From 439e2e3fc2f00d2812b2042ae548767423f54d47 Mon Sep 17 00:00:00 2001
From: Norbert Lange <nolange79@gmail.com>
Date: Wed, 3 Feb 2021 16:05:30 +0100
Subject: [PATCH] Stricter test for compiler flags

Some flags do nothing but generate dozens of warnings later,
add '-Werror' during testing to catch those early.

Main culprit is '-fvisibility-inlines-hidden' which is invalid for C files
---
 CMake/CheckAndAddFlag.cmake | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/CMake/CheckAndAddFlag.cmake b/CMake/CheckAndAddFlag.cmake
index edd0e8cc7e..226e570833 100644
--- a/CMake/CheckAndAddFlag.cmake
+++ b/CMake/CheckAndAddFlag.cmake
@@ -29,20 +29,27 @@ function(check_and_add_flag var flag)
 
   set(is_c "$<COMPILE_LANGUAGE:C>")
   set(is_cxx "$<COMPILE_LANGUAGE:CXX>")
+  set(test_flags_c)
+  set(test_flags_cxx)
 
   # The Visual Studio generators don't support COMPILE_LANGUAGE
   # So we fail all the C flags and only actually test CXX ones
   if(CMAKE_GENERATOR MATCHES "Visual Studio")
     set(is_c "0")
     set(is_cxx "1")
+  else()
+    # Otherwise assume the compile follows GCC syntax
+    # and fail when the option is known but invalid.
+    set(test_flags_c "${test_flags_c}-Werror ")
+    set(test_flags_cxx "${test_flags_cxx}-Werror ")
   endif()
 
-  check_c_compiler_flag(${flag} FLAG_C_${var})
+  check_c_compiler_flag("${test_flags_c}${flag}" FLAG_C_${var})
   if(FLAG_C_${var})
     add_compile_options("$<$<AND:${is_c},${genexp_config_test}>:${flag}>")
   endif()
 
-  check_cxx_compiler_flag(${flag} FLAG_CXX_${var})
+  check_cxx_compiler_flag("${test_flags_cxx}${flag}" FLAG_CXX_${var})
   if(FLAG_CXX_${var})
     add_compile_options("$<$<AND:${is_cxx},${genexp_config_test}>:${flag}>")
   endif()