Fix a data race between Conn creation and its automatic closing

`go test -race .` detects a data race when a Conn instance is automatically
closed when the provided context's deadline is missed.

Fix the data race by launching the corresponding goroutine only after all
Conn's fields had been initialized.

conn.go

@@ -284,10 +284,6 @@ func newConn(tr transport, opts ...ConnOption) (*Conn, error) {
 		conn.ctx = context.Background()
 	}
 	conn.ctx, conn.cancelCtx = context.WithCancel(conn.ctx)
-	go func() {
-		<-conn.ctx.Done()
-		conn.Close()
-	}()
 
 	conn.calls = newCallTracker()
 	if conn.handler == nil {
@@ -302,6 +298,11 @@ func newConn(tr transport, opts ...ConnOption) (*Conn, error) {
 	conn.outHandler = &outputHandler{conn: conn}
 	conn.names = newNameTracker()
 	conn.busObj = conn.Object("org.freedesktop.DBus", "/org/freedesktop/DBus")
+
+	go func() {
+		<-conn.ctx.Done()
+		conn.Close()
+	}()
 	return conn, nil
 }
 

conn_test.go

@@ -798,3 +798,25 @@ func TestCancellingContextClosesConnection(t *testing.T) {
 		t.Errorf("expected connection to be closed, but got: %v", err)
 	}
 }
+
+// TestTimeoutContextClosesConnection checks that a Conn instance is closed after
+// the passed context's deadline is missed.
+// The test also checks that there's no data race between Conn creation and its
+// automatic closing.
+func TestTimeoutContextClosesConnection(t *testing.T) {
+	ctx, cancel := context.WithTimeout(context.Background(), 0)
+	defer cancel()
+
+	bus, err := NewConn(rwc{}, WithContext(ctx))
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// wait until the connection is actually closed
+	time.Sleep(50 * time.Millisecond)
+
+	err = bus.BusObject().Call("org.freedesktop.DBus.Peer.Ping", 0).Store()
+	if err != ErrClosed {
+		t.Errorf("expected connection to be closed, but got: %v", err)
+	}
+}