CMake 3.15.0-rc1 is ready for testing

I am proud to announce the first CMake 3.15 release candidate.
https://cmake.org/download/

Documentation is available at:
https://cmake.org/cmake/help/v3.15

Release notes appear below and are also published at
https://cmake.org/cmake/help/v3.15/release/3.15.html

Some of the more significant changes in CMake 3.15 are:

• The “CMAKE_MSVC_RUNTIME_LIBRARY” variable and
  “MSVC_RUNTIME_LIBRARY” target property were introduced to select the
  runtime library used by compilers targeting the MSVC ABI. See policy
  “CMP0091”.
• With MSVC-like compilers the value of “CMAKE__FLAGS” no
  longer contains warning flags like “/W3” by default. See policy
  “CMP0092”.
• The “Clang” compiler variant on Windows that targets the MSVC ABI
  but has a GNU-like command line is now supported.
• Preliminary support for the “Swift” language was added to the
  “Ninja” generator.
• The “$<COMPILE_LANG_AND_ID:…>” generator expression was
  introduced to allow specification of compile options for target
  files based on the “CMAKE__COMPILER_ID” and “LANGUAGE” of each
  source file.
• The “generator expressions” “C_COMPILER_ID”, “CXX_COMPILER_ID”,
  “CUDA_COMPILER_ID”, “Fortran_COMPILER_ID”, “COMPILE_LANGUAGE”,
  “COMPILE_LANG_AND_ID”, and “PLATFORM_ID” learned to support matching
  one value from a comma-separated list.
• The “CMAKE_FIND_PACKAGE_PREFER_CONFIG” variable was added to tell
  “find_package()” calls to look for a package configuration file
  first even if a find module is available.
• The “PUBLIC_HEADER” and “PRIVATE_HEADER” properties may now be set
  on Interface Libraries. The headers specified by those properties
  can be installed using the “install(TARGETS)” command by passing the
  “PUBLIC_HEADER” and “PRIVATE_HEADER” arguments respectively.
• The “CMAKE_VS_JUST_MY_CODE_DEBUGGING” variable and
  “VS_JUST_MY_CODE_DEBUGGING” target property were added to enable the
  Just My Code feature of the Visual Studio Debugger when compiling
  with MSVC cl 19.05 and higher.
• The “FindBoost” module was reworked to expose a more consistent
  user experience between its “Config” and “Module” modes and with
  other find modules in general.
• The “message()” command learned new types: “NOTICE”, “VERBOSE”,
  “DEBUG” and “TRACE”.
• The “export(PACKAGE)” command now does nothing unless enabled via
  “CMAKE_EXPORT_PACKAGE_REGISTRY”. See policy “CMP0090”.

Changes made since CMake 3.14 include the following.


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


Generators
----------

* The "Xcode" generator now supports per-target schemes. See the
  "CMAKE_XCODE_GENERATE_SCHEME" variable and "XCODE_GENERATE_SCHEME"
  target property.

* The "Green Hills MULTI" generator has been updated:

  * It now supports the "add_custom_command()" and
    "add_custom_target()" commands.

  * It is now available on Linux.


Languages
---------

* Preliminary support for the "Swift" language was added to the
  "Ninja" generator:

  * Use the "SWIFTC" environment variable to specify a compiler.

  * The "Swift_DEPENDENCIES_FILE" target property and
    "Swift_DEPENDENCIES_FILE" source file property were added to
    customize dependency files.

  * The "Swift_MODULE_NAME" target property was added to customize
    the Swift module name.

  * The "Swift_DIAGNOSTICS_FILE" source property was added to
    indicate where to write the serialised Swift diagnostics.

  The Swift support is experimental, not considered stable, and may
  change in future releases of CMake.


Compilers
---------

* The "Clang" compiler variant on Windows that targets the MSVC ABI
  but has a GNU-like command line is now supported.

* Support for the Clang-based ARM compiler was added with compiler
  id "ARMClang".

* Support was added for the IAR compiler architectures Renesas RX,
  RL78, RH850 and Texas Instruments MSP430.

* Support was added for the IAR compilers built for Linux (IAR
  BuildLx).


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

* The "CMAKE_GENERATOR" environment variable was added to specify a
  default generator to use when "cmake(1)" is run without a "-G"
  option.  Additionally, environment variables
  "CMAKE_GENERATOR_PLATFORM", "CMAKE_GENERATOR_TOOLSET", and
  "CMAKE_GENERATOR_INSTANCE" were created to configure the generator.

