Fixed bug #30126.

When dumping database from a 4.x server, the mysqldump client
inserted a delimiter sign inside special commentaries of the form:
  /*!... CREATE DATABASE IF NOT EXISTS ... ;*/
During restoration that dump file was splitten by delimiter signs on
the client side, and the rest of some commentary strings was prepended
to following statements.

The 4x_server_emul test case option has been added for use with the
DBUG_EXECUTE_IF debugging macro. This option affects debug server
builds only to emulate particular behavior of a 4.x server for
the mysqldump client testing. Non-debugging builds are not affected.

client/mysqldump.c

@@ -2898,7 +2898,7 @@ int init_dumping_tables(char *qdatabase)
       /* Old server version, dump generic CREATE DATABASE */
       if (opt_drop_database)
         fprintf(md_result_file,
-                "\n/*!40000 DROP DATABASE IF EXISTS %s;*/\n",
+                "\n/*!40000 DROP DATABASE IF EXISTS %s*/;\n",
                 qdatabase);
       fprintf(md_result_file,
               "\nCREATE DATABASE /*!32312 IF NOT EXISTS*/ %s;\n",

mysql-test/r/mysqldump-compat.result

+CREATE DATABASE mysqldump_30126;
+USE mysqldump_30126;
+CREATE TABLE t1 (c1 int);
+DROP DATABASE mysqldump_30126;

mysql-test/t/mysqldump-compat.opt

+--loose-debug=d,4x_server_emul

mysql-test/t/mysqldump-compat.test

+# Embedded server doesn't support external clients
+--source include/not_embedded.inc
+
+#
+# Bug #30126: semicolon before closing */ in /*!... CREATE DATABASE ;*/
+#
+
+CREATE DATABASE mysqldump_30126;
+USE mysqldump_30126;
+CREATE TABLE t1 (c1 int);
+--exec $MYSQL_DUMP --add-drop-database mysqldump_30126 > $MYSQLTEST_VARDIR/tmp/bug30126.sql
+--exec $MYSQL mysqldump_30126 < $MYSQLTEST_VARDIR/tmp/bug30126.sql
+DROP DATABASE mysqldump_30126;

sql/sql_parse.cc

@@ -3990,6 +3990,8 @@ mysql_execute_command(THD *thd)
   }
   case SQLCOM_SHOW_CREATE_DB:
   {
+    DBUG_EXECUTE_IF("4x_server_emul",
+                    my_error(ER_UNKNOWN_ERROR, MYF(0)); goto error;);
     if (!strip_sp(lex->name) || check_db_name(lex->name))
     {
       my_error(ER_WRONG_DB_NAME, MYF(0), lex->name);