CMP0135

New in version 3.24.

When using the URL download method with the ExternalProject_Add() command, CMake 3.23 and below sets the timestamps of the extracted contents to the same as the timestamps in the archive. When the URL changes, the new archive is downloaded and extracted, but the timestamps of the extracted contents might not be newer than the previous contents. Anything that depends on the extracted contents might not be rebuilt, even though the contents may change.

CMake 3.24 and above prefers to set the timestamps of all extracted contents to the time of the extraction. This ensures that anything that depends on the extracted contents will be rebuilt whenever the URL changes.

The DOWNLOAD_EXTRACT_TIMESTAMP option to the ExternalProject_Add() command can be used to explicitly specify how timestamps should be handled. When DOWNLOAD_EXTRACT_TIMESTAMP is not given, this policy controls the default behavior. The OLD behavior for this policy is to restore the timestamps from the archive. The NEW behavior sets the timestamps of extracted contents to the time of extraction.

This policy was introduced in CMake version 3.24. CMake version 3.26.6 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.