Use frontend group dependency & explicit dependencies in ros2launch (#…

…256)

* Switch to package format 3

Signed-off-by: Christophe Bedard <bedard.christophe@gmail.com>

* Declare dependency on launch_{xml,yaml} in ros2launch

Signed-off-by: Christophe Bedard <bedard.christophe@gmail.com>

* Declare a 'launch_frontend_packages' group and use in ros2launch

Signed-off-by: Christophe Bedard <bedard.christophe@gmail.com>

ros2launch/package.xml

@@ -1,8 +1,8 @@
 <?xml version="1.0"?>
 <?xml-model
-  href="http://download.ros.org/schema/package_format2.xsd"
+  href="http://download.ros.org/schema/package_format3.xsd"
   schematypens="http://www.w3.org/2001/XMLSchema"?>
-<package format="2">
+<package format="3">
   <name>ros2launch</name>
   <version>0.15.0</version>
   <description>
@@ -21,11 +21,17 @@
   <depend>ros2cli</depend>
   <depend>ros2pkg</depend>
 
+  <!-- explicitly depend on the main launch frontends -->
+  <exec_depend>launch_xml</exec_depend>
+  <exec_depend>launch_yaml</exec_depend>
+
   <test_depend>ament_copyright</test_depend>
   <test_depend>ament_flake8</test_depend>
   <test_depend>ament_pep257</test_depend>
   <test_depend>python3-pytest</test_depend>
 
+  <group_depend>launch_frontend_packages</group_depend>
+
   <export>
     <build_type>ament_python</build_type>
   </export>