fix: check prefix error to contain the index of the problematic block

Author: kaimast

ledger/src/check_next_block.rs

@@ -52,8 +52,8 @@ pub enum CheckBlockError<N: Network> {
     #[error("Block has invalid hash")]
     InvalidHash,
     /// An error related to the given prefix of pending blocks.
-    #[error("Prefix of the block at height {height} is incorrect - {error:?}")]
-    InvalidPrefix { height: u32, error: Box<CheckBlockError<N>> },
+    #[error("The prefix as an error at index {index} - {error:?}")]
+    InvalidPrefix { index: usize, error: Box<CheckBlockError<N>> },
     #[error("The block contains solution '{solution_id}', but it already exists in the ledger")]
     SolutionAlreadyExists { solution_id: SolutionID<N> },
     #[error("Failed to speculate over unconfirmed transactions - {inner}")]
@@ -115,10 +115,10 @@ impl<N: Network, C: ConsensusStorage<N>> Ledger<N, C> {
         // First check that the heights and hashes of the pending block sequence and of the new block are correct.
         // The hash checks should be redundant, but we perform them out of extra caution.
         let mut expected_height = latest_block.height() + 1;
-        for prefix_block in prefix {
+        for (index, prefix_block) in prefix.iter().enumerate() {
             if prefix_block.height() != expected_height {
                 return Err(CheckBlockError::InvalidPrefix {
-                    height: prefix_block.height(),
+                    index,
                     error: Box::new(CheckBlockError::InvalidHeight {
                         expected: expected_height,
                         actual: prefix_block.height(),
@@ -128,7 +128,7 @@ impl<N: Network, C: ConsensusStorage<N>> Ledger<N, C> {
 
             if self.contains_block_hash(&prefix_block.hash())? {
                 return Err(CheckBlockError::InvalidPrefix {
-                    height: prefix_block.height(),
+                    index,
                     error: Box::new(CheckBlockError::BlockAlreadyExists { hash: prefix_block.hash() }),
                 });
             }

ledger/tests/pending_blocks.rs

@@ -121,13 +121,13 @@ fn test_prefix_with_duplicate_block_error() {
 
     // Test a prefix that contains block2 twice.
     let result = ledger.check_block_subdag(block4.clone(), &[block2.clone(), block2.clone(), block3.clone()]);
-    assert!(matches!(result, Err(CheckBlockError::InvalidPrefix { height: 2, .. })));
+    assert!(matches!(result, Err(CheckBlockError::InvalidPrefix { index: 1, .. })));
     let CheckBlockError::InvalidPrefix { error, .. } = result.unwrap_err() else { unreachable!() };
     assert!(matches!(*error, CheckBlockError::InvalidHeight { expected: 3, actual: 2 }));
 
     // Test a prefix that misses block 2.
     let result = ledger.check_block_subdag(block4.clone(), &[block3]);
-    assert!(matches!(result, Err(CheckBlockError::InvalidPrefix { height: 3, .. })));
+    assert!(matches!(result, Err(CheckBlockError::InvalidPrefix { index: 0, .. })));
     let CheckBlockError::InvalidPrefix { error, .. } = result.unwrap_err() else { unreachable!() };
     assert!(matches!(*error, CheckBlockError::InvalidHeight { expected: 2, actual: 3 }));
 }