types: Rename EphemeralLeafIndex -> UnassignedLeafIndex

consensus/merkle.go

@@ -400,7 +400,7 @@ type elementApplyUpdate struct {
 }
 
 func (eau *elementApplyUpdate) updateElementProof(e *types.StateElement) {
-	if e.LeafIndex == types.EphemeralLeafIndex {
+	if e.LeafIndex == types.UnassignedLeafIndex {
 		panic("cannot update an ephemeral element")
 	} else if e.LeafIndex >= eau.oldNumLeaves {
 		return // newly-added element
@@ -417,7 +417,7 @@ type elementRevertUpdate struct {
 }
 
 func (eru *elementRevertUpdate) updateElementProof(e *types.StateElement) {
-	if e.LeafIndex == types.EphemeralLeafIndex {
+	if e.LeafIndex == types.UnassignedLeafIndex {
 		panic("cannot update an ephemeral element")
 	} else if e.LeafIndex >= eru.numLeaves {
 		panic("cannot update an element that is not present in the accumulator")

consensus/merkle_test.go

@@ -90,8 +90,8 @@ func TestUpdateElementProof(t *testing.T) {
 		expectProofLen int
 	}{
 		{
-			name:        "EphemeralLeafIndexPanic",
-			leafIndex:   types.EphemeralLeafIndex,
+			name:        "UnassignedLeafIndexPanic",
+			leafIndex:   types.UnassignedLeafIndex,
 			numLeaves:   5,
 			expectPanic: true,
 		},

consensus/update.go

@@ -336,10 +336,7 @@ func ApplyOrphan(s State, b types.Block, targetTimestamp time.Time) State {
 
 func (ms *MidState) addSiacoinElement(id types.SiacoinOutputID, sco types.SiacoinOutput) {
 	sce := types.SiacoinElement{
-		StateElement: types.StateElement{
-			ID:        types.Hash256(id),
-			LeafIndex: types.EphemeralLeafIndex,
-		},
+		StateElement:  types.StateElement{ID: types.Hash256(id)},
 		SiacoinOutput: sco,
 	}
 	ms.sces = append(ms.sces, sce)
@@ -361,10 +358,7 @@ func (ms *MidState) spendSiacoinElement(sce types.SiacoinElement, txid types.Tra
 
 func (ms *MidState) addSiafundElement(id types.SiafundOutputID, sfo types.SiafundOutput) {
 	sfe := types.SiafundElement{
-		StateElement: types.StateElement{
-			ID:        types.Hash256(id),
-			LeafIndex: types.EphemeralLeafIndex,
-		},
+		StateElement:  types.StateElement{ID: types.Hash256(id)},
 		SiafundOutput: sfo,
 		ClaimStart:    ms.siafundPool,
 	}
@@ -382,10 +376,7 @@ func (ms *MidState) spendSiafundElement(sfe types.SiafundElement, txid types.Tra
 
 func (ms *MidState) addFileContractElement(id types.FileContractID, fc types.FileContract) {
 	fce := types.FileContractElement{
-		StateElement: types.StateElement{
-			ID:        types.Hash256(id),
-			LeafIndex: types.EphemeralLeafIndex,
-		},
+		StateElement: types.StateElement{ID: types.Hash256(id)},
 		FileContract: fc,
 	}
 	ms.fces = append(ms.fces, fce)
@@ -421,10 +412,7 @@ func (ms *MidState) resolveFileContractElement(fce types.FileContractElement, va
 
 func (ms *MidState) addV2FileContractElement(id types.FileContractID, fc types.V2FileContract) {
 	fce := types.V2FileContractElement{
-		StateElement: types.StateElement{
-			ID:        types.Hash256(id),
-			LeafIndex: types.EphemeralLeafIndex,
-		},
+		StateElement:   types.StateElement{ID: types.Hash256(id)},
 		V2FileContract: fc,
 	}
 	ms.v2fces = append(ms.v2fces, fce)

consensus/validation.go

@@ -584,7 +584,7 @@ func validateV2Siacoins(ms *MidState, txn types.V2Transaction) error {
 		spent[sci.Parent.ID] = i
 
