Use docker/metadata-action@v3 (#616)

.github/docker-build-config.sh

@@ -1,28 +0,0 @@
-#!/usr/bin/env bash
-set -o pipefail
-set -eux
-
-# only build on pull request
-if [[ $GITHUB_EVENT_NAME == pull_request ]]; then
-  # e.g. refs/pulls/1/merge -> refs-pulls-1-merge
-  echo "::set-output name=tag::${GITHUB_REF//\//-}"
-  echo "::set-output name=push::false"
-  exit 0
-fi
-
-# push latest tag on master branch
-if [[ $GITHUB_REF == refs/heads/master ]]; then
-  echo "::set-output name=tag::latest"
-  echo "::set-output name=push::true"
-  exit 0
-fi
-
-# push the corresponding tag on tag push
-if [[ $GITHUB_REF == refs/tags/* ]]; then
-  echo "::set-output name=tag::${GITHUB_REF##*/}"
-  echo "::set-output name=push::true"
-  exit 0
-fi
-
-: unknown trigger
-exit 1

.github/workflows/docker.yaml

@@ -27,8 +27,10 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v2
-      - run: .github/docker-build-config.sh
-        id: docker-build-config
+      - uses: docker/metadata-action@v3
+        id: metadata
+        with:
+          images: ghcr.io/${{ github.repository }}
       - uses: docker/login-action@v1
         with:
           registry: ghcr.io
@@ -38,8 +40,9 @@ jobs:
       - uses: docker/setup-buildx-action@v1
       - uses: docker/build-push-action@v2
         with:
-          push: ${{ steps.docker-build-config.outputs.push }}
-          tags: ghcr.io/${{ github.repository }}:${{ steps.docker-build-config.outputs.tag }}
+          push: ${{ github.event_name == 'push' }}
+          tags: ${{ steps.metadata.outputs.tags }}
+          labels: ${{ steps.metadata.outputs.labels }}
           cache-from: type=registry,ref=ghcr.io/${{ github.repository }}:buildkit-cache
           cache-to: type=registry,ref=ghcr.io/${{ github.repository }}:buildkit-cache,mode=max
           platforms: linux/amd64,linux/arm64