haskellPackages.cabal2nix-unstable: override with unstable dependencies

These dependencies need to be pulled from the same unstable commit that
cabal2nix is pulled from, otherwise changes to any of them will not be
in effect and possibly break the build.

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 -Ee 's/version = "(.*)"/version = "\1-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/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 { };