BUG: fix unexpected panic in vtgate

data/test/vtgate/dml_cases.txt

@@ -1015,6 +1015,10 @@
   }
 }
 
+# insert into a vindex not allowed
+"insert into user_index(id) values(1)"
+"inserting into a vindex not allowed: user_index"
+
 # simple replace unsharded
 "replace into unsharded values(1, 2)"
 {

data/test/vtgate/unsupported_cases.txt

@@ -253,7 +253,7 @@
 
 # multi delete multi table
 "delete user from user join user_extra on user.id = user_extra.id where user.name = 'foo'"
-"unsupported: multi-table delete statement in sharded keyspace"
+"unsupported: multi-table/vindex delete statement in sharded keyspace"
 
 # scatter delete with owned lookup vindex
 "delete from user"
@@ -289,11 +289,11 @@
 
 # join in update tables
 "update user join user_extra on user.id = user_extra.id set user.name = 'foo'"
-"unsupported: multi-table update statement in sharded keyspace"
+"unsupported: multi-table/vindex update statement in sharded keyspace"
 
 # multiple tables in update
 "update user as u, user_extra as ue set u.name = 'foo' where u.id = ue.id"
-"unsupported: multi-table update statement in sharded keyspace"
+"unsupported: multi-table/vindex update statement in sharded keyspace"
 
 # unsharded insert with cross-shard join"
 "insert into unsharded select u.col from user u join user u1"

go/vt/vtgate/planbuilder/delete.go

@@ -39,7 +39,7 @@ func buildDeletePlan(del *sqlparser.Delete, vschema ContextVSchema) (*engine.Del
 	}
 	rb, ok := pb.bldr.(*route)
 	if !ok {
-		return nil, errors.New("unsupported: multi-table delete statement in sharded keyspace")
+		return nil, errors.New("unsupported: multi-table/vindex delete statement in sharded keyspace")
 	}
 	edel.Keyspace = rb.ERoute.Keyspace
 	if !edel.Keyspace.Sharded {

go/vt/vtgate/planbuilder/insert.go

@@ -34,8 +34,11 @@ func buildInsertPlan(ins *sqlparser.Insert, vschema ContextVSchema) (*engine.Ins
 	if err := pb.processAliasedTable(aliased); err != nil {
 		return nil, err
 	}
-	// route is guaranteed because of simple table expr.
-	rb := pb.bldr.(*route)
+	rb, ok := pb.bldr.(*route)
+	if !ok {
+		// This can happen only for vindexes right now.
+		return nil, fmt.Errorf("inserting into a vindex not allowed: %s", sqlparser.String(ins.Table))
+	}
 	if rb.ERoute.TargetDestination != nil {
 		return nil, errors.New("unsupported: INSERT with a target destination")
 	}

go/vt/vtgate/planbuilder/update.go

@@ -40,7 +40,7 @@ func buildUpdatePlan(upd *sqlparser.Update, vschema ContextVSchema) (*engine.Upd
 	}
 	rb, ok := pb.bldr.(*route)
 	if !ok {
-		return nil, errors.New("unsupported: multi-table update statement in sharded keyspace")
+		return nil, errors.New("unsupported: multi-table/vindex update statement in sharded keyspace")
 	}
 	if rb.ERoute.TargetDestination != nil {
 		return nil, errors.New("unsupported: UPDATE with a target destination")