CMP0049ΒΆ
Do not expand variables in target source entries.
CMake 2.8.12 and lower performed an extra layer of variable expansion when evaluating source file names:
set(a_source foo.c)
add_executable(foo \${a_source})
This was undocumented behavior.
The OLD behavior for this policy is to expand such variables when processing
the target sources. The NEW behavior for this policy is to issue an error
if such variables need to be expanded.
This policy was introduced in CMake version 3.0.
CMake version 3.18.6 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.