Merge topic 'objc-standard-docs' into release-3.16

665954fa8d ObjC: Document ObjC/ObjCXX standard properties / variables

Acked-by: Kitware Robot <kwrobot@kitware.com>
Merge-request: !4031

6 files changed, 150 insertions, 0 deletions

diff --git a/Help/prop_tgt/OBJCXX_EXTENSIONS.rst b/Help/prop_tgt/OBJCXX_EXTENSIONS.rst
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+OBJCXX_EXTENSIONS
+-----------------
+
+Boolean specifying whether compiler specific extensions are requested.
+
+This property specifies whether compiler specific extensions should be
+used.  For some compilers, this results in adding a flag such
+as ``-std=gnu++11`` instead of ``-std=c++11`` to the compile line.  This
+property is ``ON`` by default. The basic ObjC++ standard level is
+controlled by the :prop_tgt:`OBJCXX_STANDARD` target property.
+
+See the :manual:`cmake-compile-features(7)` manual for information on
+compile features and a list of supported compilers.
+
+If the property is not set, and the project has set the :prop_tgt:`CXX_EXTENSIONS`,
+the value of :prop_tgt:`CXX_EXTENSIONS` is set for :prop_tgt:`OBJCXX_EXTENSIONS`.
+
+This property is initialized by the value of
+the :variable:`CMAKE_OBJCXX_EXTENSIONS` variable if it is set when a target
+is created.
diff --git a/Help/prop_tgt/OBJCXX_STANDARD.rst b/Help/prop_tgt/OBJCXX_STANDARD.rst
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+OBJCXX_STANDARD
+---------------
+
+The ObjC++ standard whose features are requested to build this target.
+
+This property specifies the ObjC++ standard whose features are requested
+to build this target.  For some compilers, this results in adding a
+flag such as ``-std=gnu++11`` to the compile line.
+
+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
+means that using:
+
+.. code-block:: cmake
+
+  set_property(TARGET tgt PROPERTY OBJCXX_STANDARD 11)
+
+with a compiler which does not support ``-std=gnu++11`` or an equivalent
+flag will not result in an error or warning, but will instead add the
+``-std=gnu++98`` flag if supported.  This "decay" behavior may be controlled
+with the :prop_tgt:`OBJCXX_STANDARD_REQUIRED` target property.
+Additionally, the :prop_tgt:`OBJCXX_EXTENSIONS` target property may be used to
+control whether compiler-specific extensions are enabled on a per-target basis.
+
+If the property is not set, and the project has set the :prop_tgt:`CXX_STANDARD`,
+the value of :prop_tgt:`CXX_STANDARD` is set for :prop_tgt:`OBJCXX_STANDARD`.
+
+See the :manual:`cmake-compile-features(7)` manual for information on
+compile features and a list of supported compilers.
+
+This property is initialized by the value of
+the :variable:`CMAKE_OBJCXX_STANDARD` variable if it is set when a target
+is created.
diff --git a/Help/prop_tgt/OBJCXX_STANDARD_REQUIRED.rst b/Help/prop_tgt/OBJCXX_STANDARD_REQUIRED.rst
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+OBJCXX_STANDARD_REQUIRED
+------------------------
+
+Boolean describing whether the value of :prop_tgt:`OBJCXX_STANDARD` is a requirement.
+
+If this property is set to ``ON``, then the value of the
+:prop_tgt:`OBJCXX_STANDARD` target property is treated as a requirement.  If this
+property is ``OFF`` or unset, the :prop_tgt:`OBJCXX_STANDARD` target property is
+treated as optional and may "decay" to a previous standard if the requested is
+not available.
+
+If the property is not set, and the project has set the :prop_tgt:`CXX_STANDARD_REQUIRED`,
+the value of :prop_tgt:`CXX_STANDARD_REQUIRED` is set for :prop_tgt:`OBJCXX_STANDARD_REQUIRED`.
+
+See the :manual:`cmake-compile-features(7)` manual for information on
+compile features and a list of supported compilers.
+
+This property is initialized by the value of
+the :variable:`CMAKE_OBJCXX_STANDARD_REQUIRED` variable if it is set when a
