From bf8e8c843d524c3a3371c2ea59d92d567cf85e90 Mon Sep 17 00:00:00 2001
From: Daniel Gibson <metalcaedes@gmail.com>
Date: Tue, 19 Mar 2024 01:53:53 +0100
Subject: [PATCH] CMake: Detect all variations of the clang compiler
 (hopefully)

According to
https://cmake.org/cmake/help/v3.26/variable/CMAKE_LANG_COMPILER_ID.html
there's at least "Clang" (plain LLVM clang), "AppleClang", "ARMClang",
"FujitsuClang", "XLClang" and "IBMClang" (both of which are variations
of the clang/llvm-based IBM XL compiler).

This should detect all of them (I hope they all behave close enough
to normal clang to work..)

There's also "IntelLLVM", but I have no idea if that's based on Clang
or does its own thing based on LLVM.. I also doubt dhewm3 will ever
be built with any other clang-derivate than "Clang" and "AppleClang" :-p

fixes #510
---
 CMakeLists.txt | 23 ++++++++++++++++++++---
 1 file changed, 20 insertions(+), 3 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 3b31399..6505a39 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -156,8 +156,25 @@ endif()
 include(CheckCXXCompilerFlag)
 include(TestBigEndian)
 
+set(D3_COMPILER_IS_CLANG FALSE)
+set(D3_COMPILER_IS_GCC_OR_CLANG FALSE)
+
+if(NOT MSVC)
+	# check if this is some kind of clang (Clang, AppleClang, whatever)
+	# (convert compiler ID to lowercase so we match Clang, clang, AppleClang etc, regardless of case)
+	string(TOLOWER ${CMAKE_CXX_COMPILER_ID} compiler_id_lower)
+	if(compiler_id_lower MATCHES ".*clang.*")
+		message(STATUS "Compiler \"${CMAKE_CXX_COMPILER_ID}\" detected as some kind of clang")
+		set(D3_COMPILER_IS_CLANG TRUE)
+		set(D3_COMPILER_IS_GCC_OR_CLANG TRUE)
+	elseif(CMAKE_COMPILER_IS_GNUCC)
+		set(D3_COMPILER_IS_GCC_OR_CLANG TRUE)
+	endif()
+	unset(compiler_id_lower)
+endif() # NOT MSVC
+
 # compiler specific flags
-if(CMAKE_COMPILER_IS_GNUCC OR CMAKE_C_COMPILER_ID STREQUAL "Clang")
+if(D3_COMPILER_IS_GCC_OR_CLANG)
 	add_compile_options(-pipe)
 	add_compile_options(-Wall)
 
@@ -170,7 +187,7 @@ if(CMAKE_COMPILER_IS_GNUCC OR CMAKE_C_COMPILER_ID STREQUAL "Clang")
 	if(FORCE_COLORED_OUTPUT)
 		if(CMAKE_COMPILER_IS_GNUCC)
 		   add_compile_options (-fdiagnostics-color=always)
-		elseif ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "Clang")
+		elseif (D3_COMPILER_IS_CLANG)
 		   add_compile_options (-fcolor-diagnostics)
 		endif ()
 	endif ()
@@ -569,7 +586,7 @@ if (AROS)
 		set(AROS_ARCH ${CMAKE_SYSTEM_PROCESSOR})
 	endif()
 else()
-	if(CMAKE_COMPILER_IS_GNUCC OR CMAKE_C_COMPILER_ID STREQUAL "Clang" AND NOT MINGW)
+	if(D3_COMPILER_IS_GCC_OR_CLANG AND NOT MINGW)
 		set_target_properties(idlib PROPERTIES COMPILE_FLAGS "-fPIC")
 	endif()
 endif()