clean up the cache when compiling on main

Author: erik-krogh

.github/workflows/compile-queries.yml

@@ -56,4 +56,20 @@ jobs:
         # do full compile if running on main - this populates the cache
         if : ${{ github.event_name != 'pull_request' }}
         shell: bash
-        run: codeql query compile -j0 */ql/src --keep-going --warnings=error
+        run: |
+          # Move all the existing cache into another folder, so we only preserve the cache for the current queries.
+          mkdir -p ${COMBINED_CACHE_DIR}
+          rm */ql/src/.cache/{lock,size}
+          # replicate the folder structure from the .cache folders into the combined cache folder. (because cp doesn't have a "create missing folders" option)
+          find */ql/src/.cache -type d | cut -d "/" -f 6,7 | sort | uniq > folders.txt
+          cat folders.txt | xargs -I {} mkdir -p ${COMBINED_CACHE_DIR}/{}
+          # copy the contents of the .cache folders into the combined cache folder.
+          cp -r */ql/src/.cache/* ${COMBINED_CACHE_DIR}/
+          # clean up the .cache folders
+          rm -rf */ql/src/.cache/*
+          rm folders.txt
+
+          # compile the queries
+          codeql query compile -j0 */ql/src --keep-going --warnings=error --compilation-cache ${COMBINED_CACHE_DIR}
+        env: 
+          COMBINED_CACHE_DIR: ${{ github.workspace }}/compilation-dir