From 28b85d2f58f1b2cd5730a461b031ecf84510358a Mon Sep 17 00:00:00 2001
From: Sam Edwards <CFSworks@gmail.com>
Date: Fri, 10 Jan 2020 14:17:59 -0700
Subject: [PATCH] CMake: Work around CMake issue 20206

---
 cmake/macros/CompositeSources.cmake | 11 +++++++++++
 direct/src/showbase/CMakeLists.txt  |  5 +++++
 2 files changed, 16 insertions(+)

diff --git a/cmake/macros/CompositeSources.cmake b/cmake/macros/CompositeSources.cmake
index a624cebfb6..82decc5400 100644
--- a/cmake/macros/CompositeSources.cmake
+++ b/cmake/macros/CompositeSources.cmake
@@ -37,6 +37,17 @@ set(COMPOSITE_GENERATOR "${CMAKE_SOURCE_DIR}/cmake/scripts/MakeComposite.cmake")
 function(composite_sources target sources_var)
   if(NOT CMAKE_VERSION VERSION_LESS "3.16")
     # CMake 3.16+ implements CMAKE_UNITY_BUILD* natively; no need to continue!
+
+    # Actually - <=3.16.2 has difficulty with multi-language support, so only
+    # allow .cxx in. Hopefully this can be removed soon.
+    foreach(_source ${${sources_var}})
+      get_filename_component(_source_ext "${_source}" EXT)
+      if(NOT _source_ext STREQUAL ".cxx")
+        set_source_files_properties(${_source} PROPERTIES
+          SKIP_UNITY_BUILD_INCLUSION YES)
+      endif()
+    endforeach(_source)
+
     return()
   endif()
 
diff --git a/direct/src/showbase/CMakeLists.txt b/direct/src/showbase/CMakeLists.txt
index 815aeb5bc2..a45fa14b4b 100644
--- a/direct/src/showbase/CMakeLists.txt
+++ b/direct/src/showbase/CMakeLists.txt
@@ -8,6 +8,11 @@ set(P3SHOWBASE_SOURCES
 
 if(APPLE)
   list(APPEND P3SHOWBASE_SOURCES showBase_assist.mm)
+
+  # Bug in CMake 3.16.2: it tries to put .mm with the .cxx
+  set_source_files_properties(showBase_assist.mm PROPERTIES
+    SKIP_UNITY_BUILD_INCLUSION YES)
+
 endif()
 
 add_component_library(p3showbase NOINIT SYMBOL BUILDING_DIRECT_SHOWBASE