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Haskell in Nixpkgs/NixOS

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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.org147 Servers

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10 Mar 2026
@sternenseemann:systemli.orgsterni (he/him) chreekat: well it's forever now… 10:00:30
@adrielus:matrix.orgprescientmoon changed their profile picture.11:07:59
11 Mar 2026
@itamar:apttp.xyzitamar joined the room.00:38:04
@alexfmpe:matrix.orgalexfmpeI'm truly confused... https://github.com/NixOS/nixpkgs/commit/34f316a97a3e0e69bea9b44cd1142f7e73557437 broke haskell.packages.ghc914.haskell-debugger - reverting the commit fixes it the reason is that the older hie-bios's bounds do not build with 9.14 boot libs however, switching back to recent hie-bios in configuration-9.14.nix causes failures in the test suite when building hie-bios??? oddly enough, the older hie-bios does build with jailbreak14:52:55
@alexfmpe:matrix.orgalexfmpe* I'm truly confused... https://github.com/NixOS/nixpkgs/commit/34f316a97a3e0e69bea9b44cd1142f7e73557437 broke haskell.packages.ghc914.haskell-debugger - reverting the commit fixes it the reason is that the older hie-bios's bounds do not build with 9.14 boot libs however, switching back to recent hie-bios in configuration-9.14.nix causes failures in the test suite when building hie-bios??? the older hie-bios does build with jailbreak, doesn't seem like much changed for 9.14: https://github.com/haskell/hie-bios/commits/master/14:53:23
@sternenseemann:systemli.orgsterni (he/him)alexfmpe: you probably lose an override that is otherwise applied to hie-bios19:06:52
@sternenseemann:systemli.orgsterni (he/him)the order of the overlays matters and it is not always ideal19:07:13
@alexfmpe:matrix.orgalexfmpeAaaah yeah could be, I PR'd jailbreak for now since it works19:12:42
12 Mar 2026
@sternenseemann:systemli.orgsterni (he/him)alexfpe: https://hydra.nixos.org/build/32399395820:35:21
@sternenseemann:systemli.orgsterni (he/him)* alexfmpe: https://hydra.nixos.org/build/32399395820:35:26
@sternenseemann:systemli.orgsterni (he/him) alexfmpe: probably a regression from 9.12.2 -> 9.12.3, curious 21:47:51
13 Mar 2026
@alexfmpe:matrix.orgalexfmpehmm happens for primitive and text-short02:16:36
@alexfmpe:matrix.orgalexfmpeand 9.14.104:24:40
@alexfmpe:matrix.orgalexfmpe asked in #ghc-js-backend:matrix.org 04:24:44
@sternenseemann:systemli.orgsterni (he/him)okay I figured out why and wrote there11:18:36
@sternenseemann:systemli.orgsterni (he/him)we could just downgrade the job to ghc9122 until this is resolved, not sure11:19:07
@alexfmpe:matrix.orgalexfmpeI didn't even know we had 9.12.3 what with the bug 17:53:50
@alexfmpe:matrix.orgalexfmpeWe don't have ghc912117:54:02
@sternenseemann:systemli.orgsterni (he/him)well we patched it so19:58:44
@sternenseemann:systemli.orgsterni (he/him)i thought 9.12.4 was never coming out but rc1 has been uploaded today so19:59:07
@ijouw:matrix.orgijouw I have multiple haskellPackages.developPackage projects i develop infrequently (it's ok if build fails sometimes) using cabal.
I use import <nixpkgs> {} because i do not want to manually set versions for their ghc toolchain, and have them all use the same compiler (they should update using a centrally defined value ; i used ghcup before and it installed 200gb of ghc and libs in a year). I now want to test a newer version of ghc (i want to test the haskell debugger project) but my stable nixpkgs only has ghcHEAD with version >= 9.14 (but which appears to be not yet supported by cabal (or is the cabal in my ghcHEAD an old one?)). Is there a way to have similar behavior?
I was thinking of copying haskell.packages.ghc___ from unstable into my local nixpkgs or pinning unstable in a central haskell project that i need to pull from manually. Any advice is welcome.
23:11:58
@alexfmpe:matrix.orgalexfmpeI have a "devenv" project with basically just a shell.nix with a nixpkgs pin and haskell tooling23:35:01
@alexfmpe:matrix.orgalexfmpe that way it's independent of my system nixpkgs, yet it works as a default environment for all projects where I cba doing anything fancier than <nixpkgs> 23:35:47
@alexfmpe:matrix.orgalexfmpeif you really want a nixpkgs-provisioned debugger, you probably want to point to haskell-updates branch, as https://github.com/NixOS/nixpkgs/pull/496489 is fairly recent and not yet in unstable branch23:38:09
@alexfmpe:matrix.orgalexfmpe* I have a "devenv" project with basically just a shell.nix with a nixpkgs pin for haskell tooling23:38:30
@alexfmpe:matrix.orgalexfmpe

