Support GHC 9.2

[Bodigrim]

$ cabal build -w ghc-9.2
[ 1 of 18] Compiling Data.Primitive.Unlifted.Array.Primops

src/Data/Primitive/Unlifted/Array/Primops.hs:45:25: error:
    Module ‘GHC.Exts’ does not export ‘RuntimeRep(UnliftedRep)’
   |
45 |                 , TYPE, RuntimeRep (UnliftedRep), unsafeCoerce#)

What's worse is that when I fix imports, GHC 9.2 ends up panicking with a message beyond my comprehension.

[Bodigrim]

As a Hackage Trustee I made two revisions to prohibit unbuildable configurations:
https://hackage.haskell.org/package/primitive-unlifted-0.1.0.0/revisions/
https://hackage.haskell.org/package/primitive-unlifted-0.1.1.0/revisions/

[andrewthad]

Thanks! Also, the current approach in the 1.x series was designed by @treeowl. I am not sure if it is possible to remedy the compiler panics that it causes in newer GHCs, but he might know. The older approach in the 0.x series still works with newer versions of GHC though.

[treeowl]

Lovely. barf. Have you made any progress getting this legit in GHC?

[Bodigrim]

Not really, I was experimenting in /tmp and abandoned it once discovered that fixed imports cause GHC panic.

[wz1000]

See https://gitlab.haskell.org/ghc/ghc/-/issues/20908

[sheaf]

I don't think the uses of unsafeCoerce# in the implementation of unlifted MVars are correct, as they coerce between TYPE (BoxedRep Lifted) and TYPE (BoxedRep Unlifted) (causing the issue Zubin linked to above).

In GHC MR !7299 I'm adding support for levity-polymorphic MVar# (and arrays, MutVar# etc). Do you have tests or other programs that rely on unlifted MVar#? I want to avoid releasing a version of GHC with a subtly broken feature.

[chessai]

fixed in 9b16b79

[hasufell]

Users are seeing this when compiling HLS for GHC 9.2.5.

Building library for primitive-unlifted-1.0.0.0..
[ 1 of 18] Compiling Data.Primitive.Unlifted.Array.Primops ( src/Data/Primitive/Unlifted/Array/Primops.hs, dist/build/Data/Primitive/Unlifted/Array/Primops.o, dist/build/Data/Primitive/Unlifted/Array/Primops.dyn_o )

src/Data/Primitive/Unlifted/Array/Primops.hs:45:25: error:
    Module ‘GHC.Exts’ does not export ‘RuntimeRep(UnliftedRep)’
   |
45 |                 , TYPE, RuntimeRep (UnliftedRep), unsafeCoerce#)
   |                         ^^^^^^^^^^^^^^^^^^^^^^^^