Simplify cache cleanup actions (#361)

* Simplify cache cleanup actions

For the CleanUpCache workflow run triggered by PR workflows, there is a
simple way of getting the PR number. The full event webhook payload is
available as a json file and it contains the number of the triggering PR. So
we don't need to upload the PR number as an artifact.

For the post-PR cleanup, we could also clean up the cache directly without
uploading the PR number and triggering a workflow run for cleaning.

* No need to upload PR number

.github/workflows/ci.yml

@@ -47,18 +47,3 @@ jobs:
       contents: read
       security-events: write
     uses: ./.github/workflows/codeql.yml
-
-  save_pr_number:
-    if: github.event_name != 'push'
-    runs-on: ubuntu-latest
-    steps:
-      - name: Save PR number
-        env:
-          PR_NUMBER: ${{ github.event.number }}
-        run: |
-          echo $PR_NUMBER > pr_number.txt
-      - uses: actions/upload-artifact@v4
-        with:
-          name: pr_number
-          path: pr_number.txt
-          retention-days: 1

.github/workflows/cleanup-cache.yml

@@ -17,7 +17,7 @@ jobs:
       GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
     steps:
       - uses: actions/checkout@v4
-      - name: Clean up ccahe
+      - name: Clean up ccache
         run: |
           gh extension install actions/gh-actions-cache
 
@@ -30,8 +30,8 @@ jobs:
           WORKFLOW_NAME="${{ github.event.workflow_run.name }}"
 
           if [[ $EVENT == "pull_request" ]]; then
-            gh run download ${{ github.event.workflow_run.id }} -n pr_number
-            pr_number=`cat pr_number.txt`
+            pr_number=$(jq --raw-output .workflow_run.pull_requests[0].number < ${GITHUB_EVENT_PATH})
+            echo "Clean up cache for PR ${pr_number}."
             BRANCH=refs/pull/${pr_number}/merge
           else
             BRANCH=refs/heads/${{ github.event.workflow_run.head_branch }}
@@ -54,6 +54,7 @@ jobs:
           IFS=$'\n'
           for j in $cached_jobs
           do
+            # Delete all entries except the last used one
             old_keys=$(gh actions-cache list -L 100 -R $REPO -B $BRANCH --key "${j}-git-" --sort last-used | cut -f 1 | tail -n +2)
             for k in $old_keys
             do

.github/workflows/post-pr.yml

@@ -5,16 +5,35 @@ on:
       - closed
 
 jobs:
-  cleanup:
+  cleanup_cache:
+    name: Clean Up Ccache Cache Post PR
     runs-on: ubuntu-latest
+    permissions:
+      actions: write
+      contents: read
+    env:
+      GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
     steps:
-      - name: Save PR number
-        env:
-          PR_NUMBER: ${{ github.event.number }}
+      - uses: actions/checkout@v4
+      - name: Clean up ccache
         run: |
-          echo $PR_NUMBER > pr_number.txt
-      - uses: actions/upload-artifact@v4
-        with:
-          name: pr_number
-          path: pr_number.txt
-          retention-days: 1
+          gh extension install actions/gh-actions-cache
+
+          REPO=${{ github.repository }}
+
+          pr_number=${{ github.event.number }}
+          echo "Clean up cache for PR ${pr_number}."
+          BRANCH=refs/pull/${pr_number}/merge
+
+          # Setting this to not fail the workflow while deleting cache keys.
+          set +e
+
+          # Delete all entries associated with this PR.
+          keys=$(gh actions-cache list -L 100 -R $REPO -B $BRANCH | cut -f 1)
+          # $keys might contain spaces. Thus we set IFS to \n.
+          IFS=$'\n'
+          for k in $keys
+          do
+            gh actions-cache delete "$k" -R $REPO -B $BRANCH --confirm
+          done
+          unset IFS