Hey Stéphane,

2011/1/12 Stéphane Magnenat <stephane.magnenat@mavt.ethz.ch>:
> Hello,
>
> It happens often that one has a ROS-independent library and a campanion
> ROS wrapper. Ideally, one would like a seamless integration of this
> library with ROS while still allowing people without ROS to compile the
> library. In your opinion, what is the best practice? Is it to have a
> library in its own repository and the ROS wrapper to fetch it locally,

I definitely understand the desire to avoid this one ...

> or should the library be in the ROS stack with a parallel build system
> for ROSless usage? The former is a bit complex but the later requires
> two build paths for the library, and obfuscates the build for people not
> using ROS.

... and I'm not a fan of this one either, but here is a sketch, breaking
things up into three files CMakeLists.txt, rosbuild.cmake, and
standalone.cmake:


CMakeLists.txt:

  set(mylib_SRCS src/file1.cpp src/file2.cpp)

  if (BUILDING_INSIDE_ROS_TREE) # see below
    include(rosbuild.cmake)
  else()
    include(standalone.cmake)
  endif()

rosbuild.cmake:

  include($ENV{ROS_ROOT}/core/rosbuild/rosbuild.cmake)
  set(ROS_BUILD_TYPE Release)
  rosbuild_init()

  rosbuild_add_boost_directories()

  rosbuild_genmsg()
  rosbuild_gensrv()

  rosbuild_add_library(mylib ${mylib_SRCS})
  rosbuild_link_boost(mylib thread signals)

standalone.cmake:

  add_library(mylib ${mylib_SRCS})



But this BUILDING_INSIDE_ROS_TREE doesn't exist.  Options:

- you could check to see if ENV{ROS_ROOT} is defined, but that might
  be even if you're not building inside a ros tree.  I don't know what
  would happen then, but I'm sure the error message would be
  misleading.

- you could drop an empty file that contains

     set(BUILDING_INSIDE_ROS_TREE TRUE)

  inside ROS_ROOT/rostoolchain.cmake.  But then all ros users would
  have to do this in order to build your package inside a ros tree.

- you could put the following in the toplevel 'Makefile' of the
  package:

    include $(shell rospack find mk)/cmake.mk
    CMAKE_FLAGS += -DBUILDING_INSIDE_ROS_TREE=TRUE

  but now non-ros users will be confused by the presence of both
  Makefile and CMakeLists.txt.  If they just run 'make', they will get
  a (probably misleading) error, and there appears to be no way to
  give them a good one.  But I could be wrong.

I can think of several hacks to rosbuild/rosmake, each of which also
don't solve the problem well:

- rosmake sets BUILDING_INSIDE_ROS_TREE in environment

  this doesn't work as ros packages are supposed to be buildable with
  plain 'make' in the package directory.

- ros/core/mk/cmake.mk sets BUILDING_INSIDE_ROS_TREE in CMAKE_FLAGS

  has the same problem as above.

Obviously, none of these help for already-released ROS versions
either.  So maybe the best way is to force the user to specify:

CMakeLists.txt:

  if (NOT DEFINED BUILDING_OUTSIDE_ROS)
    message(FATAL_ERROR "Please set the cmake flag
BUILDING_OUTSIDE_ROS to either TRUE or FALSE")
  endif()

  if (BULDING_OUTSIDE_ROS)
    include(standalone.cmake)
  else()
    include(rosbuild.cmake)
  endif()

Users will still get I-dont-know-what if they attempt to build via
just typing 'make' outside of ROS.  Maybe there is a way to detect
this and report something reasonable.

Troy