CMakeLists.txt confusion..

edit

Hi,

I am using Ubuntu 16.04 LTS with ROS Kinetic distro.

I have a custom package called gps_msgs in my catkin_ws directory. I have other two packages that utilize the message by including it into source.

Now, one of the packages doesn't build without having "gps_msgs" inside the find_package() macro in CMakeLists.txt whereas the other one does.

The packages are nearly identical apart from the fact that one of them utilizes a 3rd party library. Here's the CMakeLists (package.xml files are almost identical, none of them include gps_msgs, I would like to know why that works too..):

Package #1:

cmake_minimum_required(VERSION 2.8.3)
project(can_control_node)

add_compile_options(-std=c++11)

find_package(catkin REQUIRED COMPONENTS
  roscpp
  std_msgs
)

include_directories(
# include
  ${catkin_INCLUDE_DIRS}
)

add_executable(can_control_node src/control_node.cpp)
target_link_libraries(can_control_node ${catkin_LIBRARIES})

Package #2:

cmake_minimum_required(VERSION 2.8.3)
project(gps)

add_compile_options(-std=c++11)

find_package(catkin REQUIRED COMPONENTS
  roscpp
  std_msgs
)

catkin_package(
  #CATKIN_DEPENDS std_msgs roscpp
  #INCLUDE_DIRS include
)

set(SOURCES
  src/an_packet_protocol.c
  src/spatial_packets.c
  src/rs232.c
)

include_directories(include/${PROJECT_NAME} ${catkin_INCLUDE_DIRS})


add_executable(gps_node 
  src/gps_node.cpp
  ${SOURCES}
)

target_link_libraries(gps_node ${catkin_LIBRARIES})

Again, both packages have #include <gps_msgs/Navigation.h> in their source files. The gps_msgs/Navigation isn't mentioned AT ALL in either of the package.xml files. Package #1 builds, package #2 complains that gps_msgs/Navigation doesn't exist. All 3 packages are in separate directories in my catkin_ws, what's going on?