Help: Clarify and update SYSTEM-related docs

Help/command/add_subdirectory.rst

@@ -7,16 +7,16 @@ Add a subdirectory to the build.
 
   add_subdirectory(source_dir [binary_dir] [EXCLUDE_FROM_ALL] [SYSTEM])
 
-Adds a subdirectory to the build.  The source_dir specifies the
+Adds a subdirectory to the build.  The ``source_dir`` specifies the
-directory in which the source CMakeLists.txt and code files are
+directory in which the source ``CMakeLists.txt`` and code files are
-located.  If it is a relative path it will be evaluated with respect
+located.  If it is a relative path, it will be evaluated with respect
 to the current directory (the typical usage), but it may also be an
 absolute path.  The ``binary_dir`` specifies the directory in which to
-place the output files.  If it is a relative path it will be evaluated
+place the output files.  If it is a relative path, it will be evaluated
 with respect to the current output directory, but it may also be an
 absolute path.  If ``binary_dir`` is not specified, the value of
 ``source_dir``, before expanding any relative path, will be used (the
-typical usage).  The CMakeLists.txt file in the specified source
+typical usage).  The ``CMakeLists.txt`` file in the specified source
 directory will be processed immediately by CMake before processing in
 the current input file continues beyond this command.
 
@@ -28,9 +28,9 @@ meant for use when the subdirectory contains a separate part of the
 project that is useful but not necessary, such as a set of examples.
 Typically the subdirectory should contain its own :command:`project`
 command invocation so that a full build system will be generated in the
-subdirectory (such as a VS IDE solution file).  Note that inter-target
+subdirectory (such as a Visual Studio IDE solution file).  Note that
-dependencies supersede this exclusion.  If a target built by the
+inter-target dependencies supersede this exclusion.  If a target built by
-parent project depends on a target in the subdirectory, the dependee
+the parent project depends on a target in the subdirectory, the dependee
 target will be included in the parent project build system to satisfy
 the dependency.
 
@@ -38,6 +38,4 @@ the dependency.
   If the ``SYSTEM`` argument is provided, the :prop_dir:`SYSTEM` directory
   property of the subdirectory will be set to true.  This property is
   used to initialize the :prop_tgt:`SYSTEM` property of each non-imported
-  target created in that subdirectory.  The include directories of targets
+  target created in that subdirectory.
-  with :prop_tgt:`SYSTEM` set to true will be treated as ``SYSTEM`` when
-  compiling consumers.

Help/manual/cmake-buildsystem.7.rst

@@ -672,14 +672,14 @@ This is equivalent to appending ``${CMAKE_INSTALL_PREFIX}/include`` to the
 
 When the :prop_tgt:`INTERFACE_INCLUDE_DIRECTORIES` of an
 :ref:`imported target <Imported targets>` is consumed, the entries in the
-property are treated as ``SYSTEM`` include directories, as if they were
+property may be treated as system include directories.  The effects of that
-listed in the :prop_tgt:`INTERFACE_SYSTEM_INCLUDE_DIRECTORIES` of the
+are toolchain-dependent, but one common effect is to omit compiler warnings
-dependency. This can result in omission of compiler warnings for headers
+for headers found in those directories.  The :prop_tgt:`SYSTEM` property of
-found in those directories.  This behavior for :ref:`imported targets` may
+the installed target determines this behavior (see the
-be controlled by setting the :prop_tgt:`NO_SYSTEM_FROM_IMPORTED` target
+:prop_tgt:`EXPORT_NO_SYSTEM` property for how to modify the installed value
-property on the *consumers* of imported targets, or by setting the
+for a target).  It is also possible to change how consumers interpret the
-:prop_tgt:`IMPORTED_NO_SYSTEM` target property on the imported targets
+system behavior of consumed imported targets by setting the
-themselves.
+:prop_tgt:`NO_SYSTEM_FROM_IMPORTED` target property on the *consumer*.
 
 If a binary target is linked transitively to a macOS :prop_tgt:`FRAMEWORK`, the
 ``Headers`` directory of the framework is also treated as a usage requirement.

Help/prop_tgt/EXPORT_NO_SYSTEM.rst

@@ -3,8 +3,10 @@ EXPORT_NO_SYSTEM
 
 .. versionadded:: 3.25
 
-Specifies that :command:`install(EXPORT)` and :command:`export` commands will
+This property affects the behavior of the :command:`install(EXPORT)` and
-generate an imported target with :prop_tgt:`SYSTEM` property `OFF`.
+:command:`export` commands when they install or export the target respectively.
+When ``EXPORT_NO_SYSTEM`` is set to true, those commands generate an imported
+target with :prop_tgt:`SYSTEM` property set to false.
 
