From 9e25e0e1735f2ccca69679243aa8cf0885104164 Mon Sep 17 00:00:00 2001
From: Sean Griffin <sean@seantheprogrammer.com>
Date: Tue, 6 Oct 2015 08:51:14 -0600
Subject: [PATCH] Implement equality comparison on `AttributeSet` and friends

Any gems or libraries which do work with serialization or YAML will
ultimately need to compare these objects (albeit indirectly) to ensure
correctness. These will likely never get used internally (as they're
slow), but we should still expose them for others.
---
 .../lib/active_record/attribute_set.rb        |  4 +++
 .../active_record/attribute_set/builder.rb    | 30 ++++++++++++-------
 activerecord/test/cases/attribute_set_test.rb | 10 +++++++
 3 files changed, 33 insertions(+), 11 deletions(-)

diff --git a/activerecord/lib/active_record/attribute_set.rb b/activerecord/lib/active_record/attribute_set.rb
index 026b3cf014..be581ac2a9 100644
--- a/activerecord/lib/active_record/attribute_set.rb
+++ b/activerecord/lib/active_record/attribute_set.rb
@@ -91,6 +91,10 @@ module ActiveRecord
       AttributeSet.new(new_attributes)
     end
 
+    def ==(other)
+      attributes == other.attributes
+    end
+
     protected
 
     attr_reader :attributes
diff --git a/activerecord/lib/active_record/attribute_set/builder.rb b/activerecord/lib/active_record/attribute_set/builder.rb
index f974b7a876..3bd7c7997b 100644
--- a/activerecord/lib/active_record/attribute_set/builder.rb
+++ b/activerecord/lib/active_record/attribute_set/builder.rb
@@ -68,10 +68,29 @@ module ActiveRecord
       end
     end
 
+    def ==(other)
+      if other.is_a?(LazyAttributeHash)
+        materialize == other.materialize
+      else
+        materialize == other
+      end
+    end
+
     protected
 
     attr_reader :types, :values, :additional_types, :delegate_hash
 
+    def materialize
+      unless @materialized
+        values.each_key { |key| self[key] }
+        types.each_key { |key| self[key] }
+        unless frozen?
+          @materialized = true
+        end
+      end
+      delegate_hash
+    end
+
     private
 
     def assign_default_value(name)
@@ -85,16 +104,5 @@ module ActiveRecord
         delegate_hash[name] = Attribute.uninitialized(name, type)
       end
     end
-
-    def materialize
-      unless @materialized
-        values.each_key { |key| self[key] }
-        types.each_key { |key| self[key] }
-        unless frozen?
-          @materialized = true
-        end
-      end
-      delegate_hash
-    end
   end
 end
diff --git a/activerecord/test/cases/attribute_set_test.rb b/activerecord/test/cases/attribute_set_test.rb
index 5a0e463a48..7a24b85a36 100644
--- a/activerecord/test/cases/attribute_set_test.rb
+++ b/activerecord/test/cases/attribute_set_test.rb
@@ -239,5 +239,15 @@ module ActiveRecord
       assert_equal 2, new_attributes.fetch_value(:foo)
       assert_equal 3, new_attributes.fetch_value(:bar)
     end
+
+    test "comparison for equality is correctly implemented" do
+      builder = AttributeSet::Builder.new(foo: Type::Integer.new, bar: Type::Integer.new)
+      attributes = builder.build_from_database(foo: "1", bar: "2")
+      attributes2 = builder.build_from_database(foo: "1", bar: "2")
+      attributes3 = builder.build_from_database(foo: "2", bar: "2")
+
+      assert_equal attributes, attributes2
+      assert_not_equal attributes2, attributes3
+    end
   end
 end