* The "cmake(1)" "--build" tool "--target" parameter gained support
  for multiple targets, e.g. "cmake --build . --target Library1
  Library2". It now also has a short form "-t" alias, e.g. "cmake
  --build . -t Library1 Library2".

* The "cmake(1)" command gained a new "--install" option. This may
  be used after building a project to run installation without using
  the generated build system or the native build tool.

* The "cmake(1)" command learned a new CLI option "--loglevel".

* The "cmake(1)" "-E remove_directory" command-line tool learned to
  support removing multiple directories.

* The "cmake(1)" "-E tar" tool has been improved:

  * It now continues adding files to an archive even if some of the
    files are not readable.  This behavior is more consistent with the
    classic "tar" tool.

  * It now parses all flags, and if an invalid flag was provided, a
    warning is issued.

  * It now displays an error if no action flag was specified, along
    with a list of possible actions: "t" (list), "c" (create) or "x"
    (extract).

  * It now supports extracting ("-x") or listing ("-t") only
    specific files or directories.

  * It now supports Zstandard compression with a "--zstd" option.
    Zstandard was designed to give a compression ratio comparable to
    that of the DEFLATE (zip) algorithm, but faster, especially for
    decompression.


Commands
--------

* The "add_custom_command()" and "add_custom_target()" commands
  gained a new "JOB_POOL" option that works with the "Ninja" generator
  to set the pool variable on the build statement.

* The "add_library()" command "ALIAS" option learned to support
  import libraries of the "UNKNOWN" type.

* The "cmake_parse_arguments()" command gained an additional
  "_KEYWORDS_MISSING_VALUES" output variable to report keyword
  arguments that were given by the caller with no values.

* The "execute_process()" command gained a "COMMAND_ECHO" option and
  supporting "CMAKE_EXECUTE_PROCESS_COMMAND_ECHO" variable to enable
  echoing of the command-line string before execution.

* The "file(INSTALL)" command learned a new argument,
  "FOLLOW_SYMLINK_CHAIN", which can be used to recursively resolve and
  install symlinks.

* "list()" learned new sub-commands: "PREPEND", "POP_FRONT" and
  "POP_BACK".

* The "message()" command learned new types: "NOTICE", "VERBOSE",
  "DEBUG" and "TRACE".

* The "string()" learned a new sub-command "REPEAT".


Variables
---------

* The "CMAKE_CROSSCOMPILING_EMULATOR" variable and corresponding
  "CROSSCOMPILING_EMULATOR" target property learned to support
  arguments to the emulator.

* The "CMAKE_FIND_PACKAGE_PREFER_CONFIG" variable was added to tell
  "find_package()" calls to look for a package configuration file
  first even if a find module is available.

* The "CMAKE_FRAMEWORK" variable was added to initialize the
  "FRAMEWORK" property on all targets.

* The "CMAKE_VS_JUST_MY_CODE_DEBUGGING" variable and
  "VS_JUST_MY_CODE_DEBUGGING" target property were added to enable the
  Just My Code feature of the Visual Studio Debugger when compiling
  with MSVC cl 19.05 and higher.

* The "CMAKE_MSVC_RUNTIME_LIBRARY" variable and
  "MSVC_RUNTIME_LIBRARY" target property were introduced to select the
  runtime library used by compilers targeting the MSVC ABI. See policy
  "CMP0091".

* The "CMAKE_PROJECT_INCLUDE" and "CMAKE_PROJECT_INCLUDE_BEFORE"
  variables were added to allow injection of custom code at the sites
  of "project()" calls without knowing the project name a priori.


Properties
----------

* The "ADDITIONAL_CLEAN_FILES" target property and
  "ADDITIONAL_CLEAN_FILES" directory property were added. They allow
  to register additional files that should be removed during the clean
  stage.

* The "PUBLIC_HEADER" and "PRIVATE_HEADER" properties may now be set
  on Interface Libraries. The headers specified by those properties
  can be installed using the "install(TARGETS)" command by passing the
  "PUBLIC_HEADER" and "PRIVATE_HEADER" arguments respectively.

* The "VS_PACKAGE_REFERENCES" target property was added to tell
  Visual Studio Generators to add references to "nuget" packages.

* The "VS_PROJECT_IMPORT" target property was added to allow managed
  Visual Studio project files to import external ".props" files.

* The "VS_NO_SOLUTION_DEPLOY" target property was added to tell
  Visual Studio Generators whether to deploy an artifact to the WinCE
  or Windows Phone target device.


