From c3779caedefd86b9ecb24eba8cd553be065d9bb5 Mon Sep 17 00:00:00 2001
From: Paul Hauner <paul@paulhauner.com>
Date: Wed, 17 Apr 2019 13:59:40 +1000
Subject: [PATCH] Add extra info to block proc. error message

---
 eth2/state_processing/src/per_block_processing.rs        | 9 +++++++--
 eth2/state_processing/src/per_block_processing/errors.rs | 5 ++++-
 2 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/eth2/state_processing/src/per_block_processing.rs b/eth2/state_processing/src/per_block_processing.rs
index 257d92acf..58b948f62 100644
--- a/eth2/state_processing/src/per_block_processing.rs
+++ b/eth2/state_processing/src/per_block_processing.rs
@@ -107,9 +107,14 @@ pub fn process_block_header(
 ) -> Result<(), Error> {
     verify!(block.slot == state.slot, Invalid::StateSlotMismatch);
 
+    let expected_previous_block_root =
+        Hash256::from_slice(&state.latest_block_header.signed_root());
     verify!(
-        block.previous_block_root == Hash256::from_slice(&state.latest_block_header.signed_root()),
-        Invalid::ParentBlockRootMismatch
+        block.previous_block_root == expected_previous_block_root,
+        Invalid::ParentBlockRootMismatch {
+            state: expected_previous_block_root,
+            block: block.previous_block_root,
+        }
     );
 
     state.latest_block_header = block.temporary_block_header(spec);
diff --git a/eth2/state_processing/src/per_block_processing/errors.rs b/eth2/state_processing/src/per_block_processing/errors.rs
index 9c36e0238..d8627d359 100644
--- a/eth2/state_processing/src/per_block_processing/errors.rs
+++ b/eth2/state_processing/src/per_block_processing/errors.rs
@@ -67,7 +67,10 @@ impl_from_beacon_state_error!(BlockProcessingError);
 #[derive(Debug, PartialEq)]
 pub enum BlockInvalid {
     StateSlotMismatch,
-    ParentBlockRootMismatch,
+    ParentBlockRootMismatch {
+        state: Hash256,
+        block: Hash256,
+    },
     BadSignature,
     BadRandaoSignature,
     MaxAttestationsExceeded,