Basic build and cache CI job

ci.yml

name: CI Checks

on:
  pull_request:
  push:
    branches:
      - main

jobs:
  build-and-cache:
    name: Build and cache image
    runs-on: ubuntu-latest
    steps:
      -
        name: Checkout
        uses: actions/checkout@v4
      -
        name: Set up Docker Buildx
        uses: docker/setup-buildx-action@v3
      -
        name: Build and cache
        uses: docker/build-push-action@v6
        with:
          context: .
          file: ./Dockerfile
          build-args: RAILS_ENV=test
          push: false
          tags: app:latest
          cache-from: type=gha
          cache-to: type=gha,mode=min

push is set to false because a later job pushes the image but the built image remains in context for subsequent builds which will happen very quickly.