CMake 3.16 Release Notes
************************

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Changes made since CMake 3.15 include the following.

New Features
============

Languages
---------

* CMake learned to support the Objective C (``OBJC``) and Objective C++
  (``OBJCXX``) languages.  They may be enabled via the :command:`project`
  and :command:`enable_language` commands.  When ``OBJC`` or ``OBJCXX``
  is enabled, source files with the ``.m`` or ``.mm``, respectively,
  will be compiled as Objective C or C++.  Otherwise they will be treated
  as plain C++ sources as they were before.

Compilers
---------

* The ``Clang`` compiler is now supported on ``Solaris``.

Platforms
---------

* On AIX, executables using the :prop_tgt:`ENABLE_EXPORTS` target property
  now produce a linker import file with a ``.imp`` extension in addition
  to the executable file.  Plugins (created via :command:`add_library` with
  the ``MODULE`` option) that use :command:`target_link_libraries` to link
  to the executable for its symbols are now linked using the import file.
  The :command:`install(TARGETS)` command now installs the import file as
  an ``ARCHIVE`` artifact.

* On AIX, runtime linking is no longer enabled by default.  CMake provides
  the linker enough information to resolve all symbols up front.
  One may manually enable runtime linking for shared libraries and/or
  loadable modules by adding ``-Wl,-G`` to their link flags
  (e.g. in the :variable:`CMAKE_SHARED_LINKER_FLAGS` or
  :variable:`CMAKE_MODULE_LINKER_FLAGS` variable).
  One may manually enable runtime linking for executables by adding
  ``-Wl,-brtl`` to their link flags (e.g. in the
  :variable:`CMAKE_EXE_LINKER_FLAGS` variable).

Command-Line
------------

* :manual:`cmake(1)` ``-E`` now supports ``true`` and ``false`` commands,
  which do nothing while returning exit codes of 0 and 1, respectively.

* :manual:`cmake(1)` gained a ``--trace-redirect=<file>`` command line
  option that can be used to redirect ``--trace`` output to a file instead
  of ``stderr``.

* The :manual:`cmake(1)` ``--loglevel`` command line option has been
  renamed to ``--log-level`` to make it consistent with the naming of other
  command line options.  The ``--loglevel`` option is still supported to
  preserve backward compatibility.

Commands
--------

* The :command:`add_test` command learned the option ``COMMAND_EXPAND_LISTS``
  which causes lists in the ``COMMAND`` argument to be expanded, including
  lists created by generator expressions.

* The :command:`file` command learned a new sub-command,
  ``GET_RUNTIME_DEPENDENCIES``, which allows you to recursively get the list of
  libraries linked by an executable or library. This sub-command is intended as
  a replacement for :module:`GetPrerequisites`.

* The :command:`find_file`, :command:`find_library`, :command:`find_path`,
  :command:`find_package`, and :command:`find_program` commands have learned to
  check the following variables to control the default behavior for groups of
  search locations:

  * :variable:`CMAKE_FIND_USE_PACKAGE_ROOT_PATH` - Controls the default
    behavior of searching the :variable:`<PackageName>_ROOT` variables.

  * :variable:`CMAKE_FIND_USE_CMAKE_ENVIRONMENT_PATH` - Controls the default
    behavior of searching the CMake-specific environment variables.

  * :variable:`CMAKE_FIND_USE_SYSTEM_ENVIRONMENT_PATH` - Controls the default
    behavior of searching the standard system environment variables.

  * :variable:`CMAKE_FIND_USE_CMAKE_PATH` - Controls the default behavior of
    searching the CMake-specific cache variables.

  * :variable:`CMAKE_FIND_USE_CMAKE_SYSTEM_PATH` - Controls the default
    behavior of searching the platform-specific CMake variables.

* The :command:`find_package` command has learned to check the
  :variable:`CMAKE_FIND_USE_PACKAGE_REGISTRY` variable to control the default
  behavior of searching the CMake user package registry and to check the
  :variable:`CMAKE_FIND_USE_SYSTEM_PACKAGE_REGISTRY` variable to control
  the default behavior of searching the CMake system package registry.

* The :command:`message` command learned indentation control with the new
  :variable:`CMAKE_MESSAGE_INDENT` variable.

* The :command:`target_precompile_headers` command was added to specify
  a list of headers to precompile for faster compilation times.

Variables
---------

* The :variable:`CMAKE_CUDA_RESOLVE_DEVICE_SYMBOLS` variable has been
  introduced to optionally initialize the
  :prop_tgt:`CUDA_RESOLVE_DEVICE_SYMBOLS` target property.

