Bug#46086: crash when dropping a partitioned table

and the original engine is disabled

Missing check that engine is available.

mysql-test/include/not_blackhole.inc:
  new include file
mysql-test/r/partition_not_blackhole.result:
  new result file
mysql-test/std_data/parts/t1_blackhole.frm:
  blackhole partitioned table .frm file:
  create table `t1` (`id` int primary key) engine=blackhole
  partition by key () partitions 1;
mysql-test/std_data/parts/t1_blackhole.par:
  .par file matching blackhole partitioned .frm
mysql-test/t/partition_not_blackhole-master.opt:
  new master-opt to disable blackhole if compiled in.
mysql-test/t/partition_not_blackhole.test:
  New test
sql/ha_partition.cc:
  Added check that engine is available.

mysql-test/include/not_blackhole.inc

@@ -0,0 +1,5 @@
+if (`SELECT count(*) FROM information_schema.engines WHERE
+     (support = 'YES' OR support = 'DEFAULT') AND
+     engine = 'blackhole'`){
+  skip Blackhole engine enabled;
+}

mysql-test/r/partition_not_blackhole.result

@@ -0,0 +1,16 @@
+DROP TABLE IF EXISTS t1;
+#
+# Bug#46086: crash when dropping a partitioned table and
+#            the original engine is disabled
+# Copy a .frm and .par file which was created with:
+# create table `t1` (`id` int primary key) engine=blackhole
+# partition by key () partitions 1;
+SHOW TABLES;
+Tables_in_test
+t1
+SHOW CREATE TABLE t1;
+ERROR HY000: Incorrect information in file: './test/t1.frm'
+DROP TABLE t1;
+ERROR 42S02: Unknown table 't1'
+t1.frm
+t1.par

mysql-test/t/partition_not_blackhole-master.opt

@@ -0,0 +1 @@
+--loose-skip-blackhole

mysql-test/t/partition_not_blackhole.test

@@ -0,0 +1,25 @@
+--source include/have_partition.inc
+--source include/not_blackhole.inc
+
+--disable_warnings
+DROP TABLE IF EXISTS t1;
+--enable_warnings
+
+let $MYSQLD_DATADIR= `SELECT @@datadir`;
+
+--echo #
+--echo # Bug#46086: crash when dropping a partitioned table and
+--echo #            the original engine is disabled
+--echo # Copy a .frm and .par file which was created with:
+--echo # create table `t1` (`id` int primary key) engine=blackhole
+--echo # partition by key () partitions 1;
+--copy_file std_data/parts/t1_blackhole.frm $MYSQLD_DATADIR/test/t1.frm
+--copy_file std_data/parts/t1_blackhole.par $MYSQLD_DATADIR/test/t1.par
+SHOW TABLES;
+--error ER_NOT_FORM_FILE
+SHOW CREATE TABLE t1;
+--error ER_BAD_TABLE_ERROR
+DROP TABLE t1;
+--list_files $MYSQLD_DATADIR/test t1*
+--remove_file $MYSQLD_DATADIR/test/t1.frm
+--remove_file $MYSQLD_DATADIR/test/t1.par

sql/ha_partition.cc

@@ -2403,9 +2403,14 @@ bool ha_partition::get_from_handler_file(const char *name, MEM_ROOT *mem_root)
   tot_partition_words= (m_tot_parts + 3) / 4;
   engine_array= (handlerton **) my_alloca(m_tot_parts * sizeof(handlerton*));
   for (i= 0; i < m_tot_parts; i++)
+  {
     engine_array[i]= ha_resolve_by_legacy_type(ha_thd(),
                                                (enum legacy_db_type)
-                                               *(uchar *) ((file_buffer) + 12 + i));
+                                               *(uchar *) ((file_buffer) +
+                                                           12 + i));
+    if (!engine_array[i])
+      goto err3;
+  }
   address_tot_name_len= file_buffer + 12 + 4 * tot_partition_words;
   tot_name_words= (uint4korr(address_tot_name_len) + 3) / 4;
   if (len_words != (tot_partition_words + tot_name_words + 4))