Addressed an issue serializing structure request params.

Resolved an issue where structure parameter values, such as those
returned in responses, could not be serialized as input parameters
when parameter conversion is disabled.

This fix resolves the issue by changing the serializes to all enumerate
structure/hash values in a consistent manor, using #each_pair. Also
added a few minor helpers to `Aws::Structure` making it quack more
like a Hash object.

Fixes #815

aws-sdk-core/lib/aws-sdk-core/json/builder.rb

@@ -18,7 +18,7 @@ def to_json(params)
 
       def structure(ref, values)
         shape = ref.shape
-        values.each.with_object({}) do |(key, value), data|
+        values.each_pair.with_object({}) do |(key, value), data|
           if shape.member?(key) && !value.nil?
             member_ref = shape.member(key)
             member_name = member_ref.location_name || key

aws-sdk-core/lib/aws-sdk-core/query/param_builder.rb

@@ -20,7 +20,7 @@ def apply(ref, params)
 
       def structure(ref, values, prefix)
         shape = ref.shape
-        values.each do |name, value|
+        values.each_pair do |name, value|
           next if value.nil?
           member_ref = shape.member(name)
           format(member_ref, value, prefix + query_name(member_ref))

aws-sdk-core/lib/aws-sdk-core/structure.rb

@@ -8,6 +8,17 @@ class Structure < Struct
       alias orig_to_h to_h
     end
 
+    # @return [Boolean] Returns `true` if this structure has a value
+    #   set for the given member.
+    def key?(member_name)
+      !self[member_name].nil?
+    end
+
+    # @return [Boolean] Returns `true` if all of the member values are `nil`.
+    def empty?
+      values.compact == []
+    end
+
     # Deeply converts the Structure into a hash.  Structure members that
     # are `nil` are omitted from the resultant hash.
     #

aws-sdk-core/spec/aws/json/builder_spec.rb

@@ -6,16 +6,26 @@ module Json
 
       let(:shapes) { ApiHelper.sample_shapes }
 
+      let(:rules) {
+        Api::ShapeMap.new(shapes).shape_ref('shape' => 'StructureShape')
+      }
+
       def json(params)
-        shape_map = Api::ShapeMap.new(shapes)
-        rules = shape_map.shape_ref('shape' => 'StructureShape')
         Builder.new(rules).to_json(params)
       end
 
       it 'builds an empty JOSN document when there are no params' do
         expect(json({})).to eq('{}')
       end
 
+      it 'can serialize structures' do
+        params = Structure.new(*rules.shape.member_names).new
+        params.boolean = true
+        params.integer = 123
+        params.string = 'abc'
+        expect(json(params)).to eq('{"Boolean":true,"Integer":123,"String":"abc"}')
+      end
+
       it 'supports locationName traits on structure members' do
         shapes['StructureShape']['members']['String']['locationName'] = 'str'
         expect(json(string: 'abc')).to eq('{"str":"abc"}')

aws-sdk-core/spec/aws/query/param_builder_spec.rb

@@ -6,9 +6,12 @@ module Query
 
       let(:shapes) { ApiHelper.sample_shapes }
 
-      def query(params = {})
+      let(:rules) {
         shape_map = Api::ShapeMap.new(shapes)
-        rules = shape_map.shape_ref('shape' => 'StructureShape')
+        shape_map.shape_ref('shape' => 'StructureShape')
+      }
+
+      def query(params = {})
         param_list = ParamList.new
         ParamBuilder.new(param_list).apply(rules, params)
         param_list.map { |param| [param.name, param.value ] }.sort
@@ -18,6 +21,18 @@ def query(params = {})
         expect(query({})).to eq([])
       end
 
+      it 'can serialize structures' do
+        params = Structure.new(*rules.shape.member_names).new
+        params.boolean = true
+        params.integer = 123
+        params.string = 'abc'
+        expect(query(params)).to eq([
+          ['Boolean', 'true'],
+          ['Integer', '123'],
+          ['String', 'abc'],
+        ])
+      end
+
       it 'does not serialize nil values' do
         params = {
           string: 'abc',

aws-sdk-core/spec/aws/xml/builder_spec.rb

@@ -8,16 +8,30 @@ module Xml
 
       let(:ref) {{ 'shape' => 'StructureShape', 'locationName' => 'xml' }}
 
+      let(:rules) { Api::ShapeMap.new(shapes).shape_ref(ref) }
+
       def xml(params)
-        shape_map = Api::ShapeMap.new(shapes)
-        rules = shape_map.shape_ref(ref)
         Builder.new(rules).to_xml(params)
       end
 
       it 'serializes empty values as empty elements' do
         expect(xml({})).to eq("<xml/>\n")
       end
 
+      it 'can serialize structures' do
+        params = Structure.new(*rules.shape.member_names).new
+        params.boolean = true
+        params.integer = 123
+        params.string = 'abc'
+        expect(xml(params)).to eq(<<-XML)
+<xml>
+  <Boolean>true</Boolean>
+  <Integer>123</Integer>
+  <String>abc</String>
+</xml>
+        XML
+      end
+
       it 'orders xml elements by members order' do
         params = {
           string: 'a',