extract decision of used middleware implementation into separate package

rclcpp/CMakeLists.txt

@@ -8,9 +8,7 @@ ament_export_dependencies(ros_middleware_interface)
 
 ament_export_include_directories(include)
 
-ament_package(
+ament_package()
-  CONFIG_EXTRAS "rclcpp-extras.cmake"
-)
 
 install(
   DIRECTORY include/

rclcpp/rclcpp-extras.cmake

@@ -1,36 +0,0 @@
-# copied from rclcpp/rclcpp-extras.cmake
-
-ament_index_get_resources(_middleware_implementations "ros_middleware_implementation")
-if("${_middleware_implementations}" STREQUAL "")
-  message(FATAL_ERROR "Could not find any ROS middleware implementation.")
-endif()
-
-set(_middleware_implementation "")
-# option()
-if(NOT "${ROS_MIDDLEWARE_IMPLEMENTATION}" STREQUAL "")
-  set(_middleware_implementation "${ROS_MIDDLEWARE_IMPLEMENTATION}")
-elseif(NOT "$ENV{ROS_MIDDLEWARE_IMPLEMENTATION}" STREQUAL "")
-  set(_middleware_implementation "$ENV{ROS_MIDDLEWARE_IMPLEMENTATION}")
-else()
-  # TODO detemine "default" implementation based on the available ones
-  list(GET _middleware_implementations 0 _middleware_implementation)
-endif()
-
-list(FIND _middleware_implementations "${_middleware_implementation}" _index)
-if(_index EQUAL -1)
-  string(REPLACE ";" ", " _middleware_implementations_string "${_middleware_implementations}")
-  message(FATAL_ERROR "Could not find ROS middleware implementation '${_middleware_implementation}'. Choose one of the following: ${_middleware_implementations_string}")
-endif()
-
-message(STATUS "Using middleware implementation: ${_middleware_implementation}")
-find_package("${_middleware_implementation}" REQUIRED)
-
-# persist implementation decision in cache
-set(
-  ROS_MIDDLEWARE_IMPLEMENTATION "${_middleware_implementation}"
-  CACHE STRING "Select ROS middleware implementation to link against" FORCE
-)
-
-list(APPEND rclcpp_DEFINITIONS ${${ROS_MIDDLEWARE_IMPLEMENTATION}_DEFINITIONS})
-list(APPEND rclcpp_INCLUDE_DIRS ${${ROS_MIDDLEWARE_IMPLEMENTATION}_INCLUDE_DIRS})
-list(APPEND rclcpp_LIBRARIES ${${ROS_MIDDLEWARE_IMPLEMENTATION}_LIBRARIES})

ros_middleware_implementation/CMakeLists.txt

@@ -0,0 +1,14 @@
+cmake_minimum_required(VERSION 2.8.3)
+
+project(ros_middleware_implementation)
+
+find_package(ament_cmake REQUIRED)
+
+ament_package(
+  CONFIG_EXTRAS "ros_middleware_implementation-extras.cmake"
+)
+
+install(
+  DIRECTORY cmake
+  DESTINATION share/${PROJECT_NAME}
+)

ros_middleware_implementation/cmake/get_available_ros_middleware_implementations.cmake

@@ -0,0 +1,10 @@
+#
+# Get the package names of the available ROS middleware implemenations.
+#
+# :param var: the output variable name containing the package names
+# :type var: list of strings
+#
+function(get_available_ros_middleware_implementations var)
+  ament_index_get_resources(middleware_implementations "ros_middleware_implementation")
+  set(${var} ${middleware_implementations} PARENT_SCOPE)
+endfunction()

ros_middleware_implementation/cmake/get_default_ros_middleware_implementation.cmake

@@ -0,0 +1,42 @@
+#
+# Get the package name of the default ROS middleware implemenation.
+#
+# Either selcting it using the variable ROS_MIDDLEWARE_IMPLEMENTATION or
+# choosing a default from the available implementations.
+#
+# :param var: the output variable name containing the package name
+# :type var: string
+#
+function(get_default_ros_middleware_implementation var)
+  get_available_ros_middleware_implementations(middleware_implementations)
+
+  if("${middleware_implementations}" STREQUAL "")
+    message(FATAL_ERROR "Could not find any ROS middleware implementation.")
+  endif()
+
+  # option()
+  if(NOT "${ROS_MIDDLEWARE_IMPLEMENTATION}" STREQUAL "")
+    set(middleware_implementation "${ROS_MIDDLEWARE_IMPLEMENTATION}")
+  elseif(NOT "$ENV{ROS_MIDDLEWARE_IMPLEMENTATION}" STREQUAL "")
+    set(middleware_implementation "$ENV{ROS_MIDDLEWARE_IMPLEMENTATION}")
+  else()
+    # TODO detemine "default" implementation based on the available ones
+    list(GET middleware_implementations 0 middleware_implementation)
+  endif()
+
+  # verify that the selection one is available
+  list(FIND middleware_implementations "${middleware_implementation}" _index)
+  if(_index EQUAL -1)
+    string(REPLACE ";" ", " middleware_implementations_string "${middleware_implementations}")
+    message(FATAL_ERROR "Could not find ROS middleware implementation '${middleware_implementation}'. Choose one of the following: ${middleware_implementations_string}")
+  endif()
+  find_package("${middleware_implementation}" REQUIRED)
+
+  # persist implementation decision in cache
+  set(
+    ROS_MIDDLEWARE_IMPLEMENTATION "${middleware_implementation}"
+    CACHE STRING "Select ROS middleware implementation to link against" FORCE
+  )
+
+  set(${var} ${middleware_implementation} PARENT_SCOPE)
+endfunction()

ros_middleware_implementation/package.xml

@@ -0,0 +1,11 @@
+<?xml version="1.0"?>
+<package format="2">
+  <name>ros_middleware_implementation</name>
+  <version>0.0.0</version>
+  <description>The decision which ROS middleware implementation should be used for C++.</description>
+  <maintainer email="dthomas@osrfoundation.org">Dirk Thomas</maintainer>
+  <license>Apache License 2.0</license>
+
+  <buildtool_depend>ament_cmake</buildtool_depend>
+  <buildtool_export_depend>ament_cmake</buildtool_export_depend>
+</package>

ros_middleware_implementation/ros_middleware_implementation-extras.cmake

@@ -0,0 +1,12 @@
+# copied from ros_middleware_implementation/ros_middleware_implementation-extras.cmake
+
+include("${ros_middleware_implementation_DIR}/get_available_ros_middleware_implementations.cmake")
+include("${ros_middleware_implementation_DIR}/get_default_ros_middleware_implementation.cmake")
+
+get_default_ros_middleware_implementation(_middleware_implementation)
+find_package("${_middleware_implementation}" REQUIRED)
+
+# TODO should never need definitions and include dirs?
+list(APPEND ros_middleware_implementation_DEFINITIONS ${${_middleware_implementation}_DEFINITIONS})
+list(APPEND ros_middleware_implementation_INCLUDE_DIRS ${${_middleware_implementation}_INCLUDE_DIRS})
+list(APPEND ros_middleware_implementation_LIBRARIES ${${_middleware_implementation}_LIBRARIES})