CMake improvement

[topazus]

close #8

write_basic_package_version_file(<filename>
  [VERSION <major.minor.patch>]
  COMPATIBILITY <AnyNewerVersion|SameMajorVersion|SameMinorVersion|ExactVersion>
  [ARCH_INDEPENDENT] )

There are some extra questions.

1. which COMPATIBILITY mode will be appropriate to use? AnyNewerVersion, SameMajorVersion, SameMinorVersion and ExactVersion .
2. ARCH_INDEPENDENT in write_basic_package_version_file can be used when CMake version >= 3.14 since boxed-cpp is a header-only package and architecture-independent.

# https://github.com/xtensor-stack/xtl/blob/908958eb8edebc4fdb0c5cd9b86912bca3eca5c9/CMakeLists.txt#L129-L144
if(CMAKE_VERSION VERSION_LESS 3.14)
    set(BOXED_CPP_CMAKE_SIZEOF_VOID_P ${CMAKE_SIZEOF_VOID_P})
    unset(CMAKE_SIZEOF_VOID_P)
    write_basic_package_version_file(
        ${CMAKE_CURRENT_BINARY_DIR}/boxed-cpp-config-version.cmake
        VERSION ${PROJECT_VERSION}
        COMPATIBILITY SameMajorVersion
    )
    set(CMAKE_SIZEOF_VOID_P ${BOXED_CPP_CMAKE_SIZEOF_VOID_P})
else()
    write_basic_package_version_file(
        ${CMAKE_CURRENT_BINARY_DIR}/boxed-cpp-config-version.cmake
        VERSION ${PROJECT_VERSION}
        COMPATIBILITY SameMajorVersion
        ARCH_INDEPENDENT
    )
endif()

Or just update the CMake minimum version restriction to version 3.14.

Ref:

• https://cmake.org/cmake/help/latest/module/CMakePackageConfigHelpers.html#command:write_basic_package_version_file
• Remove architecture check from CMake package doctest/doctest#225

[christianparpart]

oh many thanks @topazus. I'll have a look ASAP! :)

[christianparpart]

i wonder how we can make use of this in Contour 🤔

[christianparpart]

Should we adapt this for our other libraries as well? Especially libunicode? What do you think?

[topazus]

I think it is fine if you want to use ${PROJECT_SOURCE_DIR} in this situation for libunicode.

[christianparpart]

p.s.: SameMajorVersion is fine :)