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. CMake version 3.15.7 warns when the policy is not set and uses OLD behavior. Use the cmake_policy() command to set it to OLD or NEW explicitly.