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

[Alexander Neundorf]

On Tuesday 14 February 2012, Yury G. Kudryashov wrote:
> 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)

Just a tip: since 2.8.3 or so there is ${CMAKE_CURRENT_LIST_DIR}

> get_filename_component(_PKG_PREFIX_PATH "${_PKG_CURRENT_DIR}/../../.."
> ABSOLUTE)

The ../../../ will be also calculated by the macro, using RELATIVE_PATH and 
the DESTINATION parameter, right ?
 
> #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.

If it's a function(), they are local automatically.

Also still not tested, but now it should have the right prefix:

foreach(var ${PACAKGE_HELPER_PATH_VARS})
  if(NOT DEFINED ${var})
    message(FATAL_ERROR ...)
  else if(IS_ABSOLUTE ${${var}})
    string(REPLACE "${CMAKE_INSTALL_PREFIX}" "\${_PKG_PREFIX_PATH}"
                    PACKAGE_HELPER_${var} "${${var}}"
    else()
      set(PACKAGE_HELPER_${var} ${${var}})
    endif()
  else()
    set(PACKAGE_HELPER_${var} "\${_PKG_PREFIX_PATH}/${${var}}")
  endif()
endforeach()


A nice feature of my proposed macro was that it additionally checked that the 
file/directory actually exists. That's a nice thing, because it makes sure 
that you don't get information out of the Config.cmake file which is wrong 
(due to bad packaging or whatever).

Alex