* The :variable:`CMAKE_ECLIPSE_RESOURCE_ENCODING` variable was added to
  specify the resource encoding for the the :generator:`Eclipse CDT4` extra
  generator.

* The :variable:`CMAKE_UNITY_BUILD` variable was added to initialize the
  :prop_tgt:`UNITY_BUILD` target property to tell generators to batch
  include source files for faster compilation times.

Properties
----------

* The :prop_tgt:`BUILD_RPATH` and :prop_tgt:`INSTALL_RPATH` target properties
  now support :manual:`generator expressions <cmake-generator-expressions(7)>`.

* The :prop_tgt:`INSTALL_REMOVE_ENVIRONMENT_RPATH` target property was
  added to remove compiler-defined ``RPATH`` entries from a target.
  This property is initialized by the
  :variable:`CMAKE_INSTALL_REMOVE_ENVIRONMENT_RPATH` variable.

* The :prop_tgt:`PRECOMPILE_HEADERS` target property was added to specify
  a list of headers to precompile for faster compilation times.
  Set it using the :command:`target_precompile_headers` command.

* The :prop_tgt:`UNITY_BUILD` target property was added to tell
  generators to batch include source files for faster compilation
  times.

* The :prop_tgt:`VS_CONFIGURATION_TYPE` target property now supports
  :manual:`generator expressions <cmake-generator-expressions(7)>`.

* The :prop_tgt:`VS_DPI_AWARE` target property was added to tell
  :ref:`Visual Studio Generators` to set the ``EnableDpiAwareness``
  property in ``.vcxproj`` files.

* The :prop_tgt:`XCODE_SCHEME_DEBUG_DOCUMENT_VERSIONING` target property was
  added to tell the :generator:`Xcode` generator to set the value of the
  ``Allow debugging when using document Versions Browser`` schema option.

Modules
-------

* The :module:`FindDoxygen` module :command:`doxygen_add_docs` command
  gained a new ``USE_STAMP_FILE`` option.  When this option present,
  the custom target created by the command will only re-run Doxygen if
  any of the source files have changed since the last successful run.

* The :module:`FindGnuTLS` module now provides an imported target.

* The :module:`FindPackageHandleStandardArgs` module
  :command:`find_package_handle_standard_args` command gained
  a new ``REASON_FAILURE_MESSAGE`` option to specify a message
  giving the reason for the failure.

* The :module:`FindPkgConfig` module :command:`pkg_search_module` macro
  now defines a ``<prefix>_MODULE_NAME`` result variable containing the
  first matching module name.

* The :module:`FindPython3` and :module:`FindPython` modules gained
  options to control which ``ABIs`` will be searched.

* The :module:`FindPython3`, :module:`FindPython2`, and :module:`FindPython`
  modules now support direct specification of artifacts via cache entries.

Autogen
-------

* When using :prop_tgt:`AUTOMOC`, the new :variable:`CMAKE_AUTOMOC_PATH_PREFIX`
  variable or :prop_tgt:`AUTOMOC_PATH_PREFIX` target property may be enabled
  to generate the ``-p`` path prefix
  option for ``moc``.  This ensures that ``moc`` output files are identical
  on different build setups (given, that the headers compiled by ``moc`` are
  in an :command:`include directory <target_include_directories>`).
  Also it ensures that ``moc`` output files will compile correctly when the
  source and/or build directory is a symbolic link.

CTest
-----

* :manual:`ctest(1)` now has the ability to schedule tests based on resource
  requirements for each test. See :ref:`ctest-resource-allocation` for
  details.

* A new test property, :prop_test:`SKIP_REGULAR_EXPRESSION`, has been added.
  This property is similar to :prop_test:`FAIL_REGULAR_EXPRESSION` and
  :prop_test:`PASS_REGULAR_EXPRESSION`, but with the same meaning as
  :prop_test:`SKIP_RETURN_CODE`. This is useful, for example, in cases where
  the user has no control over the return code of the test. For example, in
  Catch2, the return value is the number of assertion failed, therefore it is
  impossible to use it for :prop_test:`SKIP_RETURN_CODE`.

CPack
-----

* :manual:`cpack(1)` learned support for multiple configurations for ``-C``
  option.

* The :cpack_gen:`CPack DEB Generator` is now able to format generic text
  (usually used as the description for multiple CPack generators) according
  to the `Debian Policy Manual`_.  See the
  :variable:`CPACK_PACKAGE_DESCRIPTION_FILE` and
  :variable:`CPACK_DEBIAN_<COMPONENT>_DESCRIPTION` variables.

* The :cpack_gen:`CPack Archive Generator` learned to generate ``.tar.zst``
  packages with Zstandard compression.

