CI: only build and push images if they changed

Author: BacLuc

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

@@ -121,6 +121,8 @@ jobs:
       repo-owner: ${{ needs.build-info.outputs.repo-owner }}
     steps:
       - uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5
+        with:
+          fetch-depth: 100
 
       - run: |
           echo "inputs:"
@@ -157,13 +159,52 @@ jobs:
           username: ${{ vars.DOCKER_HUB_USERNAME || env.repo-owner }}
           password: ${{ secrets.DOCKER_HUB_PASSWORD }}
 
+      - name: find latest commit for image tag
+        id: get-latest-commit
+        run: |
+          set -x
+          context=$( echo '${{ toJSON(matrix.build-config) }}' | jq -r '.context' | sed "s|$PWD|.|g")
+          echo "context: $context"
+          dockerfile=$( echo '${{ toJSON(matrix.build-config) }}' | jq -r '.dockerfile' | sed "s|$PWD|.|g")
+          echo "dockerfile: $dockerfile"
+          git log --stat -n 1 $context $dockerfile
+          latest_commit=$(git log --pretty=format:"%H" -n 1 $context $dockerfile)
+          echo "latest_commit: $latest_commit"
+          echo "result=$latest_commit" | tr -d "\n"  >> $GITHUB_OUTPUT
+
+      - name: check if image already exists
+        id: check-image
+        run: |
+          set +e
+          docker pull ${{ matrix.build-config.image }}:${{ steps.get-latest-commit.outputs.result }}
+          image_exists=$?
+          set -e
+          if ([ $image_exists -eq 0 ]); then
+            echo "image already exists"
+            echo "result=true" | tr -d "\n"  >> $GITHUB_OUTPUT
+          else
+            echo "image does not exist"
+            echo "result=false" | tr -d "\n"  >> $GITHUB_OUTPUT
+          fi
+
+      - name: Add latest commit to image tag if image does not exist
+        id: add-latest-commit-to-tags-if-image-does-not-exist
+        uses: actions/github-script@v7
+        with:
+          script: |
+            if (!${{ steps.check-image.outputs.result }}) {
+              return [...JSON.parse('${{ env.tags }}'), '${{ steps.get-latest-commit.outputs.result }}']
+            }
+            return JSON.parse('${{ env.tags }}')
+
       - uses: actions/github-script@v7
         id: expand-tags
         with:
           script: |
-            return JSON.parse('${{ env.tags }}').map(tag => `${{ matrix.build-config.image }}:${ tag }`)
+            return JSON.parse('${{ steps.add-latest-commit-to-tags-if-image-does-not-exist.outputs.result }}').map(tag => `${{ matrix.build-config.image }}:${ tag }`)
 
       - name: populate build args from secrets/vars
+        if: steps.check-image.outputs.result == 'false'
         id: populate-build-args
         uses: actions/github-script@v7
         with:
@@ -185,6 +226,7 @@ jobs:
             return args
 
       - name: transform build args
+        if: steps.check-image.outputs.result == 'false'
         id: transform-build-args
         run: |
           set -x
@@ -193,13 +235,15 @@ jobs:
           echo 'EOF' >> $GITHUB_OUTPUT
           cat $GITHUB_OUTPUT
 
-      - name: debug output
+      - name: debug transform build args output
+        if: steps.check-image.outputs.result == 'false'
         run: |
           echo "result: ${{ steps.transform-build-args.outputs.result }}"
           echo "result: ${{ toJSON(steps.transform-build-args.outputs) }}"
 
       - name: Build and push image
         uses: docker/build-push-action@v6
+        if: steps.check-image.outputs.result == 'false'
         with:
           push: true
           file: ${{ matrix.build-config.dockerfile }}
@@ -209,3 +253,11 @@ jobs:
             ${{ steps.transform-build-args.outputs.result }}
           cache-from: type=gha,scope=${{ matrix.build-config.image }}
           cache-to: type=gha,scope=${{ matrix.build-config.image }},mode=max
+
+      - name: Retag and push images
+        if: steps.check-image.outputs.result == 'true'
+        run: |
+          for tag in $(echo '${{ env.tags }}' | jq -r '.[]'); do
+            docker tag ${{ matrix.build-config.image }}:${{ steps.get-latest-commit.outputs.result }} ${{ matrix.build-config.image }}:${tag}
+            docker push ${{ matrix.build-config.image }}:${tag}
+          done