CI: add workaround for nested composite actions issue

Because of actions/runner#2009 the deeply
nested action cache was failing to save the cache in the post run phase.

For the moment we just avoid the nesting with a copy-pasted action
snippet.

.github/actions/cache-query-compilation/action.yml

@@ -14,11 +14,49 @@ outputs:
 runs:
   using: composite
   steps:
-    - name: Cache the query compilation caches
-      uses: ./.github/actions/incremental-cache
+# FIXME: because of https://github.com/actions/runner/issues/2009, nested composite actions with inputs have their
+# post actions broken. So instead of reusing incremental-cache (which would have the nested cache action not able
+# to save the cache in the post-action phase), we are just copy-pasting the steps here
+#    - name: Cache the query compilation caches
+#      uses: ./.github/actions/incremental-cache
+#      with:
+#        path: '**/.cache'
+#        key: codeql-compile-${{ inputs.key }}
+# start of copy-paste from ./.github/actions/incremental-cache (replacing inputs.path with '**/.cache')
+    # calculate the merge-base with main, in a way that works both on PRs and pushes to main.
+    - name: Calculate merge-base
+      shell: bash
+      if: ${{ github.event_name == 'pull_request' }}
+      env:
+        BASE_BRANCH: ${{ github.base_ref }}
+      run: |
+        MERGE_BASE=$(git cat-file commit $GITHUB_SHA | grep '^parent ' | head -1 | cut -f 2 -d " ")
+        echo "merge_base=$MERGE_BASE" >> $GITHUB_ENV
+    - name: Restore read-only cache (PR)
+      if: ${{ github.event_name == 'pull_request' }}
+      uses: erik-krogh/actions-cache@a88d0603fe5fb5606db9f002dfcadeb32b5f84c6
+      with:
+<<<<<<< Updated upstream
+        path: ${{ inputs.path }}
+=======
+        path: '**/.cache'
+>>>>>>> Stashed changes
+        read-only: true
+        key: ${{ inputs.key }}-pr-${{ github.sha }}
+        restore-keys: |
+          ${{ inputs.key }}-${{ github.base_ref }}-${{ env.merge_base }}
+          ${{ inputs.key }}-${{ github.base_ref }}-
+          ${{ inputs.key }}-main-
+    - name: Fill cache (push)
+      if: ${{ github.event_name != 'pull_request' }}
+      uses: erik-krogh/actions-cache@a88d0603fe5fb5606db9f002dfcadeb32b5f84c6
       with:
         path: '**/.cache'
-        key: codeql-compile-${{ inputs.key }}
+        key: ${{ inputs.key }}-${{ github.ref_name }}-${{ github.sha }} # just fill on main
+        restore-keys: | # restore the latest cache if the exact cache is unavailable, to speed up compilation.
+          ${{ inputs.key }}-${{ github.ref_name }}-
+          ${{ inputs.key }}-main-
+# end of copy-paste
     - name: Fill compilation cache directory
       id: fill-compilation-dir
       shell: bash