Fix: cmake install shouldn't hardcode install path

[filippobrizzi]

Cmake install shouldn't hardcode install path.

[eclipse-zenoh-bot]

@filippobrizzi If this pull request contains a bugfix or a new feature, then please consider using Closes #ISSUE-NUMBER syntax to link it to an issue.

[eclipse-zenoh-bot]

@filippobrizzi If this pull request contains a bugfix or a new feature, then please consider using Closes #ISSUE-NUMBER syntax to link it to an issue.

[eclipse-zenoh-bot]

@filippobrizzi If this pull request contains a bugfix or a new feature, then please consider using Closes #ISSUE-NUMBER syntax to link it to an issue.

[filippobrizzi]

PTAL @p-avital @milyin

[milyin]

Nice approach. This should allow to move lib and include directories with zenoh-c installed into different place if necessary. I agree with the change.
@filippobrizzi can you tell, is it some standard recommendation to avoid absolute paths in cmake package file? I'd be grateful if you add some link about it

[filippobrizzi]

Nice approach. This should allow to move lib and include directories with zenoh-c installed into different place if necessary. I agree with the change. @filippobrizzi can you tell, is it some standard recommendation to avoid absolute paths in cmake package file? I'd be grateful if you add some link about it

@milyin A reference I found is from the CMake documentation https://cmake.org/cmake/help/v3.17/guide/tutorial/index.html#adding-export-configuration-step-11.

I have to admit my solution is halfway elegant as in theory this piece of code

get_filename_component(_IMPORT_PREFIX "${CMAKE_CURRENT_LIST_FILE}" PATH)
get_filename_component(_IMPORT_PREFIX "${_IMPORT_PREFIX}" PATH)
get_filename_component(_IMPORT_PREFIX "${_IMPORT_PREFIX}" PATH)
get_filename_component(_IMPORT_PREFIX "${_IMPORT_PREFIX}" PATH)
if(_IMPORT_PREFIX STREQUAL "/")
  set(_IMPORT_PREFIX "")
endif()

should be automatically generated from CMake when calling configure_package_config_file, but in this case it doesn't work as we create an IMPORTED library.

I have searched extensively on Google for an elegant solution for imported targets but with no luck. This is the best working solution I could come up with.