Bug Fix Generator

Templates and patterns for generating minimal, safe bug fixes.

Fix Generation Principles

1. Minimal Change

• Fix only what's broken
• No refactoring
• No "improvements"
• No formatting changes

2. Safe Change

• Preserve existing behavior
• Maintain API contracts
• Keep backward compatibility
• Add, don't remove

3. Tested Change

• Reproduction test first
• Fix makes test pass
• Existing tests still pass

Fix Templates by Category

Category	Patterns	See
Null Pointer	Guard clause, Null object, Optional return	templates.md
Logic Error	Condition correction, Boolean inversion, Missing case	templates.md
Boundary	Empty check, Index bounds, Range validation	templates.md
Race Condition	Database locking, Optimistic locking, Atomic operation	templates.md
Resource Leak	Try-finally, Higher-level API, Pool return	templates.md
Exception	Specific catch, Exception chaining, Proper re-throw	templates.md
Type Safety	Strict types, Type validation, Boundary coercion	templates.md
SQL Injection	Prepared statement, Query builder	templates.md
Infinite Loop	Iteration limit, Visited tracking, Depth limit	templates.md

Quick Reference

Null Pointer → Guard Clause

$entity = $this->repository->find($id);
if ($entity === null) {
    throw new EntityNotFoundException($id);
}

Logic Error → Condition Fix

// Wrong: if ($a > $b)
// Fixed: if ($a >= $b)

Boundary → Empty Check

if ($items === []) {
    throw new EmptyCollectionException();
}

Race Condition → Locking

$this->em->beginTransaction();
try {
    $entity = $this->repository->findWithLock($id);
    // ... modify ...
    $this->em->commit();
} catch (\Throwable $e) {
    $this->em->rollback();
    throw $e;
}

Resource Leak → Try-Finally

$resource = acquire();
try {
    return process($resource);
} finally {
    release($resource);
}

Fix Composition Rules

Order of Operations

1. Add validation/guards at the top
2. Make the minimal code change
3. Keep existing code paths intact
4. Add new exception types if needed

What NOT to Change

• Method signatures (unless required)
• Return types (unless fixing wrong type)
• Visibility modifiers
• Class structure
• Unrelated code

Commit Message Format

fix(<scope>): <short description>

<detailed description of what was wrong and how it's fixed>

Fixes #<issue-number>