Enable ccache / sccache on our Github CI Actions

[gpshead]

This should significantly reduce build latency, particularly rebuild latency when minor changes are pushed in PR branches.

It can help across builds, but as the main branch point of a given PR branch is not synchronized how much it helps there will be limited. A lot more likely to help on release branches for bugfix backports as C code in those trees doesn't evolve quickly.

https://github.com/hendrikmuhs/ccache-action has instructions. sccache even claims to support Windows (I've never used it).

[ammaraskar]

Looks like we even have the ccache action already hovering around in the workflow from here: https://github.com/python/cpython/pull/29935/files

Just need to use it for the C building bits.

[ammaraskar]

Actually, since the workflow uses the approach that adds the ccache folder to PATH:

https://github.com/python/cpython/blob/788154919c2d843a0a995994bf2aed2d074761ec/.github/workflows/build.yml#L67-L68

      - name: Add ccache to PATH
        run: echo "PATH=/usr/lib/ccache:$PATH" >> $GITHUB_ENV

we might already be using ccache for all the subsequent steps including Build CPython.

[ammaraskar]

Yeah, we definitely already are thanks to @tiran. Here's a comparison of the same commit built on python/cpython with a full cache vs my personal fork with no cache:

python/cpython

ammaraskar/cpython

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I think the action items here are adding the ccache action to the docs and mac build to speed them up and maybe looking at swapping out for sccache so it can be used on Windows as well.

[gpshead]

It also looked like sccache can be used with Windows if someone win-familiar could figure out how that needs to integrate with its build system.

[erlend-aasland]

We've been using ccache in our CI for a while. Should we keep this open for the Windows CI?