MDEV-16142: Merge one more fix from MySQL 5.7.22

This fix was initially missed, because there were multiple commits
with an empty message.

mysql-test/suite/gcol/r/innodb_virtual_index.result

@@ -198,3 +198,16 @@ VIRTUAL, ADD UNIQUE index idx (col1), algorithm=inplace;
 ERROR 0A000: ALGORITHM=INPLACE is not supported. Reason: INPLACE ADD or DROP of virtual columns cannot be combined with other ALTER TABLE actions. Try ALGORITHM=COPY
 DROP TABLE t1;
 SET GLOBAL innodb_purge_rseg_truncate_frequency = @saved_frequency;
+#
+# Bug 27122803 - BACKPORT FIX FOR BUG 25899959 TO MYSQL-5.7
+#
+CREATE TABLE t1 (col1 int(10)) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
+ALTER TABLE t1 ADD col2 char(21) AS (col1 * col1), ADD INDEX n (col2);
+SHOW CREATE TABLE t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `col1` int(10) DEFAULT NULL,
+  `col2` char(21) GENERATED ALWAYS AS (`col1` * `col1`) VIRTUAL,
+  KEY `n` (`col2`)
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4
+DROP TABLE t1;

mysql-test/suite/gcol/t/innodb_virtual_index.test

@@ -224,3 +224,11 @@ VIRTUAL, ADD UNIQUE index idx (col1), algorithm=inplace;
 
 DROP TABLE t1;
 SET GLOBAL innodb_purge_rseg_truncate_frequency = @saved_frequency;
+
+--echo #
+--echo # Bug 27122803 - BACKPORT FIX FOR BUG 25899959 TO MYSQL-5.7
+--echo #
+CREATE TABLE t1 (col1 int(10)) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
+ALTER TABLE t1 ADD col2 char(21) AS (col1 * col1), ADD INDEX n (col2);
+SHOW CREATE TABLE t1;
+DROP TABLE t1;

storage/innobase/handler/handler0alter.cc

@@ -4385,6 +4385,15 @@ prepare_inplace_alter_table_dict(
 
 		if (ha_alter_info->handler_flags
 		    & Alter_inplace_info::ADD_INDEX) {
+			for (ulint i = 0; i < ctx->num_to_add_vcol; i++) {
+				/* Set mbminmax for newly added column */
+				dict_col_t& col = ctx->add_vcol[i].m_col;
+				ulint mbminlen, mbmaxlen;
+				dtype_get_mblen(col.mtype, col.prtype,
+						&mbminlen, &mbmaxlen);
+				col.mbminlen = mbminlen;
+				col.mbmaxlen = mbmaxlen;
+			}
 			add_v = static_cast<dict_add_v_col_t*>(
 				mem_heap_alloc(ctx->heap, sizeof *add_v));
 			add_v->n_v_col = ctx->num_to_add_vcol;