fix: fix connection gater in transport constructor

config/constructor_types.go

@@ -28,12 +28,12 @@ var (
 	privKeyType   = reflect.TypeOf((*crypto.PrivKey)(nil)).Elem()
 	pubKeyType    = reflect.TypeOf((*crypto.PubKey)(nil)).Elem()
 	pstoreType    = reflect.TypeOf((*peerstore.Peerstore)(nil)).Elem()
+	connGaterType = reflect.TypeOf((*connmgr.ConnectionGater)(nil)).Elem()
 
 	// concrete types
 	peerIDType   = reflect.TypeOf((peer.ID)(""))
 	upgraderType = reflect.TypeOf((*tptu.Upgrader)(nil))
 	pskType      = reflect.TypeOf((pnet.PSK)(nil))
-	connGaterType = reflect.TypeOf((*connmgr.ConnectionGater)(nil))
 )
 
 var argTypes = map[reflect.Type]constructor{

config/reflection_magic.go

@@ -121,7 +121,14 @@ func makeConstructor(
 	return func(h host.Host, u *tptu.Upgrader, cg connmgr.ConnectionGater) (interface{}, error) {
 		arguments := make([]reflect.Value, len(argConstructors))
 		for i, makeArg := range argConstructors {
-			arguments[i] = reflect.ValueOf(makeArg(h, u, cg))
+			if arg := makeArg(h, u, cg); arg != nil {
+				arguments[i] = reflect.ValueOf(arg)
+			} else {
+				// ValueOf an un-typed nil yields a zero reflect
+				// value. However, we _want_ the zero value of
+				// the _type_.
+				arguments[i] = reflect.Zero(t.In(i))
+			}
 		}
 		return callConstructor(v, arguments)
 	}, nil

libp2p_test.go

@@ -7,10 +7,14 @@ import (
 	"strings"
 	"testing"
 
+	"github.com/libp2p/go-libp2p-core/connmgr"
 	"github.com/libp2p/go-libp2p-core/crypto"
 	"github.com/libp2p/go-libp2p-core/host"
 	"github.com/libp2p/go-libp2p-core/peer"
+	"github.com/libp2p/go-libp2p-core/transport"
 	"github.com/libp2p/go-tcp-transport"
+
+	tptu "github.com/libp2p/go-libp2p-transport-upgrader"
 )
 
 func TestNewHost(t *testing.T) {
@@ -33,6 +37,22 @@ func TestBadTransportConstructor(t *testing.T) {
 	}
 }
 
+func TestTransportConstructor(t *testing.T) {
+	ctx := context.Background()
+	ctor := func(
+		h host.Host,
+		_ connmgr.ConnectionGater,
+		upgrader *tptu.Upgrader,
+	) transport.Transport {
+		return tcp.NewTCPTransport(upgrader)
+	}
+	h, err := New(ctx, Transport(ctor))
+	if err != nil {
+		t.Fatal(err)
+	}
+	h.Close()
+}
+
 func TestNoListenAddrs(t *testing.T) {
 	ctx := context.Background()
 	h, err := New(ctx, NoListenAddrs)