Relax extension .c requirement for c-sources

[hamishmack]

#9200 started filtering .cc files from c-sources and does not always issue a warning (there has to be at least one .c file present before it warns you it is ignoring the others).

Some packages in hackage (double-conversion for instance) rely on the ability to include C++ source files in c-sources. This is not ideal, but we should probably continue to support these packages.

This change will relax the filtering, so that only .h files are automatically excluded (with a warning). It will also warn if other non .c files are present (suggesting the cxx-sources since C++ sources are the most likely to be used).

The bug that prevented warnings being displayed when no .c files were present is fixed.

[Mikolaj]

Thank you.

[hamishmack]

Is something wrong with mergify?

[hamishmack]

Does it only automatically merge into master?

[ulysses4ever]

@mergify refresh

[mergify]

refresh

✅ Pull request refreshed

[ulysses4ever]

@mergify rebase

[mergify]

rebase

✅ Nothing to do for rebase action

[ulysses4ever]

Mergify only merges backports to non-master branches (and those should be clearly marked: in the description and by the label), that's why this PR is not handled by it.
Why does this PR target the 3.10 branch if it's not a backport? This is rarely needed, and if it is, it has to be merged manually.

[hamishmack]

It fixes an issue with #9200 and that PR did not seem to be in master as far as I could tell.

[ulysses4ever]

@hamishmack makes sense now, thank you.

@Kleidukos are we still accepting PRs for the 3.10 branch? If so, this one will have to be merged manually (Mergify only serves backports to non-master branches).

@Kleidukos more importantly: do you know why #9200 doesn't seem to have a version of it on master? It'd be embarassing to publish a fix in 3.10.2 (3.10.3?) to only break this again in 3.12...

[Kleidukos]

@ulysses4ever yes this one is going in

@Kleidukos more importantly: do you know why #9200 doesn't seem to have a version of it on master

I forgot.

[Mikolaj]

@Kleidukos more importantly: do you know why #9200 doesn't seem to have a version of it on master? It'd be embarassing to publish a fix in 3.10.2 (3.10.3?) to only break this again in 3.12...

I think, #9200 is a quick patch to make cabal releasable, but we haven't had time to discuss at length and agree on a full long-term fix. So perhaps I closed #9190 prematurely, after all. However, given that nobody objected to my closing the issue, perhaps this two-PR fix is good enough? In that case we could just forwardport it to master. Let me ask on the closed issue again.

[hamishmack]

I think ghc 9.8.1 was released without this fix.

[Kleidukos]

@hamishmack GHC is released with lib:Cabal as a boot library because it really is needed for GHC. People who will use cabal-install will use the one we distribute, with the backport.