From 77be50b9bdd061e4587c0b8de4b3d8454c77d114 Mon Sep 17 00:00:00 2001
From: Arnout Engelen <arnout@bzzt.net>
Date: Tue, 20 Jan 2026 12:44:04 +0100
Subject: [PATCH] ghc: enable object determinism by default

This is particularly relevant for us because we include
objects in haskell derivation outputs, and this fixes
reproducibility for a significant number of those.

Towards #151347
---
 pkgs/development/haskell-modules/generic-builder.nix | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/pkgs/development/haskell-modules/generic-builder.nix b/pkgs/development/haskell-modules/generic-builder.nix
index 5cebe4aec5d0..1877244aa1a1 100644
--- a/pkgs/development/haskell-modules/generic-builder.nix
+++ b/pkgs/development/haskell-modules/generic-builder.nix
@@ -157,6 +157,7 @@ in
   coreSetup ? false, # Use only core packages to build Setup.hs.
   useCpphs ? false,
   hardeningDisable ? null,
+  enableObjectDeterminism ? lib.versionAtLeast ghc.version "9.12",
   enableSeparateBinOutput ? false,
   enableSeparateDataOutput ? false,
   enableSeparateDocOutput ? doHaddock,
@@ -355,6 +356,9 @@ let
     (enableFeature (!dontStrip) "library-stripping")
     (enableFeature (!dontStrip) "executable-stripping")
   ]
+  ++ optionals enableObjectDeterminism [
+    "--ghc-option=-fobject-determinism"
+  ]
   ++ optionals isCross (
     [
       "--configure-option=--host=${stdenv.hostPlatform.config}"