Target names should not be reserved and should match a validity pattern.
CMake 2.8.12 and lower allowed creating targets using
add_custom_target() with unrestricted
choice for the target name. Newer cmake features such
cmake-generator-expressions(7) and some
diagnostics expect target names to match a restricted pattern.
Target names may contain upper and lower case letters, numbers, the underscore character (_), dot(.), plus(+) and minus(-). As a special case, ALIAS targets and IMPORTED targets may contain two consequtive colons.
Target names reserved by one or more CMake generators are not allowed. Among others these include “all”, “help” and “test”.
The OLD behavior for this policy is to allow creating targets with reserved names or which do not match the validity pattern. The NEW behavior for this policy is to report an error if an add_* command is used with an invalid target name.
This policy was introduced in CMake version 3.0. CMake version 3.6.2 warns when the policy is not set and uses OLD behavior. Use the cmake_policy command to set it to OLD or NEW explicitly.
OLD behavior of a policy is
deprecated by definition
and may be removed in a future version of CMake.