Bug History Summarizer Agent Skill

Bug History Summarizer

Trace and summarize the complete lifecycle of a bug across code versions.

Workflow

Follow these steps to generate a comprehensive bug history summary:

1. Identify the Bug and Gather Context

Collect essential information:

• Bug identifier: Issue number, commit hash, or bug description
• Repository: Target codebase with version history
• Version range: Specific versions/commits to analyze (or entire history)
• Related artifacts: Issue reports, pull requests, commit messages, test results

2. Trace Bug Introduction

Identify when and how the bug was introduced:

Using git blame and bisect:

• Run git blame on affected files to find when problematic lines were added
• Use git bisect to pinpoint the exact commit that introduced the bug
• Analyze the introducing commit: author, date, purpose, related changes

Analyze introduction context:

• What was the original intent of the change?
• Was it a new feature, refactoring, or bug fix?
• Were there code review comments or warnings?
• What tests existed at the time?

3. Track Detection History

Document when and how the bug was discovered:

• Initial detection: When was the bug first reported or noticed?
• Detection method: User report, automated test, code review, production incident?
• Time to detection: How long between introduction and discovery?
• Severity assessment: How was the bug initially classified?

4. Analyze Fix Attempts

Chronicle all attempts to fix the bug:

For each fix attempt:

• Commit hash and date
• Author and reviewer
• Fix approach and code changes
• Test coverage added
• Whether the fix was successful or reverted

Identify patterns:

• Multiple fix attempts indicate complexity
• Reverted fixes suggest incomplete understanding
• Test additions show learning from the bug

5. Check for Regressions

Identify if the bug reappeared after being fixed:

• Search for related bug reports after the fix
• Check if the fix was reverted or modified
• Look for similar bugs in related code
• Analyze if the bug reoccurred in different contexts

6. Generate Summary Report

Create a structured timeline and analysis:

Timeline format:

## Bug History: [Bug Title/ID]

### Introduction
- **When**: [Date/Commit]
- **Where**: [File:Line]
- **How**: [Description of introducing change]
- **Context**: [Why the change was made]

### Detection
- **Discovered**: [Date]
- **Method**: [How it was found]
- **Time to Detection**: [Duration]
- **Initial Impact**: [Severity/Scope]

### Fix Attempts
1. **Attempt 1** ([Date/Commit])
   - Approach: [Description]
   - Outcome: [Success/Failure/Partial]
   - Tests Added: [Yes/No]

2. **Attempt 2** ([Date/Commit])
   - ...

### Regressions
- **Regression 1** ([Date])
  - Cause: [Why it reappeared]
  - Fix: [How it was resolved]

### Current Status
- [Fixed/Open/Recurring]
- Last modified: [Date]

### Lessons Learned
- [Key insights from the bug's history]

Example

Input:

• Repository: myapp
• Bug: "Null pointer exception in user login"
• Issue: #456

Analysis Process:

• Git blame shows the problematic code was added in commit abc123 on 2024-01-15
• Commit analysis reveals it was part of a refactoring to improve performance
• Issue tracker shows bug reported on 2024-02-20 (36 days after introduction)
• Fix attempts:
• First fix (commit def456, 2024-02-21): Added null check, but incomplete
• Second fix (commit ghi789, 2024-02-25): Comprehensive fix with tests
• Regression check: No regressions found

Generated Summary:

## Bug History: Null Pointer Exception in User Login (#456)

### Introduction
- **When**: 2024-01-15 (commit abc123)
- **Where**: src/auth/LoginHandler.java:45
- **How**: Refactoring removed null check during performance optimization
- **Context**: Part of PR #234 to reduce login latency

### Detection
- **Discovered**: 2024-02-20
- **Method**: Production incident report
- **Time to Detection**: 36 days
- **Initial Impact**: High severity - blocking user logins

### Fix Attempts
1. **Attempt 1** (2024-02-21, commit def456)
   - Approach: Added null check for user object
   - Outcome: Partial - fixed main case but missed edge case
   - Tests Added: Yes (1 unit test)

2. **Attempt 2** (2024-02-25, commit ghi789)
   - Approach: Comprehensive null handling with validation
   - Outcome: Success
   - Tests Added: Yes (3 unit tests + 1 integration test)

### Regressions
- None detected

### Current Status
- Fixed (as of 2024-02-25)
- Last modified: commit ghi789

### Lessons Learned
- Performance optimizations should maintain defensive checks
- Initial fix was too narrow - comprehensive testing revealed edge cases
- Added regression tests to prevent reintroduction

Output Format

Provide:

• Structured timeline in Markdown format
• Key metrics:
• Time to detection
• Number of fix attempts
• Time to resolution
• Regression count
• Visual timeline (optional, using ASCII or Mermaid):

   2024-01-15: Bug introduced (commit abc123)
        |
        | (36 days)
        |
   2024-02-20: Bug detected (issue #456)
        |
        | (1 day)
        |
   2024-02-21: Fix attempt 1 (partial)
        |
        | (4 days)
        |
   2024-02-25: Fix attempt 2 (success)

• Lessons learned and recommendations

Git Commands Reference

Useful commands for bug history analysis:

# Find when a line was introduced
git blame <file>

# Find the commit that introduced a bug
git bisect start
git bisect bad <bad-commit>
git bisect good <good-commit>

# Search commit messages for bug references
git log --grep="<bug-id>" --oneline

# Show commits that modified a specific file
git log --follow -- <file>

# Show commits in a date range
git log --since="2024-01-01" --until="2024-12-31"

# Find commits by author
git log --author="<name>"

# Show detailed commit information
git show <commit-hash>

Tips for Effective Bug History Analysis

• Start with the fix - Work backwards from the fix commit to understand the bug
• Check related files - Bugs often span multiple files
• Read commit messages - They provide context about intent
• Review pull requests - Comments reveal decision-making
• Check test history - Tests added after bugs show learning
• Look for patterns - Similar bugs may have related causes
• Consider context - Deadlines, team changes, and technical debt affect bug introduction