Merge topic 'features-c++20'

8570dc7f64 Help: Update compiler versions in cmake-compile-features.7.rst
874d3d2948 Help: Add release note for C++ 20 support
7f295b1bd3 Features: Activate C++ 20 support for Clang 5.0+
71cb8ce3a1 Features: Activate C++ 20 support for GNU 8.0+
8f146c4508 Features: Activate C++ 20 support for MSVC 19.12.25835+
7fe580a362 Features: Add infrastructure for C++ 20 language standard
1b328e09a3 Features: Use -std=c++17 for C++ 17 on Clang 5.0+
0bc3e5788a Features: Use -std=c++17 for C++ 17 on GNU 8.0+

Acked-by: Kitware Robot <kwrobot@kitware.com>
Merge-request: !1892

4 files changed, 15 insertions, 6 deletions

diff --git a/Help/manual/cmake-compile-features.7.rst b/Help/manual/cmake-compile-features.7.rst
index e9495c6..634da10 100644
--- a/Help/manual/cmake-compile-features.7.rst
+++ b/Help/manual/cmake-compile-features.7.rst
@@ -331,9 +331,9 @@ and :prop_gbl:`compile features <CMAKE_CXX_KNOWN_FEATURES>` available from
 the following :variable:`compiler ids <CMAKE_<LANG>_COMPILER_ID>` as of the
 versions specified for each:
 
-* ``AppleClang``: Apple Clang for Xcode versions 4.4 though 6.2.
-* ``Clang``: Clang compiler versions 2.9 through 3.4.
-* ``GNU``: GNU compiler versions 4.4 through 5.0.
+* ``AppleClang``: Apple Clang for Xcode versions 4.4 though 9.2.
+* ``Clang``: Clang compiler versions 2.9 through 6.0.
+* ``GNU``: GNU compiler versions 4.4 through 8.0.
 * ``MSVC``: Microsoft Visual Studio versions 2010 through 2017.
 * ``SunPro``: Oracle SolarisStudio versions 12.4 through 12.6.
 * ``Intel``: Intel compiler versions 12.1 through 17.0.
@@ -344,7 +344,7 @@ the following :variable:`compiler ids <CMAKE_<LANG>_COMPILER_ID>` as of the
 versions specified for each:
 
 * all compilers and versions listed above for C++.
-* ``GNU``: GNU compiler versions 3.4 through 5.0.
+* ``GNU``: GNU compiler versions 3.4 through 8.0.
 
 CMake is currently aware of the :prop_tgt:`C++ standards <CXX_STANDARD>` and
 their associated meta-features (e.g. ``cxx_std_11``) available from the
@@ -366,4 +366,4 @@ CMake is currently aware of the :prop_tgt:`CUDA standards <CUDA_STANDARD>`
 from the following :variable:`compiler ids <CMAKE_<LANG>_COMPILER_ID>` as of the
 versions specified for each:
 
-* ``NVIDIA``: NVIDIA nvcc compiler 7.5 though 8.0.
+* ``NVIDIA``: NVIDIA nvcc compiler 7.5 though 9.1.
diff --git a/Help/prop_gbl/CMAKE_CXX_KNOWN_FEATURES.rst b/Help/prop_gbl/CMAKE_CXX_KNOWN_FEATURES.rst
index 2ad8157..262a67c 100644
--- a/Help/prop_gbl/CMAKE_CXX_KNOWN_FEATURES.rst
+++ b/Help/prop_gbl/CMAKE_CXX_KNOWN_FEATURES.rst
@@ -26,6 +26,9 @@ The features known to this version of CMake are:
 ``cxx_std_17``
   Compiler mode is aware of C++ 17.
 
+``cxx_std_20``
+  Compiler mode is aware of C++ 20.
+
 ``cxx_aggregate_default_initializers``
   Aggregate default initializers, as defined in N3605_.
 
diff --git a/Help/prop_tgt/CXX_STANDARD.rst b/Help/prop_tgt/CXX_STANDARD.rst
index 0762033..ccc0147 100644
--- a/Help/prop_tgt/CXX_STANDARD.rst
+++ b/Help/prop_tgt/CXX_STANDARD.rst
@@ -9,7 +9,7 @@ flag such as ``-std=gnu++11`` to the compile line.  For compilers that
 have no notion of a standard level, such as Microsoft Visual C++ before
 2015 Update 3, this has no effect.
 
-Supported values are ``98``, ``11``, ``14``, and ``17``.
+Supported values are ``98``, ``11``, ``14``, ``17``, and ``20``.
 
 If the value requested does not result in a compile flag being added for
 the compiler in use, a previous standard flag will be added instead.  This
diff --git a/Help/release/dev/features-c++20.rst b/Help/release/dev/features-c++20.rst
new file mode 100644
index 0000000..f7d050b
--- /dev/null
+++ b/Help/release/dev/features-c++20.rst
@@ -0,0 +1,6 @@
+features-c++20
+--------------
+
+* The :manual:`Compile Features <cmake-compile-features(7)>` functionality
+  is now aware of C++ 20.  No specific features are yet enumerated besides
+  the ``cxx_std_20`` meta-feature.