CMake 3.18 Release Notes
************************

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Changes made since CMake 3.17 include the following.

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

Languages
---------

* The ``CUDA`` language can now be compiled using Clang on non-Windows
  platforms. Separable compilation is not yet supported on any platform.

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

* :manual:`cmake(1)` gained support for profiling of CMake scripts through
  the parameters ``--profiling-output`` and ``--profiling-format``.

* :manual:`cmake(1)` gained a ``cat`` command line
  option that can be used to concatenate files and print them
  on standard output.

Commands
--------

* The :command:`add_library` and :command:`add_executable` commands
  learned to create :ref:`Alias Targets` referencing non-``GLOBAL``
  :ref:`Imported Targets`.

* The :command:`cmake_language()` command was added for meta-operations on
  scripted or built-in commands, starting with a mode to ``CALL`` other
  commands, and ``EVAL CODE`` to inplace evaluate a CMake script.

* The :command:`execute_process` command gained the ``ECHO_OUTPUT_VARIABLE``
  and ``ECHO_ERROR_VARIABLE`` options.

* The :command:`export` command now raise an error if used multiple times with
  same ``FILE`` without ``APPEND``. See policy :policy:`CMP0103`.

* The :command:`file` command gained the ``ARCHIVE_CREATE`` and
  ``ARCHIVE_EXTRACT`` subcommands to expose the :manual:`cmake(1)` ``-E tar``
  functionality to CMake scripting code.

* The :command:`file(CONFIGURE)` subcommand was created in order to replicate
  the :command:`configure_file` functionality without resorting to a
  pre-existing file on disk as input. The content is instead passed as a
  string.

* The :command:`file(UPLOAD)` command gained ``TLS_VERIFY`` and ``TLS_CAINFO``
  options to control server certificate verification.

* The :command:`find_program`, :command:`find_library`, :command:`find_path`
  and :command:`find_file` commands gained a new ``REQUIRED`` option that will
  stop processing with an error message if nothing is found.

* The :command:`get_property` command with ``SOURCE`` scope gained the
  ``DIRECTORY`` and ``TARGET_DIRECTORY`` options to get a property
  from the provided directory scope.

* The :command:`get_source_file_property` command gained the ``DIRECTORY``
  and ``TARGET_DIRECTORY`` options to get a property from the
  provided directory scope.

* The :command:`list` operation ``SORT`` gained the ``NATURAL`` sort
  option to sort using natural order (see ``strverscmp(3)`` manual).

* The :command:`set_property` command with the ``SOURCE`` scope gained the
  ``DIRECTORY`` and ``TARGET_DIRECTORY`` options to set properties
  in the provided directory scopes.

* The :command:`set_source_files_properties` command gained the ``DIRECTORY``
  and ``TARGET_DIRECTORY`` options to set properties in the provided
  directory scopes.

* The :command:`string` command learned a new ``HEX`` sub-command, which
  converts strings into their hexadecimal representation.

Variables
---------

* A :variable:`CMAKE_CUDA_ARCHITECTURES` variable was added to specify
  CUDA output architectures.  Users are encouraged to use this instead of
  specifying options manually, as this approach is compiler-agnostic.
  The variable is initialized automatically when
  :variable:`CMAKE_CUDA_COMPILER_ID <CMAKE_<LANG>_COMPILER_ID>` is ``NVIDIA``.
  The variable is used to initialize the new :prop_tgt:`CUDA_ARCHITECTURES`
  target property.  See policy :policy:`CMP0104`.

* The :variable:`CMAKE_PCH_WARN_INVALID` variable was added to initialize the
  :prop_tgt:`PCH_WARN_INVALID` target property to allow the removal of the
  precompiled header invalid warning.

Properties
----------

* The :prop_tgt:`CUDA_ARCHITECTURES` target property was added to specify
  CUDA output architectures. Users are encouraged to use this instead of
  specifying options manually, as this approach is compiler-agnostic.
  The property is initialized by the new :variable:`CMAKE_CUDA_ARCHITECTURES`
  variable.  See policy :policy:`CMP0104`.

* The :prop_tgt:`Fortran_PREPROCESS` target property and
  :prop_sf:`Fortran_PREPROCESS` source-file property were added to
  control preprocessing of Fortran source files.

