MDEV-34539 Invalid "use" and "Schema" in slow query log file with multi-line schema

quote a database name in the slow log

mysql-test/main/log_slow.result

@@ -181,6 +181,30 @@ SET @@global.slow_query_log= @old_slow_query_log;
 SET SESSION slow_query_log=default;
 drop table tab_MDEV_30820, tab2;
 drop function get_zero;
-#
 # End of 10.4 tests
 #
+# MDEV-34539 Invalid "use" and "Schema" in slow query log file with multi-line schema
+#
+set global log_output='file';
+set @@log_slow_filter= 'not_using_index';
+set slow_query_log=1;
+set timestamp=1234567890;
+create database `a
+b`;
+use `a
+b`;
+select count(*) from mysql.global_priv where length(priv)>2;
+count(*)
+5
+drop database `a
+b`;
+use test;
+set global log_output= @old_log_output;
+set slow_query_log=default;
+set log_slow_filter=default;
+set timestamp=default;
+use `a
+b`;
+SET timestamp=1234567890;
+select count(*) from mysql.global_priv where length(priv)>2
+# End of 10.5 tests

mysql-test/main/log_slow.test

@@ -186,6 +186,33 @@ drop function get_zero;
 --enable_ps2_protocol
 --enable_view_protocol
 
---echo #
 --echo # End of 10.4 tests
+
 --echo #
+--echo # MDEV-34539 Invalid "use" and "Schema" in slow query log file with multi-line schema
+--echo #
+set global log_output='file';
+set @@log_slow_filter= 'not_using_index';
+set slow_query_log=1;
+set timestamp=1234567890;
+create database `a
+b`;
+use `a
+b`;
+--disable_ps_protocol
+select count(*) from mysql.global_priv where length(priv)>2;
+--enable_ps_protocol
+drop database `a
+b`;
+use test;
+set global log_output= @old_log_output;
+set slow_query_log=default;
+set log_slow_filter=default;
+set timestamp=default;
+
+let SEARCH_FILE=`select @@slow_query_log_file`;
+let SEARCH_PATTERN=use.*2;
+let SEARCH_OUTPUT=matches;
+source include/search_pattern_in_file.inc;
+
+--echo # End of 10.5 tests

sql/log.cc

@@ -3324,7 +3324,7 @@ bool MYSQL_QUERY_LOG::write(THD *thd, time_t current_time,
     }
     if (thd->db.str && strcmp(thd->db.str, db))
     {						// Database changed
-      if (my_b_printf(&log_file,"use %s;\n",thd->db.str))
+      if (my_b_printf(&log_file,"use %`s;\n",thd->db.str))
         goto err;
       strmov(db,thd->db.str);
     }