From bcab0af638f6ae0b726eeab1f7d501d7594950d9 Mon Sep 17 00:00:00 2001
From: sternenseemann <sternenseemann@systemli.org>
Date: Sun, 28 Sep 2025 16:47:01 +0200
Subject: [PATCH] haskellPackages.mkDerivation: convert .cabal file after
 prePatch

cabal2nix emits prePatch = "hpack" for packages that need it, so the
.cabal file may not exist before prePatch.
---
 pkgs/development/haskell-modules/generic-builder.nix | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/pkgs/development/haskell-modules/generic-builder.nix b/pkgs/development/haskell-modules/generic-builder.nix
index 31634958f546..6767cfa7af50 100644
--- a/pkgs/development/haskell-modules/generic-builder.nix
+++ b/pkgs/development/haskell-modules/generic-builder.nix
@@ -606,10 +606,13 @@ lib.fix (
           echo "Replace Cabal file with edited version from ${newCabalFileUrl}."
           cp ${newCabalFile} ${pname}.cabal
         ''
+        + prePatch
+        + "\n"
+        # cabal2nix-generated expressions run hpack not until prePatch to create
+        # the .cabal file (if necessary)
         + lib.optionalString (!dontConvertCabalFileToUnix) ''
           sed -i -e 's/\r$//' *.cabal
-        ''
-        + prePatch;
+        '';
 
       postPatch =
         optionalString jailbreak ''