Help: Generic language standard and extension variables documentation

Add generic documentation to improve the discoverability of language-specific
ones and to make it possible to refer to them generically from other language
generic documentation.

3 files changed, 75 insertions, 0 deletions

diff --git a/Help/prop_tgt/LANG_EXTENSIONS.rst b/Help/prop_tgt/LANG_EXTENSIONS.rst
new file mode 100644
index 0000000..2add21d
--- /dev/null
+++ b/Help/prop_tgt/LANG_EXTENSIONS.rst
@@ -0,0 +1,23 @@
+<LANG>_EXTENSIONS
+-----------------
+
+The variations are:
+
+* :prop_tgt:`C_EXTENSIONS`
+* :prop_tgt:`CXX_EXTENSIONS`
+* :prop_tgt:`CUDA_EXTENSIONS`
+* :prop_tgt:`HIP_EXTENSIONS`
+* :prop_tgt:`OBJC_EXTENSIONS`
+* :prop_tgt:`OBJCXX_EXTENSIONS`
+
+These properties specify whether compiler-specific extensions are requested.
+
+These properties are initialized by the value of the
+:variable:`CMAKE_<LANG>_EXTENSIONS` variable if it is set when a target is
+created.
+
+For supported CMake versions see the respective pages.
+To control language standard versions see :prop_tgt:`<LANG>_STANDARD`.
+
+See the :manual:`cmake-compile-features(7)` manual for information on
+compile features and a list of supported compilers.
diff --git a/Help/prop_tgt/LANG_STANDARD.rst b/Help/prop_tgt/LANG_STANDARD.rst
new file mode 100644
index 0000000..bd377ec
--- /dev/null
+++ b/Help/prop_tgt/LANG_STANDARD.rst
@@ -0,0 +1,26 @@
+<LANG>_STANDARD
+---------------
+
+The variations are:
+
+* :prop_tgt:`C_STANDARD`
+* :prop_tgt:`CXX_STANDARD`
+* :prop_tgt:`CUDA_STANDARD`
+* :prop_tgt:`HIP_STANDARD`
+* :prop_tgt:`OBJC_STANDARD`
+* :prop_tgt:`OBJCXX_STANDARD`
+
+These properties specify language standard versions which are requested. When a
+newer standard is specified than is supported by the compiler, then it will
+fallback to the latest supported standard. This "decay" behavior may be
+controlled with the :prop_tgt:`<LANG>_STANDARD_REQUIRED` target property.
+
+These properties are initialized by the value of the
+:variable:`CMAKE_<LANG>_STANDARD` variable if it is set when a target is
+created.
+
+For supported values and CMake versions see the respective pages.
+To control compiler-specific extensions see :prop_tgt:`<LANG>_EXTENSIONS`.
+
+See the :manual:`cmake-compile-features(7)` manual for information on
+compile features and a list of supported compilers.
diff --git a/Help/prop_tgt/LANG_STANDARD_REQUIRED.rst b/Help/prop_tgt/LANG_STANDARD_REQUIRED.rst
new file mode 100644
index 0000000..56ecef8
--- /dev/null
+++ b/Help/prop_tgt/LANG_STANDARD_REQUIRED.rst
@@ -0,0 +1,26 @@
+<LANG>_STANDARD_REQUIRED
+------------------------
+
+The variations are:
+
+* :prop_tgt:`C_STANDARD_REQUIRED`
+* :prop_tgt:`CXX_STANDARD_REQUIRED`
+* :prop_tgt:`CUDA_STANDARD_REQUIRED`
+* :prop_tgt:`HIP_STANDARD_REQUIRED`
+* :prop_tgt:`OBJC_STANDARD_REQUIRED`
+* :prop_tgt:`OBJCXX_STANDARD_REQUIRED`
+
+These properties specify whether the value of :prop_tgt:`<LANG>_STANDARD` is a
+requirement. When ``OFF`` or unset, the :prop_tgt:`<LANG>_STANDARD` target
+property is treated as optional and may "decay" to a previous standard if the
+requested is not available.
+
+These properties are initialized by the value of the
+:variable:`CMAKE_<LANG>_STANDARD_REQUIRED` variable if it is set when a target
+is created.
+
+For supported CMake versions see the respective pages.
+To control language standard versions see :prop_tgt:`<LANG>_STANDARD`.
+
+See the :manual:`cmake-compile-features(7)` manual for information on
+compile features and a list of supported compilers.