* The :prop_tgt:`FRAMEWORK_MULTI_CONFIG_POSTFIX_<CONFIG>` target property
  and associated :variable:`CMAKE_FRAMEWORK_MULTI_CONFIG_POSTFIX_<CONFIG>`
  variable were created to allow adding a postfix to the name of a
  framework file name when using a multi-config generator.

* The :prop_sf:`OBJECT_OUTPUTS` source file property now supports
  :manual:`generator expressions <cmake-generator-expressions(7)>`.

* The :prop_tgt:`PCH_WARN_INVALID` target property was added to allow the
  removal of the precompiled header invalid warning.

* The :prop_tgt:`UNITY_BUILD_MODE` target property was added to tell
  generators which algorithm to use for grouping included source
  files.

* The :prop_tgt:`VS_SOURCE_SETTINGS_<tool>` target property was added
  to tell :ref:`Visual Studio Generators` for VS 2010 and above to add
  metadata to non-built source files using ``<tool>``.

* The :prop_sf:`VS_SETTINGS` source file property was added to tell
  :ref:`Visual Studio Generators` for VS 2010 and above to add
  metadata to a non-built source file.

* The :prop_tgt:`VS_PLATFORM_TOOLSET` target property was added to tell
  :ref:`Visual Studio Generators` for VS 2010 and above to override
  the platform toolset.

* The :prop_tgt:`VS_SOLUTION_DEPLOY` target property was added to tell
  :ref:`Visual Studio Generators` for VS 2010 and above to mark a
  target for deployment even when not building for Windows Phone/Store/CE.

Modules
-------

* The :module:`CheckLinkerFlag` module has been added to provide a
  facility to check validity of link flags.

* The :module:`ExternalProject` module :command:`ExternalProject_Add` command
  gained a new ``GIT_REMOTE_UPDATE_STRATEGY`` keyword.  This can be used to
  specify how failed rebase operations during a git update should be handled.
  The ``CMAKE_EP_GIT_REMOTE_UPDATE_STRATEGY`` variable was also added as a
  global default and is honored by both the :module:`ExternalProject` and
  :module:`FetchContent` modules.

* The :module:`FetchContent` module :command:`FetchContent_Declare` command
  now supports a ``SOURCE_SUBDIR`` option.  It can be used to direct
  :command:`FetchContent_MakeAvailable` to look in a different location
  for the ``CMakeLists.txt`` file.

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

* The :module:`FindCUDAToolkit` module:

  * gained the variable
    ``CUDAToolkit_LIBRARY_ROOT``, which is the directory containing the
    ``nvvm`` directory and ``version.txt``.

  * uses toolkit and library root found during ``CUDA`` compiler detection.

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

* The :module:`FindPython3`, :module:`FindPython2` and :module:`FindPython`
  modules:

  * gained the possibility to create per-artifact cache variables for
    interactive editing in :manual:`cmake-gui(1)` and :manual:`ccmake(1)`.

  * gained sub-components ``Development.Module`` and
    ``Development.Embed`` under the ``Development`` component.

  * gained the capability to specify which Python implementations to find,
    including ``IronPython`` and ``PyPy``.

* The :module:`FindRuby` module input and output variables were all renamed
  from ``RUBY_`` to ``Ruby_`` for consistency with other find modules.
  Input variables of the old case will be honored if provided, and output
  variables of the old case are always provided.

* The :module:`FindSWIG` module now accepts target languages as  ``COMPONENTS``
  and ``OPTIONAL_COMPONENTS`` arguments to ``find_package``.

* The :module:`GoogleTest` module :command:`gtest_discover_tests` command:

  * gained a new ``DISCOVERY_MODE`` option to control when the test
    discovery step is run.  It offers a new ``PRE_TEST`` setting to
    run the discovery at test time instead of build time.  A new
    ``CMAKE_GTEST_DISCOVER_TESTS_DISCOVERY_MODE`` variable can be used
    to change the default globally.

  * gained a new optional parameter ``XML_OUTPUT_DIR``. When set the
    JUnit XML test results are stored in that directory.

* The :module:`FindLibXslt` module now provides imported targets.

* The :module:`UseSWIG` module now supports Fortran as a target language if
  the ``SWIG_EXECUTABLE`` is SWIG-Fortran_.

.. _`SWIG-Fortran`: https://github.com/swig-fortran/swig

Generator Expressions
---------------------

* The ``$<DEVICE_LINK:...>`` and ``$<HOST_LINK:...>``
  :manual:`generator expressions <cmake-generator-expressions(7)>` were added
  to manage device and host link steps.

