github: update docker build workflow to use cache.

Update the Docker build workflow to use premade actions so we can cache
the build.

https://github.com/docker/setup-buildx-action
https://github.com/docker/login-action
https://github.com/docker/metadata-action
https://github.com/docker/build-push-action

.github/workflows/test.yaml

@@ -10,35 +10,56 @@ on:
     - master
 
 jobs:
-  # Build Docker image and push to Github Packages registry.
+  # Build Docker image and push to Github Container Registry.
+  #
+  # https://docs.github.com/en/packages/working-with-a-github-packages-registry/working-with-the-container-registry
+  # https://docs.github.com/en/packages/managing-github-packages-using-github-actions-workflows/publishing-and-installing-a-package-with-github-actions
+  # https://docs.github.com/en/actions/guides/publishing-docker-images
   docker:
     runs-on: ubuntu-latest
 
-    defaults:
-      run:
-        shell: bash
-
-    env:
-      IMAGE_NAME: ${{ github.repository }}
-      IMAGE_ID: ghcr.io/${{ github.repository }}
-
     steps:
-      - uses: actions/checkout@v2
+      # https://github.com/docker/setup-buildx-action
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v1
 
+      # https://github.com/docker/login-action
+      - name: Login to Github Container Registry
+        uses: docker/login-action@v1
+        with:
+          registry: ghcr.io
+          username: ${{ github.repository_owner }}
+          password: ${{ github.token }}
+
+      # Generate Docker tags from Git tags.
+      # https://github.com/docker/metadata-action
+      - name: Generate Docker tags
+        uses: docker/metadata-action@v3
+        id: metadata
+        with:
+          images: ghcr.io/${{ github.repository }}
+          tags: |
+            type=sha,format=short,prefix=
+            type=ref,event=branch
+            type=ref,event=tag
+            type=ref,event=pr
+          # Tag `latest` on every commit pushed to master
+          # https://github.com/docker/metadata-action/issues/112
+          flavor: |
+            latest=${{ github.ref == 'refs/heads/master' }}
+
+      # https://github.com/docker/build-push-action
       - name: Build image
-        run: docker build . --file Dockerfile --tag "$IMAGE_NAME" --label "github_run_id=${{ github.run_id }}"
+        uses: docker/build-push-action@v2
+        with:
+          push: true
+          tags: ${{ steps.metadata.outputs.tags }}
+          labels: ${{ steps.metadata.outputs.labels }}
 
-      - name: Log in to registry
-        run: docker login ghcr.io -u "${{ github.repository_owner }}" -p "${{ github.token }}"
-
-      - name: Push image
-        run: |
-          REF=$(echo ${{ github.sha }} | cut -c1-9)
-
-          docker tag $IMAGE_NAME $IMAGE_ID:$REF
-          docker tag $IMAGE_NAME $IMAGE_ID:latest
-          docker push $IMAGE_ID:$REF
-          docker push $IMAGE_ID:latest
+          # https://github.com/docker/build-push-action/blob/master/docs/advanced/cache.md#registry-cache
+          # https://dev.to/pst418/speed-up-multi-stage-docker-builds-in-ci-cd-with-buildkit-s-registry-cache-11gi
+          cache-from: type=registry,ref=ghcr.io/${{ github.repository }}:buildcache
+          cache-to: type=registry,ref=ghcr.io/${{ github.repository }}:buildcache,mode=max
 
   test:
     runs-on: ubuntu-latest