Support caching cpp compiled object files with sccache

.github/actions/build/action.yml

@@ -42,6 +42,15 @@ runs:
           pip install -r requirements.txt -r requirements_dev.txt
         fi
 
+    - name: Setup sccache
+      uses: mozilla/sccache-action@v0.0.9
+
+    - name: Set sccache as compiler launcher
+      shell: bash
+      run: |
+        echo "CMAKE_C_COMPILER_LAUNCHER=sccache" >> $GITHUB_ENV
+        echo "CMAKE_CXX_COMPILER_LAUNCHER=sccache" >> $GITHUB_ENV
+
     - name: Cache Conan
       uses: actions/cache@v4
       with:

conanfile.py

@@ -329,6 +329,12 @@ def generate(self):
         # tc.cache_variables["CMAKE_OSX_DEPLOYMENT_TARGET"] = "10.13"
         tc.parallel = True
 
+        # Use sccache as a compiler launcher if available (e.g. in CI via CMAKE_C/CXX_COMPILER_LAUNCHER env vars)
+        if c_launcher := os.environ.get("CMAKE_C_COMPILER_LAUNCHER"):
+            tc.cache_variables["CMAKE_C_COMPILER_LAUNCHER"] = c_launcher
+        if cxx_launcher := os.environ.get("CMAKE_CXX_COMPILER_LAUNCHER"):
+            tc.cache_variables["CMAKE_CXX_COMPILER_LAUNCHER"] = cxx_launcher
+
         py_limited = resolve_py_limited_api(self.options.get_safe("pyLimitedAPI"))
         tc.cache_variables["PY_LIMITED_API"] = py_limited
         print(f"{statusColor}PY_LIMITED_API={py_limited}{endColor}")

docs/source/Build/installBuild.rst

@@ -140,6 +140,35 @@ similar amount of time to compile the messaging related files.  However, after m
 only this Basilisk module will need to be compiled and the compile times are drastically reduced.
 
 
+Speeding Up Builds with ``sccache``
+------------------------------------
+`sccache <https://github.com/mozilla/sccache>`__ is a compiler cache that caches individual C++ object
+files by content hash.  When source files have not changed, sccache returns the cached object instead of
+invoking the compiler, which can dramatically reduce clean-build times.
+
+Install sccache with your system package manager, for example on macOS::
+
+    brew install sccache
+
+Then set the following environment variables before building::
+
+    export CMAKE_C_COMPILER_LAUNCHER=sccache
+    export CMAKE_CXX_COMPILER_LAUNCHER=sccache
+
+With these set, any build invocation (``python3 conanfile.py``, ``pip install -e .``, etc.) will
+automatically use sccache.  A warm cache reduces a full rebuild to only the linking step plus any
+files that actually changed.
+
+To inspect cache statistics after a build::
+
+    sccache --show-stats
+
+.. note::
+
+    sccache is also enabled automatically in CI via ``CMAKE_C/CXX_COMPILER_LAUNCHER`` environment
+    variables set by the GitHub Actions build workflow.
+
+
 Running Project Tests
 ---------------------
 

docs/source/Support/bskReleaseNotesSnippets/1319-sccache.rst

@@ -0,0 +1 @@
+- Added ``sccache`` compiler caching to CI builds to speed up incremental C++ compilation. See :ref:`configureBuild` for how to use ``sccache`` locally.