Missing dependencies on CMake exported target

[wnts]

The cpprestsdk exported target created during the build process of the libraries
does not carry all required dependencies.
For one, the Boost and openSSL dependencies are not defined on the target.

Commit cb7ca74 seems to have broken this for openSSL, by always defaulting to pkg-config for searching OpenSSL.
The issue leading to that commit has been solved in the find_package module by kitware: https://gitlab.kitware.com/cmake/cmake/-/issues/16885

For Boost this seems to be disabled deliberately...

cpprestsdk/Release/cmake/cpprest_find_boost.cmake

Lines 55 to 76 in f4124a9

	# FindBoost continually breaks imported targets whenever boost updates.
	if(1)
	target_include_directories(cpprestsdk_boost_internal INTERFACE "$<BUILD_INTERFACE:${Boost_INCLUDE_DIR}>")
	set(_prev)
	set(_libs)
	foreach(_lib ${Boost_LIBRARIES})
	if(_lib STREQUAL "optimized" OR _lib STREQUAL "debug")
	else()
	if(_prev STREQUAL "optimized")
	list(APPEND _libs "$<$<NOT:$<CONFIG:Debug>>:${_lib}>")
	elseif(_prev STREQUAL "debug")
	list(APPEND _libs "$<$<CONFIG:Debug>:${_lib}>")
	else()
	list(APPEND _libs "${_lib}")
	endif()
	endif()
	set(_prev "${_lib}")
	endforeach()
	if (NOT IOS OR NOT EXISTS "${PROJECT_SOURCE_DIR}/../Build_iOS/boost")
	target_link_libraries(cpprestsdk_boost_internal INTERFACE "$<BUILD_INTERFACE:${_libs}>")
	endif()
	else()

Running git blame on this file shows that that comment on line 54 was made 3 years ago...
Is it still relevant?

I saw that at the time serious effort was put into using modern CMake, so it would be nice to actually be able to see that in action.

Also, because of the above, the simple CMakeLists.txt file listed on the Readme is not working.

[letrthong]

let us know version of cmake on your pc and version of cpprestsdk

[wnts]

let us know version of cmake on your pc and version of cpprestsdk

CMake 3.14
cpprestsdk: latest commit on master branch

[letrthong]

my pc: cmake version 3.10.2
cpprest is boost-1.72.0

Using cmd as below to switch to boost-1.72.0
git reset --hard
git fetch
git checkout boost-1.72.0
git submodule update --init
cd boost/libs/asio
git checkout boost-1.69.0

I can cross compiler and push lib at https://github.com/letrthong/orangepi_zero_release/tree/master/x32 with toolchain gcc-linaro-arm-linux/gcc-linaro-7.3.1-2018.05-x86_64_arm-linux-gnueabihf/bin/arm-linux-gnueabihf-g++

[garethsb]

Resolved by #1383?

[wnts]

Resolved by #1383?

Not quite. #1383 fixes only part of the problem: now Boost is searched for through the find_dependency macro calls, but it's still not present as a transitive dependency on the exported targets.

What I want to be able to do (taken directly from the project's README):

cmake_minimum_required(VERSION 3.9)
project(main)

find_package(cpprestsdk REQUIRED)

add_executable(main main.cpp)
target_link_libraries(main PRIVATE cpprestsdk::cpprest)

But this does not work. the cpprestsdk::cpprest imported target does not carry the transitive dependency on Boost::system and OpenSSL::crypto.

What I need to do now is:

cmake_minimum_required(VERSION 3.9)
project(main)

find_package(cpprestsdk REQUIRED)

add_executable(main main.cpp)
target_link_libraries(main PRIVATE cpprestsdk::cpprest Boost::system OpenSSL::Crypto)

[wnts]

The problem is that the targets imported by the calls to find_dependency in the package configuration file (Release/cmake/cpprestsdk-config.in.cmake) do not match the actual targets linked against in Release/src/CMakeLists.txt. The latter creates targets different from those created by the find_dependency macro, and are created by the cpprest_find_* wrapper macros in the Release/cmake/cpprest_find_*.cmake files.

For example, find_dependency(Boost COMPONENTS system date_time regex) uses the CMake supplied FindBoost module, which creates the following imported targets:

Boost::system
Boost::date_time
Boost::regex

But the macro cpprest_find_boost creates the target cpprestsdk_boost_internal, which is what added to the INTERFACE requirements of the cpprestsdk::cpprest target, which is ultimately exported in the package configuration file. The cpprestsdk_boost_internal target has itself transitive dependencies on the various discovered boost library components.

Now one would expect this would still work, (assuming that cprest_find_* and the find_dependency macros end up finding the same files and directories for the given library).
But the cpprest_find_boost creates the cpprestsdk_boost_internal target with a $<BUILD_INTERFACE:...> generator expression, which expands to the empty string when exported by install(EXPORT ...)

The problem described above also occurs with the other dependencies (zlib, openssl, etc)