cmake: Add support for builtin codegen target

Additionally, this change removes unnecessary braces in the `if()`
command for improved robustness, readability and consistency with CMake
guidelines.

Author: hebasto

CMakeLists.txt

@@ -9,10 +9,16 @@
 #  - CMake 3.26.5, https://mirror.stream.centos.org/9-stream/AppStream/x86_64/os/Packages/
 cmake_minimum_required(VERSION 3.22)
 
-if (${CMAKE_SOURCE_DIR} STREQUAL ${CMAKE_BINARY_DIR})
+if(CMAKE_SOURCE_DIR STREQUAL CMAKE_BINARY_DIR)
   message(FATAL_ERROR "In-source builds are not allowed.")
 endif()
 
+if(POLICY CMP0171)
+  # `codegen` is a reserved target name.
+  # See: https://cmake.org/cmake/help/latest/policy/CMP0171.html
+  cmake_policy(SET CMP0171 NEW)
+endif()
+
 #=============================
 # Project / Package metadata
 #=============================

cmake/module/TargetDataSources.cmake

@@ -7,6 +7,14 @@ macro(set_add_custom_command_options)
   if(CMAKE_VERSION VERSION_GREATER_EQUAL 3.27)
     set(DEPENDS_EXPLICIT_OPT DEPENDS_EXPLICIT_ONLY)
   endif()
+  set(CODEGEN_OPT "")
+  if(POLICY CMP0171)
+    cmake_policy(GET CMP0171 _cmp0171_status)
+    if(_cmp0171_status STREQUAL "NEW")
+      set(CODEGEN_OPT CODEGEN)
+    endif()
+    unset(_cmp0171_status)
+  endif()
 endmacro()
 
 # Specifies JSON data files to be processed into corresponding
@@ -20,6 +28,7 @@ function(target_json_data_sources target)
       COMMAND ${CMAKE_COMMAND} -DJSON_SOURCE_PATH=${CMAKE_CURRENT_SOURCE_DIR}/${json_file} -DHEADER_PATH=${header} -P ${PROJECT_SOURCE_DIR}/cmake/script/GenerateHeaderFromJson.cmake
       DEPENDS ${CMAKE_CURRENT_SOURCE_DIR}/${json_file} ${PROJECT_SOURCE_DIR}/cmake/script/GenerateHeaderFromJson.cmake
       VERBATIM
+      ${CODEGEN_OPT}
       ${DEPENDS_EXPLICIT_OPT}
     )
     target_sources(${target} PRIVATE ${header})
@@ -38,6 +47,7 @@ function(target_raw_data_sources target)
       COMMAND ${CMAKE_COMMAND} -DRAW_SOURCE_PATH=${CMAKE_CURRENT_SOURCE_DIR}/${raw_file} -DHEADER_PATH=${header} -DRAW_NAMESPACE=${__NAMESPACE} -P ${PROJECT_SOURCE_DIR}/cmake/script/GenerateHeaderFromRaw.cmake
       DEPENDS ${CMAKE_CURRENT_SOURCE_DIR}/${raw_file} ${PROJECT_SOURCE_DIR}/cmake/script/GenerateHeaderFromRaw.cmake
       VERBATIM
+      ${CODEGEN_OPT}
       ${DEPENDS_EXPLICIT_OPT}
     )
     target_sources(${target} PRIVATE ${header})