 		// check accumulator
-		if sci.Parent.LeafIndex == types.EphemeralLeafIndex {
+		if sci.Parent.LeafIndex == types.UnassignedLeafIndex {
 			if !ms.isCreated(sci.Parent.ID) {
 				return fmt.Errorf("siacoin input %v spends nonexistent ephemeral output %v", i, sci.Parent.ID)
 			}
@@ -645,7 +645,7 @@ func validateV2Siafunds(ms *MidState, txn types.V2Transaction) error {
 		spent[sfi.Parent.ID] = i
 
 		// check accumulator
-		if sfi.Parent.LeafIndex == types.EphemeralLeafIndex {
+		if sfi.Parent.LeafIndex == types.UnassignedLeafIndex {
 			if !ms.isCreated(sfi.Parent.ID) {
 				return fmt.Errorf("siafund input %v spends nonexistent ephemeral output %v", i, sfi.Parent.ID)
 			}

types/multiproof.go

@@ -48,7 +48,7 @@ func splitLeaves(ls []elementLeaf, mid uint64) (left, right []elementLeaf) {
 
 func forEachElementLeaf(txns []V2Transaction, fn func(l elementLeaf)) {
 	visit := func(l elementLeaf) {
-		if l.LeafIndex != EphemeralLeafIndex {
+		if l.LeafIndex != UnassignedLeafIndex {
 			fn(l)
 		}
 	}

types/multiproof_test.go

@@ -88,7 +88,7 @@ func multiproofTxns(numTxns int, numElems int) []types.V2Transaction {
 	for i := range txns {
 		for j := range txns[i].SiacoinInputs {
 			if (n+1)%5 == 0 {
-				txns[i].SiacoinInputs[j].Parent.LeafIndex = types.EphemeralLeafIndex
+				txns[i].SiacoinInputs[j].Parent.LeafIndex = types.UnassignedLeafIndex
 				txns[i].SiacoinInputs[j].Parent.MerkleProof = nil
 			}
 			n++

types/types.go

@@ -30,11 +30,15 @@ const (
 	// a FileContract.
 	HostContractIndex = 1
 
-	// EphemeralLeafIndex is used as the LeafIndex of StateElements that are created
-	// and spent within the same block. Such elements do not require a proof of
-	// existence. They are, however, assigned a proper index and are incorporated
-	// into the state accumulator when the block is processed.
-	EphemeralLeafIndex = math.MaxUint64
+	// UnassignedLeafIndex is a sentinel value used as the LeafIndex of
+	// StateElements that have not been added to the accumulator yet. This is
+	// necessary for constructing blocks sets where later transactions reference
+	// elements created in earlier transactions.
+	//
+	// Most clients do not need to reference this value directly, and should
+	// instead use the EphemeralSiacoinElement and EphemeralSiafundElement
+	// functions to construct dependent transaction sets.
+	UnassignedLeafIndex = 10101010101010101010
 )
 
 // Various specifiers.
@@ -687,7 +691,7 @@ func (txn *V2Transaction) EphemeralSiacoinOutput(i int) SiacoinElement {
 	return SiacoinElement{
 		StateElement: StateElement{
 			ID:        Hash256(txn.SiacoinOutputID(txn.ID(), i)),
-			LeafIndex: EphemeralLeafIndex,
+			LeafIndex: UnassignedLeafIndex,
 		},
 		SiacoinOutput: txn.SiacoinOutputs[i],
 	}
@@ -699,7 +703,7 @@ func (txn *V2Transaction) EphemeralSiafundOutput(i int) SiafundElement {
 	return SiafundElement{
 		StateElement: StateElement{
 			ID:        Hash256(txn.SiafundOutputID(txn.ID(), i)),
-			LeafIndex: EphemeralLeafIndex,
+			LeafIndex: UnassignedLeafIndex,
 		},
 		SiafundOutput: txn.SiafundOutputs[i],
 	}