github actions get ccache working

.github/workflows/build_tests.yml

@@ -22,20 +22,35 @@ jobs:
     - uses: actions/checkout@v1
       with:
         token: ${{ secrets.ACCESS_TOKEN }}
+
     - name: check_format
       env:
         CI: true
       run: make check_format
-    - uses: actions/cache@v1.1.0
-      id: ccache-persistence
+
+    - name: Prepare ccache timestamp
+      id: ccache_cache_timestamp
+      shell: cmake -P {0}
+      run: |
+        string(TIMESTAMP current_date "%Y-%m-%d-%H;%M;%S" UTC)
+        message("::set-output name=timestamp::${current_date}")
+    - name: ccache cache files
+      uses: actions/cache@v1.1.0
       with:
         path: ~/.ccache
-        key: ccache-main-tests
-        restore-keys: |
-          ccache-main-tests
+        key: ${{matrix.ubuntu_release}}-ccache-${{steps.ccache_cache_timestamp.outputs.timestamp}}
+        restore-keys: ${{matrix.ubuntu_release}}-ccache-
     - name: setup ccache
-      run: mkdir -p ~/.ccache && echo "max_size = 300M" > ~/.ccache/ccache.conf && ccache -z && ccache -s
+      run: |
+          mkdir -p ~/.ccache
+          echo "base_dir = ${GITHUB_WORKSPACE}" > ~/.ccache/ccache.conf
+          echo "compression = true" >> ~/.ccache/ccache.conf
+          echo "compression_level = 6" >> ~/.ccache/ccache.conf
+          echo "max_size = 400M" >> ~/.ccache/ccache.conf
+          ccache -s
+          ccache -z
+
     - name: main tests
       run: make tests
     - name: ccache post-run
-      run: ccache -s && ccache -z
+      run: ccache -s