 See the :prop_tgt:`NO_SYSTEM_FROM_IMPORTED` target property to set this
 behavior on the target *consuming* the include directories rather than the

Help/prop_tgt/IMPORTED_NO_SYSTEM.rst

@@ -5,27 +5,31 @@ IMPORTED_NO_SYSTEM
 
 .. deprecated:: 3.25
 
-  ``IMPORTED_NO_SYSTEM`` is deprecated. Set :prop_tgt:`SYSTEM` to `OFF`
+  ``IMPORTED_NO_SYSTEM`` is deprecated. Please use the following alternatives
-  instead if you don't want target's include directories to be ``SYSTEM``
+  instead:
-  when compiling consumers. Set :prop_tgt:`EXPORT_NO_SYSTEM` to `ON` instead
-  if you don't want the include directories of the imported target generated
-  by :command:`install(EXPORT)` and :command:`export` commands to be
-  ``SYSTEM`` when compiling consumers.
 
-Specifies that an :ref:`Imported Target <Imported Targets>` is not
+  * Set :prop_tgt:`SYSTEM` to false if you don't want a target's include
-a ``SYSTEM`` library.  This has the following effects:
+    directories to be treated as system directories when compiling consumers.
+  * Set :prop_tgt:`EXPORT_NO_SYSTEM` to true if you don't want the include
+    directories of the imported target generated by :command:`install(EXPORT)`
+    and :command:`export` commands to be treated as system directories when
+    compiling consumers.
+
+Setting ``IMPORTED_NO_SYSTEM`` to true on an
+:ref:`imported target <Imported Targets>` specifies that it is not a
+system target.  This has the following effects:
 
 * Entries of :prop_tgt:`INTERFACE_INCLUDE_DIRECTORIES` are not treated
-  as ``SYSTEM`` include directories when compiling consumers (regardless of
+  as system include directories when compiling consumers (regardless of
   the value of the consumed target's :prop_tgt:`SYSTEM` property), as they
   would be by default.   Entries of
   :prop_tgt:`INTERFACE_SYSTEM_INCLUDE_DIRECTORIES` are not affected,
-  and will always be treated as ``SYSTEM`` include directories.
+  and will always be treated as system include directories.
 
 This property can also be enabled on a non-imported target.  Doing so does
 not affect the build system, but does tell the :command:`install(EXPORT)` and
 :command:`export` commands to enable it on the imported targets they generate.
 
 See the :prop_tgt:`NO_SYSTEM_FROM_IMPORTED` target property to set this
-behavior on the target consuming the include directories rather than
+behavior on the target *consuming* the include directories rather than
-providing them.
+the one *providing* them.

Help/prop_tgt/INTERFACE_SYSTEM_INCLUDE_DIRECTORIES.rst

@@ -8,17 +8,17 @@ which contain system headers, and therefore should not result in
 compiler warnings.  Additionally, system include directories are searched
 after normal include directories regardless of the order specified.
 
-The :command:`target_include_directories(SYSTEM)` command signature
+When the :command:`target_include_directories` command is given the
-populates this property with values given to the ``PUBLIC`` and
+``SYSTEM`` keyword, it populates this property with values provided after the
-``INTERFACE`` keywords.
+``PUBLIC`` and ``INTERFACE`` keywords.
 
 Projects may also get and set the property directly, but must be aware that
 adding directories to this property does not make those directories used
 during compilation.  Adding directories to this property marks directories
-as ``SYSTEM`` which otherwise would be used in a non-``SYSTEM`` manner.  This
+as system directories which otherwise would be used in a non-system manner.
-can appear similar to 'duplication', so prefer the
+This can appear similar to duplication, so prefer the high-level
-high-level :command:`target_include_directories(SYSTEM)` command and avoid
+:command:`target_include_directories` command with the ``SYSTEM`` keyword
-setting the property by low-level means.
+and avoid setting the property directly.
 
 When target dependencies are specified using :command:`target_link_libraries`,
 CMake will read this property from all target dependencies to mark the

Help/prop_tgt/NO_SYSTEM_FROM_IMPORTED.rst

@@ -2,19 +2,27 @@ NO_SYSTEM_FROM_IMPORTED
 -----------------------
 
 Do not treat include directories from the interfaces of consumed
-:ref:`imported targets` as ``SYSTEM``.
+:ref:`imported targets` as system directories.
 
 The contents of the :prop_tgt:`INTERFACE_INCLUDE_DIRECTORIES` target property
-of imported targets are treated as ``SYSTEM`` includes by default.  If this
+are treated as system includes when the consumed target's :prop_tgt:`SYSTEM`
-property is enabled on a target, compilation of sources in that target will
+property is set to true.  By default, :prop_tgt:`SYSTEM` is true for imported
-not treat the contents of the ``INTERFACE_INCLUDE_DIRECTORIES`` of consumed
+targets and false for other target types.  If the ``NO_SYSTEM_FROM_IMPORTED``
-imported targets as system includes.  Either way, entries of
+property is set to true on a *consuming* target, compilation of sources in that
-:prop_tgt:`INTERFACE_SYSTEM_INCLUDE_DIRECTORIES` are not affected,
+consuming target will not treat the contents of the
-and will always be treated as ``SYSTEM`` include directories.
+:prop_tgt:`INTERFACE_INCLUDE_DIRECTORIES` of consumed imported targets as
+system includes, even if that imported target's :prop_tgt:`SYSTEM` property
+is false.
+
+Directories listed in the :prop_tgt:`INTERFACE_SYSTEM_INCLUDE_DIRECTORIES`
+property of consumed targets are not affected by ``NO_SYSTEM_FROM_IMPORTED``.
+Those directories will always be treated as system include directories by
+consumers.
 
