focused-fix

Focused Fix

Category: Engineering

Domain: Debugging & Maintenance

Overview

The Focused Fix skill enforces a disciplined minimal-change approach to bug fixing. Instead of refactoring or improving code during a bugfix, it identifies the smallest possible change set that resolves the issue. This reduces risk, simplifies code review, and prevents scope creep.

Use when

• The user asks to "fix a bug with minimal changes", "do a focused bugfix", or "scope a minimal repair"
• A bug report needs triage to identify the smallest set of files to touch
• A PR is at risk of scope creep (unrelated refactors, style changes, "nearby" fixes)
• A hotfix or release-blocker needs a low-risk, reviewable change set
• The user asks "what is the minimal change to fix X?" or "which files do I need to touch for this bug?"

Quick Start

# Analyze a bug description to identify minimal change scope
python scripts/change_scope_analyzer.py --bug "Login fails when email has + character" --path ./src

# Analyze with JSON output
python scripts/change_scope_analyzer.py --bug "API returns 500 on empty array input" --path ./src --format json

# Analyze with specific file extensions
python scripts/change_scope_analyzer.py --bug "CSS overflow on mobile" --path ./src --extensions .css .scss .html

Tools Overview

| Tool | Purpose | Key Flags | |------|---------|-----------| | change_scope_analyzer.py | Identify minimal files to change for a bugfix | --bug, --path, --extensions, --format |

change_scope_analyzer.py

Analyzes a bug description against a codebase to identify:

• Files most likely related to the bug (keyword matching, import tracing)
• Estimated change scope (number of files, lines)
• Risk assessment for the change
• Recommended fix approach (minimal vs. structural)

Workflows

Focused Bugfix Workflow

1. Write a clear bug description — reproduction steps, expected vs actual behavior
2. Validate: the description names the observable failure, not a guess at the cause
3. Run change_scope_analyzer.py to identify scope
4. Validate: analyzer output lists concrete files and an estimated line count
5. Review the recommended files and approach
6. Validate: recommended approach is "minimal" — if it says "structural", stop and scope a refactor PR separately
7. Make ONLY the changes needed to fix the bug
8. Validate: git diff --stat matches (or is smaller than) the analyzer's recommendation
9. Verify no unrelated changes leaked in
10. Validate: git diff shows no formatting-only changes, no unrelated imports, no "while I'm here" edits
11. Submit PR with focused change set
12. Validate: commit message states the exact bug fixed, and a regression test is included

Scope Validation

1. After making changes, re-run analyzer
2. Compare actual changes against recommended scope
3. Flag any out-of-scope modifications for separate PRs
4. Validate: any file touched that was not in the analyzer recommendation has a one-line justification or is reverted

Reference Documentation

• [Focused Fix Methodology](references/focused-fix-methodology.md) - Principles, anti-patterns, and decision framework

Common Patterns

Do

• Fix the exact bug reported
• Add a regression test for the fix
• Document why the fix works in the commit message
• Keep the diff as small as possible

Don't

• Refactor surrounding code during a bugfix
• Fix "nearby" issues in the same PR
• Change formatting or style in touched files
• Add features disguised as bugfixes

Anti-patterns

| Anti-pattern | Failure mode | Fix | |--------------|--------------|-----| | "While I'm here" refactors in the bugfix PR | Blast radius explodes; review time multiplies; unrelated regressions masked by the real fix | Open a separate PR for the refactor, tagged as refactor: not fix: | | Reformatting or auto-save style changes in touched files | Diff becomes unreadable; real fix hidden in 200 lines of whitespace | Revert style changes before committing; configure the editor to format-on-save only for new files | | Fixing the symptom in the wrong layer | Bug returns in a new form; accumulates workaround debt | Trace to the root layer — analyzer's keyword-match output is a hint, not an answer | | Skipping the regression test "because the fix is obvious" | Bug silently returns on a refactor 6 months later | Every fix: commit adds at least one failing-then-passing test | | Treating change_scope_analyzer.py output as authoritative | Analyzer is keyword/import-based, not semantic — misses dynamic dispatch, reflection, config-driven paths | Use it as a starting set; grep for callers and tests before committing to the scope | | Bundling the fix with a dependency upgrade | Two risk profiles in one PR; if rollback is needed, both are lost | Land the upgrade separately, then the fix against the upgraded baseline |