Haskell in Nixpkgs/NixOS - Public Room Timeline

	Haskell in Nixpkgs/NixOS	724 Members
	For discussions and questions about Haskell with Nix, cabal2nix and haskellPackages in nixpkgs \| Current Docs: https://haskell4nix.readthedocs.io/ \| More Nix: #community:nixos.org \| More Haskell: #haskell-space:matrix.org	145 Servers

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Sender	Message	Time
22 Feb 2025
Alex	In reply to @janus.troelsen:matrix.org is nixpkgs focused on bootstrapping as far back as possible? I thought I saw a discussion talking about how something about 8.10 had bit rotted ? AFAIK nobody here wants to maintain ancient GHC builds.	04:58:32
Janus	Right. and the bootstrapping Community have their own approach with a scheme interpreter , a C subset, TCC , old gcc versions and all that	04:59:27
Janus	iirc they patch these old gcc versions to keep them compatible with their c compiler...	05:01:36
Janus	what I am trying to get at is ... if nixpkgs is not optimized for bootstrapping, it might not be the best place to bootstrap	05:02:20
Janus	that said, in theory there is no reason why it couldn't work	05:02:36
Janus	In reply to @janus.troelsen:matrix.org it's likely that old GHC runtime systems have similar issues . even though Linux promises 100% backwards compat, they did Change the syscall Interface another example is Linux 6.1 breaking MAP_32BIT mmap. GHC needed a workaround to avoid this bug in the data structure Linux started using for paging . it was broken in like a dozen 6.1 releases	05:06:51
emily	we do have minimal bootstrap packaged	05:07:03
emily	it is not yet wired up	05:07:07
emily	there is certainly interest in it for the bootstrap binaries	05:07:21
emily	(for stdenv)	05:07:26
emily	anyway I thought the issue was simply that bootstrapping GHC from modern bindista was weird or something.	05:07:53
Janus	seems like there are still issues with musl and such... I am just following from the sidelines , don't really know. I have an excessively retro approach to this compared to everyone else , it seems	05:10:32
Janus	Joachim breitner also attempted something at munihac, where he wanted to concatenate all GHC modules into a giant file to avoid worrying about recursive module dependencies	05:11:20
Janus	not sure if microhs supports recursive modules yet. I don't think it has Interface files, but otoh it seems like you don't have a traditional linking step either	05:13:05
Janus	In reply to @emilazy:matrix.org we do have minimal bootstrap packaged how far back does it go?	05:32:52
Alex	In reply to @janus.troelsen:matrix.org not sure if microhs supports recursive modules yet. I don't think it has Interface files, but otoh it seems like you don't have a traditional linking step either I saw a hs-boot file while patching the base library so maybe? I'll need to check.	05:52:29
Janus	In reply to @emilazy:matrix.org anyway I thought the issue was simply that bootstrapping GHC from modern bindista was weird or something. as far as I understand, going from GHC to GHC is considered easy? if the minimal bootstrap you refer to is microhs, surely the biggest issue is doing the jump from microhs to GHC , and specifically choosing a suitable version of GHC.	05:59:03
Janus	In reply to @alex:tunstall.xyz I saw a hs-boot file while patching the base library so maybe? I'll need to check. i do think I saw something about this recently in the microhs release logs . so yeah, it's probably supported now , which is great	06:00:37
Janus	readme says "Mutually recursive modules are allowed the same way as with GHC, using .hs-boot files."	06:03:44
Alex	In reply to @janus.troelsen:matrix.org as far as I understand, going from GHC to GHC is considered easy? if the minimal bootstrap you refer to is microhs, surely the biggest issue is doing the jump from microhs to GHC , and specifically choosing a suitable version of GHC. Yes, that's what I foresee being the most difficult. Planned approaches, from most desirable to least: Use mhs directly as a boot compiler with the GHC build system. Unlikely to work because it would require being able to build Hadrian and probably explicit support from GHC. If the GHC maintainers are keen on it, maybe one day it'll be possible. Use mhs to build ghc-bin, then boot GHC with it. Use mhs to boot an old GHC version, then build a long chain of versions to get to the modern ones.	06:23:37
emily	In reply to @janus.troelsen:matrix.org as far as I understand, going from GHC to GHC is considered easy? if the minimal bootstrap you refer to is microhs, surely the biggest issue is doing the jump from microhs to GHC , and specifically choosing a suitable version of GHC. the minimal bootstrap is the elaborate C/Mes/etc. stuff, I wasn't talking about Haskell	14:39:17
emily	I was just saying there has been work on that for Nixpkgs	14:39:27
emily	anyway, it was something about Hadrian issues with new GHCs making us use an old GHC for bootstrap, but I wasn't clear on the details	14:40:07
emily	In reply to @emilazy:matrix.org the minimal bootstrap is the elaborate C/Mes/etc. stuff, I wasn't talking about Haskell (the "256 bytes + Linux kernel + build orchestrator" thing a la Guix)	14:41:20
alexfmpe	Thanks, worked like a charm	18:52:11
alexfmpe	I was handed a list of dozens of packages that don't need dontCheck anymore	18:52:37
alexfmpe	I don't see how to use the same approach for doJailbreak though Turns out this works for doCheck because that's a property of stdenv.mkDerivation however doJailbreak triggers splicing in postPatch so it's not directly inspectable from the outside	18:55:51
alexfmpe	also much less likely to vary between ghc versions than test suite failures	18:58:04
alexfmpe	* also much more likely to vary between ghc versions than test suite failures	18:58:10
Alex	Here's an idea: override Haskell's `mkDerivation` to add all of the function arguments to `passthru`. Since it's `passthru`, it shouldn't invalidate caching. Otherwise, there's also this ugly hack. `nix-repl> (haskell.lib.doJailbreak haskellPackages.lens).postPatch "echo \"Run jailbreak-cabal to lift version restrictions on build inputs.\"\n/nix/store/7q7kmsirmz061126189935lwjw5yhdlv-jailbreak-cabal-1.4/bin/jailbreak-cabal lens.cabal\n" nix-repl> (haskell.lib.dontJailbreak haskellPackages.lens).postPatch ""`	20:10:47

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