Fix for bug #22077 "DROP TEMPORARY TABLE fails with wrong error if read_only is set"

Do not issue a 'read-only' error in case of DROP TEMPORARY TABLE on a non-existing temporary table.
Instead produce the correct "Unknown table" error or warning (in cases when the IF EXISTS clause was specified).

To a documentor: the part of the manual describing the 'read_only' system variable should be clarified to state the following:
"When the read_only variable is set to ON, all operations which create/update/drop tables are rejected with the exceptions for:
1. Any operation performed by the replication thread on a slave server
2. Any operation performed by a user that have the SUPER privilege
3. Any operation that creates/updates/drops only temporary tables"

mysql-test/r/read_only.result

@@ -39,6 +39,11 @@ delete t1 from t1,t3 where t1.a=t3.a;
 drop table t1;
 insert into t1 values(1);
 ERROR HY000: The MySQL server is running with the --read-only option so it cannot execute this statement
+drop temporary table ttt;
+ERROR 42S02: Unknown table 'ttt'
+drop temporary table if exists ttt;
+Warnings:
+Note	1051	Unknown table 'ttt'
 drop table t1,t2;
 drop user test@localhost;
 set global read_only=0;

mysql-test/t/read_only.test

@@ -101,6 +101,18 @@ drop table t1;
 --error 1290
 insert into t1 values(1);
 
+#
+# BUG #22077 "DROP TEMPORARY TABLE fails with wrong error if read_only is set"
+#
+# check if DROP TEMPORARY on a non-existing temporary table returns the right
+# error
+
+--error ER_BAD_TABLE_ERROR
+drop temporary table ttt;
+
+# check if DROP TEMPORARY TABLE IF EXISTS produces a warning with read_only set
+drop temporary table if exists ttt;
+
 connection default;
 drop table t1,t2;
 drop user test@localhost;

sql/sql_parse.cc

@@ -2519,6 +2519,7 @@ mysql_execute_command(THD *thd)
         uc_update_queries[lex->sql_command] &&
         !((lex->sql_command == SQLCOM_CREATE_TABLE) &&
           (lex->create_info.options & HA_LEX_CREATE_TMP_TABLE)) &&
+        !((lex->sql_command == SQLCOM_DROP_TABLE) && lex->drop_temporary) &&
         ((lex->sql_command != SQLCOM_UPDATE_MULTI) &&
           some_non_temp_table_to_be_updated(thd, all_tables)))
     {