haskellPackages.cabal2nix-unstable: override with unstable dependencies (#438290)

maintainers/scripts/haskell/update-cabal2nix-unstable.sh

@@ -12,8 +12,16 @@ head_info="$(curl -H "Accept: application/vnd.github.v3+json" https://api.github
 commit="$(jq -r .commit.sha <<< "$head_info")"
 # extract commit timestamp and convert to date
 date="$(date "--date=$(jq -r .commit.commit.committer.date <<< "$head_info")" +%F)"
+
 # generate nix expression from cabal file, replacing the version with the commit date
-output=pkgs/development/haskell-modules/cabal2nix-unstable.nix
+function mkPackage() {
-echo '# This file defines cabal2nix-unstable, used by maintainers/scripts/haskell/regenerate-hackage-packages.sh.' > "$output"
+  output=pkgs/development/haskell-modules/cabal2nix-unstable/$1.nix
-cabal2nix --subpath cabal2nix "https://github.com/NixOS/cabal2nix/archive/$commit.tar.gz" | sed -e 's/version = ".*"/version = "'"unstable-$date"'"/' >> "$output"
+  echo "# This file defines $1-unstable, used by maintainers/scripts/haskell/regenerate-hackage-packages.sh." > "$output"
-nixfmt "$output"
+  cabal2nix --subpath "$1" "https://github.com/NixOS/cabal2nix/archive/$commit.tar.gz" | sed -Ee 's/version = "(.*)"/version = "\1-unstable-'"$date"'"/' >> "$output"
+  nixfmt "$output"
+}
+
+mkPackage "cabal2nix"
+mkPackage "distribution-nixpkgs"
+mkPackage "hackage-db"
+mkPackage "language-nix"

pkgs/development/haskell-modules/cabal2nix-unstable/cabal2nix.nix

@@ -35,7 +35,7 @@
 }:
 mkDerivation {
   pname = "cabal2nix";
-  version = "unstable-2025-08-10";
+  version = "2.20.1-unstable-2025-08-10";
   src = fetchzip {
     url = "https://github.com/NixOS/cabal2nix/archive/31c6db234a905bbf4e8f34c5a986f294b231de0a.tar.gz";
     sha256 = "1ifbmcm5k8mxcpq4kscfc5ddcknawxz6a4ak30jmf0kk1lrfsikf";

pkgs/development/haskell-modules/cabal2nix-unstable/distribution-nixpkgs.nix

@@ -0,0 +1,53 @@
+# This file defines distribution-nixpkgs-unstable, used by maintainers/scripts/haskell/regenerate-hackage-packages.sh.
+{
+  mkDerivation,
+  aeson,
+  base,
+  bytestring,
+  Cabal,
+  containers,
+  deepseq,
+  directory,
+  fetchzip,
+  hspec,
+  language-nix,
+  lens,
+  lib,
+  pretty,
+  process,
+}:
+mkDerivation {
+  pname = "distribution-nixpkgs";
+  version = "1.7.1.1-unstable-2025-08-10";
+  src = fetchzip {
+    url = "https://github.com/NixOS/cabal2nix/archive/31c6db234a905bbf4e8f34c5a986f294b231de0a.tar.gz";
+    sha256 = "1ifbmcm5k8mxcpq4kscfc5ddcknawxz6a4ak30jmf0kk1lrfsikf";
+  };
+  postUnpack = "sourceRoot+=/distribution-nixpkgs; echo source root reset to $sourceRoot";
+  enableSeparateDataOutput = true;
+  libraryHaskellDepends = [
+    aeson
+    base
+    bytestring
+    Cabal
+    containers
+    deepseq
+    language-nix
+    lens
+    pretty
+    process
+  ];
+  testHaskellDepends = [
+    aeson
+    base
+    Cabal
+    deepseq
+    directory
+    hspec
+    language-nix
+    lens
+  ];
+  homepage = "https://github.com/NixOS/cabal2nix/tree/master/distribution-nixpkgs#readme";
+  description = "Types and functions to manipulate the Nixpkgs distribution";
+  license = lib.licenses.bsd3;
+}

pkgs/development/haskell-modules/cabal2nix-unstable/hackage-db.nix

@@ -0,0 +1,44 @@
+# This file defines hackage-db-unstable, used by maintainers/scripts/haskell/regenerate-hackage-packages.sh.
+{
+  mkDerivation,
+  aeson,
+  base,
+  bytestring,
+  Cabal,
+  containers,
+  directory,
+  exceptions,
+  fetchzip,
+  filepath,
+  lib,
+  tar,
+  time,
+  utf8-string,
+}:
+mkDerivation {
+  pname = "hackage-db";
+  version = "2.1.3-unstable-2025-08-10";
+  src = fetchzip {
+    url = "https://github.com/NixOS/cabal2nix/archive/31c6db234a905bbf4e8f34c5a986f294b231de0a.tar.gz";
+    sha256 = "1ifbmcm5k8mxcpq4kscfc5ddcknawxz6a4ak30jmf0kk1lrfsikf";
+  };
+  postUnpack = "sourceRoot+=/hackage-db; echo source root reset to $sourceRoot";
+  isLibrary = true;
+  isExecutable = true;
+  libraryHaskellDepends = [
+    aeson
+    base
+    bytestring
+    Cabal
+    containers
+    directory
+    exceptions
+    filepath
+    tar
+    time
+    utf8-string
+  ];
+  homepage = "https://github.com/NixOS/cabal2nix/tree/master/hackage-db#readme";
+  description = "Access cabal-install's Hackage database via Data.Map";
+  license = lib.licenses.bsd3;
+}