or pinning unstable in a central haskell project that i need to pull from manually.

so I guess this, but pin current haskell-updates

23:40:08
@alexfmpe:matrix.orgalexfmpe also much better for caching than import <nixpkgs> or nix-shell -p cabal-install ghc ghcid 23:41:00
@ijouw:matrix.orgijouwIs there a binary cache? (Currently building some libraries i know i do not depend on in my project).23:58:45
14 Mar 2026
@ijouw:matrix.orgijouw🤔 Maybe i should try it with a minimal project, since nix-shell failed.00:01:21
@alexfmpe:matrix.orgalexfmpe
$ git checkout haskell-updates && git pull && git rev-parse HEAD
56381786faa2041f516ff01763773aeb74a45542

$ uname -mo
x86_64 GNU/Linux

$ nix-build -A haskell.packages.ghc914.haskell-debugger --dry-run
these 18 paths will be fetched (32.69 MiB download, 288.83 MiB unpacked):
  /nix/store/mzs5rrq8qwm7dy98lmy056fds8y1ywlr-aeson-pretty-0.8.10
  /nix/store/5pc3b8plrddq2d20zsqf36n50pd59wbp-aeson-pretty-0.8.10-doc
  /nix/store/bkksvi9rw9jfd298yib647qhlw15ai6v-attoparsec-0.14.4
  /nix/store/kdagha0cwzgp5vs3rv621ln5yp9nsaf9-attoparsec-aeson-2.2.2.0
  /nix/store/gr680f8n9mpxw6g1hxgkj8s57cwddkdy-attoparsec-aeson-2.2.2.0-doc
  /nix/store/ckj58hgwzp6nwyglm4p9v828mw5jf7lb-conduit-extra-1.3.8
  /nix/store/mcsl8ad89px6ai3l1rbywwl254h59qms-conduit-extra-1.3.8-doc
  /nix/store/xlywz2jsnx46c4b26zjimy4pvj803i7x-dap-0.4.0.0
  /nix/store/yw0kb5wskw99cw9jav1i1c4bml0f7csr-dap-0.4.0.0-doc
  /nix/store/n68wbiwivj566m2vs9lf6hz6ymz0k89l-haskell-debugger-0.12.1.0
  /nix/store/p5wd0gnlwgd86rv1laxz0lzsrv0nc0vk-haskell-debugger-0.12.1.0-doc
  /nix/store/1s5igrda049qc2b5ygz2kiscl2d2in88-hie-bios-0.18.0
  /nix/store/vs1v8lj5spa46hggfxgfpxgh8qsn96rb-hie-bios-0.18.0-doc
  /nix/store/c9jm879c940a2jridcw74b86l7qwpgmx-implicit-hie-0.1.4.0
  /nix/store/qw6ydf2ydm32l0ah5m9abq1c252wia5f-implicit-hie-0.1.4.0-doc
  /nix/store/rqmrlc2jz7vh551fs8r4w4k61v8q8p01-yaml-0.11.11.2
  /nix/store/kv1wvvb9vr8qlcvh07rz4h86pxa4khkg-yaml-0.11.11.2-bin
  /nix/store/ljqjkyfi0bg4xxqfqdbdx4qx7qkky9am-yaml-0.11.11.2-doc
00:02:10

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