From 2f68531c53f71d7343f3a6e06f3389136c80dd9b Mon Sep 17 00:00:00 2001
From: Hennadii Stepanov <32963518+hebasto@users.noreply.github.com>
Date: Sat, 26 Apr 2025 19:19:49 +0100
Subject: [PATCH] cmake: Respect user-provided configuration-specific flags

---
 CMakeLists.txt                           |  4 ++++
 cmake/module/ProcessConfigurations.cmake | 14 +++++++-------
 2 files changed, 11 insertions(+), 7 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index b272658177f..bc6f84eb97e 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -19,6 +19,10 @@ if(POLICY CMP0171)
   cmake_policy(SET CMP0171 NEW)
 endif()
 
+# When adjusting CMake flag variables, we must not override those explicitly
+# set by the user. These are a subset of the CACHE_VARIABLES property.
+get_directory_property(precious_variables CACHE_VARIABLES)
+
 #=============================
 # Project / Package metadata
 #=============================
diff --git a/cmake/module/ProcessConfigurations.cmake b/cmake/module/ProcessConfigurations.cmake
index 9a510a00a55..ce24e3b79b9 100644
--- a/cmake/module/ProcessConfigurations.cmake
+++ b/cmake/module/ProcessConfigurations.cmake
@@ -106,13 +106,13 @@ endfunction()
 
 function(replace_cxx_flag_in_config config old_flag new_flag)
   string(TOUPPER "${config}" config_uppercase)
-  string(REGEX REPLACE "(^| )${old_flag}( |$)" "\\1${new_flag}\\2" new_flags "${CMAKE_CXX_FLAGS_${config_uppercase}}")
-  set(CMAKE_CXX_FLAGS_${config_uppercase} "${new_flags}" PARENT_SCOPE)
-  set(CMAKE_CXX_FLAGS_${config_uppercase} "${new_flags}"
-    CACHE STRING
-    "Flags used by the CXX compiler during ${config_uppercase} builds."
-    FORCE
-  )
+  set(var_name CMAKE_CXX_FLAGS_${config_uppercase})
+  if("${var_name}" IN_LIST precious_variables)
+    return()
+  endif()
+  string(REGEX REPLACE "(^| )${old_flag}( |$)" "\\1${new_flag}\\2" ${var_name} "${${var_name}}")
+  set(${var_name} "${${var_name}}" PARENT_SCOPE)
+  set_property(CACHE ${var_name} PROPERTY VALUE "${${var_name}}")
 endfunction()
 
 set_default_config(RelWithDebInfo)