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NixOS / cabal2nix

Generate Nix build instructions from a Cabal file
https://haskell4nix.readthedocs.io
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Make hackage2nix locale independent #616

Closed maralorn closed 8 months ago

maralorn commented 8 months ago

Since my system is currently missing the locale C.UTF-8 which we set in regenerate-hackage-packages.nix I want to make hackage2nix locale independent. The impurity is driving me nuts. Since we all edit the same file with hackage2nix hardcoding the locale makes total sense.

From memory I think the locale can affect two things:

  1. It affects the encoding with which hackage-packages.nix get’s written.
  2. It affects the ordering of entries in hackage-packages.nix

After reading the documentation for base:System.IO I am moderately certain that this change fixes 1.

Regarding 2 I am just confused. From reading the code I think the ordering depends on the Ord instances of PackageName and Version. Those are newtypes which in the end all boil down to the Ord instances of ShortByteString or String or Int or Word64. I haven’t found any indication that any of them is locale dependent, but I might have overlooked something. Or the ordering issue is something completely else? I don’t know.

At least I think setting the locale explicitly this way won’t make things less reproducible.

maralorn commented 8 months ago

I have tested this with and without "LC_ALL=C.UTF-8" on my system and the hackage-packages.nix file always is the same. (Without the fix in this PR with LC_ALL=C.UTF-8 would just fail.)

I suggest merging this PR and the dropping the LC_ALL line from the script in nixpkgs.

sternenseemann commented 8 months ago

Does it actually affect the ordering of packages in hackage-packages.nix in practice, did you test that? I seriously doubt that was ever the case. IIRC the locale problems is only an issue due to the usage of sort(1) in the maintainer scripts.

maralorn commented 8 months ago

Aaaah, yeah. I could not reproduce any change in ordering and I was highly confused because I also couldn’t imagine the Haskell sorting being unstable but I was sure I remembered some sorting problem. It makes total sense that this is about the .yaml files.