Verify GitHub CI Matrix against `cfg` permutations

[pinkforest]

ref: #1220 (comment)

Given the bug was triggered under certain build configuration(s) that didn't involve cfg(target_feature = "SHA3")

It would be maybe feasible to extract every possible cfg permutation and verify it spits out expected object code.

This in addition to check that the permutations get generated at some level through the GitHub CI matrix as sanity CI verification.

Currently it is not verified / validated but verification might be feasible through first checking all the cfg-gates get triggetered and the resulting binary is the expected - could also leverage snapshot recording / comparison here.

[bjorn3]

Maybe you could insert some macro at the start of every conditionally compiled body which when it gets hit at runtime writes this fact to a file. And then after running the tests for all permutations you could merge all these files together and check that every macro you can find by grepping for the macro in the source code got hit at runtime.

[pinkforest]

yea tho having no changes will work too - I quickly wrote a smol syn toy last night that parses all of the (unique'd) cfg combinations out across the project level and maybe could extend that to dependencies later

But for this I just used to list them deterministically e.g. they will be unique entries that need to be simply checked that they trigger across the runs through CI matrix.

This unique list then can be attached into CI and check that matrix runs trigger all the entries from the list which is my next TODO how to integrate it idiomatically in github CI

[jschneider-bensch]

Thank you for this suggestion! It would indeed be good to ensure all cfg combinations are tested on CI. We have since added aarch64 runners, at least.