Add relocatable CMakeConfig files.

[Nicogene]

This PR introduce a deep refactor on how the Config.cmake are generated inside icub-main.

With this PR all the libraries are handled as components so:
find_package(ICUB COMPONENTS iKin) and find_package(iKin) are equivalent.

If no components are specify here is the list of the components automatically added:

-- Found ICUB 1.16.0 (Components: iCubDev ctrlLib skinDynLib iKin iDyn learningMachine perceptiveModels actionPrimitives optimization)

(depends also if you have compiled some of them that are optional like optimization, perceptiveModels etc)

Here is the content of ${ICUB_LIBRARIES}: ICUB::iCubDev;ICUB::ctrlLib;ICUB::skinDynLib;ICUB::iKin;ICUB::iDyn;ICUB::learningMachine;ICUB::perceptiveModels;ICUB::actionPrimitives;ICUB::optimization

For now the embobj libs( ethResources, canLoaderLib, ethLoaderLib) have not been ported to COMPONENTS due to :robotology/ycm-cmake-modules#340

If fixes #651

[pattacini]

Exporting ICUB_LIBRARIES is definitely needed in order to avoid breaking current code.

[traversaro]

I think that given the constraint that we need still to support ICUB_LIBRARIES exported variables, and we also need to support the non-namespaced exported targets (as they are quite used in downstream projects, see https://github.com/search?l=CMake&q=org%3Arobotology+ctrlLib&type=Code), I guess that for now we cannot remove the use of the list of targetes built within the project (that is contained in the global property ICUB_TARGETS).

For this reason, I think that for now it is a better idea to modify the existing icub_export_library macro with the logic that we need, instead of removing it and duplicate the code related to installation for each library.

Once we have the list of targets again in ICUB_TARGETS, I think we can modify the install_basic_package_files function to use a specific CONFIG_TEMPLATE CMake, so that we can put some additional logic in the CMake config file. In particular, we can start with the CMake config template automatically created by install_basic_package_files . There we can define the ICUB_LIBRARIES variable to contain all the targets defined in ICUB_TARGETS, and also add non-namespaced targets that permit to link the corresponding imported targets (i.e. add the target ctrlLib that links ICUB::ctrLib). If we want to eventually just switch to use ICUB::ctrlLib, we can also mark the non-namespaced targets as DEPRECATED targets, if the used CMake version is recent enough: https://cmake.org/cmake/help/v3.17/release/3.17.html#properties .

[CLAassistant]

All committers have signed the CLA.

[Nicogene]

In the latter two commits I made some changes in order to handle the libraries through the COMPONENTS, as it is done in YARP.

Here is the default components:

                                 iCubDev
                                 ctrlLib
                                 skinDynLib
                                 iKin
                                 iDyn
                                 icubmod

I managed to create a ICUBConfig.cmake containing the targets and ICUB_LIBRARIES.

It is super draft, probably there are some copy-paste errors, or some missing parts.

What do you think about it ?

[drdanz]

What about installing iKin, iDyn and any other libraries that could eventually be detached from the iCub-main repository one day, as separate package, and have iCubConfig.cmake find them using find_dependency? In this way, you can start searching them either with find_package(ICUB) or with find_package(iKin)`, and if they are moved to a separate repository the compatibility will not be broken

[Nicogene]

What about installing iKin, iDyn and any other libraries that could eventually be detached from the iCub-main repository one day, as separate package, and have iCubConfig.cmake find them using find_dependency? In this way, you can start searching them either with find_package(ICUB) or with find_package(iKin)`, and if they are moved to a separate repository the compatibility will not be broken

In theory porting it to the COMPONENTS should do the trick I am right?

[Nicogene]

FYI I have updated the body of the PR with the latest changes-> #652 (comment)

At this moment I have the issue that the link to <lib> is not working, while ICUB::<lib> is working.

[Nicogene]

The PR is ready to be review/merged, I successfully compiled the robotology-superbuild with almost all profiles enabled.

These changes are fully back-compatible

[pattacini]

LGTM 🚀

Only a quick request for clarification from my side.

[traversaro]

Minor comments.