Strange internal type errors with Coercible

(A really brief note about the issue, to be expanded later.)

For some reason these two lines are different (they shouldn't have to be)

https://github.com/Lysxia/generic-data/blob/ac3651d3a35f3a8e652f474c482251e6cc3fe622/src/Generic/Data/Internal/Surgery.hs#L365

https://github.com/Lysxia/generic-data/blob/ac3651d3a35f3a8e652f474c482251e6cc3fe622/src/Generic/Data/Internal/Surgery.hs#L410

And the compiler doesn't like when I try to put them in a type synonym (RmvConstr, InsConstr or ConstrSurgery).

Even in the current state some tests fail to type check on GHC 8.0 and I cannot explain why:

https://github.com/Lysxia/generic-data/blob/ac3651d3a35f3a8e652f474c482251e6cc3fe622/test/surgery.hs#L63-L72

/home/sam/code/haskell/gdata/test/surgery.hs:66:49: error:
    • Couldn't match representation of type ‘Int’
                               with that of ‘M1
                                               C
                                               ('MetaCons "B" 'PrefixI 'False)
                                               (M1
                                                  S
                                                  ('MetaSel
                                                     'Nothing
                                                     'NoSourceUnpackedness
                                                     'NoSourceStrictness
                                                     'DecidedLazy)
                                                  (K1 GHC.Generics.R Int))
                                               ()’
        arising from a use of ‘removeConstr’

These are coercible: a manually written specialization of coerce at those types type checks.

-- both ways
> coerce (coerce (3 :: Int) :: M1 C ('MetaCons "B" 'PrefixI 'False) (M1 S ('MetaSel 'Nothing 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (K1 R Int)) x) :: Int
3

Lysxia / generic-data

Strange internal type errors with Coercible #8