ccache

ccache is a compiler cache. It speeds up recompilation by caching previous compilations and detecting when the same compilation is being done again. More information can be learned about ccache on its website.

IXM provides a ccache package that allows users to use ccache as an IMPORTED executable target. This can then be used to set the CMAKE_<LANG>_COMPILER_LAUNCHER (or the properties they set).

Targets

This module only provides one imported executable target. If the ccache executable cannot be found, this target is not available.

ccache::ccache

The ccache executable (or a ccache compatible executable)

Required: YES

Usage

To get the full usage out of ccache, a few extra operations must be performed.

1. The MSVC_DEBUG_INFORMATION_FORMAT property MUST be set to Embedded, otherwise ccache will fail to cache and users will get inscrutable errors regarding PDBs or the PDB server.
2. When using target_precompile_header, source files MUST use the -fno-pch-timestamp flag if the compiler is Clang or a Clang-like. This option can only be passed in via -Xclang, and thus a generator expression is recommended.

   target_compile_options(${target}
     PRIVATE
       $<$<CXX_COMPILER_ID:Clang>:SHELL:-Xclang$<SEMICOLON>-fno-pch-timestamp>)

   Additionally, users must ensure that pch_defines,time_macros are present for the sloppiness ccache setting.
3. ccache does not support C++ Modules at this time. It does however support clang C++ modules, which are a wholly separate concept altogether.

Lastly, to ensure that the correct ccache configuration settings are found, it's recommended to use CMake Presets to set environment variables for build preset execution:

{
    "buildPresets": [
        {
            "name": "base",
            "hidden": true,
            "environment": {
                "CCACHE_BASEDIR": "${sourceDir}",
                "CCACHE_CONFIGPATH": "${sourceDir}/my/path/to/ccache.conf"
            }
        }
    ]
}

With this work in place, users will be able to get the best experience out of ccache.

NOTE

It is not necessary to use the CCACHE_CONFIGPATH environment variable or a separate ccache configuration file, however it can save time when editing/working with ccache inside of a large CMake based build system.