itest: add taproot chan support to basic channel funding

We keep in line with the existing test that uses implicit negotiation.
In the future, we should modify to also have explicit negotiation as
well.

lntest/utils.go

@@ -123,6 +123,16 @@ func channelPointStr(chanPoint *lnrpc.ChannelPoint) string {
 	return cp.String()
 }
 
+// CommitTypeHasTaproot returns whether commitType is a taproot commitment.
+func CommitTypeHasTaproot(commitType lnrpc.CommitmentType) bool {
+	switch commitType {
+	case lnrpc.CommitmentType_SIMPLE_TAPROOT:
+		return true
+	default:
+		return false
+	}
+}
+
 // CommitTypeHasAnchors returns whether commitType uses anchor outputs.
 func CommitTypeHasAnchors(commitType lnrpc.CommitmentType) bool {
 	switch commitType {
@@ -149,6 +159,11 @@ func NodeArgsForCommitType(commitType lnrpc.CommitmentType) []string {
 			"--protocol.anchors",
 			"--protocol.script-enforced-lease",
 		}
+	case lnrpc.CommitmentType_SIMPLE_TAPROOT:
+		return []string{
+			"--protocol.anchors",
+			"--protocol.simple-taproot-chans",
+		}
 	}
 
 	return nil
@@ -172,11 +187,23 @@ func CalcStaticFee(c lnrpc.CommitmentType, numHTLCs int) btcutil.Amount {
 		feePerKw     = chainfee.SatPerKWeight(DefaultFeeRateSatPerKw)
 	)
 
+	switch {
+	// The taproot commitment type has the extra anchor outputs, but also a
+	// smaller witness field (will just be a normal key spend), so we need
+	// to account for that here as well.
+	case CommitTypeHasTaproot(c):
+		feePerKw = chainfee.SatPerKVByte(
+			defaultSatPerVByte * scale,
+		).FeePerKWeight()
+
+		commitWeight = input.TaprootCommitWeight
+		anchors = anchorSize
+
 	// The anchor commitment type is slightly heavier, and we must also add
 	// the value of the two anchors to the resulting fee the initiator
 	// pays. In addition the fee rate is capped at 10 sat/vbyte for anchor
 	// channels.
-	if CommitTypeHasAnchors(c) {
+	case CommitTypeHasAnchors(c):
 		feePerKw = chainfee.SatPerKVByte(
 			defaultSatPerVByte * scale,
 		).FeePerKWeight()