multi: refactor NewAnchorResolutions to return fixed values

This commit adds a new struct AnchorResolutions which wraps the anchor
resolutions for local/remote/pending remote commitment transactions. It
is then returned from NewAnchorResolutions. Thus the caller knows how to
retrieve a certain anchor resolution.

contractcourt/chain_arbitrator.go

@@ -241,7 +241,7 @@ type arbChannel struct {
 // commitment transactions.
 //
 // NOTE: Part of the ArbChannel interface.
-func (a *arbChannel) NewAnchorResolutions() ([]*lnwallet.AnchorResolution,
+func (a *arbChannel) NewAnchorResolutions() (*lnwallet.AnchorResolutions,
 	error) {
 
 	// Get a fresh copy of the database state to base the anchor resolutions

contractcourt/channel_arbitrator.go

@@ -91,7 +91,7 @@ type ArbChannel interface {
 
 	// NewAnchorResolutions returns the anchor resolutions for currently
 	// valid commitment transactions.
-	NewAnchorResolutions() ([]*lnwallet.AnchorResolution, error)
+	NewAnchorResolutions() (*lnwallet.AnchorResolutions, error)
 }
 
 // ChannelArbitratorConfig contains all the functionality that the
@@ -1087,14 +1087,18 @@ func (c *ChannelArbitrator) stateStep(
 // sweepAnchors offers all given anchor resolutions to the sweeper. It requests
 // sweeping at the minimum fee rate. This fee rate can be upped manually by the
 // user via the BumpFee rpc.
-func (c *ChannelArbitrator) sweepAnchors(anchors []*lnwallet.AnchorResolution,
+func (c *ChannelArbitrator) sweepAnchors(anchors *lnwallet.AnchorResolutions,
 	heightHint uint32) error {
 
 	// Use the chan id as the exclusive group. This prevents any of the
 	// anchors from being batched together.
 	exclusiveGroup := c.cfg.ShortChanID.ToUint64()
 
-	for _, anchor := range anchors {
+	// TODO: refactor this function in next commit.
+	for _, anchor := range []*lnwallet.AnchorResolution{
+		anchors.Local, anchors.Remote, anchors.RemotePending,
+	} {
+
 		log.Debugf("ChannelArbitrator(%v): pre-confirmation sweep of "+
 			"anchor of tx %v", c.cfg.ChanPoint, anchor.CommitAnchor)
 

contractcourt/channel_arbitrator_test.go

@@ -2119,9 +2119,7 @@ func TestChannelArbitratorAnchors(t *testing.T) {
 
 	// Setup two pre-confirmation anchor resolutions on the mock channel.
 	chanArb.cfg.Channel.(*mockChannel).anchorResolutions =
-		[]*lnwallet.AnchorResolution{
-			{}, {},
-		}
+		&lnwallet.AnchorResolutions{}
 
 	if err := chanArb.Start(nil); err != nil {
 		t.Fatalf("unable to start ChannelArbitrator: %v", err)
@@ -2286,13 +2284,16 @@ func assertResolverReport(t *testing.T, reports chan *channeldb.ResolverReport,
 }
 
 type mockChannel struct {
-	anchorResolutions []*lnwallet.AnchorResolution
+	anchorResolutions *lnwallet.AnchorResolutions
 }
 
-func (m *mockChannel) NewAnchorResolutions() ([]*lnwallet.AnchorResolution,
+func (m *mockChannel) NewAnchorResolutions() (*lnwallet.AnchorResolutions,
 	error) {
+	if m.anchorResolutions != nil {
+		return m.anchorResolutions, nil
+	}
 
-	return m.anchorResolutions, nil
+	return &lnwallet.AnchorResolutions{}, nil
 }
 
 func (m *mockChannel) ForceCloseChan() (*lnwallet.LocalForceCloseSummary, error) {