Issue using CPM

[siemjlonn]

So I'm trying to build everest-core using CPM (I know it's recommended to use edm) anyway, I have already added mqttc to my CPM because it is a dependency on this repository(everest-framework), so this conflict will always happen in your find-mqttc.cmake because it will try to add_library(mqttc STATIC IMPORTED) again.

Is kind of a forced error since i have to add mqttc to continue but inside your repository it will conflict because it tries to add again.

[sieukrem]

We stumbled across same issue by building without of usage of EDM.

Further investigation uncovered that it begins with Line 92 in CMakeLists.txt

everest-framework/CMakeLists.txt

Lines 82 to 93 in 1f8bce3

	find_package(everest-log REQUIRED)
	if (EVEREST_ENABLE_ADMIN_PANEL_BACKEND)
	find_package(libwebsockets REQUIRED)
	endif()
	if (BUILD_TESTING)
	find_package(Catch2 REQUIRED)
	endif()
	include(find-mqttc)
	endif()

and continuous with confession in find-mqttc.cmake

everest-framework/cmake/find-mqttc.cmake

Lines 1 to 14 in 1f8bce3

	# FIXME (aw): quite hacky, should check at least if target already exists
	add_library(mqttc STATIC IMPORTED)
	find_library(MQTTC_LIB_FILE mqttc)
	find_path(MQTTC_INCLUDE_DIR mqtt.h)
	if(NOT MQTTC_LIB_FILE OR NOT MQTTC_INCLUDE_DIR)
	message(FATAL_ERROR "Could not find mqttc library")
	endif()
	set_target_properties(mqttc PROPERTIES
	IMPORTED_LOCATION ${MQTTC_LIB_FILE}
	INTERFACE_INCLUDE_DIRECTORIES ${MQTTC_INCLUDE_DIR}
	)

I wonder why include is used instead of find_package like few lines above?
The find_package allows to separate the declaration/definition of the target from the expression of dependency to this target and solves in particular the issue we observe here.

Our current solution is to replace the include(find-mqttc.cmake) by find_package(mqttc REQUIRED) and we are done. The declaration of the target mqttc is already accomplished in the overall CMakeLists.txt outside of this repository by using CPM

CPMAddPackage(
  NAME mqttc
  GIT_REPOSITORY https://github.com/LiamBindle/MQTT-C.git
  GIT_TAG v1.1.6
  GIT_PROGRESS TRUE
  OPTIONS
  "MQTT_C_EXAMPLES OFF"
  "CMAKE_POSITION_INDEPENDENT_CODE ON"
)

@corneliusclaussen what is your opinion to, can we proceed with PR!

[hikinggrass]

how about guarding this

everest-framework/CMakeLists.txt

Line 92 in 1f8bce3

include(find-mqttc)

with
if(NOT TARGET mqttc)
and using find_package in the else branch of that? this way we could keep the find-mqttc intact as well

[sieukrem]

For sure I can try it, but before I do it I would like to know, how can I ensure that the fix does not break existing solution.

• Did it ever work?

I still have doubts that it would be right solution in comparison to pure find_package which is supporting the principle inversion of control.

[sieukrem]

@hikinggrass do you know whether the existing solution (the include(find-mqttc)) was working, because this is only executed in case EDM is disabled?

[hikinggrass]

It works in combination with the yocto build with this pretty simple recipe: https://github.com/EVerest/meta-everest/tree/kirkstone/recipes-connectivity/mqttc
The patch there might be relevant