[cmake-developers] Making Config.cmake files easier to write

[Yury G. Kudryashov]

Alexander Neundorf wrote:

> On Tuesday 14 February 2012, Yury G. Kudryashov wrote:
>> will substitute @PACKAGE_INCLUDE_INSTALL_DIR@ by "../../../include" and
>> @PACKAGE_MYPKGDATA_INSTALL_DIR@ by "../../../share/mypkg" (both
>> transformed to be relative to DESTINATION).
> 
> A problem I see here (and which we discussed already before on kde-
> buildsystem) is the handling of the install() command.
> 
> I thought a bit about a syntax like this, which I would like:
> 
> configure_config_file(BarConfig.cmake.in BarConfig.cmake
>               INSTALL_DESTINATION ${CMAKECONFIG_INSTALL_DIR}
>               PATH_VARS INCLUDE_INSTALL_DIR DATA_INSTALL_DIR
>               EXPORT_FILE BarExport.cmake)
Why do you need EXPORT_FILE parameter? How can you use it? Include 
automatically? Then you need VERSION_FILE parameter as well.

> 
> but this can't work, can it ?
> 
> In the BarConfig.cmake file there would still be either a
> 
> set(BAR_INCLUDE_DIR "@INCLUDE_INSTALL_DIR@")
> which would work for absolute paths, or a
> 
> set(BAR_INCLUDE_DIR "${SomePrefix}/@INCLUDE_INSTALL_DIR@")
> which would work only for relative paths, but a simple set() cannot work
> for both cases. Am I missing something ?
You'll have in BarConfig.cmake.in
set(BAR_INCLUDE_DIR "@PACKAGE_HELPER_INCLUDE_INSTALL_DIR@)

After configure_config_file() you'll have
# At top
get_filename_component(_PKG_CURRENT_DIR "${CURRENT_LIST_FILE}" PATH)
get_filename_component(_PKG_PREFIX_PATH "${_PKG_CURRENT_DIR}/../../.." 
ABSOLUTE)

#in place of your set()
set(BAR_INCLUDE_DIR "${_PKG_PREFIX_PATH}/include")
> 
> Do you have a working example ?
Not yet. I think about something like this (not tested).

  foreach(var ${PACAKGE_HELPER_PATH_VARS})
    if(NOT DEFINED ${var})
      message(FATAL_ERROR ...)
    else if(IS_ABSOLUTE ${${var}})
      file(RELATIVE_PATH PACKAGE_HELPER_${var} ${CMAKE_INSTALL_PREFIX} 
${${var}})
    else()
      set(PACKAGE_HELPER_${var} ${${var}})
    endif()
  endforeach()

It would be nice to make those PACKAGE_HELPER_* vars local to 
configure_config_file() function.
-- 
Yury G. Kudryashov,
mailto: urkud at mccme.ru