[release-19.0] Fix panic in schema tracker in presence of keyspace ro…

…uting rules (#16383) (#16406)

Signed-off-by: Manan Gupta <manan@planetscale.com>

go/vt/vtgate/vschema_manager.go

@@ -212,9 +212,9 @@ func (vm *VSchemaManager) updateFromSchema(vschema *vindexes.VSchema) {
 		// Now that we have ensured that all the tables are created, we can start populating the foreign keys
 		// in the tables.
 		for tblName, tblInfo := range m {
-			rTbl, err := vschema.FindRoutedTable(ksName, tblName, topodatapb.TabletType_PRIMARY)
-			if err != nil {
-				log.Errorf("error finding routed table %s: %v", tblName, err)
+			rTbl := ks.Tables[tblName]
+			if rTbl == nil {
+				log.Errorf("unable to find table %s in %s", tblName, ksName)
 				continue
 			}
 			for _, fkDef := range tblInfo.ForeignKeys {
@@ -223,7 +223,7 @@ func (vm *VSchemaManager) updateFromSchema(vschema *vindexes.VSchema) {
 					continue
 				}
 				parentTbl, err := vschema.FindRoutedTable(ksName, fkDef.ReferenceDefinition.ReferencedTable.Name.String(), topodatapb.TabletType_PRIMARY)
-				if err != nil {
+				if err != nil || parentTbl == nil {
 					log.Errorf("error finding parent table %s: %v", fkDef.ReferenceDefinition.ReferencedTable.Name.String(), err)
 					continue
 				}

go/vt/vtgate/vschema_manager_test.go

@@ -1,6 +1,7 @@
 package vtgate
 
 import (
+	"fmt"
 	"testing"
 
 	"github.com/stretchr/testify/require"
@@ -336,6 +337,48 @@ func TestVSchemaUpdate(t *testing.T) {
 	}
 }
 
+// TestRoutingRules tests that the vschema manager uses the correct tables despite the routing rules.
+func TestRoutingRules(t *testing.T) {
+	cols1 := []vindexes.Column{{
+		Name: sqlparser.NewIdentifierCI("id"),
+		Type: querypb.Type_INT64,
+	}}
+	// Create a vschema manager with a fake vschema that returns a table with a column and a primary key.
+	vm := &VSchemaManager{}
+	vm.schema = &fakeSchema{t: map[string]*vindexes.TableInfo{
+		"t1": {
+			Columns: cols1,
+			Indexes: []*sqlparser.IndexDefinition{
+				{
+					Info: &sqlparser.IndexInfo{Type: sqlparser.IndexTypePrimary},
+					Columns: []*sqlparser.IndexColumn{
+						{
+							Column: sqlparser.NewIdentifierCI("id"),
+						},
+					},
+				},
+			},
+		},
+	}}
+	// Define a vschema that has a keyspace routing rule.
+	vs := &vindexes.VSchema{
+		Keyspaces: map[string]*vindexes.KeyspaceSchema{
+			"ks": {
+				Tables:   map[string]*vindexes.Table{},
+				Keyspace: &vindexes.Keyspace{Name: "ks", Sharded: true},
+			},
+		},
+		RoutingRules: map[string]*vindexes.RoutingRule{
+			"ks.t1": {
+				Error: fmt.Errorf("error in routing rules"),
+			},
+		},
+	}
+	// Ensure that updating the vschema manager from the vschema doesn't cause a panic.
+	vm.updateFromSchema(vs)
+	require.Len(t, vs.Keyspaces["ks"].Tables["t1"].PrimaryKey, 1)
+}
+
 func TestRebuildVSchema(t *testing.T) {
 	cols1 := []vindexes.Column{{
 		Name: sqlparser.NewIdentifierCI("id"),