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    Codebase Bug Fixer

    1

    Diagnose software bugs, trace execution paths, and generate minimal patches with targeted validation tests.

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    Codebase Bug Fixer

    Codebase Bug Fixer

    Example session with this skill installed

    I'm getting 'TypeError: Cannot read properties of undefined (reading 'map')' in my React app when the user filters results too quickly. Here is the component and the stack trace.

    • Read your context and instructions
    • Compiled the codebase bug fixer

    I have analyzed the stack trace and the filtering logic. The crash occurs because the results state is briefly set to null during the transition between rapid filter updates, but the render method assumes an array.

    Bug Analysis and Fix Plan

    Bug Summary

    • Symptom: Application crash (TypeError)
    • Expected: Component should show a loading state or empty list during filter transitions.
    • Actual: results.map is called on an undefined variable.
    • Root-cause confidence: Confirmed

    Execution Trace

    Filter Change Event → handleFilter (Async) → State Update (setResults(undefined)) → Component Re-render → results.map() → Crash

    Recommended Fix

    • File: src/components/SearchGrid.tsx

    Change: Add optional chaining and a fallback empty array to the mapping logic, and initialize state as an empty array.

    • Reason: Prevents the UI from attempting to iterate over non-iterable state during async updates.

    Patch

    // src/components/SearchGrid.tsx

// Before:
// const [results, setResults] = useState();
// {results.map(item => <Card key={item.id} data={item} />)}

// After:
const [results, setResults] = useState<Item[]>([]);

return (
  <div className="grid">
    {results?.map(item => (
      <Card key={item.id} data={item} />
    )) ?? <p>No results found.</p>}
  </div>
);

    Validation Plan

    TestExpected ResultPriority
    Rapid Filter TriggerUI remains stable; no TypeErrorCritical
    Null API ResponseDisplays "No results found"High
    Regression: Valid DataItems render correctly in gridHigh

    Next steps

    1. Apply the initialization change to useState([]) to ensure a consistent data type.
    2. Replace the .map call with the optional chaining implementation.
    3. Verify the fix by spamming the filter inputs in the dev environment.

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    What you get

    Trace 'undefined' errors to the specific point of failure in a call stack.Identify race conditions in async logic and provide thread-safe patches.Generate unit tests that reproduce a reported bug and verify the fix.Audit existing patches for regression risks and side effects on shared state.

    About this skill

    The problem

    Debugging often involves hours of aimless console logging and chasing red herrings. Developers struggle to isolate root causes in complex execution paths or provide minimal fixes that don't break existing functionality.

    What it does

    • Analyzes stack traces and reproduction steps to map the execution flow from trigger to failure.
    • Identifies root causes like race conditions, state synchronization issues, and null handling gaps with evidence-based confidence levels.
    • Designs minimal, architecture-compliant patches that fix the bug without unnecessary refactoring.
    • Generates targeted validation plans including reproduction tests, edge cases, and regression checks.
    • Evaluates side effects on shared state, API consumers, and performance.

    Frameworks & tools

    Works across JavaScript/TypeScript, React/Next.js, Python, Java, C#, Go, PHP, Ruby, and SQL-backed applications.

    Why this beats prompting it yourself

    Generic prompts often suggest "best guess" fixes or rewrite entire modules. This skill enforces a strict REPRODUCE-LOCATE-TRACE workflow that demands evidence before proposing code changes, ensuring you get a surgical patch rather than a destructive hallucination.

    Use cases

    • Tracing an obscure 'undefined' error through a deeply nested React component tree.
    • Debugging race conditions in asynchronous Python or Go backend services.
    • Fixing incorrect state transitions in complex Vue or Angular forms.
    • Patching API contract mismatches between microservices without breaking backward compatibility.

    How to install

    Works the same in every agent - Claude, Cursor, Codex, Copilot and 20+ more.

    ~30 seconds
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    Verified clean 4 days ago

    • Passed all security checks, Safe to install

    Listed4 days ago

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