Getting CMake to build out of source without wrapping scripts

Question

I\'m trying to get CMake to build into a directory \'build\', as in project/build, where the CMakeLists.txt is in project/.

I know I can do

Answer 1

Based on the previous answers, I wrote the following module that you can include to enforce an out-of-source build.

set(DEFAULT_OUT_OF_SOURCE_FOLDER "cmake_output")

if (${CMAKE_SOURCE_DIR} STREQUAL ${CMAKE_BINARY_DIR})
    message(WARNING "In-source builds not allowed. CMake will now be run with arguments:
        cmake -H. -B${DEFAULT_OUT_OF_SOURCE_FOLDER}
")

    # Run CMake with out of source flag
    execute_process(
            COMMAND ${CMAKE_COMMAND} -H. -B${DEFAULT_OUT_OF_SOURCE_FOLDER}
            WORKING_DIRECTORY ${CMAKE_SOURCE_DIR})

    # Cause fatal error to stop the script from further execution
    message(FATAL_ERROR "CMake has been ran to create an out of source build.
This error prevents CMake from running an in-source build.")
endif ()

This works, however I already noticed two downsides:

• When the user is lazy and simply runs cmake ., they will always see a FATAL_ERROR. I could not find another way to prevent CMake from doing any other operations and exit early.
• Any command line arguments passed to the original call to cmake will not be passed to the "out-of-source build call".

Suggestions to improve this module are welcome.