Code Quality Guide

Core Principle

Production database. Correctness paramount. Crash > corrupt.

Correctness Rules

1. No workarounds or quick hacks. Handle all errors, check invariants
2. Assert often. Never silently fail or swallow edge cases
3. Crash on invalid state if it risks data integrity. Don't continue in undefined state
4. Consider edge cases. On long enough timeline, all possible bugs will happen

Rust Patterns

• Make illegal states unrepresentable
• Exhaustive pattern matching
• Prefer enums over strings/sentinels
• Minimize heap allocations
• Write CPU-friendly code (microsecond = long time)

Avoid unwrap()

Never use bare unwrap(). Instead:

For truly unreachable states (invariants that should never be violated):

// Good: documents the invariant
let value = option.expect("value must be set in Init phase");

For recoverable errors (states that could happen at runtime):

// Good: proper error handling
let Some(value) = option else {
    return Err(LimboError::InvalidArgument("value not provided".into()));
};

The choice depends on whether the None/Err case represents:

• A bug in the code (use expect with descriptive message)
• A valid runtime condition (use let ... else or match)

If-Statements

Wrong:

if condition {
    // happy path
} else {
    // "shouldn't happen" - silently ignored
}

Right:

// If only one branch should ever be hit:
assert!(condition, "invariant violated: ...");
// OR
return Err(LimboError::InternalError("unexpected state".into()));
// OR
unreachable!("impossible state: ...");

Use if-statements only when both branches are expected paths.

Comments

Do:

• Document WHY, not what
• Document functions, structs, enums, variants
• Focus on why something is necessary
• Preserve explanatory comments when refactoring

Don't:

• Comments that repeat code
• References to AI conversations ("This test should trigger the bug")
• Temporal markers ("added", "existing code", "Phase 1")

Avoid Over-Engineering

• Only changes directly requested or clearly necessary
• Don't add features beyond what's asked
• Don't add docstrings/comments to unchanged code
• Don't add error handling for impossible scenarios
• Don't create abstractions for one-time operations
• Three similar lines > premature abstraction

Ensure understanding of IO model

• Async IO model

Cleanup

• Delete unused code completely
• No backwards-compat hacks (renamed _vars, re-exports, // removed comments)