+target is created.
diff --git a/Help/prop_tgt/OBJC_EXTENSIONS.rst b/Help/prop_tgt/OBJC_EXTENSIONS.rst
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index 0000000..2de9e48
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+++ b/Help/prop_tgt/OBJC_EXTENSIONS.rst
@@ -0,0 +1,20 @@
+OBJC_EXTENSIONS
+---------------
+
+Boolean specifying whether compiler specific extensions are requested.
+
+This property specifies whether compiler specific extensions should be
+used.  For some compilers, this results in adding a flag such
+as ``-std=gnu11`` instead of ``-std=c11`` to the compile line.  This
+property is ``ON`` by default. The basic OBJC standard level is
+controlled by the :prop_tgt:`OBJC_STANDARD` target property.
+
+If the property is not set, and the project has set the :prop_tgt:`C_EXTENSIONS`,
+the value of :prop_tgt:`C_EXTENSIONS` is set for :prop_tgt:`OBJC_EXTENSIONS`.
+
+See the :manual:`cmake-compile-features(7)` manual for information on
+compile features and a list of supported compilers.
+
+This property is initialized by the value of
+the :variable:`CMAKE_OBJC_EXTENSIONS` variable if it is set when a target
+is created.
diff --git a/Help/prop_tgt/OBJC_STANDARD.rst b/Help/prop_tgt/OBJC_STANDARD.rst
new file mode 100644
index 0000000..d1e1b24
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@@ -0,0 +1,35 @@
+OBJC_STANDARD
+-------------
+
+The OBJC standard whose features are requested to build this target.
+
+This property specifies the OBJC standard whose features are requested
+to build this target.  For some compilers, this results in adding a
+flag such as ``-std=gnu11`` to the compile line.
+
+Supported values are ``90``, ``99`` and ``11``.
+
+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
+means that using:
+
+.. code-block:: cmake
+
+  set_property(TARGET tgt PROPERTY OBJC_STANDARD 11)
+
+with a compiler which does not support ``-std=gnu11`` or an equivalent
+flag will not result in an error or warning, but will instead add the
+``-std=gnu99`` or ``-std=gnu90`` flag if supported.  This "decay" behavior may
+be controlled with the :prop_tgt:`OBJC_STANDARD_REQUIRED` target property.
+Additionally, the :prop_tgt:`OBJC_EXTENSIONS` target property may be used to
+control whether compiler-specific extensions are enabled on a per-target basis.
+
+If the property is not set, and the project has set the :prop_tgt:`C_STANDARD`,
+the value of :prop_tgt:`C_STANDARD` is set for :prop_tgt:`OBJC_STANDARD`.
+
+See the :manual:`cmake-compile-features(7)` manual for information on
+compile features and a list of supported compilers.
+
+This property is initialized by the value of
+the :variable:`CMAKE_OBJC_STANDARD` variable if it is set when a target
+is created.
diff --git a/Help/prop_tgt/OBJC_STANDARD_REQUIRED.rst b/Help/prop_tgt/OBJC_STANDARD_REQUIRED.rst
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+OBJC_STANDARD_REQUIRED
+----------------------
+
+Boolean describing whether the value of :prop_tgt:`OBJC_STANDARD` is a requirement.
+
+If this property is set to ``ON``, then the value of the
+:prop_tgt:`OBJC_STANDARD` target property is treated as a requirement.  If this
+property is ``OFF`` or unset, the :prop_tgt:`OBJC_STANDARD` target property is
+treated as optional and may "decay" to a previous standard if the requested is
+not available.
+
+If the property is not set, and the project has set the :prop_tgt:`C_STANDARD_REQUIRED`,
+the value of :prop_tgt:`C_STANDARD_REQUIRED` is set for :prop_tgt:`OBJC_STANDARD_REQUIRED`.
+
+See the :manual:`cmake-compile-features(7)` manual for information on
+compile features and a list of supported compilers.
+
+This property is initialized by the value of
+the :variable:`CMAKE_OBJC_STANDARD_REQUIRED` variable if it is set when a
+target is created.