Optimize images on pull requests (#25377)

* Add two images

* two more images

* Run optimize images on pull requests

* Update optimize-images-pull-request.yml

* Add more images

* Update optimize-images-pull-request.yml

* Update optimize-images-pull-request.yml

* Update optimize-images-pull-request.yml

* Update optimize-images-pull-request.yml

* Update optimize-images-pull-request.yml

* Update optimize-images-pull-request.yml

* Update optimize-images-pull-request.yml

* Update optimize-images-pull-request.yml

* Update optimize-images-pull-request.yml

* Update optimize-images-pull-request.yml

* Update optimize-images-pull-request.yml

* Update optimize-images-pull-request.yml

* Update optimize-images-pull-request.yml

* Update optimize-images-pull-request.yml

* Update optimize-images-pull-request.yml

* Update optimize-images-pull-request.yml

* Update optimize-images-pull-request.yml

* Update optimize-images-pull-request.yml

* Optimize images

* Update optimize-images-pull-request.yml

* Remove images

* Delete optimize-images.yml

* Update optimize-images-pull-request.yml

* Update optimize-images-pull-request.yml

* Move in place

Co-authored-by: github-actions <github-actions@github.com>

.github/workflows/optimize-images.yml

@@ -6,28 +6,47 @@ name: Optimize images
 
 on:
   workflow_dispatch:
-  schedule:
-    - cron: '45 17 * * 2' # Run Tuesdays at 17:45 UTC / 9:45 PST
+  pull_request:
+    paths:
+      - '**/*.png'
 
 permissions:
   contents: write
   pull-requests: write
 
 jobs:
-  optimize-images:
-    if: github.repository == 'github/docs-internal'
+  optimize-images-on-pr:
+    if: github.repository == 'github/docs-internal' || github.repository == 'github/docs'
     runs-on: ubuntu-latest
     steps:
-      - name: Check out repo
+      - name: Check out repo on head ref
         uses: actions/checkout@ec3a7ce113134d7a93b817d10a8272cb61118579
+        with:
+          ref: ${{ github.head_ref }}
+
+      - name: Check out base ref
+        run: git fetch --no-tags --depth=1 origin $GITHUB_BASE_REF
 
       - name: Install the Optipng package
         run: sudo apt-get update && sudo apt-get -y install optipng
 
-      - name: Run the Optipng package
-        run: find . -name '*.png' -print0 | xargs -0 optipng -nx
+      - name: Run optipng on new or changed images
+        run: |
+          set -e # exit when any command fails
 
-      - name: Make a branch, commit, push, and pull request
+          echo "Ensure we can view $GITHUB_BASE_REF"
+          git checkout $GITHUB_BASE_REF
+
+          echo "Ensure we can view $GITHUB_HEAD_REF"
+          git checkout $GITHUB_HEAD_REF
+
+          echo "List the files that changed"
+          git diff --name-only $GITHUB_HEAD_REF $GITHUB_BASE_REF
+
+          echo "Run optipng on pngs in from the diff"
+          git diff --name-only -z $GITHUB_HEAD_REF $GITHUB_BASE_REF -- '*.png' | xargs -0 optipng -nx
+
+      - name: Make a commit and a push
         run: |
           echo "If there's no changes, exit"
           if [[ !  `git status --porcelain` ]]
@@ -36,10 +55,6 @@ jobs:
             exit 0
           fi
 
-          echo "Make a new branch"
-          BRANCH="optimize-images-$(date +'%Y%m%d%H%M%S')"
-          git checkout -b $BRANCH
-
           echo "Make a commit"
           git config user.name github-actions
           git config user.email github-actions@github.com
@@ -47,9 +62,6 @@ jobs:
           git commit --message="Optimize images"
 
           echo "Push up changes"
-          git push --set-upstream origin $BRANCH
-
-          echo "Open a pull request"
-          gh pr create --title "Optimize images" --body "Optimize images"
+          git push
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}