catkin: When are the install directives in CMakeLists.txt effective?

edit

I tested a simple catkin package, and have some questions about the install directives in CMakeLists.txt.

My environment is:

• OS: Ubuntu 18.04
• ROS: melodic
• catkin system: python-catkin-tools

The package consists of:

~/catkin_ws/src/test_hoge1:

• CMakeLists.txt
• package.xml
• scripts/
  • test2_node.py
• src/
  • test1_node.cpp

So, there are two noes in the package (one is made with C++ and the other is a Python script).

The first version of CMakeLists.txt is:

cmake_minimum_required(VERSION 3.0.2)
project(test_hoge1)
find_package(catkin REQUIRED
  roscpp
  rospy
  std_msgs)

catkin_package(
)

include_directories(
${catkin_INCLUDE_DIRS}
)
add_executable(${PROJECT_NAME}_test1_node src/test1_node.cpp)
set_target_properties(${PROJECT_NAME}_test1_node PROPERTIES OUTPUT_NAME test1_node PREFIX "")
add_dependencies(${PROJECT_NAME}_test1_node ${${PROJECT_NAME}_EXPORTED_TARGETS} ${catkin_EXPORTED_TARGETS})
target_link_libraries(${PROJECT_NAME}_test1_node
  ${catkin_LIBRARIES}
)

After executing $ catkin build --this, the following (executable-related) files were produced:

• ./devel/lib/test_hoge1/test1_node (symbolic link to the below file)
• ./devel/.private/test_hoge1/lib/test_hoge1/test1_node

Running nodes by rosrun,

$ rosrun test_hoge1 test1_node
#--> ./devel/lib/test_hoge1/test1_node is executed.
$ rosrun test_hoge1 test2_node.py
#--> ./src/test_hoge1/scripts/test2_node.py is executed.

Then I added the following directives into CMakeLists.txt:

catkin_install_python(PROGRAMS
  scripts/test2_node.py
  DESTINATION ${CATKIN_PACKAGE_BIN_DESTINATION}
)
install(TARGETS ${PROJECT_NAME}_test1_node
  RUNTIME DESTINATION ${CATKIN_PACKAGE_BIN_DESTINATION}
)

catkin build --this produced the following:

• ./build/test_hoge1/catkin_generated/installspace/test2_node.py
• ./devel/lib/test_hoge1/test1_node (symbolic link to the below file)
• ./devel/.private/test_hoge1/lib/test_hoge1/test1_node

test2_node.py is a copy (not a symbolic link) of the script in src/scripts/, so it is a snapshot at building the package.

However executing the script by $ rosrun test_hoge1 test2_node.py still uses ./src/test_hoge1/scripts/test2_node.py.

Based on those experiments, my questions are:

• The install directive (for C++ nodes) in CMakeLists.txt looks doing nothing. When is it effective? Or, if we work only with Ubuntu, is it unnecessary?
• Although the catkin_install_python directive copies the scripts as their snapshots, rosrun executes the original scripts. This behavior is confusing. Did I make some mistakes in CMakeLists.txt, or is it a designed behavior? If it is the normal behavior, When and why do we need to use catkin_install_python? If we work only with Ubuntu, is it unnecessary?