Don't bust AR query cache when types are not same object

AR's query cache currently depends on the type objects being not only
equivalent but also to be the same object. Either reloading the type
information or using custom type objects that aren't cached will
unnecessarily bust the cache.

This is fixed in 5.0 as an ancillary part of 574f255
but here I also add a test for the condition.

activerecord/CHANGELOG.md

@@ -1,3 +1,9 @@
+*   Fix query caching when type information is reset
+
+    Backports ancillary fix in 5.0.
+
+    *James Coleman*
+
 *   Allow `joins` to be unscoped.
 
     Fixes #13775.

activerecord/lib/active_record/type/value.rb

@@ -86,6 +86,11 @@ def ==(other)
           scale == other.scale &&
           limit == other.limit
       end
+      alias eql? ==
+
+      def hash
+        [self.class, precision, scale, limit].hash
+      end
 
       private
 

activerecord/test/cases/query_cache_test.rb

@@ -243,6 +243,26 @@ def test_query_cache_doesnt_leak_cached_results_of_rolled_back_queries
       assert_equal 0, Post.where(title: 'rollback').to_a.count
     end
   end
+
+  def test_query_cached_even_when_types_are_reset
+    Task.cache do
+      # Warm the cache
+      task = Task.find(1)
+
+      Task.connection.type_map.clear
+
+      # Preload the type cache again (so we don't have those queries issued during our assertions)
+      Task.connection.send(:initialize_type_map, Task.connection.type_map)
+
+      # Clear places where type information is cached
+      Task.reset_column_information
+      Task.find_by_statement_cache.clear
+
+      assert_queries(0) do
+        Task.find(1)
+      end
+    end
+  end
 end
 
 class QueryCacheExpiryTest < ActiveRecord::TestCase