README: document that sccache is incompatible with /Zi with MSVC

README.md

@@ -108,6 +108,21 @@ To use sccache with cmake, provide the following command line arguments to cmake
 -DCMAKE_CXX_COMPILER_LAUNCHER=sccache
 ```
 
+To generate PDB files for debugging with MSVC, only the [`/Z7` option](https://docs.microsoft.com/en-us/cpp/build/reference/z7-zi-zi-debug-information-format?view=msvc-160) works with sccache; the PDB files generated with the `/Zi` and `/ZI` options cannot be cached. Note that CMake sets `/Zi` by default, so if you use CMake, you will need something like this in your CMakeLists.txt:
+
+```
+if(CMAKE_BUILD_TYPE STREQUAL "Debug")
+  string(REPLACE "/Zi" "/Z7" CMAKE_CXX_FLAGS_DEBUG "${CMAKE_CXX_FLAGS_DEBUG}")
+  string(REPLACE "/Zi" "/Z7" CMAKE_C_FLAGS_DEBUG "${CMAKE_C_FLAGS_DEBUG}")
+elseif(CMAKE_BUILD_TYPE STREQUAL "Release")
+  string(REPLACE "/Zi" "/Z7" CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE}")
+  string(REPLACE "/Zi" "/Z7" CMAKE_C_FLAGS_RELEASE "${CMAKE_C_FLAGS_RELEASE}")
+elseif(CMAKE_BUILD_TYPE STREQUAL "RelWithDebInfo")
+  string(REPLACE "/Zi" "/Z7" CMAKE_CXX_FLAGS_RELWITHDEBINFO "${CMAKE_CXX_FLAGS_RELWITHDEBINFO}")
+  string(REPLACE "/Zi" "/Z7" CMAKE_C_FLAGS_RELWITHDEBINFO "${CMAKE_C_FLAGS_RELWITHDEBINFO}")
+endif()
+```
+
 ---
 
 Build Requirements