Enforce Semi-Linear History

A reusable GitHub Action that ensures pull request branches maintain a semi-linear (rebase) history — no merge commits, and always rebased on top of the base branch.

Usage

name: Enforce Semi-Linear History

on:
  pull_request:
    branches: [main]

jobs:
  check-linear-branch:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
        with:
          fetch-depth: 0
          ref: ${{ github.event.pull_request.head.sha }}

      - uses: your-org/enforce-semi-linear@v1

Inputs

Name	Description	Default
base_ref	Base branch to check against	github.base_ref

Requirements

The checkout step must use:

• fetch-depth: 0 — full history is needed to detect merge commits
• ref: ${{ github.event.pull_request.head.sha }} — checks out the actual branch head, not GitHub's synthetic merge commit