fix: use latest block for eth_fillTransaction gas estimation

[luchenqun]

Summary

• use EthLatestBlockNumber instead of numeric 0 when eth_fillTransaction estimates gas
• keep eth_fillTransaction aligned with the latest state instead of block 1

Why

SetTxDefaults currently builds a BlockNumberOrHash with NewBlockNumber(big.NewInt(0)) before calling EstimateGas.
That is not equivalent to latest in this codebase:

• BlockNumberFromComet returns the numeric block number unchanged
• BlockNumber.Int64() maps numeric 0 to 1
• so CometHeaderByNumber resolves block 1, not the latest block

Using EthLatestBlockNumber makes the call match the intended latest-state behavior.

Verification

• go test ./rpc/backend -run TestDoesNotExist -count=0

Related: #1120

[luchenqun]

@swift1337 the crux is in getHeightByBlockNum itself. Here is the relevant code path:

func (b *Backend) getHeightByBlockNum(ctx context.Context, blockNum rpctypes.BlockNumber) (height int64, err error) {
	ctx, span := tracer.Start(ctx, "getHeightByBlockNum", trace.WithAttributes(attribute.Int64("blockNum", blockNum.Int64())))
	defer func() { evmtrace.EndSpanErr(span, err) }()

	if blockNum == rpctypes.EthEarliestBlockNumber {
		status, err := b.ClientCtx.Client.Status(ctx)
		if err != nil {
			return 0, errors.New("failed to get earliest block height")
		}

		return status.SyncInfo.EarliestBlockHeight, nil
	}

	height = blockNum.Int64()
	if height <= 0 {
		// In cometBFT, LatestBlockNumber, FinalizedBlockNumber, SafeBlockNumber all map to the latest block height.

The important detail is that eth_fillTransaction was not passing EthLatestBlockNumber. It was passing plain numeric 0 via NewBlockNumber(big.NewInt(0)).

In this codebase, when blockNum is plain numeric 0, height = blockNum.Int64() becomes 1, not 0.
So if height <= 0 is never reached in that case. That behavior comes from rpc/types/block.go:

// Int64 converts block number to primitive type
func (bn BlockNumber) Int64() int64 {
	if bn < 0 {
		return 0
	} else if bn == 0 {
		return 1
	}

	return int64(bn)
}

That means the old flow is effectively:

• eth_fillTransaction passes numeric 0
• BlockNumberFromComet returns that numeric 0 unchanged
• height = blockNum.Int64() turns it into 1
• the height <= 0 fallback is skipped
• the RPC resolves block 1, not latest

So the comment in getHeightByBlockNum is correct for the special negative enum values like EthLatestBlockNumber, but it does not apply to plain numeric 0.

This is also easy to verify in practice: if you deploy a contract after block 1 and then call eth_fillTransaction against that contract to estimate gas, the old path will still resolve block 1, so the estimation fails reproducibly.

[vladjdk]

@greptile review

[vladjdk]

We should add a test for the intended behaviour here to prevent future regressions.

[greptile-apps]

Greptile Summary

Fixes a bug in SetTxDefaults where gas estimation for eth_fillTransaction used NewBlockNumber(big.NewInt(0)), which resolves to block 1 instead of the latest block. The fix replaces it with EthLatestBlockNumber so gas is estimated against the current chain state.

Confidence Score: 5/5

Safe to merge — targeted one-line bug fix with no regressions expected.

The change is a single-line, well-understood bug fix. The old code resolved block 1 due to a quirk in BlockNumber.Int64() mapping numeric 0 to 1; using EthLatestBlockNumber correctly targets the latest state. No surrounding logic is changed and the fix directly matches the stated intent.

No files require special attention.

Important Files Changed

Filename	Overview
rpc/backend/call_tx.go	Single-line fix replacing NewBlockNumber(big.NewInt(0)) with EthLatestBlockNumber to correctly target the latest block for gas estimation.
CHANGELOG.md	Adds a changelog entry for PR #1138 under the unreleased section.

Sequence Diagram

sequenceDiagram
    participant Client
    participant Backend as rpc/backend
    participant EstimateGas
    participant Comet as CometHeaderByNumber

    Client->>Backend: eth_fillTransaction(tx without gas)
    Note over Backend: args.Gas == nil
    Backend->>EstimateGas: EstimateGas(callArgs, EthLatestBlockNumber)
    EstimateGas->>Comet: resolve "latest" block
    Comet-->>EstimateGas: current head header
    EstimateGas-->>Backend: estimated gas
    Backend-->>Client: filled transaction (with gas)

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_{Reviews (1): Last reviewed commit: "Merge branch 'main' into fix-fill-transa..." | Re-trigger Greptile}

[aljo242]

fix is correct, but two issues:

ci has not run: all workflows are action_required -- fork pr, needs maintainer approval to trigger.

test doesn't pin the fix: the "estimate gas with latest block" case mocks EstimateGas with mock.AnythingOfType("*types.EthCallRequest"), which matches any request regardless of block number. the specific regression (block 1 vs latest) isn't asserted and could be reintroduced without breaking the test. assert that the BlockNumber on the EthCallRequest is EthLatestBlockNumber.