Don't warn on `mhs-options` (MicroHs options)

[sol]

When developing a package that supports both MicroHs and GHC it is useful to specify both mhs-options
and ghc-options, for each respective compiler.

mhs-options are interpreted by MicroCabal and are ignored by Cabal, which is the desired behavior.

However, cabal check currently emits a warning on mhs-options, which it should not.

[Bodigrim]

This would presumably require a new version of Cabal format?..

[geekosaur]

I don't see why, since we're not supporting it, only allowing other cabal implementations (specifically, MicroCabal) to support it.

[sol]

This would presumably require a new version of Cabal format?..

I don't see why, since we're not supporting it, only allowing other cabal implementations (specifically, MicroCabal) to support it.

That makes sense.

[sol]

It's a one line change (#11344). Reviews appreciated.

[Bodigrim]

mhs-options are interpreted by MicroCabal and are ignored by Cabal, which is the desired behavior.

My perspective is that Cabal should strive to be able to drive MicroHs and not ignore mhs-options, properly parse, retain and interpret it.

If we do not bump format version now, in future we would have to say "oh, mhs-options are completely ignored with cabal-version: 3.16 (even if parsed by Cabal 3.18), but suddenly get used as soon as you say cabal-version: 3.18". Which would be rather awkward.

But maybe I'm making too many assumptions here? My understanding is that @augustss wrote MicroCabal to have a self-bootstrapable ecosystem, but ideally in glorious future:

• Cabal-the-tool should be able to drive MicroHaskell on its own (as it used to be able to drive other Haskell compilers),
• Similar to Stack, MicroCabal should reuse Cabal-the-library (or at least Cabal-syntax) once MicroHaskell is capable to compile them.

[geekosaur]

He wrote it because cabal uses too many unsupported ghc options for it to build with MicroHS. You can find a comment somewhere in PRs where I asked him about an extension someone was using and he told me he'd already given up on cabal ever being buildable.

[Bodigrim]

Yes, I remember that discussion, but it was long time ago and MicroHs covered a lot of ground since then. I suspect that by now the only thing MicroHaskell really lacks to compile Cabal-syntax is to do with Generics, and even that isn't certain.