From ce33395a4a70db801467fbdfc6ef81734b98695a Mon Sep 17 00:00:00 2001
From: Jean-Paul Pelteret <jppelteret@gmail.com>
Date: Sat, 1 Oct 2022 21:36:52 +0200
Subject: [PATCH] CMake: Refine mechanism for checking compiler flags

---
 cmake/setup_compiler_flags.cmake | 44 ++++++++++++++++++++++++--------
 1 file changed, 34 insertions(+), 10 deletions(-)

diff --git a/cmake/setup_compiler_flags.cmake b/cmake/setup_compiler_flags.cmake
index 4fe1d3ef..eb3e568c 100644
--- a/cmake/setup_compiler_flags.cmake
+++ b/cmake/setup_compiler_flags.cmake
@@ -17,20 +17,44 @@
 # CMake macros that are used to add compiler flags
 #
 # Source: https://stackoverflow.com/a/33266748
+#         https://stackoverflow.com/q/45248393
 ##
 include(CheckCXXCompilerFlag)
 
-function(enable_cxx_compiler_flag_if_supported flag)
-    string(FIND "${CMAKE_CXX_FLAGS}" "${flag}" flag_already_set)
-    if(flag_already_set EQUAL -1)
-        MESSAGE(STATUS "Compiler flag check: ${flag}")
-        check_cxx_compiler_flag("${flag}" flag_supported)
-        if(flag_supported)
-            set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${flag}" PARENT_SCOPE)
-        endif()
-        unset(flag_supported CACHE)
+# function(enable_cxx_compiler_flag_if_supported flag)
+#     string(FIND "${CMAKE_CXX_FLAGS}" "${flag}" flag_already_set)
+#     if(flag_already_set EQUAL -1)
+#         MESSAGE(STATUS "Compiler flag check: ${flag}")
+#         check_cxx_compiler_flag("${flag}" flag_supported)
+#         if(flag_supported)
+#             set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${flag}" PARENT_SCOPE)
+#         endif()
+#         unset(flag_supported CACHE)
+#     endif()
+# endfunction()
+
+MACRO(enable_cxx_compiler_flag_if_supported flag)
+    # We cannot check for -Wno-foo as this won't throw a warning so we must check for the -Wfoo option directly
+    # http://stackoverflow.com/questions/38785168/cc1plus-unrecognized-command-line-option-warning-on-any-other-warning
+    STRING(REGEX REPLACE "^-Wno-" "-W" checkedFlag ${flag})
+
+    SET(VarName ${checkedFlag})
+    STRING(REPLACE "+" "X" VarName ${VarName})
+    STRING(REGEX REPLACE "[-=]" "_" VarName ${VarName})
+
+    # Avoid double checks. A compiler will not magically support a flag it did not before
+    if(NOT ${VarName}_CHECKED)
+        CHECK_CXX_COMPILER_FLAG(${checkedFlag} CXX_FLAG_${VarName}_SUPPORTED)
+        set(${VarName}_CHECKED YES CACHE INTERNAL "")
     endif()
-endfunction()
+
+    IF (CXX_FLAG_${VarName}_SUPPORTED)
+        set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${flag}" PARENT_SCOPE)
+    ENDIF ()
+
+    unset(VarName)
+    unset(checkedFlag)
+ENDMACRO()
 
 
 ##