[ghc-steering-committee] Warnings

[Simon Marlow]

+1 - fix the bug with a warning cycle.

Maybe a good rule of thumb for when GR2 applies is: does the current
behaviour contradict the documentation? (probably not applicable in all
cases, of course)

Cheers
Simon

On Mon, 25 Sept 2023 at 12:49, Eric Seidel <eric at seidel.io> wrote:

> I agree with Moritz that a GHC Proposal is not necessary. Proposals should
> be used for changes in *intended* user-facing behavior, this is just a
> routine bugfix.
>
> I also agree that a warning/deprecation period would be good, but I
> wouldn't spend overly on it. This sounds like a very easy issue to work
> around, just enable the extension explicitly. (Or would that have potential
> second-order consequences?)
>
> On Mon, Sep 25, 2023, at 05:03, Simon Peyton Jones wrote:
> > Dear GHC SC
> >
> > You may or may not have been following GHC ticket #22141
> > <https://gitlab.haskell.org/ghc/ghc/-/issues/22141>, and Ryan's merge
> > request !11314
> > <https://gitlab.haskell.org/ghc/ghc/-/merge_requests/11314>.
> >
> > The story is this:
> >  • There is a bug in GHC that allows programs to use DataKinds without
> > the -XDataKinds extension.
> >  • The MR fixes the bug.
> >  • But of course that will mean that some programs that previously
> > compiled (exploiting the bug) will now fail to compile (correctly).
> > It seems like an example of our (GR2) discussion, but with a very
> > different flavour than the  (3+4=8) example.
> >
> > Personally I think we should do it -- with a deprecation cycle saying
> > "You need DataKinds for this program, and you don't have it on, but you
> > will need it in the next release".   I don't want us to grandfather
> > bugs into GHC indefinitely -- although you could argue that the status
> > quo does little harm, I suppose.
> >
> > Any views?   We will have some idea of the impact on head.hackage
> shortly.
> >
> > *And specifically: do you want a GHC proposal for this change?*
> >
> > Simon
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