From 8a2977ba55367c91f2f66055ea2cc1304e1a42b1 Mon Sep 17 00:00:00 2001
From: Cristian Adam <cristian.adam@gmail.com>
Date: Tue, 29 Sep 2020 08:24:27 -0700
Subject: OBJCXX: Fix regression for compiling cpp files as objcxx

In commit 8d61294c3e (PCH: Mark CMake PCH source files as -x
<lang>-header, 2020-09-04, v3.18.3~14^2) we removed the explicit `-x
objective-c++` flag.  This broke cases with custom source extensions.

Restore the explicit `-x objective-c[++]` flag and put it before the
`<FLAGS>` placeholder.  The latter will contain the proper `-x
objective-c[++]-header` value and will override the `-x objective-c[++]`
value set before.

Fixes: #21234
---
 Modules/CMakeOBJCInformation.cmake        | 2 +-
 Modules/CMakeOBJCXXInformation.cmake      | 2 +-
 Tests/ObjCXX/CMakeLists.txt               | 1 +
 Tests/ObjCXX/cxx-as-objcxx/CMakeLists.txt | 5 +++++
 Tests/ObjCXX/cxx-as-objcxx/main.cpp       | 6 ++++++
 5 files changed, 14 insertions(+), 2 deletions(-)
 create mode 100644 Tests/ObjCXX/cxx-as-objcxx/CMakeLists.txt
 create mode 100644 Tests/ObjCXX/cxx-as-objcxx/main.cpp

diff --git a/Modules/CMakeOBJCInformation.cmake b/Modules/CMakeOBJCInformation.cmake
index b3da82d..d530191 100644
--- a/Modules/CMakeOBJCInformation.cmake
+++ b/Modules/CMakeOBJCInformation.cmake
@@ -170,7 +170,7 @@ endif()
 # compile an Objective-C file into an object file
 if(NOT CMAKE_OBJC_COMPILE_OBJECT)
   set(CMAKE_OBJC_COMPILE_OBJECT
-    "<CMAKE_OBJC_COMPILER> <DEFINES> <INCLUDES> <FLAGS> -x objective-c -o <OBJECT> -c <SOURCE>")
+    "<CMAKE_OBJC_COMPILER> <DEFINES> <INCLUDES> -x objective-c <FLAGS> -o <OBJECT> -c <SOURCE>")
 endif()
 
 if(NOT CMAKE_OBJC_LINK_EXECUTABLE)
diff --git a/Modules/CMakeOBJCXXInformation.cmake b/Modules/CMakeOBJCXXInformation.cmake
index 4be9762..7a3b9d7 100644
--- a/Modules/CMakeOBJCXXInformation.cmake
+++ b/Modules/CMakeOBJCXXInformation.cmake
@@ -263,7 +263,7 @@ endif()
 # compile an Objective-C++ file into an object file
 if(NOT CMAKE_OBJCXX_COMPILE_OBJECT)
   set(CMAKE_OBJCXX_COMPILE_OBJECT
-    "<CMAKE_OBJCXX_COMPILER> <DEFINES> <INCLUDES> <FLAGS> -o <OBJECT> -c <SOURCE>")
+    "<CMAKE_OBJCXX_COMPILER> <DEFINES> <INCLUDES> -x objective-c++ <FLAGS> -o <OBJECT> -c <SOURCE>")
 endif()
 
 if(NOT CMAKE_OBJCXX_LINK_EXECUTABLE)
diff --git a/Tests/ObjCXX/CMakeLists.txt b/Tests/ObjCXX/CMakeLists.txt
index a2a907a..cf03771 100644
--- a/Tests/ObjCXX/CMakeLists.txt
+++ b/Tests/ObjCXX/CMakeLists.txt
@@ -2,3 +2,4 @@ ADD_TEST_MACRO(ObjCXX.ObjC++ ObjC++)
 ADD_TEST_MACRO(ObjCXX.simple-build-test simple-build-test)
 ADD_TEST_MACRO(ObjCXX.cxx-file-extension-test cxx-file-extension-test)
 ADD_TEST_MACRO(ObjCXX.objcxx-file-extension-test objcxx-file-extension-test)
+ADD_TEST_MACRO(ObjCXX.cxx-as-objcxx cxx-as-objcxx)
diff --git a/Tests/ObjCXX/cxx-as-objcxx/CMakeLists.txt b/Tests/ObjCXX/cxx-as-objcxx/CMakeLists.txt
new file mode 100644
index 0000000..23f6891
--- /dev/null
+++ b/Tests/ObjCXX/cxx-as-objcxx/CMakeLists.txt
@@ -0,0 +1,5 @@
+cmake_minimum_required(VERSION 3.18)
+project(cxx-as-objcxx LANGUAGES OBJCXX)
+
+add_executable(cxx-as-objcxx main.cpp)
+set_source_files_properties(main.cpp PROPERTIES LANGUAGE OBJCXX)
diff --git a/Tests/ObjCXX/cxx-as-objcxx/main.cpp b/Tests/ObjCXX/cxx-as-objcxx/main.cpp
new file mode 100644
index 0000000..701c567
--- /dev/null
+++ b/Tests/ObjCXX/cxx-as-objcxx/main.cpp
@@ -0,0 +1,6 @@
+#import <Foundation/Foundation.h>
+
+int main(int argc, char* argv[])
+{
+  return 0;
+}
-- 
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