add ccache by default for GH actions?

[jakoch]

When cpp-devbox is used as a build container on GHA:

• figure out, if a mount for ccache allows restoring the ccache and makes sense in GHA
  • https://ccache.dev/manual/4.11.html#_common_options
  • consult gha docs for optimal cache settings?

VOLUME /ccache_folder
ENV CCACHE_DIR=/ccache_folder \
    CCACHE_COMPRESS=TRUE \
    CCACHE_COMPRESSLEVEL=5 \
    CCACHE_MAXSIZE=500M

• then, a user would need to setup the ccache_folder handling in their own GHA workflow like this:
  • mkdir ccache_folder
  • mount it during docker run of the container
    • docker run --env=xy -v pwd /ccache_folder:/ccache_folder /user/project/src make configure

[jakoch]

For mozilla/sccache

ENV SCCACHE=0.10.0
RUN curl -fsSL https://github.com/mozilla/sccache/releases/download/v$SCCACHE/sccache-v$SCCACHE-x86_64-unknown-linux-musl.tar.gz | tar -xzv --strip-components=1 -C /usr/local/bin sccache-v$SCCACHE-x86_64-unknown-linux-musl/sccache && \
    chmod +x /usr/local/bin/sccache
ARG SCCACHE_GHA_ENABLED

The outer workflow defines

    env:
      SCCACHE_GHA_ENABLED: "true"

This is passed as ARG into the container and enables the caching strat.

CMake needs the following arguments:

-DCMAKE_C_COMPILER_LAUNCHER=sccache
-DCMAKE_CXX_COMPILER_LAUNCHER=sccache

Non-Cmake

./configure CC="sccache gcc" CXX="sccache gcc"
./configure CC="sccache clang" CXX="sccache clang"

[jakoch]

Implemented.
Change ships starting with tag v1.0.15 - 2025-10-14.

[jakoch]

# Run the container with CCache enabled
docker run --rm -e CCACHE_DISABLE=0 \
    -v /path/to/local/ccache:/ccache \
    cpp-devbox \
    zsh -c "gcc -o hello hello.c"

Explanation:

-e CCACHE_DISABLE=0              → enables CCache
-v /path/to/local/ccache:/ccache → mounts a persistent folder on the host for caching
zsh -c "gcc -o hello hello.c"    → example compilation command

To verify that the compiler cache is working:

docker run --rm -e CCACHE_DISABLE=0 -v /path/to/local/ccache:/ccache cpp-devbox zsh

Inside the container zsh run ccache stats:
ccache -s