build: CMake API parameter values handling and documentation improved

Relates to #581

src/CMakeLists.txt

@@ -85,7 +85,7 @@ check_cxx_feature_supported(__cpp_explicit_this_parameter ${projectPrefix}EXPLIC
 
 # validate settings
 if(NOT ${projectPrefix}API_FREESTANDING
-   AND ${projectPrefix}API_STD_FORMAT STREQUAL "TRUE"
+   AND "${projectPrefix}API_STD_FORMAT"
    AND NOT
        (${projectPrefix}LIB_FORMAT_SUPPORTED
         # libc++ has a basic supports for std::format but does not set __cpp_lib_format
@@ -96,13 +96,11 @@ if(NOT ${projectPrefix}API_FREESTANDING
     message(FATAL_ERROR "`std::format` enabled but not supported")
 endif()
 
-if(${projectPrefix}API_STRING_VIEW_RET STREQUAL "TRUE" AND NOT
-                                                           ${projectPrefix}STATIC_CONSTEXPR_VARS_IN_CONSTEXPR_FUNCTIONS
-)
+if("${projectPrefix}API_STRING_VIEW_RET" AND NOT ${projectPrefix}STATIC_CONSTEXPR_VARS_IN_CONSTEXPR_FUNCTIONS)
     message(FATAL_ERROR "`std::string_view` returns enabled but not supported")
 endif()
 
-if(${projectPrefix}API_NO_CRTP STREQUAL "TRUE" AND NOT ${projectPrefix}EXPLICIT_THIS_PARAMETER_SUPPORTED)
+if("${projectPrefix}API_NO_CRTP" AND NOT ${projectPrefix}EXPLICIT_THIS_PARAMETER_SUPPORTED)
     message(FATAL_ERROR "`NO_CRTP` mode enabled but explicit `this` parameter is not supported")
 endif()
 

src/core/CMakeLists.txt

@@ -23,8 +23,7 @@
 cmake_minimum_required(VERSION 3.23)
 
 function(set_feature_flag name)
-    set(val_list "TRUE" "FALSE")
-    if(${projectPrefix}${name} IN_LIST val_list)
+    if(NOT ${projectPrefix}${name} STREQUAL "AUTO")
         target_compile_definitions(
             mp-units-core ${${projectPrefix}TARGET_SCOPE} ${projectPrefix}${name}=$<BOOL:${${projectPrefix}${name}}>
         )
@@ -99,8 +98,8 @@ set_feature_flag(API_NO_CRTP)
 
 # Text formatting
 if(NOT ${projectPrefix}API_FREESTANDING
-   AND (${projectPrefix}API_STD_FORMAT STREQUAL "FALSE" OR (${projectPrefix}API_STD_FORMAT STREQUAL "AUTO"
-                                                            AND NOT ${projectPrefix}LIB_FORMAT_SUPPORTED))
+   AND (NOT ${projectPrefix}API_STD_FORMAT OR (${projectPrefix}API_STD_FORMAT STREQUAL "AUTO"
+                                               AND NOT ${projectPrefix}LIB_FORMAT_SUPPORTED))
 )
     if(NOT TARGET fmt::fmt)
         find_package(fmt REQUIRED)