pr-auto-update

name: pr-auto-update description: Auto-update PR descriptions based on Git change analysis argument-hint: "[--pr ] [--dry-run] [--lang <en|ja>]" allowed-tools: Bash(git *), Bash(gh *), Read, Grep

PR Auto Update

Update Pull Request descriptions based on the repository's PR template and the latest commits. Re-evaluates existing content against the latest diff: sections that still accurately describe the diff are kept as-is, sections describing removed or changed behavior are rewritten, and empty sections are filled.

Arguments

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

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, use that PR
• Otherwise, find the PR associated with the current branch
• If no PR is found, inform the user and stop

2. Load PR Template

Look up the repository's PR template in this order and use the first one found:

1. .github/PULL_REQUEST_TEMPLATE.md
2. .github/pull_request_template.md
3. docs/PULL_REQUEST_TEMPLATE.md
4. PULL_REQUEST_TEMPLATE.md

# Example
cat .github/PULL_REQUEST_TEMPLATE.md 2>/dev/null

If no template exists, fall back to a minimal structure:

## Summary

## Changes

3. Analyze Changes

# Changed files
gh pr diff <number> --name-only

# Diff content (cap at 1000 lines for large PRs)
gh pr diff <number> | head -1000

# All commits in the PR
gh pr view <number> --json commits --jq '.commits[].messageHeadline'

Use this information to populate template sections — not to invent sections the template doesn't define.

4. Generate/Update Description

Per-section behavior

For each template section:

• If the existing text still accurately describes the latest diff → keep as-is
• If the existing text describes behavior that no longer exists or has changed → rewrite to match current state
• If the section is empty or contains only a placeholder → fill with generated content

Before applying, show a section-by-section diff preview and require user confirmation.

Always preserved

• HTML comments (<!-- ... -->)
• Checklist check states (- [x] / - [ ])
• Separators (---)

Idempotence

When regenerating a section, if the new content is semantically equivalent to the existing text, keep the existing text byte-for-byte. Do not rewrite only to change wording, order, or formatting. This applies to the whole body as well: if nothing meaningful changed, the update is a no-op and the PR body is left untouched.

Language detection

1. If --lang is specified, use that language
2. Otherwise match the existing PR body language
3. Otherwise match the majority language of recent commit messages
4. Default: English

5. Update PR

If --dry-run, print the generated body and stop.

Otherwise show the section-by-section diff and wait for user confirmation before proceeding.

# Use gh api to preserve HTML comments
# gh pr edit --body escapes <!-- --> to &lt;!-- --&gt;
gh api \
  --method PATCH \
  "/repos/{owner}/{repo}/pulls/<number>" \
  --field body="<description>"

6. Verify and Report

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

Report the PR URL and a one-line summary of what changed.

Rules

• Follow the repo's PR template — do not add or remove sections it doesn't define
• Preserve unchanged text byte-for-byte — if a section's new content is semantically equivalent to the existing text, keep the existing text. Skip the update entirely if the whole body is unchanged.
• Preserve HTML comments, checklist states, and separators
• Confirm before applying — always show a section-by-section diff preview and require user confirmation (unless --dry-run)
• Use gh api --field body= for the update (gh pr edit --body escapes HTML comments)
• Warn on sensitive content: alert if the diff touches secrets, credentials, or .env files
• No code pushes: this skill only updates PR metadata