add support for legacy deserialization

Mongoid specs, for instance, rely on BSON::Binary defining only two
instance variables, and build testing data around that assumption.

lib/bson/binary.rb

@@ -147,7 +147,17 @@ def as_extended_json(**options)
     #
     # @since 2.0.0
     def initialize(data = '', type = :generic)
-      @type = validate_type!(type)
+      init_with('data' => data, 'type' => type)
+    end
+
+    # For legacy deserialization support where BSON::Binary objects are
+    # expected to have a specific internal representation (with only
+    # @type and @data instance variables).
+    #
+    # @api private
+    def init_with(coder)
+      @type = validate_type!(coder['type'])
+      data = coder['data']
 
       # The Binary class used to force encoding to BINARY when serializing to
       # BSON. Instead of doing that during serialization, perform this

spec/bson/binary_spec.rb

@@ -82,7 +82,7 @@
       end
     end
 
-    context "when he type is invalid" do
+    context "when the type is invalid" do
 
       it "raises an error" do
         expect {
@@ -93,6 +93,15 @@
         }
       end
     end
+
+    context 'when initialized via legacy YAML' do
+      let(:yaml) { "--- !ruby/object:BSON::Binary\ndata: hello\ntype: :generic\n" }
+      let(:deserialized) { YAML.safe_load(yaml, permitted_classes: [ Symbol, BSON::Binary ]) }
+
+      it 'correctly sets the raw_type' do
+        expect(deserialized.raw_type).to be == BSON::Binary::SUBTYPES[:generic]
+      end
+    end
   end
 
   describe '#inspect' do