* The ``$<LINK_LANGUAGE:...>`` and ``$<LINK_LANG_AND_ID:...>``
  :manual:`generator expressions <cmake-generator-expressions(7)>` were added.

CTest
-----

* :manual:`ctest(1)` gained a new :variable:`CTEST_RESOURCE_SPEC_FILE`
  variable, which can be used to specify a
  :ref:`resource specification file <ctest-resource-specification-file>`.

* :manual:`ctest(1)` gained a ``--stop-on-failure`` option,
  which can be used to stop running the tests once one has failed.

* The :command:`ctest_test` command gained a ``STOP_ON_FAILURE`` option
  which can be used to stop running the tests once one has failed.

* The :module:`CTestCoverageCollectGCOV` module
  :command:`ctest_coverage_collect_gcov` command gained a
  ``TARBALL_COMPRESSION`` option to control compression of the
  tarball of collected results.

CPack
-----

* The :cpack_gen:`CPack Archive Generator`'s ``TXZ`` format learned the
  :variable:`CPACK_ARCHIVE_THREADS` variable to enable parallel compression.
  Requires support in the ``liblzma`` used by CMake.

* The :cpack_gen:`CPack NSIS Generator` gained a new variable
  :variable:`CPACK_NSIS_MANIFEST_DPI_AWARE` to declare that the
  installer is DPI-aware.

* The :cpack_gen:`CPack RPM Generator` gained
  :variable:`CPACK_RPM_PRE_TRANS_SCRIPT_FILE` and
  :variable:`CPACK_RPM_POST_TRANS_SCRIPT_FILE`
  variables to specify pre- and post-transaction scripts.

Other
-----

* :manual:`cmake-gui(1)` now populates its generator selection
  widget default value from the :envvar:`CMAKE_GENERATOR` environment
  variable.  Additionally, environment variables
  :envvar:`CMAKE_GENERATOR_PLATFORM` and :envvar:`CMAKE_GENERATOR_TOOLSET`
  are used to populate their respective widget defaults.

* :manual:`ccmake(1)` learned to read a :envvar:`CCMAKE_COLORS`
  environment variable to customize colors.

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

* The :module:`Documentation` module has been deprecated via
  :policy:`CMP0106`. This module was essentially VTK code that CMake should
  not be shipping anymore.

* An explicit deprecation diagnostic was added for policy ``CMP0070``
  and policy ``CMP0071`` (``CMP0069`` 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.

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

* On Windows, the :generator:`Ninja` and :generator:`Ninja Multi-Config`
  generators, when a compiler is not explicitly specified, now select
  the first compiler (of any name) found in directories listed by the
  ``PATH`` environment variable.

* The :prop_tgt:`LINK_OPTIONS` and :prop_tgt:`INTERFACE_LINK_OPTIONS` target
  properties are now used for the device link step.
  See policy :policy:`CMP0105`.

* Creation of an ``ALIAS`` target overwriting an existing target now raises an
  error. See policy :policy:`CMP0107`.

* Linking a target to itself through an alias now raises an error.
  See policy :policy:`CMP0108`.

* The :module:`FindPackageHandleStandardArgs` module option ``REQUIRED_VARS``
  is now optional if ``HANDLE_COMPONENTS`` is specified.

* The :command:`source_group` command now also recognizes forward slashes
  as subgroup delimiters, not just backslashes.

* :manual:`ctest(1)` now logs environment variables that it sets for each test,
  either due to the :prop_test:`ENVIRONMENT` property or the
  :ref:`resource allocation <ctest-resource-allocation>` feature, and submits
  this log to CDash. It does not log environment variables that were set
  outside of CTest.

* When building CMake itself from source and not using a system-provided
  libcurl, HTTP/2 support is now enabled for commands supporting
  network communication via ``http(s)``, such as :command:`file(DOWNLOAD)`,
  :command:`file(UPLOAD)`, and :command:`ctest_submit`.
  The precompiled binaries provided on ``cmake.org`` now support HTTP/2.

* The :manual:`cmake-file-api(7)` "codemodel" version 2 ``version`` field has
  been updated to 2.1.

* The :manual:`cmake-file-api(7)` "codemodel" version 2 "target" object gained
  a new ``precompileHeaders`` field in the ``compileGroups`` objects.
