RUBY-3533 Make BSON::Binary objects comparable

The comparison is only meaningful if the two objects have the
same Binary type, as well.

lib/bson/binary.rb

@@ -24,6 +24,7 @@ module BSON
   # @since 2.0.0
   class Binary
     include JSON
+    include Comparable
 
     # A binary is type 0x05 in the BSON spec.
     #
@@ -90,6 +91,20 @@ def ==(other)
     end
     alias eql? ==
 
+    # Compare this binary object to another object. The two objects must have
+    # the same type for any meaningful comparison.
+    #
+    # @param [ Object ] other The object to compare against.
+    # 
+    # @return [ Integer | nil ] If the objects have the same type, the result
+    #   is -1 if self < other, 0 if self == other, and 1 if self > other. If
+    #   other is not a Binary, or is a Binary of a different type, returns nil.
+    def <=>(other)
+      return nil unless other.is_a?(Binary) && type == other.type
+
+      data <=> other.data
+    end
+
     # Generates a Fixnum hash value for this object.
     #
     # Allows using Binary as hash keys.

spec/bson/binary_spec.rb

@@ -20,17 +20,56 @@
   let(:testing1)  { described_class.new("testing") }
   let(:testing2)  { described_class.new("testing") }
   let(:not_testing) { described_class.new("not testing") }
+  let(:testing3) { described_class.new("testing", :user) }
 
-  describe "#eql?" do
-    context "for two equal objects" do
-      it "returns true" do
-        expect(testing1).to eql(testing2)
+  describe "Comparable" do
+    describe "#eql?" do
+      context "for two equal objects" do
+        it "returns true" do
+          expect(testing1).to eql(testing2)
+        end
+      end
+
+      context "for two different objects" do
+        it "returns false" do
+          expect(testing1).not_to eql(not_testing)
+        end
+      end
+
+      context 'for objects with identical data but different types' do
+        it 'returns false' do
+          expect(testing1).not_to eql(testing3)
+        end
       end
     end
 
-    context "for two different objects" do
-      it "returns false" do
-        expect(testing1).not_to eql(not_testing)
+    describe '#<=>' do
+      context 'with a non-Binary object' do
+        it 'returns nil' do
+          expect(testing1 <=> 'bogus').to be_nil
+        end
+      end
+
+      context 'with identical type and data' do
+        it 'returns 0' do
+          expect(testing1 <=> testing2).to be == 0
+        end
+      end
+
+      context 'with mismatched type' do
+        it 'returns nil' do
+          expect(testing1 <=> testing3).to be_nil
+        end
+      end
+
+      context 'with identical type but mismatched data' do
+        it 'returns -1 when a < b' do
+          expect(not_testing <=> testing1).to be == -1
+        end
+
+        it 'returns 1 when a > b' do
+          expect(testing1 <=> not_testing).to be == 1
+        end
       end
     end
   end