How to tell execute_process to preserve ansi colors in its output?

Code
1

Sample project

cmake_minimum_required(VERSION 3.16)

if(NOT CMAKE_SCRIPT_MODE_FILE)
    project(proj LANGUAGES NONE)
endif()

message(WARNING "This is a warning")

if(NOT NESTED_CALL)
    execute_process(
        COMMAND
            "${CMAKE_COMMAND}"
            -DNESTED_CALL=1
            -P
            "${CMAKE_CURRENT_LIST_FILE}"
    )
endif()

When I configure the sample project with a recent cmake (v4.1) on macOS in the iTerm2 terminal, I get

CMake Warning at CMakeLists.txt:7 (message):
  This is a warning <--------------------- this shows as yellow text


CMake Warning at /Users/alex/Dev/projects/cmake/general/nested_cmake_ansi_colors/CMakeLists.txt:7 (message):
  This is a warning <--------------------- this shows as white text

So the second message gets its color lost.

I can force the color to show if I set the export CLICOLOR_FORCE=1 env variable before the execute_process call, but I can’t do this universally because I don’t know if the outer cmake call is connected to a terminal / tty and whether the terminal supports colors.

Is this a bug or a missing feature in execute_process?

Shouldn’t execute_process treat the stdout as just another piped output to the cmake’s stdout, because it doesn’t have the OUTPUT_FILE / ERROR_FILE options set to redirect to a different file?

2

execute_process by default captures the output so that it can be printed wherever CMake’s output is going, which might be cmake-gui or ccmake display buffers instead of a real terminal. One could add an option to pass through the real pipes, at least when called from a command-line tool like cmake.