Commit 9bbcc3be authored by Committed by Marge Bot
Refactor UnliftedNewtypes-relation kind signature validity checks
This fixes three infelicities related to the programs that are (and aren't) accepted with `UnliftedNewtypes`: * Enabling `UnliftedNewtypes` would permit newtypes to have return kind `Id Type`, which had disastrous results (i.e., GHC panics). * Data family declarations ending in kind `TYPE r` (for some `r`) weren't being accepted if `UnliftedNewtypes` wasn't enabled, despite the GHC proposal specifying otherwise. * GHC wasn't warning about programs that _would_ typecheck if `UnliftedNewtypes` were enabled in certain common cases. As part of fixing these issues, I factored out the logic for checking all of the various properties about data type/data family return kinds into a single `checkDataKindSig` function. I also cleaned up some of the formatting in the existing error message that gets thrown. Fixes #16821, fixes #16827, and fixes #16829.
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