From cf3406746ad285da3b4ca9d0509f57f6dc93b23f Mon Sep 17 00:00:00 2001
From: Caio Amaral <caioaamaral@gmail.com>
Date: Fri, 26 Mar 2021 18:43:18 -0300
Subject: [PATCH] Fix #133

Signed-off-by: Caio Amaral <caioaamaral@gmail.com>
---
 ros_ign_gazebo/launch/ign_gazebo.launch.py | 30 +++++++++++++++++++---
 ros_ign_gazebo/package.xml                 |  3 +++
 2 files changed, 29 insertions(+), 4 deletions(-)

diff --git a/ros_ign_gazebo/launch/ign_gazebo.launch.py b/ros_ign_gazebo/launch/ign_gazebo.launch.py
index c889a351..55d8c7c8 100644
--- a/ros_ign_gazebo/launch/ign_gazebo.launch.py
+++ b/ros_ign_gazebo/launch/ign_gazebo.launch.py
@@ -14,7 +14,10 @@
 
 """Launch Ignition Gazebo with command line arguments."""
 
-from os import environ
+import os
+
+from ament_index_python.packages import get_package_share_directory,
+from catkin_pkg.package import parse_package
 
 from launch import LaunchDescription
 from launch.actions import DeclareLaunchArgument
@@ -24,18 +27,37 @@
 
 def generate_launch_description():
     env = {'IGN_GAZEBO_SYSTEM_PLUGIN_PATH':
-           ':'.join([environ.get('IGN_GAZEBO_SYSTEM_PLUGIN_PATH', default=''),
-                     environ.get('LD_LIBRARY_PATH', default='')])}
+           ':'.join([os.environ.get('IGN_GAZEBO_SYSTEM_PLUGIN_PATH', default=''),
+                     os.environ.get('LD_LIBRARY_PATH', default='')])}
 
     return LaunchDescription([
         DeclareLaunchArgument('ign_args', default_value='',
                               description='Arguments to be passed to Ignition Gazebo'),
         ExecuteProcess(
             cmd=['ign gazebo',
-                 LaunchConfiguration('ign_args'),
+                 __get_ign_args(LaunchConfiguration('ign_args')),
                  ],
             output='screen',
             additional_env=env,
             shell=True
         )
     ])
+
+
+def __get_ign_args(ign_args):
+    if '--force_version' not in ign_args:
+        ign_args += '--force_version {}'.format(__IGN_GAZEBO_DEFAULT_VERSION)
+    
+    return ign_args
+
+
+def __get_ign_gazebo_default_version(): # this will fail if the package build was performed with '--merge-install'
+    this_pkg = parse_package(os.path.join(*[get_package_share_directory('ros_ign_gazebo'), 'package.xml']))
+    this_pkg.evaluate_conditions(os.environ)
+    lookup_name = next(dep.name for dep in this_pkg.exec_depends 
+                            if dep.evaluated_condition 
+                            if 'ignition-gazebo' in dep.name)
+    
+    return lookup_name.replace('ignition-gazebo', '')
+    
+__IGN_GAZEBO_DEFAULT_VERSION=__get_ign_gazebo_default_version()
diff --git a/ros_ign_gazebo/package.xml b/ros_ign_gazebo/package.xml
index 47ea5c4e..dc665c5f 100644
--- a/ros_ign_gazebo/package.xml
+++ b/ros_ign_gazebo/package.xml
@@ -17,6 +17,9 @@
   <depend>rclcpp</depend>
   <depend>ignition-math6</depend>
 
+  <exec_depend>ament_index_python</exec_depend>
+  <exec_depend>python3-catkin-pkg-modules</exec_depend>
+
   <!-- Dome -->
   <exec_depend condition="$IGNITION_VERSION == dome">ignition-gazebo4</exec_depend>
   <depend condition="$IGNITION_VERSION == dome">ignition-msgs6</depend>