MDEV-22465: DROP indexed COLUMN is wrongly claimed to be ALGORITHM=INSTANT

ha_innobase::check_if_supported_inplace_alter(): Do not allow
ALGORITHM=INSTANT for operations that avoid a table rebuild
but involve dropping (or creating) secondary indexes.

mysql-test/suite/innodb/r/instant_alter,4k.rdiff

@@ -318,8 +318,8 @@
  FROM information_schema.global_status
  WHERE variable_name = 'innodb_instant_alter_column';
  instants
--205
-+207
+-206
++208
  SET GLOBAL innodb_purge_rseg_truncate_frequency= @saved_frequency;
  SET GLOBAL innodb_instant_alter_column_allowed = @saved_allowance;
  #

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

@@ -2812,11 +2812,19 @@ CREATE TABLE t1 (a INT, b INT, PRIMARY KEY(a,b)) ENGINE=InnoDB ROW_FORMAT=DYNAMI
 ALTER TABLE t1 MODIFY b INT FIRST;
 DROP TABLE t1;
 disconnect analyze;
+#
+# MDEV-22465: DROP COLUMN is wrongly claimed to be ALGORITHM=INSTANT
+#
+CREATE TABLE t1(a INT PRIMARY KEY, b INT UNIQUE) ENGINE=InnoDB;
+ALTER TABLE t1 DROP b, ALGORITHM=INSTANT;
+ERROR 0A000: ALGORITHM=INSTANT is not supported. Reason: DROP INDEX. Try ALGORITHM=NOCOPY
+ALTER TABLE t1 DROP b, ALGORITHM=NOCOPY;
+DROP TABLE t1;
 SELECT variable_value-@old_instant instants
 FROM information_schema.global_status
 WHERE variable_name = 'innodb_instant_alter_column';
 instants
-205
+206
 SET GLOBAL innodb_purge_rseg_truncate_frequency= @saved_frequency;
 SET GLOBAL innodb_instant_alter_column_allowed = @saved_allowance;
 #

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

@@ -877,6 +877,17 @@ dec $format;
 let $redundant_4k= 0;
 }
 disconnect analyze;
+
+--echo #
+--echo # MDEV-22465: DROP COLUMN is wrongly claimed to be ALGORITHM=INSTANT
+--echo #
+
+CREATE TABLE t1(a INT PRIMARY KEY, b INT UNIQUE) ENGINE=InnoDB;
+--error ER_ALTER_OPERATION_NOT_SUPPORTED_REASON
+ALTER TABLE t1 DROP b, ALGORITHM=INSTANT;
+ALTER TABLE t1 DROP b, ALGORITHM=NOCOPY;
+DROP TABLE t1;
+
 SELECT variable_value-@old_instant instants
 FROM information_schema.global_status
 WHERE variable_name = 'innodb_instant_alter_column';

storage/innobase/handler/handler0alter.cc

@@ -2474,7 +2474,8 @@ ha_innobase::check_if_supported_inplace_alter(
 		}
 	}
 
-	if (supports_instant) {
+	if (supports_instant && !(ha_alter_info->handler_flags
+				  & INNOBASE_ALTER_NOREBUILD)) {
 		DBUG_RETURN(HA_ALTER_INPLACE_INSTANT);
 	}
 
@@ -2584,7 +2585,7 @@ ha_innobase::check_if_supported_inplace_alter(
 		online = false;
 	}
 
-	if (need_rebuild || fts_need_rebuild) {
+	if ((need_rebuild && !supports_instant) || fts_need_rebuild) {
 		ha_alter_info->handler_flags |= ALTER_RECREATE_TABLE;
 		DBUG_RETURN(online
 			    ? HA_ALTER_INPLACE_COPY_NO_LOCK