docker build dependent on event type

.github/workflows/ci-docker.yml

@@ -202,8 +202,7 @@ jobs:
           # get branch name
           BRANCH=${GITHUB_HEAD_REF}
 
-          if [ -z "$BRANCH" ]
-          then
+          if [ -z "$BRANCH" ]; then
             echo "This is a PUSH event"
             BRANCH=${{ github.ref_name }}
           fi
@@ -237,6 +236,19 @@ jobs:
 
           # parse custom directives out of dockerfile
           # try to get the platforms from the dockerfile custom directive, i.e. `# platforms: xxx,yyy`
+          # directives for PR event, i.e. not push event
+          if [[ ${PUSH} == "false" ]]; then
+            while read -r line; do
+              if [[ $line == "# platforms_pr: "* && $PLATFORMS == "" ]]; then
+                # echo the line and use `sed` to remove the custom directive
+                PLATFORMS=$(echo -e "$line" | sed 's/# platforms_pr: //')
+              elif [[ $PLATFORMS != ""]]; then
+                # break while loop once all custom "PR" event directives are found
+                break
+              fi
+            done <"${{ matrix.dockerfile }}"
+          fi
+          # directives for all events... above directives will not be parsed if they were already found
           while read -r line; do
             if [[ $line == "# platforms: "* && $PLATFORMS == "" ]]; then
               # echo the line and use `sed` to remove the custom directive

docker/debian-bullseye.dockerfile

@@ -1,5 +1,7 @@
+# syntax=docker/dockerfile:1.4
 # artifacts: true
 # platforms: linux/amd64,linux/arm64/v8
+# platforms_pr: linux/amd64
 ARG BASE=debian
 ARG TAG=bullseye
 FROM ${BASE}:${TAG} AS sunshine-base

docker/fedora-36.dockerfile

@@ -1,5 +1,7 @@
+# syntax=docker/dockerfile:1.4
 # artifacts: true
 # platforms: linux/amd64,linux/arm64/v8
+# platforms_pr: linux/amd64
 ARG BASE=fedora
 ARG TAG=36
 FROM ${BASE}:${TAG} AS sunshine-base

docker/fedora-37.dockerfile

@@ -1,5 +1,7 @@
+# syntax=docker/dockerfile:1.4
 # artifacts: true
 # platforms: linux/amd64,linux/arm64/v8
+# platforms_pr: linux/amd64
 ARG BASE=fedora
 ARG TAG=37
 FROM ${BASE}:${TAG} AS sunshine-base

docker/ubuntu-18.04.dockerfile-todo

@@ -1,5 +1,7 @@
+# syntax=docker/dockerfile:1.4
 # artifacts: true
 # platforms: linux/amd64,linux/arm64/v8
+# platforms_pr: linux/amd64
 ARG BASE=ubuntu
 ARG TAG=18.04
 FROM ${BASE}:${TAG} AS sunshine-base

docker/ubuntu-20.04.dockerfile

@@ -1,5 +1,7 @@
+# syntax=docker/dockerfile:1.4
 # artifacts: true
 # platforms: linux/amd64,linux/arm64/v8
+# platforms_pr: linux/amd64
 ARG BASE=ubuntu
 ARG TAG=20.04
 FROM ${BASE}:${TAG} AS sunshine-base

docker/ubuntu-22.04.dockerfile

@@ -1,5 +1,7 @@
+# syntax=docker/dockerfile:1.4
 # artifacts: true
 # platforms: linux/amd64,linux/arm64/v8
+# platforms_pr: linux/amd64
 ARG BASE=ubuntu
 ARG TAG=22.04
 FROM ${BASE}:${TAG} AS sunshine-base