[ghc-steering-committee] Warnings

[Simon Peyton Jones]

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
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.haskell.org/pipermail/ghc-steering-committee/attachments/20230925/191fcc67/attachment-0001.html>