nixos/mysql: fix service so it works with mysql80 package

nixos/modules/services/databases/mysql.nix

@@ -10,16 +10,8 @@ let
 
   isMariaDB = lib.getName mysql == lib.getName pkgs.mariadb;
 
-  isMysqlAtLeast57 =
-    (lib.getName mysql == lib.getName pkgs.mysql57)
-     && (builtins.compareVersions mysql.version "5.7" >= 0);
-
   mysqldOptions =
     "--user=${cfg.user} --datadir=${cfg.dataDir} --basedir=${mysql}";
-  # For MySQL 5.7+, --insecure creates the root user without password
-  # (earlier versions and MariaDB do this by default).
-  installOptions =
-    "${mysqldOptions} ${lib.optionalString isMysqlAtLeast57 "--insecure"}";
 
   settingsFile = pkgs.writeText "my.cnf" (
     generators.toINI { listsAsDuplicateKeys = true; } cfg.settings +
@@ -366,9 +358,14 @@ in
           pkgs.nettools
         ];
 
-        preStart = ''
+        preStart = if isMariaDB then ''
           if ! test -e ${cfg.dataDir}/mysql; then
-            ${mysql}/bin/mysql_install_db --defaults-file=/etc/my.cnf ${installOptions}
+            ${mysql}/bin/mysql_install_db --defaults-file=/etc/my.cnf ${mysqldOptions}
+            touch /tmp/mysql_init
+          fi
+        '' else ''
+          if ! test -e ${cfg.dataDir}/mysql; then
+            ${mysql}/bin/mysqld --defaults-file=/etc/my.cnf ${mysqldOptions} --initialize-insecure
             touch /tmp/mysql_init
           fi
         '';