Code Quality Guide Skill

Code Quality Guide

Core Principle

Production database. Correctness paramount. Crash > corrupt.

Correctness Rules

No workarounds or quick hacks. Handle all errors, check invariants
Assert often. Never silently fail or swallow edge cases
Crash on invalid state if it risks data integrity. Don't continue in undefined state
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)

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

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

Index Mutations

When code involves index inserts, deletes, or conflict resolution, double-check the ordering against SQLite. Wrong ordering causes index inconsistencies. and easy to miss.

Ensure understanding of IO model

Async IO model

Cleanup

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

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