From 0b49ef0e313eb8a8fc36285ed98ea47d44b33235 Mon Sep 17 00:00:00 2001
From: teor <teor@riseup.net>
Date: Wed, 7 Apr 2021 14:03:27 +1000
Subject: [PATCH] Rename the NU5 block commitment variant based on what it
 commits to

This change helps avoid confusion with block commitment variants in
future network upgrades, which may add more hashes to the commitment
list.
---
 zebra-chain/src/block/commitment.rs | 29 +++++++++++++++--------------
 1 file changed, 15 insertions(+), 14 deletions(-)

diff --git a/zebra-chain/src/block/commitment.rs b/zebra-chain/src/block/commitment.rs
index 1251bc7cb0b..7d01a95bc2c 100644
--- a/zebra-chain/src/block/commitment.rs
+++ b/zebra-chain/src/block/commitment.rs
@@ -31,11 +31,11 @@ pub enum Commitment {
     /// Subsequent `Commitment` variants also commit to the `FinalSaplingRoot`,
     /// via their `EarliestSaplingRoot` and `LatestSaplingRoot` fields.
     ///
-    /// TODO: this field is verified during semantic verification
-    ///
     /// Since Zebra checkpoints on Canopy, we don't need to validate this
     /// field, but since it's included in the ChainHistoryRoot, we are
     /// already calculating it, so we might as well validate it.
+    ///
+    /// TODO: this field is verified during semantic verification
     FinalSaplingRoot(sapling::tree::Root),
 
     /// [Heartwood activation block] Reserved field.
@@ -63,7 +63,7 @@ pub enum Commitment {
     /// chain history hash in their activation block, via the previous block
     /// hash field.)
     ///
-    /// TODO: this field is verified during semantic verification
+    /// TODO: this field is verified during contextual verification
     ChainHistoryRoot(ChainHistoryMmrRootHash),
 
     /// [NU5 activation onwards] A commitment to:
@@ -79,11 +79,8 @@ pub enum Commitment {
     ///
     /// See also the [`ChainHistoryRoot`] variant.
     ///
-    /// TODO: this field is verified during semantic verification
-    //
-    // TODO: Do block commitments activate at NU5 activation, or (NU5 + 1)?
-    // https://github.com/zcash/zips/pull/474
-    BlockCommitments(BlockCommitmentsHash),
+    /// TODO: this field is verified during contextual verification
+    ChainHistoryBlockTxAuthCommitment(ChainHistoryBlockTxAuthCommitmentHash),
 }
 
 /// The required value of reserved `Commitment`s.
@@ -116,7 +113,9 @@ impl Commitment {
                 }
             }
             Heartwood | Canopy => Ok(ChainHistoryRoot(ChainHistoryMmrRootHash(bytes))),
-            Nu5 => Ok(BlockCommitments(BlockCommitmentsHash(bytes))),
+            Nu5 => Ok(ChainHistoryBlockTxAuthCommitment(
+                ChainHistoryBlockTxAuthCommitmentHash(bytes),
+            )),
         }
     }
 
@@ -130,7 +129,7 @@ impl Commitment {
             FinalSaplingRoot(hash) => hash.0,
             ChainHistoryActivationReserved => RESERVED_BYTES,
             ChainHistoryRoot(hash) => hash.0,
-            BlockCommitments(hash) => hash.0,
+            ChainHistoryBlockTxAuthCommitment(hash) => hash.0,
         }
     }
 }
@@ -143,17 +142,19 @@ impl Commitment {
 #[derive(Clone, Copy, Debug, Eq, PartialEq, Serialize, Deserialize)]
 pub struct ChainHistoryMmrRootHash([u8; 32]);
 
-/// The Block Commitments for a block. As of NU5, these cover:
+/// A block commitment to chain history and transaction auth.
 /// - the chain history tree for all ancestors in the current network upgrade,
 ///   and
 /// - the transaction authorising data in this block.
+///
+/// Introduced in NU5.
 //
 // TODO:
 //    - add auth data type
 //    - add a method for hashing chain history and auth data together
 //    - move to a separate file
 #[derive(Clone, Copy, Debug, Eq, PartialEq, Serialize, Deserialize)]
-pub struct BlockCommitmentsHash([u8; 32]);
+pub struct ChainHistoryBlockTxAuthCommitmentHash([u8; 32]);
 
 /// Errors that can occur when checking RootHash consensus rules.
 ///
@@ -186,8 +187,8 @@ pub enum CommitmentError {
         actual: [u8; 32],
     },
 
-    #[error("invalid block commitment: expected {expected:?}, actual: {actual:?}")]
-    InvalidBlockCommitment {
+    #[error("invalid chain history + block transaction auth commitment: expected {expected:?}, actual: {actual:?}")]
+    InvalidChainHistoryBlockTxAuthCommitment {
         expected: [u8; 32],
         actual: [u8; 32],
     },