CMake warning : the target is mentionned as dependency but not declared

[ankou29666]

Hi

After a little refactoring of my CMakeLists.txt files in my project, I'm now facing the warning message :

CMake Warning at /Volumes/User/Users/yann/Qt/6.9.1/macos/lib/cmake/Qt6/QtPublicWalkLibsHelpers.cmake:285 (message):
[cmake]   The HttpServer target is mentioned as a dependency for HttpManagerLib, but
[cmake]   not declared.  The linking might be incomplete.
[cmake] Call Stack (most recent call first):
[cmake]   /Volumes/User/Users/yann/Qt/6.9.1/macos/lib/cmake/Qt6/QtPublicWalkLibsHelpers.cmake:249 (__qt_internal_walk_libs)
[cmake]   /Volumes/User/Users/yann/Qt/6.9.1/macos/lib/cmake/Qt6/QtPublicWalkLibsHelpers.cmake:337 (__qt_internal_walk_libs)
[cmake]   /Volumes/User/Users/yann/Qt/6.9.1/macos/lib/cmake/Qt6Core/Qt6CoreMacros.cmake:713 (__qt_internal_collect_all_target_dependencies)
[cmake]   /Volumes/User/Users/yann/Qt/6.9.1/macos/lib/cmake/Qt6Core/Qt6CoreMacros.cmake:818 (_qt_internal_finalize_executable)
[cmake]   /Volumes/User/Users/yann/Qt/6.9.1/macos/lib/cmake/Qt6Core/Qt6CoreMacros.cmake:787:EVAL:1 (qt6_finalize_target)
[cmake]   Src/Main/CMakeLists.txt:DEFERRED

I've had this issue a few days ago, but it was among my own modules, I had found a link suggesting that it was due to a missordered add_subdirectories, the depending one being built before the depended one. and indeed Placing the add_subdirectories in the right order fixed the problem.

Now the issue occurs but between one of mine and a Qt one (Qt6::HttpServer).
Here's Src/Application/HttpManager/CMakeLists.txt

set (LIBNAME HttpManager)
set (QT_LIBS Core Qml Concurrent Network HttpServer)
set (CPP_FILES somesources.h somesources.cpp)

################################################################################
project(${LIBNAME}Lib LANGUAGES CXX)

find_package(Qt6 REQUIRED COMPONENTS ${QT_LIBS})

qt_add_library(${PROJECT_NAME} STATIC ${CPP_FILES})
qt_add_resources (${PROJECT_NAME} ...) # SSL certificate files for HTTPS server

target_include_directories (${PROJECT_NAME} PUBLIC ${CMAKE_SOURCE_DIR}/Src/Entities)
target_link_directories    (${PROJECT_NAME} PUBLIC ${CMAKE_BINARY_DIR}/Entities)

foreach (module IN LISTS QT_LIBS)
    target_link_libraries(${PROJECT_NAME} PUBLIC Qt6::${module})
endforeach()

target_link_libraries(${PROJECT_NAME} PUBLIC EntitiesLib)

I've checked and rechecked again in other CMakeList.txt files, and all add_subdirectory directives are called in the right build order, dependencies first, dependent libs next, then executables last.

In Src/CMakeLists.txt

add_subdirectory (Entities ${CMAKE_BINARY_DIR}/Entities)
add_subdirectory (Application) # HttpManager module inside that directory, along with another plugin manager module, both depending on Entities, no dependency one to the other
add_subdirectory (Plugins) # dynamic plugins, depends on Entities
add_subdirectory (GlobalManager ${CMAKE_BINARY_DIR}/GlobalManager) # Depends on both modules in Application, serves as facade pattern in both main.cpp in Main and TestUI executables
# add_subdirectory (UI) # for user interface, not implemented yet
# add_subdirectory (TestUI ${CMAKE_BINARY_DIR}/TestUI) # QML hot reloader executable, not imported yet from another project, depends on GlobalManager
add_subdirectory (Main ${CMAKE_BINARY_DIR}/Main) # release executable, same depends on GlobalManager

Qt is my sole external dependency, no other library added

Does anyone have any idea about what I'm doing wrong ?

[jsulm]

@ankou29666 How does CMakeLists.txt look like for EntitiesLib?

[Paul Colby]

Hi @ankou29666,

It's not entirely clear, but given that your CMake error call stack ends (ie starts) with:

[cmake]   Src/Main/CMakeLists.txt:DEFERRED

The issue is likely that you have not found the Qt HttpServer package in that CMakeLists.txt file.

Although you've included Main after Application, ie:

add_subdirectory (Application) # HttpManager module inside that directory, along with another plugin manager module, both
...
add_subdirectory (Main ${CMAKE_BINARY_DIR}/Main) # release executable, same depends on GlobalManager

The modules found in Application/CMakeLists.txt are (by default) scoped to that subdirectory only. Try doing a web search for "add_subdirectory scope".

I would guess you need to either:

1. remove the dependency from Src/Main/CMakeLists.txt; or
2. more likely, move the find_package(Qt6 ...) to the top Src/CMakeLists.txt file, before the add_subdirectory calls.

Cheers.

[ankou29666]

Hi Paul and thanks for your reply.

Yes I had completely missed the Src/Main/CMakeLists.txt Line, thank you very much for pointing it out.

Yes indeed that was it. As I had turned some dependencies from PRIVATE to PUBLIC, I had removed that dependency from Main/CMakeLists.txt file and adding it back again fixes the problem.
However I'm still a little surprized that, as my module HttpManager relies non only on Qt's HttpServer, but also on Concurrent and Network, the warning is gone only if I add back HttpServer, without adding back Concurrent and Network.
So even though topic is solved, I still would like to add one more question : as Qt::HttpServer module depends on classes defined Qt::Network module (QTcpServer, as as QHttpServer depends on QTcpServer), and also likely QFuture in Qt::Concurrent module, I guess that importing Qt::HttpServer module also brings Qt::Concurrent and Qt::Network as implicit dependencies, that don't need to be declared explicitly ?

@Paul-Colby said in CMake warning : the target is mentionned as dependency but not declared:

more likely, move the find_package(Qt6 ...) to the top Src/CMakeLists.txt file, before the add_subdirectory calls.

Yeah I currently have a find_package statement near the beginning of EVERY subfolder's CMakeLists.txt. I've been watching a few CMake videos on youtube and find one that was making the same suggestion.
That's what I'm planning to do this afternoon.

[Christian Ehrlicher]

@ankou29666 said in CMake warning : the target is mentionned as dependency but not declared:

guess that importing Qt::HttpServer module also brings Qt::Concurrent and Qt::Network as implicit dependencies, that don't need to be declared explicitly ?

correct, that's why you have to use PRIVATE, PUBLIC and INTERFACE in your target_link_libraries() call: https://cmake.org/cmake/help/latest/command/target_link_libraries.html#libraries-for-a-target-and-or-its-dependents