast_stored(term, params) do
    {:ok, value} ->
      {:ok, value}

    _ ->
      :error
  end
end

@impl true
def dump(term, _dumper, params) do
  parent = @parent

  case parent.dump_to_native(term, params) do
    {:ok, value} ->
      {:ok, value}

    _ ->
      :error
  end
end

I also ran ASH_VERSION=local mix test in ash_postgres (full test suite to be sure) and they passed.

Is there anything else you'd like me to test or check?

[zachdaniel]

Ah, yeah so there is one more major thing to test. What we want to do is set up a resource that works against ETS, manipulate the ETS table to have a value that can't be loaded, and ensure that the error bubbles up in a way that is not exposed to the end user. It will likely need a custom error built to function that way.

Both dump_to_native and cast_stored should produce errors different from InvalidAttribute or InvalidArgument for example.