CMP0079

target_link_libraries() allows use with targets in other directories.

Prior to CMake 3.13 the target_link_libraries() command did not accept targets not created in the calling directory as its first argument for calls that update the LINK_LIBRARIES of the target itself. It did accidentally accept targets from other directories on calls that only update the INTERFACE_LINK_LIBRARIES, but would simply add entries to the property as if the call were made in the original directory. Thus link interface libraries specified this way were always looked up by generators in the scope of the original target rather than in the scope that called target_link_libraries().

CMake 3.13 now allows the target_link_libraries() command to be called from any directory to add link dependencies and link interface libraries to targets created in other directories. The entries are added to LINK_LIBRARIES and INTERFACE_LINK_LIBRARIES using a special (internal) suffix to tell the generators to look up the names in the calling scope rather than the scope that created the target.

This policy provides compatibility with projects that already use target_link_libraries() with the INTERFACE keyword on a target in another directory to add INTERFACE_LINK_LIBRARIES entries to be looked up in the target’s directory. Such projects should be updated to be aware of the new scoping rules in that case.

The OLD behavior of this policy is to disallow target_link_libraries() calls naming targets from another directory except in the previously accidentally allowed case of using the INTERFACE keyword only. The NEW behavior of this policy is to allow all such calls but use the new scoping rules.

This policy was introduced in CMake version 3.13. CMake version 3.17.5 warns when the policy is not set and uses OLD behavior. Use the cmake_policy() command to set it to OLD or NEW explicitly.