Simon Peyton Jones authored 2 years ago and Marge Bot committed 2 years ago

This MR fixes #23022 and #23023.  Specifically

* Beef up Note [Type data declarations] in GHC.Rename.Module,
  to make invariant (I1) explicit, and to name the several
  wrinkles.

  And add references to these specific wrinkles.

* Add a Lint check for invariant (I1) above.
  See GHC.Core.Lint.checkTypeDataConOcc

* Disable the `caseRules` for dataToTag# for `type data` values.
  See Wrinkle (W2c) in the Note above.  Fixes #23023.

* Refine the assertion in dataConRepArgTys, so that it does not
  complain about the absence of a wrapper for a `type data` constructor
  Fixes #23022.

Acked-by: Simon Peyton Jones <simon.peytonjones@gmail.com>