[SharovBot] fix: prestate tracer missing zero-codeHash accounts in post diffMode state

[erigon-copilot]

[SharovBot]

Problem

In debug_traceBlockByNumber (and related RPC methods) using the prestateTracer in diffMode, accounts that are touched for the first time during a transaction (e.g. the target of a CALL with zero balance) should appear in the post state with codeHash: 0x0. Erigon was not including these entries, while the reference node (go-ethereum) was.

Failing CI test: mainnet-rpc-integ-tests-latest → debug_traceBlockByNumber/test_42.json (consistent across all 10 recent release/3.4 commits)

Root Cause

In processDiffState(), the comparison to detect codeHash changes used common.Hash{} (all zeros) as the default prevCodeHash. For non-existent accounts, newCodeHash was also computed as common.Hash{} (since GetCode returns empty bytes). This meant prevCodeHash == newCodeHash → modified = false → the account was pruned from both pre and post.

go-ethereum uses EmptyCodeHash (keccak256("") = 0xc5d246...) as the default prevCodeHash. For non-existent accounts, GetCodeHash returns 0x0 (NilCodeHash), so 0x0 != EmptyCodeHash → modified = true → the account appears in post with codeHash: 0x0.

Fix

Mirror go-ethereum's logic in processDiffState():

1. Use Exist() to distinguish non-existent accounts (codeHash = 0x0) from existing codeless accounts (codeHash = EmptyCodeHash).
2. Use accounts.EmptyCodeHash as the default prevCodeHash when no codeHash is stored in the pre-state.

Testing

• go build ./execution/tracing/tracers/native/ ✅
• go test ./execution/tracing/... ✅ all pass
• This fix addresses the consistent debug_traceBlockByNumber/test_42 failure in mainnet-rpc-integ-tests-latest CI

[erigon-copilot]

[SharovBot] pushed a follow-up fix to this branch.

Problem: The previous commit changed prevCodeHash to default to EmptyCodeHash in processDiffState, but this broke debug_traceBlockByNumber/test_33.tar and test_34.tar — accounts that existed with no code before the tx were no longer distinguishable from accounts that didn't exist at all.

Root cause: In lookupAccount, existing codeless accounts had their CodeHash set to nil, same as non-existent accounts. In processDiffState, a nil CodeHash was then ambiguous.

Fix: Moved the Exist() check into lookupAccount itself: existing codeless accounts now get EmptyCodeHash stored, while non-existent accounts keep nil CodeHash. processDiffState reverts to the natural common.Hash{} default for prevCodeHash — so:

• Existing codeless pre-tx: prevCodeHash=EmptyCodeHash = newCodeHash=EmptyCodeHash → not in diff ✓
• Non-existent pre-tx + touched: prevCodeHash=0x0 ≠ newCodeHash=EmptyCodeHash → in diff with codeHash=0x0 ✓ (test_42 fix preserved)