Record of a GitHub Actions Optimization (Docker Build)

## Key Improvements (What's Done Well)

1.  Checkout added `fetch-depth: 0`: Before the improvement, it defaulted to shallow clone (`depth=1`), and `git describe --tags` often failed to correctly retrieve historical tags, leading to version extraction failures. Adding `fetch-depth: 0` significantly improves reliability.
2.  Version number output changed to `$GITHUB_OUTPUT`: This is the correct and recommended practice. Before the improvement, using `>> $GITHUB_ENV` worked, but `GITHUB_OUTPUT` is a more modern and clearly scoped approach (especially for referencing in subsequent steps).
3.  Switched to the official `docker/build-push-action@v5`: This is the biggest and most important improvement.
    *   No longer manually writing `docker buildx build ...` commands, reducing the risk of syntax errors.
    *   Automatically handles multi-platform manifests, pushes, tags, etc.
    *   Code is more concise and readable.
4.  Added `setup-qemu-action`: For `linux/arm64` platforms, QEMU emulation is required when building on `ubuntu-latest (x86_64)`. The previous version lacked this step, making arm64 builds very likely to fail or be extremely slow. Adding it provides more complete multi-platform support.
5.  Enabled Buildx cache (`cache-from + cache-to: type=gha,mode=max`): This can significantly speed up subsequent build times, especially with multi-platform + multi-stage Dockerfiles.
6.  Explicitly specified `context: .` and `file: ./Dockerfile`: This is clearer. Although `.` is the default, writing it out makes it easier to maintain.
7.  Used `steps.get_version.outputs.VERSION` for referencing the version: This works in conjunction with `GITHUB_OUTPUT`.

## Original Configuration

```yaml
name: Docker

on:
  push:
    tags:
      - v*.*.*

jobs:
  docker_build:
    environment: docker_hub
    runs-on: ubuntu-latest

    steps:
      - name: Checkout code
        uses: actions/checkout@v4

      - name: Get version
        id: get_version
        run: |
          VERSION=$(git describe --tags --always --match 'v*' | sed -n 's|^v\([0-9]*\.[0-9]*\.[0-9]*\)\(-.*\)\{0,1\}|\1|p')
          echo "VERSION=$VERSION" >> $GITHUB_ENV  # Store version as an environment variable

      - name: Log in to Docker Hub
        uses: docker/login-action@v3
        with:
          username: ${{ secrets.DOCKER_USERNAME }}
          password: ${{ secrets.DOCKER_PASSWORD }}

      # Set up Docker Buildx (supports multi-platform builds)
      - name: Set up Docker Buildx
        uses: docker/setup-buildx-action@v3

      # Build and push multi-platform image in a single step
      - name: Build and push multi-platform image
        run: |
          docker buildx build \
            --platform linux/amd64,linux/arm64 \
            --tag dingdangdog/jimily:${VERSION} \
            --tag dingdangdog/jimily:latest \
            --push .

      - name: Clean up Docker images
        run: docker system prune -af

```

## New Configuration

```yaml
name: Docker

on:
  push:
    tags:
      - v*.*.*

jobs:
  docker_build:
    environment: docker_hub
    runs-on: ubuntu-latest

    steps:
      - name: Checkout code
        uses: actions/checkout@v4
        with:
          fetch-depth: 0 # Ensure tags are fetched for version generation

      - name: Get version
        id: get_version
        # Extract semantic version, e.g., extract 5.1.3 from v5.1.3
        run: |
          VERSION=$(git describe --tags --always --match 'v*' | sed -n 's|^v\([0-9]*\.[0-9]*\.[0-9]*\)\(-.*\)\{0,1\}|\1|p')
          echo "VERSION=$VERSION" >> $GITHUB_OUTPUT

      - name: Log in to Docker Hub
        uses: docker/login-action@v3
        with:
          username: ${{ secrets.DOCKER_USERNAME }}
          password: ${{ secrets.DOCKER_PASSWORD }}

      - name: Set up QEMU
        uses: docker/setup-qemu-action@v3
        with:
          platforms: arm64 # Explicitly specify platforms to emulate

      - name: Set up Docker Buildx
        uses: docker/setup-buildx-action@v3

      - name: Build and push multi-platform image
        uses: docker/build-push-action@v5
        with:
          context: .
          file: ./Dockerfile
          platforms: linux/amd64,linux/arm64
          push: true
          tags: |
            dingdangdog/jimily:${{ steps.get_version.outputs.VERSION }}
            dingdangdog/jimily:latest
          # Key improvement: Enable GitHub Actions cache backend
          cache-from: type=gha
          cache-to: type=gha,mode=max
          # Pass build arguments (if your Dockerfile needs the VERSION variable, uncomment the following line)
          # build-args: |
          #   APP_VERSION=${{ steps.get_version.outputs.VERSION }}

```