CMP0027

Conditionally linked imported targets with missing include directories.

CMake 2.8.11 introduced introduced the concept of INTERFACE_INCLUDE_DIRECTORIES, and a check at cmake time that the entries in the INTERFACE_INCLUDE_DIRECTORIES of an IMPORTED target actually exist. CMake 2.8.11 also introduced generator expression support in the target_link_libraries() command. However, if an imported target is linked as a result of a generator expression evaluation, the entries in the INTERFACE_INCLUDE_DIRECTORIES of that target were not checked for existence as they should be.

The OLD behavior of this policy is to report a warning if an entry in the INTERFACE_INCLUDE_DIRECTORIES of a generator-expression conditionally linked IMPORTED target does not exist.

The NEW behavior of this policy is to report an error if an entry in the INTERFACE_INCLUDE_DIRECTORIES of a generator-expression conditionally linked IMPORTED target does not exist.

This policy was introduced in CMake version 3.0. Prior to removal in CMake version 4.0, it could be set by cmake_policy() or cmake_minimum_required(). If it was not set, CMake warned, and used OLD behavior.