CMP0028ΒΆ
Double colon in target name means ALIAS or IMPORTED target.
CMake 2.8.12 and lower allowed the use of targets and files with double
colons in target_link_libraries(), with some buildsystem generators.
The use of double-colons is a common pattern used to namespace IMPORTED
targets and ALIAS targets. When computing the link dependencies of
a target, the name of each dependency could either be a target, or a file
on disk. Previously, if a target was not found with a matching name, the name
was considered to refer to a file on disk. This can lead to confusing error
messages if there is a typo in what should be a target name.
See also the LINK_LIBRARIES_ONLY_TARGETS target property.
The OLD behavior for this policy is to search for targets, then files on
disk, even if the search term contains double-colons. The NEW behavior
for this policy is to issue a FATAL_ERROR if a link dependency contains
double-colons but is not an IMPORTED target or an ALIAS target.
This policy was introduced in CMake version 3.0. CMake version
3.23.3 warns when the policy is not set and uses OLD behavior. Use
the cmake_policy() command to set it to OLD or NEW explicitly.
Note
The OLD behavior of a policy is
deprecated by definition
and may be removed in a future version of CMake.