tapfreighter: trim altLeaves from passive vPkts

In this commit, we update the passive asset handling to not consider
altLeaves as assets. Specifically, any altLeaf in an input Tap
commitment should be set in the vInput for a passive asset vPkt, but
should not have its own vPkt where it is an input. Overall, input
altLeaves do not need to be re-anchored.

Author: jharveyb

tapfreighter/wallet.go

@@ -271,7 +271,8 @@ func (f *AssetWallet) FundAddressSend(ctx context.Context,
 func createPassivePacket(params *address.ChainParams, passiveAsset *asset.Asset,
 	activePackets []*tappsbt.VPacket, anchorOutputIndex uint32,
 	anchorOutputInternalKey keychain.KeyDescriptor, prevOut wire.OutPoint,
-	inputProof *proof.Proof) (*tappsbt.VPacket, error) {
+	inputProof *proof.Proof,
+	inputAltLeaves []*asset.Asset) (*tappsbt.VPacket, error) {
 
 	// Specify virtual input.
 	inputAsset := passiveAsset.Copy()
@@ -281,8 +282,12 @@ func createPassivePacket(params *address.ChainParams, passiveAsset *asset.Asset,
 			SighashType: txscript.SigHashDefault,
 		},
 	}
+	err := vInput.SetAltLeaves(inputAltLeaves)
+	if err != nil {
+		return nil, err
+	}
 
-	err := tapsend.ValidateVPacketVersions(activePackets)
+	err = tapsend.ValidateVPacketVersions(activePackets)
 	if err != nil {
 		return nil, err
 	}
@@ -597,7 +602,18 @@ func (f *AssetWallet) hasOtherAssets(inputCommitments tappsbt.InputCommitments,
 			return false, err
 		}
 
-		if len(passiveCommitments.CommittedAssets()) > 0 {
+		// We're trying to find out if there are any other assets in the
+		// commitment. We don't want to count alt leaves as "assets" per
+		// se in this context, so we trim them out, just for the next
+		// check.
+		trimmedPassiveCommitments, _, err := commitment.TrimAltLeaves(
+			passiveCommitments,
+		)
+		if err != nil {
+			return false, err
+		}
+
+		if len(trimmedPassiveCommitments.CommittedAssets()) > 0 {
 			return true, nil
 		}
 	}
@@ -1260,7 +1276,18 @@ func (f *AssetWallet) CreatePassiveAssets(ctx context.Context,
 			return nil, err
 		}
 
-		passiveAssets := passiveCommitments.CommittedAssets()
+		// We're trying to determine what assets are left over after
+		// removing the active assets. But we don't want to count the
+		// alt leaves as "assets" in this context, so we'll trim them
+		// out.
+		trimmedPassives, altLeaves, err := commitment.TrimAltLeaves(
+			passiveCommitments,
+		)
+		if err != nil {
+			return nil, err
+		}
+
+		passiveAssets := trimmedPassives.CommittedAssets()
 		if len(passiveAssets) == 0 {
 			continue
 		}
@@ -1289,7 +1316,7 @@ func (f *AssetWallet) CreatePassiveAssets(ctx context.Context,
 			passivePacket, err := createPassivePacket(
 				f.cfg.ChainParams, passiveAsset, activePackets,
 				anchorOutIdx, *anchorOutDesc, prevID.OutPoint,
-				inputProof,
+				inputProof, altLeaves,
 			)
 			if err != nil {
 				return nil, fmt.Errorf("unable to create "+