feat: CI job for building Docker binary-only images

.github/workflows/release.yml

@@ -38,3 +38,77 @@ jobs:
         if: ${{startsWith(github.ref, 'refs/tags/') }}
         with:
           files: pie.phar
+
+  docker-binary-only-image:
+    needs: build-phar
+    name: Docker binary-only image
+    runs-on: ubuntu-latest
+    if: ${{ startsWith(github.ref, 'refs/tags/') }}
+
+    permissions:
+      # attestations:write is required for build provenance attestation.
+      attestations: write
+      # id-token:write is required for build provenance attestation.
+      id-token: write
+      # packages:write is required to publish Docker images to GitHub's registry.
+      packages: write
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Fetch built PHAR from artifacts
+        uses: actions/download-artifact@v4
+        with:
+          name: pie-${{ github.sha }}.phar
+
+      - name: Verify the PHAR
+        env:
+          GH_TOKEN: ${{ github.token }}
+        run: gh attestation verify pie.phar --repo ${{ github.repository }}
+
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@v3
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+
+      - name: Log in to the Container registry
+        uses: docker/login-action@v3
+        with:
+          registry: ghcr.io
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Extract metadata (tags, labels) for Docker
+        id: meta
+        uses: docker/metadata-action@v5
+        with:
+          flavor: |
+            latest=false
+          images: ghcr.io/${{ github.repository }}
+          # @TODO v1.0 Consider introducing more granular tags (major and major.minor)
+          # @see https://github.com/php/pie/pull/122#pullrequestreview-2477496308
+          # @see https://github.com/php/pie/pull/122#discussion_r1867331273
+          tags: |
+            type=raw,value=bin
+            type=semver,pattern={{version}}-bin
+
+      - name: Build and push Docker image
+        id: build-and-push
+        uses: docker/build-push-action@v5
+        with:
+          context: .
+          platforms: linux/amd64,linux/arm64
+          file: Dockerfile
+          target: standalone-binary
+          push: true
+          tags: ${{ steps.meta.outputs.tags }}
+          labels: ${{ steps.meta.outputs.labels }}
+
+      - name: Generate artifact attestation
+        uses: actions/attest-build-provenance@v1
+        with:
+          subject-name: ghcr.io/${{ github.repository }}
+          subject-digest: ${{ steps.build-and-push.outputs.digest }}
+          push-to-registry: true

Dockerfile

@@ -0,0 +1,4 @@
+FROM scratch AS standalone-binary
+
+# @TODO change to --chmod=+x when https://github.com/moby/buildkit/pull/5380 is released
+COPY --chmod=0755 pie.phar /pie

docs/usage.md

@@ -27,6 +27,19 @@ system:
 sudo curl -L --output /usr/local/bin/pie https://github.com/php/pie/releases/latest/download/pie.phar && sudo chmod +x /usr/local/bin/pie
 ```
 
+### Docker installation
+
+PIE is published as binary-only Docker image, so you can install it easily during your Docker build:
+
+```Dockerfile
+COPY --from=ghcr.io/php/pie:bin /pie /usr/bin/pie
+```
+
+Instead of `bin` tag (which represents latest binary-only image) you can also use explicit version (in `x.y.z-bin` format). Use [GitHub registry](https://ghcr.io/php/pie) to find available tags.
+
+> [!IMPORTANT]  
+> Binary-only images don't include PHP runtime so you can't use them for _running_ PIE. This is just an alternative way of distributing PHAR file, you still need to satisfy PIE's runtime requirements on your own.
+
 ## Prerequisites for PIE
 
 Running PIE requires PHP 8.1 or newer. However, you may still use PIE to install