From 45bd9eeb76e9d6f60bc6c0851e8818943ba49c5f Mon Sep 17 00:00:00 2001
From: Mohcine Chraibi <m.chraibi@fz-juelich.de>
Date: Tue, 11 Aug 2026 11:07:32 +0200
Subject: [PATCH] Fix macOS superbuild for Apple Silicon toolchains

Three failures prevented the Assimp superbuild step from completing on
macOS. All fixes are scoped to the elseif(APPLE) branch; Windows and
Linux behaviour is unchanged.

- Assimp 5.4.3 predates AppleClang's -Wnontrivial-memcall, which its own
  -Werror escalates to a hard failure in SceneCombiner.cpp. Disable
  ASSIMP_WARNINGS_AS_ERRORS.
- pkg-config resolved minizip to an x86_64 Homebrew prefix, which cannot
  link against the arm64 build. Use the bundled contrib/unzip instead.
- The staging step chose its source directory with a configure-time
  EXISTS check against a path Assimp only creates during install, so a
  clean tree always fell back to lib/ and staged a nested Mac/ folder.
  CMAKE_INSTALL_LIBDIR is already forced to lib/Mac, so the check was
  redundant.

Verified by a full superbuild plus a successful ProjectMobiusEditor Mac
Development build against UE 5.5.4.
---
 UnrealFolder/ProjectMobius/CMakeLists.txt | 20 +++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

diff --git a/UnrealFolder/ProjectMobius/CMakeLists.txt b/UnrealFolder/ProjectMobius/CMakeLists.txt
index d1b3f2e9c..80cd75ac9 100644
--- a/UnrealFolder/ProjectMobius/CMakeLists.txt
+++ b/UnrealFolder/ProjectMobius/CMakeLists.txt
@@ -119,6 +119,15 @@ elseif(APPLE)
     -DCMAKE_OSX_ARCHITECTURES=arm64
     -DCMAKE_OSX_DEPLOYMENT_TARGET=11.0
 
+    # Assimp 5.4.3 predates AppleClang's -Wnontrivial-memcall, which its own
+    # -Werror then turns into a hard failure in SceneCombiner.cpp.
+    -DASSIMP_WARNINGS_AS_ERRORS=OFF
+
+    # Use the bundled contrib/unzip rather than pkg-config's minizip, which on a
+    # machine with an Intel Homebrew prefix resolves to an x86_64 library and
+    # fails to link against this arm64 build.
+    -DASSIMP_BUILD_MINIZIP=ON
+
     # Assimp on UNIX derives ASSIMP_LIB_INSTALL_DIR from CMAKE_INSTALL_LIBDIR.
     # Force libs into lib/Mac to match UE_Assimp expectations.
     -DCMAKE_INSTALL_LIBDIR=lib/Mac
@@ -171,13 +180,10 @@ if(WIN32)
     COMMENT "Staging Assimp DLLs to ${ASSIMP_STAGE_DIR}"
   )
 elseif(APPLE)
-  # Assimp 5.x layouts differ a bit between versions.
-  # Prefer lib/Mac if it exists (old layout), otherwise fall back to lib/.
-  if(EXISTS "${ASSIMP_INST}/lib/Mac")
-    set(ASSIMP_MAC_LIB_DIR "${ASSIMP_INST}/lib/Mac")
-  else()
-    set(ASSIMP_MAC_LIB_DIR "${ASSIMP_INST}/lib")
-  endif()
+  # CMAKE_INSTALL_LIBDIR is forced to lib/Mac above, so the layout is known.
+  # An EXISTS check here would run at configure time, before Assimp is installed,
+  # and on a clean tree would fall back to lib/ and stage a nested Mac/ folder.
+  set(ASSIMP_MAC_LIB_DIR "${ASSIMP_INST}/lib/Mac")
 
   add_custom_command(TARGET assimp_stage POST_BUILD
     COMMAND ${CMAKE_COMMAND} -E rm -rf "${ASSIMP_STAGE_DIR}"