Critical Issues Skill

Detection of bugs, logic errors, and correctness issues in Compact smart contracts.

When to Use

This skill activates for queries about:

• Bug detection and logic errors
• Assertion problems
• Type mismatches
• Dead code and unreachable paths
• Control flow issues
• State management bugs

Trigger words: bug, logic error, assertion, unreachable, dead code, type mismatch, correctness

Quick Reference

Common Bug Categories

Bug Detection Patterns

// ❌ Assertion that always fails
export circuit verify(x: Uint<64>, y: Uint<64>): [] {
    assert x > y;     // Called with x = 0
    assert x <= y;    // Contradictory assertions
}

// ❌ Dead code after return
export circuit process(): Uint<64> {
    return 42;
    const x = 1;  // Never executes
}

// ❌ Off-by-one error
export circuit fill_array(): [] {
    for i in 0..100 {
        items[i + 1].write(0);  // Skips index 0, overflows at 100
    }
}

Review Process

1. Assertion Analysis

For each assertion:

1. Determine if condition can ever be true/false
2. Check for contradictory assertions
3. Verify assertion is meaningful

Patterns to flag:

• assert true - Useless
• assert false - Circuit always fails
• assert x && !x - Contradiction
• Assertion after assignment that makes it always pass

2. Control Flow Analysis

Trace all execution paths:

1. Identify unreachable code
2. Check all branches return appropriate values
3. Verify loop bounds

Patterns to flag:

• Code after return
• if with identical branches
• Loops that never execute (for i in 0..0)
• Infinite loops (if possible)

3. Type Correctness

Verify type usage:

1. Comparisons between compatible types
2. Arithmetic within bounds
3. Array/map access with correct index types

4. State Consistency

Check ledger operations:

1. Read-before-write patterns
2. Inconsistent state updates
3. Missing initialization

References

• Common Bugs - Catalog of Compact-specific bugs
• Logic Error Patterns - Detection patterns

Related Skills

• security-review - Security vulnerabilities
• compact-core/language-reference - Type system