Try speeding up build with ccache

"Inspired" by Bergamot

.github/workflows/macos-all.yml

@@ -11,6 +11,13 @@ on:
 env:
   # Customize the CMake build type here (Release, Debug, RelWithDebInfo, etc.)
   BUILD_TYPE: Release
+  ccache_basedir: ${{ github.workspace }}
+  ccache_dir: "${{ github.workspace }}/.ccache"
+  ccache_compilercheck: content
+  ccache_compress: 'true'
+  ccache_compresslevel: 9
+  ccache_maxsize: 200M
+  ccache_cmake: -DCMAKE_CXX_COMPILER_LAUNCHER=ccache -DCMAKE_C_COMPILER_LAUNCHER=ccache
 
 jobs:
   build-macos:
@@ -35,14 +42,45 @@ jobs:
     - name: Dependencies  # This qt6 build and we suppose apple accelerate was installed, but we can use openblas as a fallback until this is merged.
       run: | 
            brew update
-           brew install protobuf coreutils qt libarchive openblas
+           brew install protobuf coreutils qt libarchive openblas ccache
     
     # Openblas location is exported explicitly because openblas is keg-only,
     # which means it was not symlinked into /usr/local/.
     - name: Set BLAS Environment variables
       run: |
           echo "LDFLAGS=-L/usr/local/opt/openblas/lib" >> $GITHUB_ENV
           echo "CPPFLAGS=-I/usr/local/opt/openblas/include" >> $GITHUB_ENV
+
+    - name: Generate ccache_vars for ccache based on machine
+      shell: bash
+      id: ccache_vars
+      run: |-
+        echo "::set-output name=hash::$(echo ${{ env.ccache_compilercheck }})"
+        echo "::set-output name=timestamp::$(date '+%Y-%m-%dT%H.%M.%S')"
+    
+    - name: Cache-op for build-cache through ccache
+      uses: actions/cache@v2
+      with:
+        path: ${{ env.ccache_dir }}
+        key: ccache-${{ matrix.identifier }}-${{ steps.ccache_vars.outputs.hash }}-${{ github.ref }}-${{ steps.ccache_vars.outputs.timestamp }}
+        restore-keys: |-
+          ccache-${{ matrix.identifier }}-${{ steps.ccache_vars.outputs.hash }}-${{ github.ref }}
+          ccache-${{ matrix.identifier }}-${{ steps.ccache_vars.outputs.hash }}
+          ccache-${{ matrix.identifier }}
+    
+    - name: ccache environment setup
+      run: |-
+        echo "CCACHE_COMPILER_CHECK=${{ env.ccache_compilercheck }}" >> $GITHUB_ENV
+        echo "CCACHE_BASEDIR=${{ env.ccache_basedir }}" >> $GITHUB_ENV
+        echo "CCACHE_COMPRESS=${{ env.ccache_compress }}" >> $GITHUB_ENV
+        echo "CCACHE_COMPRESSLEVEL=${{ env.ccache_compresslevel }}" >> $GITHUB_ENV
+        echo "CCACHE_DIR=${{ env.ccache_dir }}" >> $GITHUB_ENV
+        echo "CCACHE_MAXSIZE=${{ env.ccache_maxsize }}" >> $GITHUB_ENV
+    
+    - name: ccache prolog
+      run: |-
+        ccache -s # Print current cache stats
+        ccache -z # Zero cache entry
     
     - name: Create Build Environment
       # Some projects don't allow in-source building, so create a separate build directory
@@ -61,14 +99,17 @@ jobs:
       # Note the current convention is to use the -S and -B options here to specify source 
       # and build directories, but this is only available with CMake 3.13 and higher.  
       # The CMake binaries on the Github Actions machines are (as of this writing) 3.12
-      run: cmake $GITHUB_WORKSPACE -DCMAKE_BUILD_TYPE=$BUILD_TYPE
+      run: cmake $GITHUB_WORKSPACE -DCMAKE_BUILD_TYPE=$BUILD_TYPE ${{ env.ccache_cmake }}
 
     - name: Build
       working-directory: ${{github.workspace}}/build
       shell: bash
       # Execute the build.  You can specify a specific target with "--target <NAME>"
       run: cmake --build . --config $BUILD_TYPE -j3 --target translateLocally-bin translateLocally.dmg
 
+    - name: ccache epilog
+      run: 'ccache -s # Print current cache stats'
+
     - name: Output test # @TODO some more complicated test, perhaps a unit test
       working-directory: ${{github.workspace}}/build
       shell: bash