[Bug] aliases "zenohc::static" and "zenohhc::lib" not globally visible, with CMake 3.16

[kjrusscher]

Describe the bug

Zenoh-cpp cannot be compiled because the cmake file zenohcConfig.cmake throws an error when using CMake 3.16. The reason is that "zenohc::static" and "zenohhc::lib" are not globally visible. In CMake 3.18+ this problem is solved, but not in CMake 3.16 which is the default option in Ubuntu 20.04.

Why is this zenoh-cpp compilation error a zenoh-c problem? Because the file that causes it (zenohcConfig.cmake) is generated when compiling zenoh-c.

More details can be found in eclipse-zenoh/zenoh-cpp#7

To reproduce

1. Compile zenoh-c.

git clone https://github.com/eclipse-zenoh/zenoh-c.git && \
cd zenoh-c && mkdir -p build && cd build && \
cmake .. -DCMAKE_INSTALL_PREFIX=/home/username/local && \
cmake --build . --target install

2. Use cmake on zenoh-cpp

git clone https://github.com/eclipse-zenoh/zenoh-cpp.git && \
cd zenoh-cpp && mkdir -p build && cd build && \
cmake .. -DCMAKE_INSTALL_PREFIX=/home/username/local

3. Error:

  add_library cannot create ALIAS target "zenohc::static" because target
  "__zenohc_static" is imported but not globally visible.
Call Stack (most recent call first):
  CMakeLists.txt:42 (find_package)


CMake Error at /home/username/local/lib/cmake/zenohc/zenohcConfig.cmake:46 (add_library):
  add_library cannot create ALIAS target "zenohc::lib" because target
  "__zenohc_lib" is imported but not globally visible.
Call Stack (most recent call first):
  CMakeLists.txt:42 (find_package)

System info

• Ubuntu 20.04
• CMake 3.16.3

[kjrusscher]

It's a problem with CMake 3.16. It can be solved by editing PackageConfig.cmake.in.

Lines 17 and 21 have the functions add_library(__zenohc_static STATIC IMPORTED) and add_library(__zenohc_lib STATIC IMPORTED). Adding GLOBAL to those functions solves the problem.

I will try to change the generation of those files in zenoh-c and upload them as a pull request.