[CMake] Two toolchains simultaneously within the same project?

[Ingolf Steinbach]

Hi

2012/7/24 Alexander Neundorf <a.neundorf-work at gmx.net>:
> Maybe you can use external_project() for that subdirectory ?

I have not been successful with that command. Probably, I have
misunderstood something. Please see this example:

my_project
  |
  +- CMakeLists.txt
  |
  +- external
       +...

The top level CMakeLists.txt content:
cmake_minimum_required(VERSION 2.8)
include(ExternalProject)
ExternalProject_Add(external SOURCE_DIR "${CMAKE_SOURCE_DIR}/external")

When I run cmake (2.8.0), I get the following error message:
CMake Error at /usr/share/cmake-2.8/Modules/ExternalProject.cmake:710 (message):
  error: no download info for 'external' -- please specify existing
  SOURCE_DIR or one of URL, CVS_REPOSITORY and CVS_MODULE, SVN_REPOSITORY or
  DOWNLOAD_COMMAND
Call Stack (most recent call first):
  /usr/share/cmake-2.8/Modules/ExternalProject.cmake:941
(_ep_add_download_command)
  CMakeLists.txt:3 (ExternalProject_Add)


What is wrong with the SOURCE_DIR specification in the top level
CMakeLists.txt? "${CMAKE_SOURCE_DIR}/external" expands to the correct
absolute path to the (existing) "external" subdirectory of my_project.

Kind regards
Ingolf