CMake/Help/policy/CMP0135.rst

CMP0135
-------

.. versionadded:: 3.24

When using the ``URL`` download method with the :command:`ExternalProject_Add`
or :command:`FetchContent_Declare` commands, 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 :command:`ExternalProject_Add`
and :command:`FetchContent_Declare` commands 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.

.. |INTRODUCED_IN_CMAKE_VERSION| replace:: 3.24
.. |WARNS_OR_DOES_NOT_WARN| replace:: warns
.. include:: include/STANDARD_ADVICE.rst

.. include:: include/DEPRECATED.rst