MDEV-31475 Spider: only reset wide_handler when owning it

A wide_handler is shared among ha_spider of partitions of the same
spider table, where the last partition is designated the owner of the
wide_handler, and is responsible for its deallocation. Therefore in
case of failure, we only reset wide_handler in error handling if the
current ha_spider is the owner of the wide_handler, otherwise it will
result in segv in the destructor of ha_spider, or during
ha_spider::close().

storage/spider/ha_spider.cc

@@ -614,7 +614,8 @@ int ha_spider::open(
     owner->wide_handler = NULL;
     owner->wide_handler_owner = FALSE;
   }
-  wide_handler = NULL;
+  if (!wide_handler_owner)
+    wide_handler = NULL;
 error_wide_handler_alloc:
   DBUG_RETURN(error_num);
 }

storage/spider/ha_spider.h

@@ -94,6 +94,7 @@ class ha_spider final : public handler
 #ifdef WITH_PARTITION_STORAGE_ENGINE
   SPIDER_PARTITION_HANDLER *partition_handler;
 #endif
+  /* Whether this ha_spider is the owner of its wide_handler. */
   bool                wide_handler_owner = FALSE;
   SPIDER_WIDE_HANDLER *wide_handler = NULL;
 

storage/spider/mysql-test/spider/bugfix/r/mdev_31475.result

+for master_1
+for child2
+for child3
+CREATE TABLE t3 (c1 MEDIUMINT NULL, c2 CHAR(5)) ENGINE=Spider PARTITION BY KEY(c1) PARTITIONS 2;
+ALTER TABLE t3 DROP PRIMARY KEY;
+ERROR 42000: Can't DROP INDEX `PRIMARY`; check that it exists
+SELECT * FROM t3 WHERE c1 <=> '1000-00-01 00:00:00' ORDER BY c1,c2 LIMIT 2;
+ERROR HY000: Unable to connect to foreign data source: localhost
+CREATE TABLE t1 (a INT UNSIGNED NOT NULL PRIMARY KEY, b INT UNSIGNED NOT NULL, c INT UNSIGNED, UNIQUE (b, c) USING HASH) ENGINE=Spider;
+SELECT t1.c1 FROM t3 RIGHT JOIN t1 ON t1.c1=current_date() UNION SELECT t1.c2 FROM t1 LEFT OUTER JOIN t3 ON t1.c2;
+ERROR HY000: Unable to connect to foreign data source: localhost
+drop table t1, t3;
+set spider_same_server_link= 1;
+CREATE SERVER srv FOREIGN DATA WRAPPER mysql
+OPTIONS (SOCKET "$MASTER_1_MYSOCK", DATABASE 'test',user 'root');
+CREATE TABLE t1 (a INT, b VARCHAR(255), PRIMARY KEY(a)) ENGINE=Spider PARTITION BY RANGE (a) (PARTITION p1 VALUES LESS THAN (3), PARTITION p2 VALUES LESS THAN MAXVALUE COMMENT='srv "srv"');
+DROP SERVER srv;
+SELECT * FROM t1;
+ERROR HY000: The foreign server name you are trying to reference does not exist. Data source error:  srv
+drop table t1;
+for master_1
+for child2
+for child3

storage/spider/mysql-test/spider/bugfix/t/mdev_31475.test

+--disable_query_log
+--disable_result_log
+--source ../../t/test_init.inc
+--enable_result_log
+--enable_query_log
+
+# test 1
+CREATE TABLE t3 (c1 MEDIUMINT NULL, c2 CHAR(5)) ENGINE=Spider PARTITION BY KEY(c1) PARTITIONS 2;
+--error ER_CANT_DROP_FIELD_OR_KEY
+ALTER TABLE t3 DROP PRIMARY KEY;
+--error ER_CONNECT_TO_FOREIGN_DATA_SOURCE
+SELECT * FROM t3 WHERE c1 <=> '1000-00-01 00:00:00' ORDER BY c1,c2 LIMIT 2;
+CREATE TABLE t1 (a INT UNSIGNED NOT NULL PRIMARY KEY, b INT UNSIGNED NOT NULL, c INT UNSIGNED, UNIQUE (b, c) USING HASH) ENGINE=Spider;
+--error ER_CONNECT_TO_FOREIGN_DATA_SOURCE
+SELECT t1.c1 FROM t3 RIGHT JOIN t1 ON t1.c1=current_date() UNION SELECT t1.c2 FROM t1 LEFT OUTER JOIN t3 ON t1.c2;
+drop table t1, t3;
+
+# test 2
+set spider_same_server_link= 1;
+evalp CREATE SERVER srv FOREIGN DATA WRAPPER mysql
+OPTIONS (SOCKET "$MASTER_1_MYSOCK", DATABASE 'test',user 'root');
+CREATE TABLE t1 (a INT, b VARCHAR(255), PRIMARY KEY(a)) ENGINE=Spider PARTITION BY RANGE (a) (PARTITION p1 VALUES LESS THAN (3), PARTITION p2 VALUES LESS THAN MAXVALUE COMMENT='srv "srv"');
+DROP SERVER srv;
+--error 1477
+SELECT * FROM t1;
+drop table t1;
+
+--disable_query_log
+--disable_result_log
+--source ../../t/test_deinit.inc
+--enable_result_log
+--enable_query_log

storage/spider/spd_include.h

@@ -879,6 +879,10 @@ enum spider_hnd_stage {
   SPD_HND_STAGE_CLEAR_TOP_TABLE_FIELDS
 };
 
+/*
+  A wide handler is shared among ha_spider of partitions of the same
+  table. It is owned by the last partition.
+*/
 typedef struct st_spider_wide_handler
 {
   spider_hnd_stage   stage;