Allow PRs to build images

.github/workflows/build.yaml

@@ -1,15 +1,8 @@
 name: Build firmwares
 
 on:
+  pull_request:
   push:
-    paths:
-      - Dockerfile
-      - .github/workflows/build.yaml
-      - manifests/**/*.yaml
-    branches:
-      - main
-    tags:
-      - '*'
 
 env:
   REGISTRY: ghcr.io
@@ -22,39 +15,60 @@ jobs:
       packages: write
     steps:
       - uses: actions/[email protected]
-      - name: Create container name
-        id: create-container-name
-        run: |
-          repository_owner=$(echo $GITHUB_REPOSITORY_OWNER | tr [:upper:] [:lower:])
-          image_name="${{ env.REGISTRY }}/$repository_owner/silabs-firmware-builder"
-          tag_name="${{ hashFiles('Dockerfile') }}"
-
-          echo "image_name=$image_name" >> $GITHUB_OUTPUT
-          echo "tag_name=$tag_name" >> $GITHUB_OUTPUT
-          echo "container_name=$image_name:$tag_name" >> $GITHUB_OUTPUT
       - name: Log in to the GitHub container registry
         uses: docker/[email protected]
         with:
           registry: ${{ env.REGISTRY }}
           username: ${{ github.repository_owner }}
           password: ${{ secrets.GITHUB_TOKEN }}
+      - name: Create container name
+        id: create-container-info
+        run: |
+          base_image=$(echo ${{ github.event.pull_request.base.repo.full_name }} | tr [:upper:] [:lower:])
+          head_image=$(echo ${{ github.event.pull_request.head.repo.full_name }} | tr [:upper:] [:lower:])
+          tag_name="${{ hashFiles('Dockerfile') }}"
+
+          # Default to building a new container under the original repo
+          image_name=$head_image
+          build=true
+
+          # Check if we can use the base image (Nabu Casa)
+          if docker manifest inspect ${{ env.REGISTRY }}/$base_image:$tag_name; then
+            image_name=$base_image
+            build=false
+          fi
+
+          # Check if we can use the head image (PR)
+          if docker manifest inspect ${{ env.REGISTRY }}/$head_image:$tag_name; then
+            image_name=$head_image
+            build=false
+          fi
+
+          echo "build=$build" >> $GITHUB_OUTPUT
+          echo "tag_name=$tag_name" >> $GITHUB_OUTPUT
+          echo "image_name=$image_name" >> $GITHUB_OUTPUT
+          echo "container_name=${{ env.REGISTRY }}/$image_name:$tag_name" >> $GITHUB_OUTPUT
       - name: Set up Docker Buildx
         uses: docker/[email protected]
+        if: steps.create-container-info.outputs.build == 'true'
       - name: Build and Push
         uses: docker/[email protected]
+        if: steps.create-container-info.outputs.build == 'true'
         with:
           context: .
           file: Dockerfile
-          tags: ${{ steps.create-container-name.outputs.container_name }}
-          cache-from: ${{ steps.create-container-name.outputs.image_name }}:cache-${{ steps.create-container-name.outputs.tag_name }}
-          cache-to: ${{ steps.create-container-name.outputs.image_name }}:cache-${{ steps.create-container-name.outputs.tag_name }}
+          tags: ${{ steps.create-container-info.outputs.tag_name }}
+          cache-from: ${{ steps.create-container-info.outputs.image_name }}:cache-${{ steps.create-container-info.outputs.tag_name }}
+          cache-to: ${{ steps.create-container-info.outputs.image_name }}:cache-${{ steps.create-container-info.outputs.tag_name }}
           push: true
     outputs:
-      container_name: ${{ steps.create-container-name.outputs.container_name }}
+      tag_name: ${{ steps.create-container-info.outputs.tag_name }}
+      image_name: ${{ steps.create-container-info.outputs.image_name }}
+      container_name: ${{ steps.create-container-info.outputs.container_name }}
+
 
   list-manifests:
     name: List firmware manifests
-    needs: build-container
     runs-on: ubuntu-latest
     outputs:
       matrix: ${{ steps.set-matrix.outputs.matrix }}