Ensure all properties are set on exported Dash

When exporting a Dash via `#to_h` or `#to_hash`, we expect all
properties to be exported whether or not they are set. However, in the
change that allows codependent properties to be nilified, we regressed
the behavior of exporting all properties.

There is a gotcha here, which I note in the tests for the specs. For
posterity, MRI does not send the `#to_hash` method to anything that
subclasses `Hash` when you double-splat it. Thus, we cannot override the
behavior within MRI. For more information, see [this comment][1] where I
detail the behavior of double-splat within MRI.

Currently, JRuby also follows this behavior, but it's not guaranteed
that other Rubies will.

[1]: https://github.com/hashie/hashie/issues/353#issuecomment-363294886

1 files changed, 76 insertions, 0 deletions

diff --git a/spec/hashie/dash_spec.rb b/spec/hashie/dash_spec.rb
index c64e400..e75ad1a 100644
--- a/spec/hashie/dash_spec.rb
+++ b/spec/hashie/dash_spec.rb
@@ -416,6 +416,7 @@ describe DashTest do
         Class.new(Hashie::Dash) do
           property :a, required: -> { b.nil? }, message: 'is required if b is not set.'
           property :b, required: -> { a.nil? }, message: 'is required if a is not set.'
+          property :c, default: -> { 'c' }
         end
       end
 
@@ -434,6 +435,44 @@ describe DashTest do
       it 'raises an error when neither property is set' do
         expect { codependent.new(a: nil, b: nil) }.to raise_error(ArgumentError)
       end
+
+      context 'exporting nil values' do
+        describe '#to_h' do
+          it 'does not prune nil values' do
+            expect(codependent.new(a: 'hi', b: nil).to_h).to eq(a: 'hi', b: nil, c: 'c')
+            expect(codependent.new(a: 'hi', b: nil, c: nil).to_hash).to eq(a: 'hi', b: nil, c: 'c')
+            expect(codependent.new(a: 'hi', b: nil).merge(c: nil).to_h).to(
+              eq(a: 'hi', b: nil, c: nil)
+            )
+          end
+        end
+
+        describe '#to_hash' do
+          it 'does not prune nil values' do
+            expect(codependent.new(a: 'hi', b: nil).to_hash).to eq(a: 'hi', b: nil, c: 'c')
+            expect(codependent.new(a: 'hi', b: nil, c: nil).to_hash).to eq(a: 'hi', b: nil, c: 'c')
+            expect(codependent.new(a: 'hi', b: nil).merge(c: nil).to_hash).to(
+              eq(a: 'hi', b: nil, c: nil)
+            )
+          end
+        end
+
+        describe '**' do
+          # Note: This test is an implementation detail of MRI and may not hold for
+          # other Ruby interpreters. But it's important to note in the test suite
+          # because it can be surprising for people unfamiliar with the semantics of
+          # double-splatting.
+          #
+          # For more information, see [this link][1]:
+          #
+          # [1]: https://github.com/hashie/hashie/issues/353#issuecomment-363294886
+          it 'prunes nil values because they are not set in the dash' do
+            dash = codependent.new(a: 'hi', b: nil)
+
+            expect(**dash).to eq(a: 'hi', c: 'c')
+          end
+        end
+      end
     end
   end
 end
@@ -482,6 +521,43 @@ describe Hashie::Dash, 'inheritance' do
     expect(@bottom.new).to have_key(:echo)
     expect(@bottom.new).to_not have_key('echo')
   end
+
+  context 'exporting nil values' do
+    let(:test) do
+      Class.new(Hashie::Dash) do
+        property :foo
+        property :bar
+      end
+    end
+
+    describe '#to_h' do
+      it 'does not prune nil values' do
+        expect(test.new(foo: 'hi', bar: nil).to_h).to eq(foo: 'hi', bar: nil)
+      end
+    end
+
+    describe '#to_hash' do
+      it 'does not prune nil values' do
+        expect(test.new(foo: 'hi', bar: nil).to_hash).to eq(foo: 'hi', bar: nil)
+      end
+    end
+
+    describe '**' do
+      # Note: This test is an implementation detail of MRI and may not hold for
+      # other Ruby interpreters. But it's important to note in the test suite
+      # because it can be surprising for people unfamiliar with the semantics of
+      # double-splatting.
+      #
+      # For more information, see [this link][1]:
+      #
+      # [1]: https://github.com/hashie/hashie/issues/353#issuecomment-363294886
+      it 'prunes nil values because they are not set in the dash' do
+        dash = test.new(foo: 'hi', bar: nil)
+
+        expect(**dash).to eq(foo: 'hi')
+      end
+    end
+  end
 end
 
 describe SubclassedTest do