Mise Cpp Cmake Ninja Ccache

CCACHE_DIR — why project-local

The default is ~/.ccache or ~/.cache/ccache, shared across every project. This is fine for solo work but:

• You can't blow away one project's cache without nuking all of them.
• Multiple projects with different compiler versions thrash the cache.
• CI caching is harder (you can't just upload one dir).

Setting CCACHE_DIR to {{config_root}}/.cache/ccache puts the cache next to mise.toml. Add it to .gitignore:

.cache/
build/

ninja parallelism

ninja defaults to nproc + 2 parallel jobs. For most machines this is fine. Tune only if:

• You're OOMing on a laptop — pass -j <smaller>.
• You want deterministic build times in CI — pass -j <fixed>.

In mise.toml:

[tasks.build]
run = "ninja -C build"  # default parallelism

For CI with fixed parallelism:

[tasks."build:ci"]
run = "ninja -C build -j {{env.CI_BUILD_JOBS | default(value='4')}}"

CMake presets integration

CMake presets (CMakePresets.json) are the modern way to store "how to configure this build". They compose cleanly with mise:

{
  "version": 6,
  "configurePresets": [
    {
      "name": "dev",
      "generator": "Ninja",
      "binaryDir": "${sourceDir}/build",
      "cacheVariables": {
        "CMAKE_BUILD_TYPE": "Debug",
        "CMAKE_EXPORT_COMPILE_COMMANDS": "ON"
      }
    },
    {
      "name": "release",
      "inherits": "dev",
      "cacheVariables": { "CMAKE_BUILD_TYPE": "Release" }
    }
  ]
}

And in mise.toml:

[tasks.configure]
run = "cmake --preset dev"

[tasks."configure:release"]
run = "cmake --preset release"

[tasks.build]
depends = ["configure"]
run = "cmake --build build"

Note: when you use cmake --build, it picks up the generator from the preset — you don't need CMAKE_GENERATOR in env if every configure goes through a preset. But it doesn't hurt.

CMAKE_EXPORT_COMPILE_COMMANDS=ON

Always set this. It produces build/compile_commands.json, which clangd reads to give you accurate IDE support. Without it, clangd falls back to heuristics and gets confused on complex projects.

Symlink it from the project root so tools find it:

[tasks.configure]
run = [
  "cmake --preset dev",
  "ln -sf build/compile_commands.json ."
]

ccache stats

Periodically run ccache -s to see your hit rate. Aim for >80% on incremental builds. If it's lower:

• Cache miss on "different time macros" → CCACHE_SLOPPINESS=time_macros.
• Cache miss on precompiled headers → CCACHE_SLOPPINESS=pch_defines,time_macros.
• Cache miss on path differences → CCACHE_BASEDIR={{config_root}} (rebases absolute paths).

CI caching

In GitHub Actions, cache the ccache dir between runs:

- uses: actions/cache@v4
  with:
    path: .cache/ccache
    key: ccache-${{ runner.os }}-${{ hashFiles('**/CMakeLists.txt', 'mise.lock') }}
    restore-keys: ccache-${{ runner.os }}-

This gives CI the same 5-10x speedup you get locally.

Anti-patterns

• Using make instead of ninja — slower, worse parallelism, no pretty progress.
• Not setting CMAKE_*_COMPILER_LAUNCHER=ccache — you install ccache but it never runs because nothing invokes it.
• Global CCACHE_DIR — cross-project pollution.
• Turning off compression to "save CPU" — compression usually makes the cache bigger in effective hit rate. Leave it on.
• Setting CCACHE_MAXSIZE too low — the cache silently evicts your build.

See also

• mise-cpp-toolchain-overview — the big picture.
• mise-cpp-linker-fast — the next layer of speed after ccache.
• mise-cpp-package-managers — conan/vcpkg integration.
• ccache docs: ccache.dev/manual/latest.html.
• CMake presets: cmake.org/cmake/help/latest/manual/cmake-presets.7.html.