`rake db:create` does not change permissions of root user.

Closes #8079.

I had to rework some of the tests because the mock allowed any arguments
for `connection.exeucte`. I think this is very dangerous as there could
anything be executed without the tests noticing it.

activerecord/CHANGELOG.md

 ## Rails 4.0.0 (unreleased) ##
 
+*   `rake db:create` does not change permissions of the MySQL root user.
+    Fixes #8079.
+
+    *Yves Senn*
+
 *   The length of the `version` column in the `schema_migrations` table
     created by the `mysql2` adapter is 191 if the encoding is "utf8mb4".
 

activerecord/lib/active_record/tasks/mysql_database_tasks.rb

@@ -26,7 +26,9 @@ def create
           $stdout.print error.error
           establish_connection root_configuration_without_database
           connection.create_database configuration['database'], creation_options
-          connection.execute grant_statement.gsub(/\s+/, ' ').strip
+          if configuration['username'] != 'root'
+            connection.execute grant_statement.gsub(/\s+/, ' ').strip
+          end
           establish_connection configuration
         else
           $stderr.puts "Couldn't create database for #{configuration.inspect}, #{creation_options.inspect}"

activerecord/test/cases/tasks/mysql_rake_test.rb

@@ -71,7 +71,7 @@ def setup
         return skip("only tested on mysql")
       end
 
-      @connection    = stub(:create_database => true, :execute => true)
+      @connection    = stub("Connection", create_database: true)
       @error         = Mysql::Error.new "Invalid permissions"
       @configuration = {
         'adapter'  => 'mysql',
@@ -90,6 +90,7 @@ def setup
     end
 
     def test_root_password_is_requested
+      assert_permissions_granted_for "pat"
       skip "only if mysql is available" unless defined?(::Mysql)
       $stdin.expects(:gets).returns("secret\n")
 
@@ -97,6 +98,7 @@ def test_root_password_is_requested
     end
 
     def test_connection_established_as_root
+      assert_permissions_granted_for "pat"
       ActiveRecord::Base.expects(:establish_connection).with(
         'adapter'  => 'mysql',
         'database' => nil,
@@ -108,6 +110,7 @@ def test_connection_established_as_root
     end
 
     def test_database_created_by_root
+      assert_permissions_granted_for "pat"
       @connection.expects(:create_database).
         with('my-app-db', :charset => 'utf8', :collation => 'utf8_unicode_ci')
 
@@ -115,12 +118,18 @@ def test_database_created_by_root
     end
 
     def test_grant_privileges_for_normal_user
-      @connection.expects(:execute).with("GRANT ALL PRIVILEGES ON my-app-db.* TO 'pat'@'localhost' IDENTIFIED BY 'wossname' WITH GRANT OPTION;")
+      assert_permissions_granted_for "pat"
+      ActiveRecord::Tasks::DatabaseTasks.create @configuration
+    end
 
+    def test_do_not_grant_privileges_for_root_user
+      @configuration['username'] = 'root'
+      @configuration['password'] = ''
       ActiveRecord::Tasks::DatabaseTasks.create @configuration
     end
 
     def test_connection_established_as_normal_user
+      assert_permissions_granted_for "pat"
       ActiveRecord::Base.expects(:establish_connection).returns do
         ActiveRecord::Base.expects(:establish_connection).with(
           'adapter'  => 'mysql',
@@ -142,6 +151,13 @@ def test_sends_output_to_stderr_when_other_errors
 
       ActiveRecord::Tasks::DatabaseTasks.create @configuration
     end
+
+    private
+      def assert_permissions_granted_for(db_user)
+        db_name = @configuration['database']
+        db_password = @configuration['password']
+        @connection.expects(:execute).with("GRANT ALL PRIVILEGES ON #{db_name}.* TO '#{db_user}'@'localhost' IDENTIFIED BY '#{db_password}' WITH GRANT OPTION;")
+      end
   end
 
   class MySQLDBDropTest < ActiveRecord::TestCase