Hit rate 0.00 % for cache in GitHub Actions CI - cmake

Question

I have a dummy C++ project for which I have the following github actions config:
name: CI
on: [push, pull_request] # on all pushes and PRs
jobs:
dummy:
runs-on: ubuntu-latest
strategy:
matrix:
distro: ["ros:foxy-ros-base-focal"]
container:
image: ${{ matrix.distro }}
env:
CCACHE_DIR: "${{ github.workspace }}/.ccache"
steps:
- uses: actions/checkout#v2
- name: install ccache
run: |
sudo apt-get update -y
sudo apt-get -qq install ccache
- name: ccache cache
uses: actions/cache#v2
with:
path: ${{ env.CCACHE_DIR }}
key: ccache-${{ matrix.distro }}-${{github.run_id}}
restore-keys: |
ccache-${{ matrix.distro }}
- name: ccache stats
run: ccache -s
- name: Build workspace
run: |
bash ./build_bridge.sh
I am testing ccache by adding / removing libs in CMakeLists.txt, but each time the ccache hit rate is 0%
cache directory /__w/action_test/action_test/.ccache
primary config /__w/action_test/action_test/.ccache/ccache.conf
secondary config (readonly) /etc/ccache.conf
cache hit (direct) 0
cache hit (preprocessed) 0
cache miss 0
cache hit rate 0.00 %
cleanups performed 0
files in cache 0
cache size 0.0 kB
max cache size 5.0 GB
The previous job from which the cache was restored from had an output:
Post job cleanup.
/usr/bin/docker exec b170bb77ebaac32aed0561984bb959d515d8a025b9329b6309b986f6b676c6c4 sh -c "cat /etc/*release | grep ^ID"
/usr/bin/tar --posix -z -cf cache.tgz -P -C /__w/action_test/action_test --files-from manifest.txt
Cache saved successfully
Do I need to do anything specific to save cmake-specific cache?

Answer 1

CMake should use the ccache's compiler wrappers Reference: "Enabling ccache in your project". I modified the build step to:
- name: Build workspace
run: |
sudo /usr/sbin/update-ccache-symlinks
export PATH="/usr/lib/ccache:$PATH"
bash ./build_bridge.sh
CMake output:
-- Check for working C compiler: /usr/lib/ccache/cc -- works
-- Check for working CXX compiler: /usr/lib/ccache/c++ -- works
Now the ccache stats look good
stats updated Wed Mar 31 17:30:50 2021
cache hit (direct) 1
cache hit (preprocessed) 0
cache miss 48
cache hit rate 2.04 %
called for link 41
cleanups performed 0
files in cache 94
cache size 42.8 MB
max cache size 5.0 GB
And the build time reduced from 1min ~20sec to 24sec.