Run container build action as a pull_request_target

Ensuring that it can only be run on PRs from the same repository. This means
that it will be run even when the PR doesn't merge, and against the PR head
rather than the merge.

.github/workflows/build-container.yml

@@ -2,17 +2,16 @@ name: Build Compiler Service Container
 
 on:
   push:
-    branches:
-      - "main"
     tags:
       - "*"
-  pull_request:
+  pull_request_target:
     branches:
       - main
 
 jobs:
   build:
-    if: github.repository == 'moergo-sc/zmk'
+    # This job must never be run on a PR from outside the same repository
+    if: github.repository == 'moergo-sc/zmk' && (github.event.pull_request == null || github.event.pull_request.head.repo.full_name == github.repository)
     runs-on: ubuntu-latest
     # These permissions are needed to interact with GitHub's OIDC Token endpoint.
     permissions:
@@ -22,9 +21,14 @@ jobs:
       ECR_REPOSITORY: zmk-builder-lambda
       VERSIONS_BUCKET: glove80firmwarepipelines-compilerversionsbucket44-zubaquiyjdam
       UPDATE_COMPILER_VERSIONS_FUNCTION: arn:aws:lambda:us-east-1:431227615537:function:Glove80FirmwarePipelineSt-UpdateCompilerVersions2A-CNxPOHb4VSuV
-      REVISION_TAG: ${{ github.sha }}
+      REVISION_TAG: ${{ github.event.pull_request && github.event.pull_request.head.sha || github.sha  }}
+      PR_NUMBER: ${{ github.event.number }}
     steps:
       - uses: actions/[email protected]
+        with:
+          repository: moergo-sc/zmk
+          ref: ${{ github.event.pull_request && github.event.pull_request.head.sha || github.sha }}
+          fetch-depth: 0
       - name: Configure AWS credentials
         uses: aws-actions/configure-aws-credentials@v1
         with:
@@ -33,16 +37,12 @@ jobs:
       - name: Extract container name from branch name
         shell: bash
         run: |
-          if [ "$GITHUB_REF" = "refs/heads/main" ]; then
-            tag="branch.main"
-          elif [ "$GITHUB_HEAD_REF" ]; then
-            pr=${GITHUB_REF#refs/pull/}
-            pr=${pr%/merge}
-            tag="pr${pr}.${GITHUB_HEAD_REF}"
+          if [ "$GITHUB_HEAD_REF" ]; then
+            tag="pr${PR_NUMBER}.${GITHUB_HEAD_REF}"
           elif [[ "$GITHUB_REF" == refs/tags/* ]]; then
             tag="${GITHUB_REF#refs/tags/}"
           else
-            echo "Not a release branch or tag" >&2
+            echo "Not a pull request or release tag" >&2
             exit 1
           fi
           # Replace / with . in container tag names
@@ -76,12 +76,13 @@ jobs:
         run: |
           digest="$(docker inspect --format='{{index .RepoDigests 0}}' $REGISTRY/$ECR_REPOSITORY:$REVISION_TAG)"
           digest="${digest##*@}"
+          api_version="$(cat lambda/api_version.txt)"
           jq -n '$ARGS.named' \
             --arg name     "$CONTAINER_NAME" \
             --arg revision "$REVISION_TAG" \
             --arg branch   "$GITHUB_REF" \
             --arg digest   "$digest" \
-            --arg api_version "2" \
+            --arg api_version "$api_version" \
             > "/tmp/$CONTAINER_NAME.json"
       - name: Upload image metadata file to versions bucket
         run: aws s3 cp "/tmp/$CONTAINER_NAME.json" "s3://$VERSIONS_BUCKET/images/$CONTAINER_NAME.json"

lambda/api_version.txt

@@ -0,0 +1 @@
+2