lnwire: add new feature bits for explicit channel type negotiation

If these bits are present, then both sides can examine the new
CommitmentType TLV field that's present and use this in place of the
existing implicit commiment type negotiation. With this change, it's now
possible to actually deprecate old unsupported commitment types
properly.

feature/default_sets.go

@@ -60,4 +60,8 @@ var defaultSetDesc = setDesc{
 	lnwire.AMPRequired: {
 		SetInvoiceAmp: {}, // 9A
 	},
+	lnwire.ExplicitChannelTypeOptional: {
+		SetInit:    {}, // I
+		SetNodeAnn: {}, // N
+	},
 }

feature/deps.go

@@ -58,9 +58,13 @@ var deps = depDesc{
 	lnwire.AnchorsOptional: {
 		lnwire.StaticRemoteKeyOptional: {},
 	},
+	lnwire.AnchorsZeroFeeHtlcTxOptional: {
+		lnwire.StaticRemoteKeyOptional: {},
+	},
 	lnwire.AMPOptional: {
 		lnwire.PaymentAddrOptional: {},
 	},
+	lnwire.ExplicitChannelTypeOptional: {},
 }
 
 // ValidateDeps asserts that a feature vector sets all features and their

lnwire/features.go

@@ -139,6 +139,26 @@ const (
 	// sender-generated preimages according to BOLT XX.
 	AMPOptional FeatureBit = 31
 
+	// ExplicitChannelTypeRequired is a required bit that denotes that a
+	// connection established with this node is to use explicit channel
+	// commitment types for negotiation instead of the existing implicit
+	// negotiation methods. With this bit, there is no longer a "default"
+	// implicit channel commitment type, allowing a connection to
+	// open/maintain types of several channels over its lifetime.
+	//
+	// TODO: Decide on actual feature bit value.
+	ExplicitChannelTypeRequired = 2020
+
+	// ExplicitChannelTypeOptional is an optional bit that denotes that a
+	// connection established with this node is to use explicit channel
+	// commitment types for negotiation instead of the existing implicit
+	// negotiation methods. With this bit, there is no longer a "default"
+	// implicit channel commitment type, allowing a connection to
+	// open/maintain types of several channels over its lifetime.
+	//
+	// TODO: Decide on actual feature bit value.
+	ExplicitChannelTypeOptional = 2021
+
 	// maxAllowedSize is a maximum allowed size of feature vector.
 	//
 	// NOTE: Within the protocol, the maximum allowed message size is 65535
@@ -184,6 +204,8 @@ var Features = map[FeatureBit]string{
 	WumboChannelsOptional:         "wumbo-channels",
 	AMPRequired:                   "amp",
 	AMPOptional:                   "amp",
+	ExplicitChannelTypeOptional:   "explicit-commitment-type",
+	ExplicitChannelTypeRequired:   "explicit-commitment-type",
 }
 
 // RawFeatureVector represents a set of feature bits as defined in BOLT-09.  A