failed to use find_package(zenohpico) [Bug]

[milyin]

Describe the bug

There are 3 proper ways to use zenoh-pico library in customer cmake project:

• find_package(zenohpico)
• add_subdirectory(../zenoh-pico)
• FetchContent from github repository, which is just a wrapper over the add_subdirectory command

The find_package includes file lib/cmake/zenohpico/zenohpicoConfig.cmake generated from https://github.com/eclipse-zenoh/zenoh-pico/blob/master/PackageConfig.cmake.in

The add_subdirectory includes project's CMakeLists.txt: https://github.com/eclipse-zenoh/zenoh-pico/blob/master/CMakeLists.txt

This approach works well for zenoh-c and zenoh-cpp. See for example testing of these featues in zenoh-c CI:

Install zenohc package:
https://github.com/eclipse-zenoh/zenoh-c/blob/master/.github/workflows/ci.yml#L43-L45
Test building examples using zenoh-c directory as subproject:
https://github.com/eclipse-zenoh/zenoh-c/blob/master/.github/workflows/ci.yml#L72-L74
Test building examples using installed zenohc package:
https://github.com/eclipse-zenoh/zenoh-c/blob/master/.github/workflows/ci.yml#L79-L81

The CMakeLists.txt in examples directory of zenoh-pico also allows to test both approaches. At this moment building with find_package doesnt work for zenoh-pico

It's necessary to fix it and add testing of both approaches to CI, like it's done in zenoh-c

To reproduce

Install zenohpico as a package locally

git clone [email protected]:eclipse-zenoh/zenoh-pico.git
cmake -S zenoh-pico -B build -DCMAKE_INSTALL_PREFIX=~/FOO/install
cmake --build build --target install

Build examples using zenoh-pico as package:

cmake -S zenoh-pico/examples -B build_examples -DZENOHPICO_SOURCE=PACKAGE -DCMAKE_INSTALL_PREFIX=~/FOO/install
cmake --build build_examples 

This fails due to misconfigured line
https://github.com/eclipse-zenoh/zenoh-pico/blob/master/examples/CMakeLists.txt#L7
(zenohc instead of zenohpico::static)

But even after fix this the more problem comes: include direcrories and preprocessor settings are not provided to dependent project correctly

System info

Ubuntu 22.04

[Mallets]

@milyin @jean-roland checking wether this issue is still open?

[jean-roland]

Yeah, this haven't been fixed yet.

[milyin]

When reviewing fix for bug, it was found that zenop-pico package installation is not correct now, this is not only single typo in example.

First, I'll describe the whole concept and how package installation works:

1. package is searched by cmake's command find_package by it's name: "zenohc" or "zenohpico".
2. techninally, package is a file "/lib/cmake/zenohc/zenohcConfig.cmake" which is included into user's CMakeLists.txt. This file is generated from template https://github.com/eclipse-zenoh/zenoh-c/blob/main/install/PackageConfig.cmake.in
3. inside the file the lbrary targets are declared. Zenoh-c declares 3 targets: zenohc::static, zenohc::shared and zenohc::lib which is shared or static, depending on ZENOHC_LIB_STATIC setting
4. each target is configured with set of properties, some of them specific to target. These properties are:

# path to library file
set_property(TARGET __zenohc_static PROPERTY IMPORTED_LOCATION "/home/milyin/FOO/install/lib/libzenohc.a")
# additional libraries to be linked when linking this library
target_link_libraries(__zenohc_static INTERFACE rt;pthread;m;dl)
# include directories for the library
target_include_directories(__zenohc_static INTERFACE "/home/milyin/FOO/install/include")
# say that shared library doesn't contain soname property: https://en.wikipedia.org/wiki/Soname
set_target_properties(__zenohc_shared PROPERTIES IMPORTED_NO_SONAME TRUE)
# define additional preprocessor settings
target_compile_definitions(__zenohc_shared INTERFACE ZENOHC_DYN_LIB)

5. on the user's side it's enough to include the package and add dependency on necessary library. No additional settings are required:

find_package(zenohc)
add_executable(app)
add_dependencies(app zenohc::lib)
target_link_libraries(app PRIVATE zenohc::lib)

For zenoh-pico there are several problems:

• IMPORTED_LOCATION is not set to correct path of the library file
• target_compile_definitions is not set (ZENOH_LINUX or ZENOH_WINDOWS, depending on platform, defintion for shared library import should be here also, I suppose)
• the library target names in zenoh-pico main CMakeLists.txt are not in accord with names in package: it's just zenohpico in CMakeLists.txt, but zenohpico::static and zenohpico::lib in package. This doesn't alllow to interchange find_package / add_subdirectory
  ...may be more of it

The main problem with zenoh-pico is that it don't use target-local properties (i.e. it uses global add_definitions instead of target_compile_definitions for example, same thing for paths, etc.). There is a hack to make zenoh-pico work with zenoh-cpp build: https://github.com/eclipse-zenoh/zenoh-pico/blob/main/CMakeLists.txt#L48-L51. But using global properties in package config file is definitely wrong.
So the choice is:

1. refactor zenoh-pico CMakeLists.txt, getting rid of global properties
2. only implement correct https://github.com/eclipse-zenoh/zenoh-pico/blob/main/PackageConfig.cmake.in with all necessary target properties, keep main CMakeLists with global properties for now

In the second case it will be hard to keep PackageConfig and CmakeLists.txt in sync, as they will be significantly different. Compare with how it's made in zenoh-cpp, where these files are practically the same:
https://github.com/eclipse-zenoh/zenoh-cpp/blob/main/CMakeLists.txt
https://github.com/eclipse-zenoh/zenoh-cpp/blob/main/install/PackageConfig.cmake.in