Modules
-------

* The "FindBoost" module was reworked to expose a more consistent
  user experience between its “Config” and “Module” modes and with
  other find modules in general.

  * A new imported target "Boost::headers" is now defined (same as
    "Boost::boost").

  * New output variables "Boost_VERSION_MACRO",
    "Boost_VERSION_MAJOR", "Boost_VERSION_MINOR",
    "Boost_VERSION_PATCH", and "Boost_VERSION_COUNT" were added.

  * The "QUIET" argument passed to "find_package()" is no longer
    ignored in config mode.  Note that the CMake package shipped with
    Boost "1.70.0" ignores the "QUIET" argument passed to
    "find_package()".  This is fixed in the next Boost release.

  * The input switch "Boost_DETAILED_FAILURE_MSG" was removed.

  * "Boost_VERSION" now reports the version in "x.y.z" format in
    module mode.  See policy "CMP0093".

* The "FindCups" module now provides imported targets.

* The "FindEnvModules" module was added to use Lua- and TCL-based
  environment modules in CTest Scripts.

* The "FindGLEW" module now provides an interface more consistent
  with what upstream GLEW provides in its own CMake package files.

* The "FindPkgConfig" now populates "INTERFACE_LINK_OPTIONS"
  property of imported targets with other (non-library) linker flags.

* The "FindPostgreSQL" module learned to find debug and release
  variants separately.

* Modules "FindPython3", "FindPython2" and "FindPython" gained
  additional lookup strategies and controls, and a new default. See
  policy "CMP0094".

* Modules "FindPython", "FindPython2" and "FindPython3" gain a new
  target (respectively "Python::Module", "Python2::Module" and
  "Python3::Module") which can be used to develop Python modules.

* Modules "FindPython3", "FindPython2" and "FindPython" gain
  capability to control how virtual environments are handled.

* The "UseSWIG" module learned to manage alternate library names by
  passing "-interface       " for "python" language or
  "-dllimport       " for "CSharp" language to the "SWIG"
  compiler.


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

* The "generator expressions" "C_COMPILER_ID", "CXX_COMPILER_ID",
  "CUDA_COMPILER_ID", "Fortran_COMPILER_ID", "COMPILE_LANGUAGE",
  "COMPILE_LANG_AND_ID", and "PLATFORM_ID" learned to support matching
  one value from a comma-separated list.


CTest
-----

* The "ctest_submit()" command learned a new option: "BUILD_ID".
  This can be used to store the ID assigned to this build by CDash to
  a variable.

* The "ctest_update()" command learned to honor a new variable:
  "CTEST_UPDATE_VERSION_OVERRIDE". This can be used to specify the
  current version of your source tree rather than using the update
  command to discover the current version that is checked out.

CPack
-----

* The "CPack IFW Generator" gained a new
  "CPACK_IFW_PACKAGE_STYLE_SHEET" variable to customize the installer
  stylesheet.

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

* The "cmake-server(7)" mode has been deprecated and will be removed
  from a future version of CMake.  Please port clients to use the
  "cmake-file-api(7)" instead.

* The "ADDITIONAL_MAKE_CLEAN_FILES" directory property is now
  deprecated.  Use the "ADDITIONAL_CLEAN_FILES" directory property
  instead.

* The variable "CMAKE_AUTOMOC_RELAXED_MODE" is considered
  deprecated. Support still exists but will be removed in future
  versions.

* The "export(PACKAGE)" command now does nothing unless enabled via
  "CMAKE_EXPORT_PACKAGE_REGISTRY". See policy "CMP0090".

* The "Xcode" generator now requires at least Xcode 5.

* An explicit deprecation diagnostic was added for policy "CMP0066"
  ("CMP0065" and below were already deprecated). The "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
=============

* CMake learned how to compile C++14 with the IBM AIX XL compiler
  and the SunPro compiler and to compile C++20 with the AppleClang
  compiler.

* With MSVC-like compilers the value of "CMAKE__FLAGS" no
  longer contains warning flags like "/W3" by default. See policy
  "CMP0092".

* IBM Clang-based XL compilers that define "__ibmxl__" now use the
  compiler id "XLClang" instead of "XL".  See policy "CMP0089".

* The "file(REMOVE)" and "file(REMOVE_RECURSE)" commands were
  changed to ignore empty arguments with a warning instead of treating
  them as a relative path and removing the contents of the current
  directory.