MDEV-22939 Server crashes in row_make_new_pathname()

The statement ALTER TABLE...DISCARD TABLESPACE is problematic,
because its designed purpose is to break the referential integrity
of the data dictionary and make a table point to nowhere.

ha_innobase::commit_inplace_alter_table(): Check whether the
table has been discarded. (This is a bit late to check it, right
before committing the change.) Previously, we performed this check
only in a specific branch of the function commit_set_autoinc().

Note: We intentionally allow non-rebuilding ALTER TABLE even if
the tablespace has been discarded, to remain compatible with MySQL.
(See the various tests with "wl5522" in the name, such as
innodb.innodb-wl5522.)

The test case would crash starting with 10.3 only, but it does not hurt
to minimize the code and test difference between 10.2 and 10.3.

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

@@ -60,3 +60,13 @@ CREATE TABLE t1(a INT NOT NULL UNIQUE) ENGINE=InnoDB;
 INSERT INTO t1 SELECT * FROM seq_1_to_128;
 ALTER TABLE t1 ADD b TINYINT AUTO_INCREMENT PRIMARY KEY, DROP KEY a;
 DROP TABLE t1;
+#
+# MDEV-22939 Server crashes in row_make_new_pathname()
+#
+CREATE TABLE t (a INT) ENGINE=INNODB;
+ALTER TABLE t DISCARD TABLESPACE;
+ALTER TABLE t ENGINE INNODB;
+ERROR HY000: Tablespace has been discarded for table `t`
+ALTER TABLE t FORCE;
+ERROR HY000: Tablespace has been discarded for table `t`
+DROP TABLE t;

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

@@ -68,3 +68,14 @@ CREATE TABLE t1(a INT NOT NULL UNIQUE) ENGINE=InnoDB;
 INSERT INTO t1 SELECT * FROM seq_1_to_128;
 ALTER TABLE t1 ADD b TINYINT AUTO_INCREMENT PRIMARY KEY, DROP KEY a;
 DROP TABLE t1;
+
+--echo #
+--echo # MDEV-22939 Server crashes in row_make_new_pathname()
+--echo #
+CREATE TABLE t (a INT) ENGINE=INNODB;
+ALTER TABLE t DISCARD TABLESPACE;
+--error ER_TABLESPACE_DISCARDED
+ALTER TABLE t ENGINE INNODB;
+--error ER_TABLESPACE_DISCARDED
+ALTER TABLE t FORCE;
+DROP TABLE t;

storage/innobase/handler/handler0alter.cc

@@ -7209,12 +7209,6 @@ commit_set_autoinc(
 		   && (ha_alter_info->create_info->used_fields
 		       & HA_CREATE_USED_AUTO)) {
 
-		if (dict_table_is_discarded(ctx->old_table)) {
-			my_error(ER_TABLESPACE_DISCARDED, MYF(0),
-				 old_table->s->table_name.str);
-			DBUG_RETURN(true);
-		}
-
 		/* An AUTO_INCREMENT value was supplied by the user.
 		It must be persisted to the data file. */
 		const Field*	ai	= old_table->found_next_number_field;
@@ -8411,9 +8405,15 @@ ha_innobase::commit_inplace_alter_table(
 			= static_cast<ha_innobase_inplace_ctx*>(*pctx);
 
 		DBUG_ASSERT(new_clustered == ctx->need_rebuild());
-
-		fail = commit_set_autoinc(ha_alter_info, ctx, altered_table,
-					  table);
+		if (ctx->need_rebuild()
+		    && dict_table_is_discarded(ctx->old_table)) {
+			my_error(ER_TABLESPACE_DISCARDED, MYF(0),
+				 table->s->table_name.str);
+			fail = true;
+		} else {
+			fail = commit_set_autoinc(ha_alter_info, ctx,
+						  altered_table, table);
+		}
 
 		if (fail) {
 		} else if (ctx->need_rebuild()) {