nixos/mysql: turn ExecStartPost into a shell script and simplify code

nixos/modules/services/databases/mysql.nix

@@ -317,11 +317,10 @@ in
           RuntimeDirectoryMode = "0755";
           # The last two environment variables are used for starting Galera clusters
           ExecStart = "${mysql}/bin/mysqld --defaults-file=/etc/my.cnf ${mysqldOptions} $_WSREP_NEW_CLUSTER $_WSREP_START_POSITION";
-        };
-
-        postStart =
+          ExecStartPost =
             let
-            cmdWatchForMysqlSocket = ''
+              setupScript = pkgs.writeShellScript "mysql-setup" ''
+                ${optionalString (!hasNotify) ''
                   # Wait until the MySQL server is available for use
                   count=0
                   while [ ! -e /run/mysqld/mysqld.sock ]
@@ -336,8 +335,11 @@ in
                       count=$((count++))
                       sleep 1
                   done
-            '';
-            cmdInitialDatabases = concatMapStrings (database: ''
+                ''}
+
+                if [ -f /tmp/mysql_init ]
+                then
+                    ${concatMapStrings (database: ''
                       # Create initial databases
                       if ! test -e "${cfg.dataDir}/${database.name}"; then
                           echo "Creating initial database: ${database.name}"
@@ -358,13 +360,8 @@ in
                             ''}
                           ) | ${mysql}/bin/mysql -u root -N
                       fi
-            '') cfg.initialDatabases;
-          in
+                    '') cfg.initialDatabases}
 
-          lib.optionalString (!hasNotify) cmdWatchForMysqlSocket + ''
-            if [ -f /tmp/mysql_init ]
-            then
-                ${cmdInitialDatabases}
                     ${optionalString (cfg.replication.role == "master")
                       ''
                         # Set up the replication master
@@ -413,8 +410,10 @@ in
                       '') user.ensurePermissions)}
                     ) | ${mysql}/bin/mysql -u root -N
                   '') cfg.ensureUsers}
-
-          ''; # */
+              '';
+            in
+              setupScript;
+        };
       };
 
   };