Check for non-empty params and return changeset in cast_attachments

[Kuret]

Closes #54

Previously, the documentation stated a default of :invalid for the changeset function (and in extension the cast_attachments function).

def changeset(user, params \\ :invalid) do

The cast_attachments function would then check the params for :invalid and return :invalid, which would get passed to the Ecto.Changeset.cast function as the params argument.

waffle_params =
  case params do
    :invalid ->
      :invalid

[...]

Ecto.Changeset.cast(changeset_or_data, waffle_params, allowed)

Since the improved type checking of Elixir 1.18 this causes a typespec warning, since the Changeset.cast function's signature does not specify :invalid as a valid type for the params.

Solved by checking if the params are a non-empty map and returning a proper Changeset error:

case params do
  params when is_map(params) and map_size(params) > 0 ->
    [...]
    Ecto.Changeset.cast(changeset_or_data, waffle_params, allowed)

  _ ->
    Ecto.Changeset.add_error(
      changeset_or_data,
      :missing_attachment,
      "no attachment(s) given to cast"
    )

[Kuret]

Updated the code, I incorrectly assumed there should always be something in the params to cast, while attachments may as well be optional.

Just returning the changeset as-is if there is nothing to cast now.

[philipgiuliani]

Works & solves the warning for us!

[achempion]

Thanks for the fix!