Merge Conflict Radar

A GitHub Action that checks every open pull request for file overlaps and warns you before two PRs collide — instead of after someone hits a merge conflict on main.

When a PR opens or updates, it compares that PR's changed files against every other open PR in the repo. If they share files, it posts (and keeps updated) a comment naming exactly which PRs and which files, so you can coordinate merge order or plan a rebase ahead of time.

Usage

Add this to .github/workflows/merge-conflict-radar.yml in the repo you want to watch:

name: Merge Conflict Radar

on:
  pull_request:
    types: [opened, synchronize, reopened]

permissions:
  pull-requests: write

jobs:
  radar:
    runs-on: ubuntu-latest
    steps:
      - uses: johnnyhett/merge-conflict-radar@v1.0.0
        with:
          ignore-paths: '*.lock,package-lock.json,dist/**'
          min-shared-files: '1'

Tip: once you publish the release, you can also create a moving v1 tag so consumers can pin to @v1 and pick up patch updates automatically.

Inputs

Input	Required	Default	Description
github-token	No	${{ github.token }}	Token used to read PRs and post comments.
ignore-paths	No	''	Comma-separated glob patterns to exclude (lockfiles, build output, etc).
min-shared-files	No	1	Minimum number of shared files before a warning is posted.

Output

Output	Description
collisions	JSON array of { number, title, files } for each PR that overlaps with the current one.

How it works

1. Fetches the changed files for the triggering PR.
2. Lists every other open PR and its changed files.
3. Filters out anything matching ignore-paths, then intersects file sets.
4. If the overlap meets min-shared-files, upserts a single tagged comment (found via a hidden marker) so re-runs update the same comment instead of spamming new ones — and clears the warning automatically once the overlap is gone.

Development

npm install
npm run test:syntax   # quick syntax check
npm run build          # bundles src/index.js -> dist/index.js via ncc

dist/index.js is committed on purpose — GitHub Actions runs the compiled file directly, without an install step, so the bundle has to be checked in. The included .github/workflows/self-test.yml runs the action against its own repo's PRs, which is a simple way to keep it exercised in a real workflow run.

License

MIT