Improve main entrypoint error reporting

[dicethedev]

🗒️ Description / Motivation

• Replaces panic-based startup error handling in bin/ethlambda with eyre errors and contextual messages.
• This is needed so initialization failures report useful causes and paths instead of panicking through unwrap/expect.
• Solves issue Improve error reporting in main entrypoint #100 for the main entrypoint by improving error reporting in non-library binary code.

What Changed

• Updated bin/ethlambda/src/main.rs.
• Added eyre::WrapErr usage around startup IO, parsing, tracing setup, RocksDB initialization, validator key loading, and swarm construction.
• Changed helper functions to return eyre::Result instead of panicking or exiting internally.

Correctness / Behavior Guarantees

• Startup still fails fast on invalid configuration, keys, storage, or swarm setup.
• Failure mode changed from panic/internal exit to structured eyre errors with context.
• No consensus, networking, storage, or RPC behavior changes are intended.

Tests Added / Run

• No new tests were added.
• Ran:
  • cargo fmt --check
  • cargo check -p ethlambda
  • cargo test -p ethlambda
  • cargo test -p ethlambda-p2p

Related Issues / PRs

• Closes Improve error reporting in main entrypoint #100
• Related to #

✅ Verification Checklist

• Ran cargo fmt --check — clean
• [ x] Ran make fmt — not run
• [ x] Ran make lint (clippy with -D warnings) — not run
• [ x] Ran cargo test --workspace --release — not run

[greptile-apps]

Greptile Summary

This PR replaces all unwrap/expect/process::exit startup error paths in bin/ethlambda/src/main.rs with structured eyre::Result propagation, adding contextual messages (including file paths) at each failure site.

• Helper functions (read_hex_file_bytes, read_validator_config_file, read_bootnodes, read_validator_keys) now return eyre::Result instead of panicking or calling process::exit, and all callsites are updated with ?.
• Error messages are enriched with file paths and operation context using wrap_err_with, making startup failures significantly easier to diagnose.

Confidence Score: 4/5

Safe to merge — all changes are confined to startup error-path refactoring with no logic or behavior modifications.

The change is a straightforward mechanical refactor of startup error handling. The only notable issue is a redundant map_err before wrap_err_with in the RocksDB open call that needlessly stringifies the error and drops its chain — a cosmetic concern that doesn't affect correctness.

No files require special attention; bin/ethlambda/src/main.rs is the sole changed file and the changes are isolated to error-handling plumbing.

Important Files Changed

Filename	Overview
bin/ethlambda/src/main.rs	Replaces all unwrap/expect/process::exit startup paths with eyre::Result propagation; one minor redundant map_err for the RocksDB open call, but otherwise clean.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[main] --> B[set_global_default tracing subscriber]
    B -->|Err| Z1[eyre: failed to set global tracing subscriber]
    B --> C[read_hex_file_bytes node_key]
    C -->|Err| Z2[eyre: failed to load node key from path]
    C --> D[read_to_string config_path]
    D -->|Err| Z3[eyre: failed to read genesis config from path]
    D --> E[serde_yaml_ng::from_str GenesisConfig]
    E -->|Err| Z4[eyre: failed to parse genesis config from path]
    E --> F[read_validator_config_file]
    F -->|Err| Z5[eyre: failed to read/parse validator config]
    F --> G[read_bootnodes]
    G -->|Err| Z6[eyre: failed to read/parse bootnodes]
    G --> H[read_validator_keys]
    H -->|Err| Z7[eyre: failed to load validator keys]
    H --> I[create_dir_all data_dir]
    I -->|Err| Z8[eyre: failed to create data directory]
    I --> J[RocksDBBackend::open]
    J -->|Err| Z9[eyre: failed to open RocksDB at path]
    J --> K[build_swarm]
    K -->|Err| Z10[eyre: failed to build swarm]
    K --> L[P2P::spawn — node running]

Loading

Prompt To Fix All With AI

Fix the following 1 code review issue. Work through them one at a time, proposing concise fixes.

---

### Issue 1 of 1
bin/ethlambda/src/main.rs:225-229
Redundant `map_err` before `wrap_err_with` loses the original error chain. `RocksDBBackend::open` returns `Result<_, Box<dyn std::error::Error + Send + Sync>>`, which already satisfies the `std::error::Error` bound required by `WrapErr`, so the intermediate `map_err(|err| eyre::eyre!("{err}"))` step — which stringifies the error and discards its chain — is unnecessary. Removing it lets eyre preserve the source error as a proper cause.

```suggestion
    let backend = Arc::new(
        RocksDBBackend::open(&data_dir)
            .wrap_err_with(|| format!("failed to open RocksDB at {}", data_dir.display()))?,
    );
```

_{Reviews (1): Last reviewed commit: "Improve main entrypoint error reporting" | Re-trigger Greptile}

[greptile-apps]

Redundant map_err before wrap_err_with loses the original error chain. RocksDBBackend::open returns Result<_, Box<dyn std::error::Error + Send + Sync>>, which already satisfies the std::error::Error bound required by WrapErr, so the intermediate map_err(|err| eyre::eyre!("{err}")) step — which stringifies the error and discards its chain — is unnecessary. Removing it lets eyre preserve the source error as a proper cause.

Suggested change

	let backend = Arc::new(
	RocksDBBackend::open(&data_dir)
	.map_err(|err| eyre::eyre!("{err}"))
	.wrap_err_with(|| format!("failed to open RocksDB at {}", data_dir.display()))?,
	);
	let backend = Arc::new(
	RocksDBBackend::open(&data_dir)
	.wrap_err_with(|| format!("failed to open RocksDB at {}", data_dir.display()))?,
	);

Prompt To Fix With AI

This is a comment left during a code review.
Path: bin/ethlambda/src/main.rs
Line: 225-229

Comment:
Redundant `map_err` before `wrap_err_with` loses the original error chain. `RocksDBBackend::open` returns `Result<_, Box<dyn std::error::Error + Send + Sync>>`, which already satisfies the `std::error::Error` bound required by `WrapErr`, so the intermediate `map_err(|err| eyre::eyre!("{err}"))` step — which stringifies the error and discards its chain — is unnecessary. Removing it lets eyre preserve the source error as a proper cause.

```suggestion
    let backend = Arc::new(
        RocksDBBackend::open(&data_dir)
            .wrap_err_with(|| format!("failed to open RocksDB at {}", data_dir.display()))?,
    );
```

How can I resolve this? If you propose a fix, please make it concise.

Note: If this suggestion doesn't match your team's coding style, reply to this and let me know. I'll remember it for next time!