GitHub Actions: Cache dependencies

.github/workflows/CI.yml

@@ -41,11 +41,33 @@ jobs:
         # See: https://github.com/actions/virtual-environments/tree/main/images/macos
         run: sudo xcode-select -switch /Applications/Xcode_12.2.app/Contents/Developer
 
-      - name: Create Build Logs Dir
+      - name: Prep
+        id: prep
         run: |
+          echo "Create Build Logs Dir"
           mkdir -p "${HOME}/build_logs"
+          echo "Get Xcode version info"
+          XCODE_VERSION="$(xcodebuild -version)"
+          echo "${XCODE_VERSION}"
+          XCODE_VERSION="$(echo "${XCODE_VERSION}" | tr '\t\r\n ' '_')"
+          echo "${XCODE_VERSION}"
+          echo "::set-output name=XCODE_VERSION::${XCODE_VERSION}"
+
+      - name: Cache Dependencies
+        id: cache-dependencies
+        if: success() && !(github.event_name == 'push' && contains(github.ref, 'refs/tags/')) # never cache dependencies for pushed tags
+        uses: actions/cache@v2
+        with:
+          path: External/build/
+          key: ${{ runner.os }}-${{ steps.prep.outputs.XCODE_VERSION }}-${{ matrix.platform }}-${{ hashFiles('fetchDependencies','ExternalRevisions/**','ExternalDependencies.xcodeproj/**','Scripts/**') }}
+
+      - name: Fetch Dependencies (Use Built Cache)
+        if: steps.cache-dependencies.outputs.cache-hit == 'true'
+        run: |
+          ./fetchDependencies -v --no-parallel-build --none
 
       - name: Fetch Dependencies
+        if: steps.cache-dependencies.outputs.cache-hit != 'true'
         run: |
           ./fetchDependencies -v --no-parallel-build --${{ matrix.platform }}