Stringify variables names for mysql connections

For mysql2/mysql adapters, `sql_mode` variable name set in `database.yml`
as string, was ignored and `sql_mode` was set to use strict mode.

Fixes #14895

activerecord/CHANGELOG.md

@@ -1,3 +1,12 @@
+*   Stringify all variables keys of mysql connection configuration.
+
+    When `sql_mode` variable for mysql adapters set in configuration as `String`
+    was ignored and overwritten by strict mode option.
+
+    Fixes #14895
+
+    *Paul Nikitochkin*
+
 *   When using a custom `join_table` name on a `habtm`, rails was not saving it
     on Reflections. This causes a problem when rails loads fixtures, because it
     uses the reflections to set database with fixtures.

activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb

@@ -765,22 +765,22 @@ def column_for(table_name, column_name)
       end
 
       def configure_connection
-        variables = @config[:variables] || {}
+        variables = @config.fetch(:variables, {}).stringify_keys
 
         # By default, MySQL 'where id is null' selects the last inserted id.
         # Turn this off. http://dev.rubyonrails.org/ticket/6778
-        variables[:sql_auto_is_null] = 0
+        variables['sql_auto_is_null'] = 0
 
         # Increase timeout so the server doesn't disconnect us.
         wait_timeout = @config[:wait_timeout]
         wait_timeout = 2147483 unless wait_timeout.is_a?(Fixnum)
-        variables[:wait_timeout] = self.class.type_cast_config_to_integer(wait_timeout)
+        variables['wait_timeout'] = self.class.type_cast_config_to_integer(wait_timeout)
 
         # Make MySQL reject illegal values rather than truncating or blanking them, see
         # http://dev.mysql.com/doc/refman/5.0/en/server-sql-mode.html#sqlmode_strict_all_tables
         # If the user has provided another value for sql_mode, don't replace it.
-        if strict_mode? && !variables.has_key?(:sql_mode)
-          variables[:sql_mode] = 'STRICT_ALL_TABLES'
+        if strict_mode? && !variables.has_key?('sql_mode')
+          variables['sql_mode'] = 'STRICT_ALL_TABLES'
         end
 
         # NAMES does not have an equals sign, see

activerecord/test/cases/adapters/mysql/connection_test.rb

@@ -151,6 +151,14 @@ def test_mysql_set_session_variable
     end
   end
 
+  def test_mysql_sql_mode_variable_overides_strict_mode
+    run_without_connection do |orig_connection|
+      ActiveRecord::Base.establish_connection(orig_connection.deep_merge(variables: { 'sql_mode' => 'ansi' }))
+      result = ActiveRecord::Base.connection.exec_query 'SELECT @@SESSION.sql_mode'
+      assert_not_equal [['STRICT_ALL_TABLES']], result.rows
+    end
+  end
+
   def test_mysql_set_session_variable_to_default
     run_without_connection do |orig_connection|
       ActiveRecord::Base.establish_connection(orig_connection.deep_merge({:variables => {:default_week_format => :default}}))

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

@@ -77,6 +77,14 @@ def test_mysql_set_session_variable
     end
   end
 
+  def test_mysql_sql_mode_variable_overides_strict_mode
+    run_without_connection do |orig_connection|
+      ActiveRecord::Base.establish_connection(orig_connection.deep_merge(variables: { 'sql_mode' => 'ansi' }))
+      result = ActiveRecord::Base.connection.exec_query 'SELECT @@SESSION.sql_mode'
+      assert_not_equal [['STRICT_ALL_TABLES']], result.rows
+    end
+  end
+
   def test_mysql_set_session_variable_to_default
     run_without_connection do |orig_connection|
       ActiveRecord::Base.establish_connection(orig_connection.deep_merge({:variables => {:default_week_format => :default}}))