CMP0051

List TARGET_OBJECTS in SOURCES target property.

CMake 3.0 and lower did not include the TARGET_OBJECTS generator expression when returning the SOURCES target property.

Configure-time CMake code is not able to handle generator expressions. If using the SOURCES target property at configure time, it may be necessary to first remove generator expressions using the string(GENEX_STRIP) command. Generate-time CMake code such as file(GENERATE) can handle the content without stripping.

The OLD behavior for this policy is to omit TARGET_OBJECTS expressions from the SOURCES target property. The NEW behavior for this policy is to include TARGET_OBJECTS expressions in the output.

This policy was introduced in CMake version 3.1. CMake version 3.19.0-rc3 warns when the policy is not set and uses OLD behavior. Use the cmake_policy() command to set it to OLD or NEW explicitly.