steps to run make distcheck via Github actions take quite long with caching

[alexg9010]

@rekado I thought we are caching current guix build with: https://github.com/BIMSBbioinfo/pigx_bsseq/blob/e9650a197d1fd81d5b7686d4e4f8d848d6962b42/.github/workflows/build.yml#L13-L19

Thus, I was wondering why most of the checking is actually spent creating the build-environment.

To understand what I am talking about, see this screenshot of a recent run

[alexg9010]

I was wondering whether happens since we are caching the build for each commit (github.sha). Maybe we should cache for $(md5sum guix.scm) instead ?

[rekado]

We're discussing this over at https://github.com/PromyLOPh/guix-install-action/issues/13. There are two things I'd like to change about that action:

• do not run guix pull --- we're not using special channels and we're already starting with a recent Guix
• export the environment and cache that

We're not actually using the cache properly at all, because we can't cache everything we'd have to. With the two changes proposed above we could reduce set up time dramatically.

[rekado]

"export" above means: "guix archive --export --recursive $GUIX_ENVIRONMENT > /path/to/cache/the-environment"; also need to save the Guix signing key. Then on restore we do the opposite: authorize the signing key and then guix archive --import < /path/to/cache/the-environment.