From 9cc5b1ec94d260383b7743b123edc7799ce1bcab Mon Sep 17 00:00:00 2001
From: Alex Tunstall <alex@tunstall.xyz>
Date: Sat, 7 Feb 2026 12:57:27 +0000
Subject: [PATCH] ghc: Fix regression in unregisterised builds

The default GCC compiler in Nixpkgs was recently changed, bringing in a
new default C standard (gnu23), which GHC's C backend is not compatible
with.
This fix adds a flag to force GCC to use an older compatible C standard.
---
 pkgs/development/compilers/ghc/common-make-native-bignum.nix | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/pkgs/development/compilers/ghc/common-make-native-bignum.nix b/pkgs/development/compilers/ghc/common-make-native-bignum.nix
index 2300e0470ca79..5d05d4b298b8a 100644
--- a/pkgs/development/compilers/ghc/common-make-native-bignum.nix
+++ b/pkgs/development/compilers/ghc/common-make-native-bignum.nix
@@ -536,6 +536,8 @@ stdenv.mkDerivation (
     ]
     ++ lib.optionals enableUnregisterised [
       "--enable-unregisterised"
+      # The C backend generates code incompatible with gnu23
+      "CONF_CC_OPTS_STAGE2=-std=gnu17"
     ];
 
     # Make sure we never relax`$PATH` and hooks support for compatibility.