pkgs/development/haskell-modules/cabal2nix-unstable/language-nix.nix

@@ -0,0 +1,32 @@
+# This file defines language-nix-unstable, used by maintainers/scripts/haskell/regenerate-hackage-packages.sh.
+{
+  mkDerivation,
+  base,
+  deepseq,
+  fetchzip,
+  lens,
+  lib,
+  parsec-class,
+  pretty,
+  QuickCheck,
+}:
+mkDerivation {
+  pname = "language-nix";
+  version = "2.2.0-unstable-2025-08-10";
+  src = fetchzip {
+    url = "https://github.com/NixOS/cabal2nix/archive/31c6db234a905bbf4e8f34c5a986f294b231de0a.tar.gz";
+    sha256 = "1ifbmcm5k8mxcpq4kscfc5ddcknawxz6a4ak30jmf0kk1lrfsikf";
+  };
+  postUnpack = "sourceRoot+=/language-nix; echo source root reset to $sourceRoot";
+  libraryHaskellDepends = [
+    base
+    deepseq
+    lens
+    parsec-class
+    pretty
+    QuickCheck
+  ];
+  homepage = "https://github.com/NixOS/cabal2nix/tree/master/language-nix#readme";
+  description = "Data types and functions to represent the Nix language";
+  license = lib.licenses.bsd3;
+}

pkgs/development/haskell-modules/configuration-common.nix

@@ -191,6 +191,7 @@ with haskellLib;
 
   # cabal2nix depends on hpack which doesn't support Cabal >= 3.16
   cabal2nix-unstable = super.cabal2nix-unstable.override (
+    prev:
     # Manually override the relevant dependencies to reduce rebuild amount
     let
       cabalOverride = {
@@ -199,7 +200,7 @@ with haskellLib;
     in
     cabalOverride
     // lib.mapAttrs (_: drv: drv.override cabalOverride) {
-      inherit (self)
+      inherit (prev)
         distribution-nixpkgs
         hackage-db
         hpack

pkgs/development/haskell-modules/configuration-darwin.nix

@@ -341,22 +341,24 @@ self: super:
     # after verifying they are indeed erroneous (e.g. cabal2nix) or just disable
     # the check, sticking with the status quo. Ideally there'll be zero cases of
     # the latter in the future!
-    inherit
+    cabal2nix = overrideCabal (old: {
-      (lib.mapAttrs (
+      postInstall = ''
-        _:
+        remove-references-to -t ${self.hpack} "$out/bin/cabal2nix"
-        overrideCabal (old: {
+        # Note: The `data` output is needed at runtime.
-          postInstall = ''
+        remove-references-to -t ${self.distribution-nixpkgs.out} "$out/bin/hackage2nix"
-            remove-references-to -t ${self.hpack} "$out/bin/cabal2nix"
-            # Note: The `data` output is needed at runtime.
-            remove-references-to -t ${self.distribution-nixpkgs.out} "$out/bin/hackage2nix"
 
-            ${old.postInstall or ""}
+        ${old.postInstall or ""}
-          '';
+      '';
-        })
+    }) super.cabal2nix;
-      ) super)
+    cabal2nix-unstable = overrideCabal (old: {
-      cabal2nix
+      postInstall = ''
-      cabal2nix-unstable
+        remove-references-to -t ${self.hpack} "$out/bin/cabal2nix"
-      ;
+        # Note: The `data` output is needed at runtime.
+        remove-references-to -t ${self.distribution-nixpkgs-unstable.out} "$out/bin/hackage2nix"
+
+        ${old.postInstall or ""}
+      '';
+    }) super.cabal2nix-unstable;
 
     # https://github.com/fpco/unliftio/issues/87
     unliftio = dontCheck super.unliftio;

pkgs/development/haskell-modules/non-hackage-packages.nix

@@ -28,7 +28,16 @@ self: super:
 
   # Used by maintainers/scripts/regenerate-hackage-packages.sh, and generated
   # from the latest master instead of the current version on Hackage.
-  cabal2nix-unstable = self.callPackage ./cabal2nix-unstable.nix { };
+  cabal2nix-unstable = self.callPackage ./cabal2nix-unstable/cabal2nix.nix {
+    distribution-nixpkgs = self.distribution-nixpkgs-unstable;
+    hackage-db = self.hackage-db-unstable;
+    language-nix = self.language-nix-unstable;
+  };
+  distribution-nixpkgs-unstable = self.callPackage ./cabal2nix-unstable/distribution-nixpkgs.nix {
+    language-nix = self.language-nix-unstable;
+  };
+  hackage-db-unstable = self.callPackage ./cabal2nix-unstable/hackage-db.nix { };
+  language-nix-unstable = self.callPackage ./cabal2nix-unstable/language-nix.nix { };
 
   ghc-settings-edit = self.callPackage ../tools/haskell/ghc-settings-edit { };