ci: add ccache to libuvc build check

.github/workflows/build.yml

@@ -10,6 +10,10 @@ jobs:
   build:
     name: Build (${{ matrix.os }})
     runs-on: ${{ matrix.os }}
+    env:
+      CCACHE_DIR: ${{ github.workspace }}/.ccache
+      CCACHE_MAXSIZE: 200M
+      CCACHE_COMPILERCHECK: content
     strategy:
       fail-fast: false
       matrix:
@@ -23,7 +27,26 @@ jobs:
           sudo apt-get update -qq
           sudo apt-get install -y \
             build-essential cmake pkg-config \
-            libusb-1.0-0-dev libjpeg-dev
+            libusb-1.0-0-dev libjpeg-dev ccache
+
+      - name: Record compiler identity
+        id: compiler
+        run: |
+          fingerprint="$({ cc --version; c++ --version; } | sha256sum | cut -d' ' -f1)"
+          echo "fingerprint=$fingerprint" >> "$GITHUB_OUTPUT"
+
+      - name: Cache ccache
+        uses: actions/cache@v6
+        with:
+          path: ${{ env.CCACHE_DIR }}
+          key: ccache-${{ runner.os }}-${{ runner.arch }}-${{ matrix.os }}-${{ steps.compiler.outputs.fingerprint }}-${{ hashFiles('CMakeLists.txt', 'cmake/**', 'include/**', 'src/**', '.github/workflows/build.yml') }}
+          restore-keys: |
+            ccache-${{ runner.os }}-${{ runner.arch }}-${{ matrix.os }}-${{ steps.compiler.outputs.fingerprint }}-
+
+      - name: Configure bounded ccache
+        run: |
+          ccache -M "$CCACHE_MAXSIZE"
+          ccache --zero-stats
 
       - name: Configure (auto-detach ON)
         run: |
@@ -32,7 +55,9 @@ jobs:
             -DBUILD_SHARED_LIBS=ON \
             -DBUILD_EXAMPLE=OFF \
             -DBUILD_TEST=OFF \
-            -DLIBUVC_AUTO_DETACH_KERNEL_DRIVER=ON
+            -DLIBUVC_AUTO_DETACH_KERNEL_DRIVER=ON \
+            -DCMAKE_C_COMPILER_LAUNCHER=ccache \
+            -DCMAKE_CXX_COMPILER_LAUNCHER=ccache
 
       - name: Build
         run: cmake --build build --parallel
@@ -55,7 +80,9 @@ jobs:
             -DBUILD_SHARED_LIBS=ON \
             -DBUILD_EXAMPLE=OFF \
             -DBUILD_TEST=OFF \
-            -DLIBUVC_AUTO_DETACH_KERNEL_DRIVER=OFF
+            -DLIBUVC_AUTO_DETACH_KERNEL_DRIVER=OFF \
+            -DCMAKE_C_COMPILER_LAUNCHER=ccache \
+            -DCMAKE_CXX_COMPILER_LAUNCHER=ccache
           cmake --build build-off --parallel
           echo "PASS: OFF variant builds cleanly"
 
@@ -65,3 +92,11 @@ jobs:
           echo "PASS: shared library produced"
           test -f build/libuvc.a
           echo "PASS: static library produced"
+
+      - name: Show ccache statistics
+        if: ${{ always() }}
+        run: ccache --show-stats
+
+      - name: Enforce ccache bound
+        if: ${{ always() }}
+        run: ccache -c

README.md

@@ -56,4 +56,14 @@ Then you can start them with `./example` and `./uvc_test` respectively. Note tha
 
 The documentation for `libuvc` can currently be found at https://libuvc.github.io/.
 
+The GitHub Actions build check uses a bounded compiler cache for both CMake build
+variants. It caches only the workspace-local `.ccache` directory, keyed by the
+runner, compiler identity, and source/build workflow inputs; the `build/` and
+`build-off/` directories are never cached. Local builds do not require ccache, but
+you can enable it with CMake's compiler launcher options:
+
+    cmake -B build \
+      -DCMAKE_C_COMPILER_LAUNCHER=ccache \
+      -DCMAKE_CXX_COMPILER_LAUNCHER=ccache
+
 Happy hacking!