PR Auto Update

PR Auto Update

Automatically update Pull Request descriptions by analyzing Git changes. Preserves existing content and only fills in empty sections.

Arguments

• --pr <number>: Target PR number (auto-detected from current branch if omitted)
• --dry-run: Show generated content without actually updating
• --lang <en|ja>: Force output language (en or ja)

Steps

1. Detect Target PR

# Auto-detect from current branch
gh pr list --head $(git branch --show-current) --json number,title,url --jq '.[0]'

# Or use specified PR number
gh pr view <number> --json number,title,url,body,labels

• If --pr <number> is specified in $ARGUMENTS, use that PR
• Otherwise, find the PR associated with the current branch
• If no PR is found, inform the user and stop

2. Analyze Changes

# Get changed files
gh pr diff <number> --name-only

# Get diff content (limit to first 1000 lines for large PRs)
gh pr diff <number> | head -1000

# Get commit history
gh pr view <number> --json commits --jq '.commits[].messageHeadline'

Analyze the following dimensions:

• File patterns: docs, tests, CI/CD, dependencies, source code
• Change content: bug fixes, new features, refactoring, performance, security
• Commit messages: semantic prefixes (feat, fix, docs, etc.)

3. Generate/Update Description

Template priority

1. Existing PR body: Preserve all existing content — never modify written sections
2. Project template: Use .github/PULL_REQUEST_TEMPLATE.md structure if available
3. Default format: Simple ## What does this change? format as fallback

Content preservation rules

• Sections with user-written content: keep exactly as-is
• Empty sections or placeholder comments: fill with generated content
• HTML comments (<!-- ... -->): always preserve
• Functional comments (e.g., Copilot review rules): always preserve
• Separators (---): always preserve

Language detection

1. If --lang is specified, use that language
2. Check existing PR body language
3. Check recent commit messages (50%+ Japanese → Japanese)
4. Default: English

4. Update PR

Dry-run mode

If --dry-run is specified, display the generated description without updating:

=== DRY RUN ===
Description:
<generated description>

Actual update

Description — Use GitHub API to preserve HTML comments:

# IMPORTANT: Use gh api with --field to avoid HTML comment escaping
# Do NOT use `gh pr edit --body` as it escapes <!-- --> to &lt;!-- --&gt;
gh api \
  --method PATCH \
  "/repos/{owner}/{repo}/pulls/<number>" \
  --field body="<description>"

5. Verify and Report

# Verify the update
gh pr view <number> --json body --jq '{body: .body[:100]}'

• Confirm that the description was updated correctly
• Report the PR URL and summary to the user

Rules

Content Preservation

• Never modify existing content: Do not change a single character of user-written text
• Fill empty sections only: Only populate placeholder/comment sections
• Preserve all HTML comments: <!-- ... --> must remain intact
• Preserve functional comments: Copilot review rules, bot directives, etc.
• Backup before update: Store the original body in case of rollback needs

HTML Comment Handling

• Use gh api --field body= for description updates (preserves HTML comments)
• Do NOT use gh pr edit --body (escapes HTML comments)
• Avoid complex shell pipe operations that could corrupt content

Safety

• Recommend --dry-run for first-time use on a repository
• Warn on sensitive content: Alert if changes include secrets, credentials, or .env files
• No auto-push: This skill only updates PR metadata — never pushes code
• Match project style: Follow existing PR description patterns in the repository