feat: build on pull request as well as release

This change:

- adds "pull_request" as an event that will trigger the workflow.
- marks the "docker login" step as conditional, only to run if the "container_username" secret is present.
- alters the original "Build and push" step such that it only runs on a release
- adds two new "build and push" steps
  - one runs on pull_request if a container_username secret is present, and caches layers
  - one runs on pull_request if a container_username secret is NOT present, and DOES NOT cache layers

Signed-off-by: Matthew Weier O'Phinney <[email protected]>

Author: weierophinney

.github/workflows/build-and-push-containers.yml

@@ -3,10 +3,13 @@ name: Build and push containers
 on:
   release:
     types: [published]
+  pull_request:
 
 jobs:
   release-container:
     runs-on: ubuntu-latest
+    env:
+      DOCKER_USER: ${{ secrets.CONTAINER_USERNAME }}
     steps:
       - name: Compile tag list
         id: tags
@@ -28,13 +31,15 @@ jobs:
         uses: docker/setup-buildx-action@v1
 
       - name: Login to GitHub Container Registry
+        if: ${{ secrets.CONTAINER_USERNAME }}
         uses: docker/login-action@v1
         with:
           registry: ghcr.io
-          username: ${{ secrets.CONTAINER_USERNAME }}
+          username: ${{ env.DOCKER_USER }}
           password: ${{ secrets.CONTAINER_PAT }}
 
-      - name: Build and push
+      - name: Build and push for release
+        if: ${{ github.event_name == 'release' }}
         uses: docker/build-push-action@v2
         with:
           context: .
@@ -45,3 +50,26 @@ jobs:
           tags: ${{ join(fromJSON(steps.tags.outputs.tags), ',') }}
           cache-from: type=registry,ref=ghcr.io/laminas/laminas-continuous-integration-action:build-cache
           cache-to: type=registry,ref=ghcr.io/laminas/laminas-continuous-integration-action:build-cache,mode=max
+
+      - name: Build for local pull request
+        if: ${{ github.event_name == 'pull_request' && env.DOCKER_USER }}
+        uses: docker/build-push-action@v2
+        with:
+          context: .
+          file: ./Dockerfile
+          platforms: linux/amd64
+          pull: true
+          push: false
+          cache-from: type=registry,ref=ghcr.io/laminas/laminas-continuous-integration-action:build-cache
+          cache-to: type=registry,ref=ghcr.io/laminas/laminas-continuous-integration-action:build-cache,mode=max
+
+      - name: Build for fork pull request
+        if: ${{ github.event_name == 'pull_request' && ! env.DOCKER_USER }}
+        uses: docker/build-push-action@v2
+        with:
+          context: .
+          file: ./Dockerfile
+          platforms: linux/amd64
+          pull: true
+          push: false
+          cache-from: type=registry,ref=ghcr.io/laminas/laminas-continuous-integration-action:build-cache