From d613d39bd99b750ea59b4a17448213695939dd5f Mon Sep 17 00:00:00 2001
From: Guilhem Saurel <guilhem.saurel@laas.fr>
Date: Mon, 1 Jun 2026 18:54:30 +0200
Subject: [PATCH 1/2] eigen_5: add withDoc option, fix #526648

---
 pkgs/by-name/ei/eigen_5/package.nix | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/pkgs/by-name/ei/eigen_5/package.nix b/pkgs/by-name/ei/eigen_5/package.nix
index 4f2f8f6135ce..9e03b7c319d4 100644
--- a/pkgs/by-name/ei/eigen_5/package.nix
+++ b/pkgs/by-name/ei/eigen_5/package.nix
@@ -10,6 +10,8 @@
   doxygen,
   cmake,
   graphviz,
+
+  withDoc ? true, # upstream disable for cross, even if it seems to build fine
 }:
 
 stdenv.mkDerivation (finalAttrs: {
@@ -34,16 +36,22 @@ stdenv.mkDerivation (finalAttrs: {
 
   outputs = [
     "out"
-    "doc"
-  ];
+  ]
+  ++ lib.optional withDoc "doc";
 
   nativeBuildInputs = [
-    doxygen
     cmake
+  ]
+  ++ lib.optionals withDoc [
+    doxygen
     graphviz
   ];
 
-  postInstall = ''
+  cmakeFlags = [
+    (lib.cmakeBool "EIGEN_BUILD_DOC" withDoc)
+  ];
+
+  postInstall = lib.optionalString withDoc ''
     cmake --build . -t install-doc
   '';
 

From 6ebea2cd59a2f1bf43e8322a2d5ba190f94ffd11 Mon Sep 17 00:00:00 2001
From: Guilhem Saurel <guilhem.saurel@laas.fr>
Date: Mon, 1 Jun 2026 19:07:13 +0200
Subject: [PATCH 2/2] eigen_5: fix Fontconfig error

---
 pkgs/by-name/ei/eigen_5/package.nix | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/pkgs/by-name/ei/eigen_5/package.nix b/pkgs/by-name/ei/eigen_5/package.nix
index 9e03b7c319d4..83c2928b6eb6 100644
--- a/pkgs/by-name/ei/eigen_5/package.nix
+++ b/pkgs/by-name/ei/eigen_5/package.nix
@@ -52,6 +52,9 @@ stdenv.mkDerivation (finalAttrs: {
   ];
 
   postInstall = lib.optionalString withDoc ''
+    # Fontconfig error: No writable cache directories
+    export XDG_CACHE_HOME="$(mktemp -d)"
+
     cmake --build . -t install-doc
   '';