fix attachMerkleProofs to support multiple deposits (#4932)

`attachMerkleProofs` is used by `mockUpdateStateForNewDeposit` to create
a single deposit. The function doesn't work correctly when trying with
with multiple deposits, though. Fix this to enable more complex tests,
and also return the `deposit_root` for forming matching `Eth1Data`.

beacon_chain/eth1/merkle_minimal.nim

@@ -19,17 +19,8 @@ import
   ../spec/[eth2_merkleization, digest],
   ../spec/datatypes/base
 
-func attachMerkleProofs*(deposits: var openArray[Deposit]) =
-  let depositsRoots = mapIt(deposits, hash_tree_root(it.data))
-
-  var incrementalMerkleProofs = createMerkleizer(DEPOSIT_CONTRACT_LIMIT)
-
-  for i in 0 ..< depositsRoots.len:
-    incrementalMerkleProofs.addChunkAndGenMerkleProof(depositsRoots[i], deposits[i].proof)
-    deposits[i].proof[32] = default(Eth2Digest)
-    deposits[i].proof[32].data[0..7] = toBytesLE uint64(i + 1)
-
-template getProof*(proofs: seq[Eth2Digest], idxParam: int): openArray[Eth2Digest] =
+template getProof*(
+    proofs: seq[Eth2Digest], idxParam: int): openArray[Eth2Digest] =
   let
     idx = idxParam
     ## TODO: It's surprising that we have to do +1 here.
@@ -38,3 +29,15 @@ template getProof*(proofs: seq[Eth2Digest], idxParam: int): openArray[Eth2Digest
     endIdx = startIdx + DEPOSIT_CONTRACT_TREE_DEPTH - 1
   proofs.toOpenArray(startIdx, endIdx)
 
+func attachMerkleProofs*(deposits: var openArray[Deposit]): Eth2Digest =
+  let depositsRoots = mapIt(deposits, hash_tree_root(it.data))
+
+  var merkleizer = createMerkleizer(DEPOSIT_CONTRACT_LIMIT)
+  let proofs = merkleizer.addChunksAndGenMerkleProofs(depositsRoots)
+  for i in 0 ..< depositsRoots.len:
+    deposits[i].proof[0 ..< DEPOSIT_CONTRACT_TREE_DEPTH] = getProof(proofs, i)
+    deposits[i].proof[DEPOSIT_CONTRACT_TREE_DEPTH] = default(Eth2Digest)
+    deposits[i].proof[DEPOSIT_CONTRACT_TREE_DEPTH].data[0..7] =
+      toBytesLE deposits.lenu64
+
+  mixInLength(merkleizer.getFinalHash(), deposits.len)

tests/mocking/mock_deposits.nim

@@ -126,12 +126,11 @@ proc mockUpdateStateForNewDeposit*(
   )
 
   var result_seq = @[result]
-  attachMerkleProofs(result_seq)
+  let deposit_root = attachMerkleProofs(result_seq)
   result.proof = result_seq[0].proof
 
   # TODO: this logic from the consensus-specs test suite seems strange
   #       but confirmed by running it
   state.eth1_deposit_index = 0
-  state.eth1_data.deposit_root =
-     hash_tree_root(List[DepositData, 2'i64^DEPOSIT_CONTRACT_TREE_DEPTH](@[result.data]))
+  state.eth1_data.deposit_root = deposit_root
   state.eth1_data.deposit_count = 1