MDEV-19085 Assertion failures due to virtual columns after upgrading from 10.1

MariaDB before MDEV-5800 in version 10.2.2 did not support
indexed virtual columns. Non-persistent virtual columns were
hidden from storage engines. Only starting with MDEV-5800, InnoDB
would create internal metadata on virtual columns.

Similar to what was done in MDEV-18084, MDEV-18090, MDEV-18960, we adjust
one more code path for the old tables.

innobase_build_col_map(): Allocate space for virtual columns in col_map[]
but leave the entries at ULINT_UNDEFINED, noting that the virtual columns
were missing before the table was being rebuilt.

storage/innobase/handler/handler0alter.cc

@@ -3022,10 +3022,17 @@ innobase_build_col_map(
 				     & Alter_inplace_info::ADD_COLUMN));
 	DBUG_ASSERT(!add_cols || dtuple_get_n_fields(add_cols)
 		    == dict_table_get_n_cols(new_table));
+	DBUG_ASSERT(table->s->stored_fields > 0);
+
+	size_t old_n_v_cols = old_n_v_cols = table->s->fields
+		- table->s->stored_fields;
+	DBUG_ASSERT(old_n_v_cols == old_table->n_v_cols
+		    || table->s->frm_version < FRM_VER_EXPRESSSIONS);
+	DBUG_ASSERT(!old_n_v_cols || table->s->virtual_fields);
 
 	ulint*	col_map = static_cast<ulint*>(
 		mem_heap_alloc(
-			heap, (old_table->n_cols + old_table->n_v_cols)
+			heap, (size_t(old_table->n_cols) + old_n_v_cols)
 			* sizeof *col_map));
 
 	List_iterator_fast<Create_field> cf_it(
@@ -3039,10 +3046,12 @@ innobase_build_col_map(
 		col_map[old_i] = ULINT_UNDEFINED;
 	}
 
-	for (uint old_i = 0; old_i < old_table->n_v_cols; old_i++) {
+	for (uint old_i = 0; old_i < old_n_v_cols; old_i++) {
 		col_map[old_i + old_table->n_cols] = ULINT_UNDEFINED;
 	}
 
+	const bool omits_virtual = ha_innobase::omits_virtual_cols(*table->s);
+
 	while (const Create_field* new_field = cf_it++) {
 		bool	is_v = !new_field->stored_in_db();
 		ulint	num_old_v = 0;
@@ -3051,8 +3060,11 @@ innobase_build_col_map(
 			const Field* field = table->field[old_i];
 			if (!field->stored_in_db()) {
 				if (is_v && new_field->field == field) {
-					col_map[old_table->n_cols + num_v]
-						= num_old_v;
+					if (!omits_virtual) {
+						col_map[old_table->n_cols
+							+ num_v]
+							= num_old_v;
+					}
 					num_old_v++;
 					goto found_col;
 				}
@@ -3081,7 +3093,7 @@ innobase_build_col_map(
 
 	DBUG_ASSERT(i == altered_table->s->fields - num_v);
 
-	i = table->s->fields - old_table->n_v_cols;
+	i = table->s->fields - old_n_v_cols;
 
 	/* Add the InnoDB hidden FTS_DOC_ID column, if any. */
 	if (i + DATA_N_SYS_COLS < old_table->n_cols) {