From e21b41e36e772bf52199aa456535f5c2975b94f7 Mon Sep 17 00:00:00 2001
From: Florian Agbuya <fa@m-labs.ph>
Date: Thu, 8 Jan 2026 14:47:43 +0800
Subject: [PATCH] python313Packages.pybind11: fix cross-compilation when CPU
 bit depth differs

---
 .../development/python-modules/pybind11/default.nix | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/pkgs/development/python-modules/pybind11/default.nix b/pkgs/development/python-modules/pybind11/default.nix
index 4b49b52abe82..c4505f01ea50 100644
--- a/pkgs/development/python-modules/pybind11/default.nix
+++ b/pkgs/development/python-modules/pybind11/default.nix
@@ -14,6 +14,9 @@
   numpy,
   pytest,
   makeSetupHook,
+  # Build tests to verify cross-compilation works, but only when CPU bit
+  # depth matches (otherwise Python headers cause LONG_BIT mismatch errors)
+  buildTests ? stdenv.hostPlatform.parsed.cpu.bits == stdenv.buildPlatform.parsed.cpu.bits,
 }:
 let
   setupHook = makeSetupHook {
@@ -44,9 +47,7 @@ buildPythonPackage rec {
     pybind11.passthru.scikit-build-core-no-tests
   ];
 
-  buildInputs = [
-    # Used only for building tests - something we do even when cross
-    # compiling.
+  buildInputs = lib.optionals buildTests [
     catch2
     boost
     eigen
@@ -65,13 +66,11 @@ buildPythonPackage rec {
   ];
 
   cmakeFlags = [
-    # Always build tests, because even when cross compiling building the tests
-    # is another confirmation that everything is OK.
-    (lib.cmakeBool "BUILD_TESTING" true)
+    (lib.cmakeBool "BUILD_TESTING" buildTests)
 
     # Override the `PYBIND11_NOPYTHON = true` in `pyproject.toml`. This
     # is required to build the tests.
-    (lib.cmakeBool "PYBIND11_NOPYTHON" false)
+    (lib.cmakeBool "PYBIND11_NOPYTHON" (!buildTests))
   ];
 
   dontUseCmakeConfigure = true;