Fail faster when defining invalidly nested defaults

[tfausak]

For array and hash filters, it's invalid to set defaults on nested attributes. However, we don't catch that error until you call run. As noted in the specs, we should raise an error when the class is defined.

For instance, this code should raise an ArgumentError:

class InvalidInteraction < ActiveInteraction::Base
  array :a do
    array default: []
  end
end

As it is, you'd have to call InvalidInteraction.run(a: []) to get that to fail.

[tfausak]

For what it's worth, Mutations allows nested defaults. As far as I can tell, they don't do anything on arrays:

class ArrayMutation < Mutations::Command
  optional { array :a do; array default: [] end }
  def execute; a end
end
p ArrayMutation.run!
# => nil

Default nested hashes get merged with the input, like you'd expect:

class HashMutation < Mutations::Command
  required do
    hash :h do
      hash :x, default: { b: false } do
        boolean :b
      end
    end
  end
  def execute; h end
end
p HashMutation.run!(h: {})
# => {"x"=>{"b"=>false}}
p HashMutation.run!(h: { x: { b: true } })
# => {"x"=>{"b"=>true}}

I know I argued against defaults in nested blocks before, but I guess I'm not that opposed to them. I can see how they make sense.

[tfausak]

• Nested defaults arrays should be silently ignored instead of throwing an error.
• Hashes should permit nested defaults. They should be merged with the user-supplied input.