Cache docker layers

.github/workflows/docker-test.yml

@@ -29,24 +29,50 @@ jobs:
         echo "OWNER_LC=$OWNER_LC" >>${GITHUB_ENV}
         echo "IMAGE=ghcr.io/$OWNER_LC/vs-fltk:build-env" >>${GITHUB_ENV}
 
-    - name: Install dependencies
-      run: sudo apt install -y docker-compose
-
     - name: Check if Dockerfile has changed
       run: |
-        FILES=$(git log -1 -p ./ | grep +++ | cut -d '/' -f 2-| sed -e 's|dev/null||g')
-        if echo "$FILES" | grep -qE "^(Dockerfile)$"; then
-          echo "changed=true" >> $GITHUB_ENV
+        if [ "${{ github.ref }}" != "refs/heads/master" ]; then
+          FILES=$(git log -1 -p ./ | grep +++ | cut -d '/' -f 2-| sed -e 's|dev/null||g')
+          if echo "$FILES" | grep -qE "^(Dockerfile)$"; then
+            echo "do_build=true" >> $GITHUB_ENV
+          else
+            echo "do_build=false" >> $GITHUB_ENV
+          fi
         else
-          echo "changed=false" >> $GITHUB_ENV
+          # If there was a push to trunk, we don't want the docker build
+          # to run. All the builds in docker.yml will be pushed when *that*
+          # workflow runs, so we really don't want to be adding extra builds
+          # that won't become "permanent".
+          # Theoretically, if changes to Dockerfile are pushed to master, it should
+          # already have been tested anyway.
+          #
+          # That may mean the test will fail if the image don't exist yet
+          # in the registry or there was a dramatic change in the Dockerfile
+          # that might break the test that runs via docker compose.
+          # That's ok for now. We'll see how things go...
+          echo "do_build=false" >> $GITHUB_ENV
         fi
 
+    - name: Cache Docker layers
+      if: ${{ env.do_build == 'true' }}
+      id: docker-cache
+      uses: actions/cache@v3
+      with:
+        path: ${{ github.workspace }}/.docker/buildx-cache
+        key: ${{ runner.os }}-docker-${{ github.ref_name }}
+        restore-keys: |
+          ${{ runner.os }}-docker-
+
+    - name: Set up Docker Buildx
+      if: ${{ env.do_build == 'true' }}
+      uses: docker/setup-buildx-action@v3
+
     - name: Build Docker image
-      if: ${{ env.changed == 'true' }}
+      if: ${{ env.do_build == 'true' }}
       run: docker build -t $IMAGE -f docker/Dockerfile ./docker
 
     - name: Run commands in Docker container
       run: |
         export HOSTUID=$(id -u)
         export HOSTGID=$(id -g)
-        docker-compose -f docker/docker-compose.yml run --rm  dev
+        docker compose -f docker/docker-compose.yml run --rm  dev

docker/Dockerfile

@@ -24,8 +24,7 @@ RUN \
         sudo \
         swiftlang \
         unzip \
-        wget && \
-    update-ca-certificates -f
+        wget
 
 RUN useradd -m builder && passwd -d builder
 RUN echo "builder ALL=(ALL) ALL" >> /etc/sudoers