Allow codependent Dash attributes to initialize

Definition: Codependent properties
A set of two or more properties who have "required" validations that are based
on each other.

Example:

```ruby
class OneOrMore < Hashie::Dash
  property :a, required: -> { b.nil? }
  property :b, required: -> { a.nil? }
end
```

When constructing a Dash via the merge initializer, codependent properties have
their "required" validation run too early when their values are set to `nil`,
which causes an `ArgumentError` to be raised in the case that the first property
is set to `nil`.

This is an order-dependence bug that is fixed by this commit. By pruning off
`nil` values only during initialization via the merge initializer, we can
prevent this problem from occurring for the case of `nil` values.

However, this is an indication of a larger problem with the architecture of
Dash. We should be setting all the properties before running the validations.
Rearchitecting this will be quite an undertaking.

1 files changed, 11 insertions, 2 deletions

diff --git a/lib/hashie/dash.rb b/lib/hashie/dash.rb
index 4ac7676..a111e4b 100644
--- a/lib/hashie/dash.rb
+++ b/lib/hashie/dash.rb
@@ -160,7 +160,7 @@ module Hashie
     end
 
     def update_attributes!(attributes)
-      initialize_attributes(attributes)
+      update_attributes(attributes)
 
       self.class.defaults.each_pair do |prop, value|
         self[prop] = begin
@@ -175,9 +175,18 @@ module Hashie
     private
 
     def initialize_attributes(attributes)
+      return unless attributes
+
+      cleaned_attributes = attributes.reject { |_attr, value| value.nil? }
+      update_attributes(cleaned_attributes)
+    end
+
+    def update_attributes(attributes)
+      return unless attributes
+
       attributes.each_pair do |att, value|
         self[att] = value
-      end if attributes
+      end
     end
 
     def assert_property_exists!(property)