Installing CMake package config files for MacOS frameworks

Code
1

I created a versioned MacOS framework with CMake and stumbled over the question where to install the package config files sample-config.cmake, sample-config-version.cmake, sample-exports.cmake, sample-exports-release.cmake.

The framework is versioned so the structure is roughly as follows:

<sample.framework>
   |-- Headers                 # link to Versions/Current/Headers
   |-- Resources               # link to Versions/Current/Resources
   +-- Versions
       |-- Current             # link to B
       +-- B
           |-- Headers
           +-- Resources
               |-- CMake
               +-- Info.plist

I use CMakes CMakePackageConfigHelpers macros to generate a package config file from a template sample-config.cmake.in with the content

@PACKAGE_INIT@
include("${CMAKE_CURRENT_LIST_DIR}/sample-export.cmake")

CMake does not mention versioned frameworks and recommends to install the files into the directory Resources/CMake.

I did so by calling

install(FILES "${CMAKE_CURRENT_BINARY_DIR}/sample-config.cmake"
  DESTINATION sample.framework/Resources/CMake
  COMPONENT development
)

The generated file looks like this:

####### Expanded from @PACKAGE_INIT@ by configure_package_config_file() #######
####### Any changes to this file will be overwritten by the next CMake run ####
####### The input file was sample-config.cmake.in                            ########

get_filename_component(PACKAGE_PREFIX_DIR "${CMAKE_CURRENT_LIST_DIR}/../../../" ABSOLUTE)

macro(set_and_check _var _file)
  set(${_var} "${_file}")
  if(NOT EXISTS "${_file}")
    message(FATAL_ERROR "File or directory ${_file} referenced by variable ${_var} does not exist !")
  endif()
endmacro()

macro(check_required_components _NAME)
  foreach(comp ${${_NAME}_FIND_COMPONENTS})
    if(NOT ${_NAME}_${comp}_FOUND)
      if(${_NAME}_FIND_REQUIRED_${comp})
        set(${_NAME}_FOUND FALSE)
      endif()
    endif()
  endforeach()
endmacro()

include("${CMAKE_CURRENT_LIST_DIR}/sample-export.cmake")

Error:

There’s a difference in the generated config file whether I install those files to Resources/CMake or to Versions/B/Resources/CMake although both point to the same directory.

When installing via the Resources link to Resources/CMake the call to set PACKAGE_PREFIX_DIR is generated as

get_filename_component(PACKAGE_PREFIX_DIR "${CMAKE_CURRENT_LIST_DIR}/../../../" ABSOLUTE)

but when installing via Versions/B/Resources/CMake it is generated as

get_filename_component(PACKAGE_PREFIX_DIR "${CMAKE_CURRENT_LIST_DIR}/../../../../../" ABSOLUTE)

As a consequence of this the package cannot be found by find_package(sample CONFIG) when installing to Versions/B/Resources/CMake.

Did anybody was facing this error before?

Thanks for any input on this.

2

It seems like also searching Versions/B for Resources/CMake is a reasonable thing to do to me. Thoughts @brad.king?

3

The find_package search procedure does search <prefix>/<name>.framework/Versions/*/Resources/CMake/ inside frameworks. One can see the implementation here.

@vre what actually goes wrong?

4

My question is why the PACKAGE_PREFIX_DIR is set to different values when installing to Resources/CMake and to Versions/B/Resources/CMake although both point to the same physical directory? If I have some variables dependent on PACKAGE_PREFIX_DIR they will not resolve properly when I use the one or the other path.

5

The logic generating the code to compute PACKAGE_PREFIX_DIR assumes that there are no symbolic links involved. I don’t know if anyone has actually used CMakePackageConfigHelpers for a package configuration file inside a framework before.

The presence of symbolic links inside the framework may be problematic. MyPackage_DIR can be set by users to be either

  • <prefix>/MyPackage.framework/Resources/CMake, or
  • <prefix>/MyPackage.framework/Versions/Current/Resources/CMake, or
  • <prefix>/MyPackage.framework/Versions/B/Resources/CMake.

In all of those cases we need to be able to recover the <prefix>, but the number of components that needs to be removed is not the same for all cases.

6

Thank you for the enlightening explanations. Good to know that symbolic links are problematic when placing configure files. I can work around that.