[ignition-cmake2/ignition-modularscripts/ignition-common3] Add options, support pkgconfig and fix usage for common3-graph

[JackBoosY]

Fix usage when using find_package(ignition-common3-graphics CONFIG REQUIRED):

CMake Error at /home/work/vcpkg/scripts/buildsystems/vcpkg.cmake:573 (_add_executable):
  Target "sample" links to target "GTS::GTS" but the target was not found.
  Perhaps a find_package() call is missing for an IMPORTED target, or an
  ALIAS target is missing?
Call Stack (most recent call first):
  CMakeLists.txt:45 (add_executable)


CMake Error at /home/work/vcpkg/scripts/buildsystems/vcpkg.cmake:573 (_add_executable):
  Target "sample" links to target "FreeImage::FreeImage" but the target was
  not found.  Perhaps a find_package() call is missing for an IMPORTED
  target, or an ALIAS target is missing?
Call Stack (most recent call first):
  CMakeLists.txt:45 (add_executable)


CMake Error at /home/work/vcpkg/scripts/buildsystems/vcpkg.cmake:573 (_add_executable):
  Target "sample" links to target "TINYXML2::TINYXML2" but the target was not
  found.  Perhaps a find_package() call is missing for an IMPORTED target, or
  an ALIAS target is missing?
Call Stack (most recent call first):
  CMakeLists.txt:45 (add_executable)

Related: #24969

Already tested this usage in x64-linux.

[talregev]

Thank you for the fix

[ras0219-msft]

First, we should wait for #25034 to merge which adds a standardized method for consuming GTS (pkg-config).

Then,

1. FindGTS.cmake should be replaced/implemented via the pkgconfig mechanism above
2. ign_find_package should probably be patched to make PRIVATE_FOR not suppress find_dependency
3. We should not need a vcpkg-cmake-wrapper here. Any changes needed should be written into the -config.cmake created by the port.

[JackBoosY]

@ras0219-msft The official doc said:

# [PRIVATE_FOR]: Optional. If provided, the list that follows it must indicate
#                which library components depend on this package privately (i.e.
#                the package should not be included in its list of interface
#                libraries). This is only relevant for components that follow
#                the REQUIRED_BY command. Note that the PRIVATE argument does
#                not apply to components specified by REQUIRED_BY. This argument
#                MUST be given for components whose private dependencies have
#                been specified with REQUIRED_BY.

This parameter only affects cmake-config.cmake and pkgconfig.pc:
https://github.com/gazebosim/gz-cmake/blob/5adbd46a4e8a96f2bc67538bcca2406bb464ace3/cmake/IgnUtils.cmake#L325-L327

      foreach(component ${ign_find_package_PRIVATE_FOR})
        set(${component}_${PACKAGE_NAME}_PRIVATE true)
      endforeach()

https://github.com/gazebosim/gz-cmake/blob/5adbd46a4e8a96f2bc67538bcca2406bb464ace3/cmake/IgnUtils.cmake#L332-L336

      foreach(component ${ign_find_package_REQUIRED_BY})
        if(NOT ${component}_${PACKAGE_NAME}_PRIVATE)
          ign_string_append(${component}_CMAKE_DEPENDENCIES "${${PACKAGE_NAME}_find_dependency}" DELIM "\n")
        endif()
      endforeach()

https://github.com/gazebosim/gz-cmake/blob/5adbd46a4e8a96f2bc67538bcca2406bb464ace3/cmake/IgnUtils.cmake#L433-L439

            if(${component}_${PACKAGE_NAME}_PRIVATE)
              # If this is a private library or module, use the _PRIVATE suffix
              set(${component}_${PACKAGE_NAME}_PKGCONFIG_TYPE ${component}_${${PACKAGE_NAME}_PKGCONFIG_TYPE}_PRIVATE)
            else()
              # Otherwise, use the plain type
              set(${component}_${PACKAGE_NAME}_PKGCONFIG_TYPE ${component}_${${PACKAGE_NAME}_PKGCONFIG_TYPE})
            endif()

https://github.com/gazebosim/gz-cmake/blob/5adbd46a4e8a96f2bc67538bcca2406bb464ace3/cmake/IgnUtils.cmake#L433-L443

            if(${component}_${PACKAGE_NAME}_PRIVATE)
              # If this is a private library or module, use the _PRIVATE suffix
              set(${component}_${PACKAGE_NAME}_PKGCONFIG_TYPE ${component}_${${PACKAGE_NAME}_PKGCONFIG_TYPE}_PRIVATE)
            else()
              # Otherwise, use the plain type
              set(${component}_${PACKAGE_NAME}_PKGCONFIG_TYPE ${component}_${${PACKAGE_NAME}_PKGCONFIG_TYPE})
            endif()

            # Append the entry as a string onto the component-specific variable
            # for whichever required type we selected
            ign_string_append(${${component}_${PACKAGE_NAME}_PKGCONFIG_TYPE} ${${PACKAGE_NAME}_PKGCONFIG_ENTRY})

https://github.com/gazebosim/gz-cmake/blob/ign-cmake2/cmake/ignition-component-config.cmake.in#L80

@component_cmake_dependencies@

In fact, the configuration of cmake should be the same as that of pkgconfig. So I think "make PRIVATE_FOR not suppress find_dependency" is consistent with the modification (current modification) of directly removing PRIVATE_FOR from these ports that should be exported.

[dg0yt]

In fact, the configuration of cmake should be the same as that of pkgconfig. So I think "make PRIVATE_FOR not suppress find_dependency" is consistent with the modification (current modification) of directly removing PRIVATE_FOR from these ports that should be exported.

I cannot test it now but I disagree. I expect that your current modification changes the link type from PRIVATE to PUBLIC. This would be notable in the generated config by losing the $<LINK_ONLY:...> wrapping in INTERFACE_LINK_LIBRARIES properties, having side effects on consumers (e.g. adding definitions and include paths).
That's the whole point: You need a find_dependency for every library (which is not header-only), to satisfy static linkage.

[JackBoosY]

Already tested usage on x64-linux.