Merge PR #43141

activerecord/CHANGELOG.md

@@ -1,3 +1,8 @@
+*   Add a deprecation warning when `prepared_statements` configuration is not
+    set for the mysql2 adapter.
+
+    *Thiago Araujo and Stefanni Brasil*
+
 *   Fix `QueryMethods#in_order_of` to handle empty order list.
 
     ```ruby

activerecord/lib/active_record/connection_adapters/mysql2_adapter.rb

@@ -56,6 +56,7 @@ module ActiveRecord
       end
 
       def initialize(connection, logger, connection_options, config)
+        check_prepared_statements_deprecation(config)
         superclass_config = config.reverse_merge(prepared_statements: false)
         super(connection, logger, connection_options, superclass_config)
         configure_connection
@@ -140,6 +141,14 @@ module ActiveRecord
       end
 
       private
+        def check_prepared_statements_deprecation(config)
+          if !config.key?(:prepared_statements)
+            ActiveSupport::Deprecation.warn(<<-MSG.squish)
+              The default value of `prepared_statements` for the mysql2 adapter will be changed from +false+ to +true+ in Rails 7.2.
+            MSG
+          end
+        end
+
         def connect
           @connection = self.class.new_client(@config)
           configure_connection

activerecord/test/cases/adapters/mysql2/mysql2_adapter_test.rb

@@ -40,6 +40,38 @@ class Mysql2AdapterTest < ActiveRecord::Mysql2TestCase
     end
   end
 
+  def test_mysql2_prepared_statements_default_deprecation_warning
+    fake_connection = Class.new do
+      def query_options
+        {}
+      end
+
+      def query(*)
+      end
+
+      def close
+      end
+    end.new
+
+    assert_deprecated do
+      ActiveRecord::ConnectionAdapters::Mysql2Adapter.new(
+        fake_connection,
+        ActiveRecord::Base.logger,
+        nil,
+        { socket: File::NULL }
+      )
+    end
+
+    assert_not_deprecated do
+      ActiveRecord::ConnectionAdapters::Mysql2Adapter.new(
+        fake_connection,
+        ActiveRecord::Base.logger,
+        nil,
+        { socket: File::NULL, prepared_statements: false }
+      )
+    end
+  end
+
   def test_exec_query_nothing_raises_with_no_result_queries
     assert_nothing_raised do
       with_example_table do

activerecord/test/config.example.yml

@@ -42,6 +42,8 @@ connections:
       collation: utf8mb4_unicode_ci
 <% if ENV['MYSQL_PREPARED_STATEMENTS'] %>
       prepared_statements: true
+<% else %>
+      prepared_statements: false
 <% end %>
 <% if ENV['MYSQL_HOST'] %>
       host: <%= ENV['MYSQL_HOST'] %>
@@ -55,6 +57,8 @@ connections:
       collation: utf8mb4_general_ci
 <% if ENV['MYSQL_PREPARED_STATEMENTS'] %>
       prepared_statements: true
+<% else %>
+      prepared_statements: false
 <% end %>
 <% if ENV['MYSQL_HOST'] %>
       host: <%= ENV['MYSQL_HOST'] %>