Missing Enum instance for IoSubSystem

[Tom Ellis]

As a core libraries committee member I can say this was probably not
intentional (at least, I wouldn't have voted for it).  Perhaps it is
related to:

https://github.com/haskell/core-libraries-committee/issues/289

But the situation is strange, because it seems like the instance was
removed in 2022:

https://gitlab.haskell.org/ghc/ghc/-/commit/85b0f87a298c8e54b06a8f8c6ce88669c5cad3bc#f7c61f967f2b5c4951224837ae809183449da146_116_105

So I don't understand why it still seems to exist in base-4.20.0.1:

https://hackage.haskell.org/package/base-4.20.0.1/docs/GHC-RTS-Flags.html#t:IoSubSystem

and why the source location still seems to contain it:

https://hackage.haskell.org/package/ghc-internal-9.1001.0/docs/src/GHC.Internal.RTS.Flags.html#IoSubSystem

Tom



On Wed, Dec 04, 2024 at 03:06:39PM +0530, Adithya Kumar wrote:
> Hi all,
> 
> In ghc 9.12-alpha the Enum instance for IoSubSystem no longer exists. I
> don't
> see this change mentioned anywhere in the docs (release notes/changelog)
> here:
> https://downloads.haskell.org/ghc/9.12.1-alpha1/docs/users_guide/9.12.1-notes.html
> 
> Was this change intended or was it a refactoring issue?
> 
> The datatype itself was moved from GHC.Internal.RTS.Flags to
> GHC.Internal.IO.SubSystem.
> 
> The enum instance was earlier defined in GHC.Internal.RTS.Flags but now
> isn't
> defined in either of the modules.
> 
> Best,
> Adithya

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