.. _`Debian Policy Manual`: https://www.debian.org/doc/debian-policy/ch-controlfields.html#description

Deprecated and Removed Features
===============================

* An explicit deprecation diagnostic was added for policy ``CMP0067``
  (``CMP0066`` and below were already deprecated).
  The :manual:`cmake-policies(7)` manual explains that the OLD behaviors
  of all policies are deprecated and that projects should port to the
  NEW behaviors.

* The :variable:`CMAKE_FIND_PACKAGE_NO_PACKAGE_REGISTRY` variable has been
  deprecated.  Use the :variable:`CMAKE_FIND_USE_PACKAGE_REGISTRY` variable
  instead.

* The :module:`GetPrerequisites` module has been deprecated, as it has been
  superceded by :command:`file(GET_RUNTIME_DEPENDENCIES)`.

* The ``CPACK_INSTALL_SCRIPT`` variable has been deprecated in favor of the
  new, more accurately named :variable:`CPACK_INSTALL_SCRIPTS` variable.

Other Changes
=============

* The :manual:`cmake(1)` ``-C <initial-cache>`` option now evaluates the
  initial cache script with :variable:`CMAKE_SOURCE_DIR` and
  :variable:`CMAKE_BINARY_DIR` set to the top-level source and build trees.

* The :manual:`cmake(1)` ``-E remove_directory`` command-line tool,
  when given the path to a symlink to a directory, now removes just
  the symlink.  It no longer removes content of the linked directory.

* The :manual:`ctest(1)`  ``--build-makeprogram`` command-line option now
  specifies the make program used when configuring a project with the
  :generator:`Ninja` generator or the :ref:`Makefile Generators`.

* The :module:`ExternalProject` module :command:`ExternalProject_Add` command
  has been updated so that ``GIT_SUBMODULES ""`` initializes no submodules.
  See policy :policy:`CMP0097`.

* The :module:`FindGTest` module has been updated to recognize
  MSVC build trees generated by GTest 1.8.1.

* The :command:`project` command no longer strips leading zeros in version
  components.  See policy :policy:`CMP0096`.

* The Qt Compressed Help file is now named ``CMake.qch``, which no longer
  contains the release version in the file name.  When CMake is upgraded
  in-place, the name and location of this file will remain constant.
  Tools such as IDEs, help viewers, etc. should now be able to refer to this
  file at a fixed location that remains valid across CMake upgrades.

* ``RPATH`` entries are properly escaped in the generated CMake scripts
  used for installation.  See policy :policy:`CMP0095`.

* When using :variable:`CMAKE_WINDOWS_EXPORT_ALL_SYMBOLS` on Windows the
  auto-generated exports are now updated only when the object files
  providing the symbols are updated.

Updates
=======

Changes made since CMake 3.16.0 include the following.

3.16.2
------

* CMake 3.16.0 and 3.16.1 processed ``.hh`` files with :prop_tgt:`AUTOMOC`.
  This was a behavior change from CMake 3.15 and below that can break
  existing projects, so it has been reverted as of 3.16.2.

3.16.5
------

* The :module:`FindPython`, :module:`FindPython2`, and :module:`FindPython3`
  modules no longer create cache entries for ``Python{,2,3}_LIBRARY_RELEASE``
  and ``Python{,2,3}_LIBRARY_DEBUG``.  Those values are always computed from
  other results and so should not be cached.  The entries were created by
  CMake 3.16.0 through 3.16.4 but were always ``FORCE``-set and could not
  be meaningfully edited by users.

  Additionally, the modules no longer expose their internal ``_Python*``
  cache entries publicly.  CMake 3.16.0 through 3.16.4 accidentally
  made them visible as advanced cache entries.

3.16.7
------

* Selection of the Objective C or C++ compiler now considers the
  :envvar:`CC` or :envvar:`CXX` environment variable if the
  :envvar:`OBJC` or :envvar:`OBJCXX` environment variable is not set.

* The :module:`FindPkgConfig` module now extracts include directories
  prefixed with ``-isystem`` into the ``*_INCLUDE_DIRS`` variables and
  :prop_tgt:`INTERFACE_INCLUDE_DIRECTORIES` target properties.
  Previously they would be places in ``*_CFLAGS_OTHER`` variables and
  :prop_tgt:`INTERFACE_COMPILE_OPTIONS` target properties.

3.16.9
------

* The default value of :variable:`CMAKE_AUTOMOC_PATH_PREFIX` was changed to
  ``OFF`` because this feature can break existing projects that have
  identically named header files in different include directories.
  This restores compatibility with behavior of CMake 3.15 and below.