drop support for old-style Merkle txn root commitment

config/consensus.go

@@ -145,9 +145,8 @@ type ConsensusParams struct {
 	FastRecoveryLambda    time.Duration // time between fast recovery attempts
 	FastPartitionRecovery bool          // set when fast partition recovery is enabled
 
-	// commit to payset using a hash of entire payset,
-	// instead of txid merkle tree
-	PaysetCommitFlat bool
+	// how to commit to the payset: flat or merkle tree
+	PaysetCommit PaysetCommitType
 
 	MaxTimestampIncrement int64 // maximum time between timestamps on successive blocks
 
@@ -344,6 +343,20 @@ type ConsensusParams struct {
 	CompactCertSecKQ uint64
 }
 
+// PaysetCommitType enumerates possible ways for the block header to commit to
+// the set of transactions in the block.
+type PaysetCommitType int
+
+const (
+	// PaysetCommitUnsupported is the zero value, reflecting the fact
+	// that some early protocols used a Merkle tree to commit to the
+	// transactions in a way that we no longer support.
+	PaysetCommitUnsupported PaysetCommitType = iota
+
+	// PaysetCommitFlat hashes the entire payset array.
+	PaysetCommitFlat
+)
+
 // ConsensusProtocols defines a set of supported protocol versions and their
 // corresponding parameters.
 type ConsensusProtocols map[protocol.ConsensusVersion]ConsensusParams
@@ -618,7 +631,7 @@ func initConsensusProtocols() {
 	// v11 introduces SignedTxnInBlock.
 	v11 := v10
 	v11.SupportSignedTxnInBlock = true
-	v11.PaysetCommitFlat = true
+	v11.PaysetCommit = PaysetCommitFlat
 	v11.ApprovedUpgrades = map[protocol.ConsensusVersion]uint64{}
 	Consensus[protocol.ConsensusV11] = v11
 

config/consensus_test.go

@@ -25,14 +25,14 @@ import (
 func TestConsensusParams(t *testing.T) {
 	for proto, params := range Consensus {
 		// Our implementation of Payset.Commit() assumes that
-		// SupportSignedTxnInBlock implies PaysetCommitFlat.
-		if params.SupportSignedTxnInBlock && !params.PaysetCommitFlat {
-			t.Errorf("Protocol %s: SupportSignedTxnInBlock without PaysetCommitFlat", proto)
+		// SupportSignedTxnInBlock implies not PaysetCommitUnsupported.
+		if params.SupportSignedTxnInBlock && params.PaysetCommit == PaysetCommitUnsupported {
+			t.Errorf("Protocol %s: SupportSignedTxnInBlock with PaysetCommitUnsupported", proto)
 		}
 
-		// ApplyData requires PaysetCommitFlat.
-		if params.ApplyData && !params.PaysetCommitFlat {
-			t.Errorf("Protocol %s: ApplyData without PaysetCommitFlat", proto)
+		// ApplyData requires not PaysetCommitUnsupported.
+		if params.ApplyData && params.PaysetCommit == PaysetCommitUnsupported {
+			t.Errorf("Protocol %s: ApplyData with PaysetCommitUnsupported", proto)
 		}
 	}
 }