MDEV-31014 Database privileges are insufficient for CONVERT TABLE TO PARTITION

check_access() updates ACL of first TABLE_LIST (t1), but not second
(tp). After it is done we copy t1 ACL to tp.

mysql-test/suite/parts/r/alter_table.result

@@ -344,3 +344,17 @@ connection default;
 drop database EXISTENT;
 drop user alan;
 drop tables t1, tp1, tp2, tp4;
+#
+# MDEV-31014 Database privileges are insufficient for CONVERT TABLE TO PARTITION
+#
+create database db;
+create user u@localhost;
+grant all on db.* to u@localhost;
+connect  con1,localhost,u,,db;
+create table t1 (a int) partition by range(a) (p1 values less than (100), p2 values less than (1000));
+alter table t1 convert partition p2 to table tp;
+alter table t1 convert table tp to partition p2 values less than (1000);
+disconnect con1;
+connection default;
+drop user u@localhost;
+drop database db;

mysql-test/suite/parts/t/alter_table.test

@@ -301,3 +301,21 @@ alter table t1 convert partition p1 to table tp1;
 drop database EXISTENT;
 drop user alan;
 drop tables t1, tp1, tp2, tp4;
+
+--echo #
+--echo # MDEV-31014 Database privileges are insufficient for CONVERT TABLE TO PARTITION
+--echo #
+create database db;
+create user u@localhost;
+grant all on db.* to u@localhost;
+
+--connect (con1,localhost,u,,db)
+create table t1 (a int) partition by range(a) (p1 values less than (100), p2 values less than (1000));
+alter table t1 convert partition p2 to table tp;
+alter table t1 convert table tp to partition p2 values less than (1000);
+
+# Cleanup
+--disconnect con1
+--connection default
+drop user u@localhost;
+drop database db;

sql/sql_alter.cc

@@ -493,6 +493,14 @@ bool Sql_cmd_alter_table::execute(THD *thd)
                    0, 0))
     DBUG_RETURN(TRUE);                  /* purecov: inspected */
 
+  if ((alter_info.partition_flags & ALTER_PARTITION_CONVERT_IN))
+  {
+    TABLE_LIST *tl= first_table->next_local;
+    tl->grant.privilege= first_table->grant.privilege;
+    tl->grant.m_internal= first_table->grant.m_internal;
+  }
+
+
   /* If it is a merge table, check privileges for merge children. */
   if (create_info.merge_list)
   {