 This property is initialized by the value of the
 :variable:`CMAKE_NO_SYSTEM_FROM_IMPORTED` variable if it is set when a target
 is created.
 
-See the :prop_tgt:`IMPORTED_NO_SYSTEM` target property to set this behavior
+See the :prop_tgt:`EXPORT_NO_SYSTEM` target property to set this behavior
-on the target providing the include directories rather than consuming them.
+on the target providing the include directories rather than the target
+consuming them.

Help/prop_tgt/SYSTEM.rst

@@ -3,20 +3,20 @@ SYSTEM
 
 .. versionadded:: 3.25
 
-Specifies that a target is a ``SYSTEM`` library.  This has the following
+Specifies that a target is a system target.  This has the following
 effects:
 
 * Entries of :prop_tgt:`INTERFACE_INCLUDE_DIRECTORIES` are treated as
-  ``SYSTEM`` include directories when compiling consumers.
+  system include directories when compiling consumers.
   Entries of :prop_tgt:`INTERFACE_SYSTEM_INCLUDE_DIRECTORIES` are not
-  affected, and will always be treated as ``SYSTEM`` include directories.
+  affected, and will always be treated as system include directories.
 
 For imported targets, this property defaults to true, which means
 that their :prop_tgt:`INTERFACE_INCLUDE_DIRECTORIES` are treated
-as ``SYSTEM`` by default. If their ``SYSTEM`` property is false,
+as system directories by default.  If their ``SYSTEM`` property is false,
 then their :prop_tgt:`INTERFACE_INCLUDE_DIRECTORIES` will not be
-treated as ``SYSTEM``, regardless of the value of the
+treated as system.  Use the :prop_tgt:`EXPORT_NO_SYSTEM` property to change
-:prop_tgt:`IMPORTED_NO_SYSTEM` property.
+how a target's ``SYSTEM`` property is set when it is installed.
 
 For non-imported targets, this target property is initialized from
 the :prop_dir:`SYSTEM` directory property when the target is created.

Help/release/3.25.rst

@@ -159,9 +159,10 @@ Properties
 Modules
 -------
 
-* The :module:`FetchContent` module :command:`FetchContent_Declare`
+* The :module:`FetchContent` module's :command:`FetchContent_Declare`
-  command gained a ``SYSTEM`` option to enable the :prop_dir:`SYSTEM`
+  command gained a ``SYSTEM`` option which sets the :prop_dir:`SYSTEM`
-  directory property in the subdirectory.
+  directory property on subdirectories created by
+  :command:`FetchContent_MakeAvailable`.
 
 * The :module:`FindCUDAToolkit` module now provides a target for
   :ref:`nvtx3 <cuda_toolkit_nvtx3>` for CUDA 10.0+, which supersedes

Modules/FetchContent.cmake

@@ -233,12 +233,12 @@ Commands
   .. versionadded:: 3.25
 
     ``SYSTEM``
-      If the ``SYSTEM`` argument is provided, targets created by
+      If the ``SYSTEM`` argument is provided, the :prop_dir:`SYSTEM` directory
-      the dependency will have their :prop_tgt:`SYSTEM` property
+      property of a subdirectory added by
-      set to true when populated by :command:`FetchContent_MakeAvailable`.
+      :command:`FetchContent_MakeAvailable` will be set to true.  This will
-      The entries in their  :prop_tgt:`INTERFACE_INCLUDE_DIRECTORIES`
+      affect non-imported targets created as part of that command.
-      will be treated as ``SYSTEM`` include directories when
+      See the :prop_tgt:`SYSTEM` target property documentation for a more
-      compiling consumers.
+      detailed discussion of the effects.
 
 .. command:: FetchContent_MakeAvailable
 
@@ -353,6 +353,11 @@ Commands
       adding a project that contains a ``CMakeLists.txt`` file in its top
       directory.
 
+    .. versionadded:: 3.25
+      If the ``SYSTEM`` keyword was included in the call to
+      :command:`FetchContent_Declare`, the ``SYSTEM`` keyword will be
+      added to the :command:`add_subdirectory` command as well.
+
   Projects should aim to declare the details of all dependencies they might
   use before they call ``FetchContent_MakeAvailable()`` for any of them.
   This ensures that if any of the dependencies are also sub-dependencies of