From 9dfa02e05539bdefd4fe1a4acc5e39b93ac6f818 Mon Sep 17 00:00:00 2001
From: whispers <whispersofthedawn@duck.com>
Date: Wed, 23 Sep 2026 15:44:46 -0400
Subject: [PATCH] dftd4: fix build with gfortran 16

get_numerical_hessian was not declared as part of the public API,
leading to link errors with gfortran 16.
---
 pkgs/by-name/df/dftd4/package.nix | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/pkgs/by-name/df/dftd4/package.nix b/pkgs/by-name/df/dftd4/package.nix
index b4bc8271cf33..26cd71b5ecc0 100644
--- a/pkgs/by-name/df/dftd4/package.nix
+++ b/pkgs/by-name/df/dftd4/package.nix
@@ -2,6 +2,7 @@
   stdenv,
   lib,
   fetchFromGitHub,
+  fetchpatch,
   gfortran,
   buildType ? "meson",
   cmake,
@@ -40,6 +41,14 @@ stdenv.mkDerivation (finalAttrs: {
   patches = [
     # Fix pkg-config, meson and cmake paths for include and lib dirs
     ./build-paths.patch
+
+    # This was not declared as part of the public API, which led to linking
+    # failures with gfortran 16.
+    (fetchpatch {
+      name = "add-get_numerical_hessian_api-to-public-api.patch";
+      url = "https://github.com/dftd4/dftd4/commit/f84dc4033d9ce036e74e709b9cf42c72249f4f52.patch";
+      hash = "sha256-mdKWIKz8A92lI0sMl5rXwhzKd2UDej0yPYiKllH1Asc=";
+    })
   ];
 
   nativeBuildInputs = [