Merge topic 'doc-file-sets'

4286b72240 Help: Update install() docs to better reflect preference for file sets
ab1b573f41 Help: Reorganise FILE_SETS and related properties

Acked-by: Kitware Robot <kwrobot@kitware.com>
Merge-request: !7031

2 files changed, 80 insertions, 76 deletions

diff --git a/Help/command/install.rst b/Help/command/install.rst
index 8216a69..14f7ff7 100644
--- a/Help/command/install.rst
+++ b/Help/command/install.rst
@@ -207,11 +207,13 @@ that may be installed:
 ``FILE_SET <set>``
   .. versionadded:: 3.23
 
+  File sets are defined by the :command:`target_sources(FILE_SET)` command.
   If the file set ``<set>`` exists and is ``PUBLIC`` or ``INTERFACE``, any
-  files added to the file set ``<set>`` created by
-  :command:`target_sources(FILE_SET)` are installed in the specified
-  destination, preserving their directory structure relative to the file set's
-  base directories.
+  files in the set are installed under the destination (see below).
+  The directory structure relative to the file set's base directories is
+  preserved. For example, a file added to the file set as
+  ``/blah/include/myproj/here.h`` with a base directory ``/blah/include``
+  would be installed to ``myproj/here.h`` below the destination.
 
 For each of these arguments given, the arguments following them only apply
 to the target or file type specified in the argument. If none is given, the
@@ -223,13 +225,13 @@ For regular executables, static libraries and shared libraries, the
 ``DESTINATION`` argument is not required.  For these target types, when
 ``DESTINATION`` is omitted, a default destination will be taken from the
 appropriate variable from :module:`GNUInstallDirs`, or set to a built-in
-default value if that variable is not defined.  The same is true for the
-public and private headers associated with the installed targets through the
-:prop_tgt:`PUBLIC_HEADER` and :prop_tgt:`PRIVATE_HEADER` target properties.
-A destination must always be provided for module libraries, Apple bundles and
-frameworks.  A destination can be omitted for interface and object libraries,
-but they are handled differently (see the discussion of this topic toward the
-end of this section).
+default value if that variable is not defined.  The same is true for file
+sets, and the public and private headers associated with the installed
+targets through the :prop_tgt:`PUBLIC_HEADER` and :prop_tgt:`PRIVATE_HEADER`
+target properties. A destination must always be provided for module libraries,
+Apple bundles and frameworks.  A destination can be omitted for interface and
+object libraries, but they are handled differently (see the discussion of this
+topic toward the end of this section).
 
 The following table shows the target types with their associated variables and
 built-in defaults that apply when no destination is given:
@@ -246,8 +248,9 @@ built-in defaults that apply when no destination is given:
 =============================== =============================== ======================
 
 Projects wishing to follow the common practice of installing headers into a
-project-specific subdirectory will need to provide a destination rather than
-rely on the above.
+project-specific subdirectory may prefer using file sets with appropriate
+paths and base directories. Otherwise, they must provide a ``DESTINATION``
+instead of being able to rely on the above (see next example below).
 
 To make packages compliant with distribution filesystem layout policies, if
 projects must specify a ``DESTINATION``, it is recommended that they use a
@@ -256,7 +259,7 @@ This allows package maintainers to control the install destination by setting
 the appropriate cache variables.  The following example shows a static library
 being installed to the default destination provided by
 :module:`GNUInstallDirs`, but with its headers installed to a project-specific
-subdirectory that follows the above recommendation:
+subdirectory without using file sets:
 
 .. code-block:: cmake
 
@@ -493,6 +496,12 @@ Installing Files
 .. _FILES:
 .. _PROGRAMS:
 
+.. note::
+
+  If installing header files, consider using file sets defined by
+  :command:`target_sources(FILE_SET)` instead. File sets associate
+  headers with a target and they install as part of the target.
+
 .. code-block:: cmake
 
   install(<FILES|PROGRAMS> files...
@@ -549,7 +558,8 @@ file type if they wish to explicitly define the install destination.
 
 Projects wishing to follow the common practice of installing headers into a
 project-specific subdirectory will need to provide a destination rather than
-rely on the above.
+rely on the above. Using file sets for headers instead of ``install(FILES)``
+would be even better (see :command:`target_sources(FILE_SET)`).
 
 Note that some of the types' built-in defaults use the ``DATAROOT`` directory as
 a prefix. The ``DATAROOT`` prefix is calculated similarly to the types, with
@@ -562,13 +572,14 @@ projects must specify a ``DESTINATION``, it is recommended that they use a
 path that begins with the appropriate :module:`GNUInstallDirs` variable.
 This allows package maintainers to control the install destination by setting
 the appropriate cache variables.  The following example shows how to follow
-this advice while installing headers to a project-specific subdirectory:
+this advice while installing an image to a project-specific documentation
+subdirectory:
 
 .. code-block:: cmake
 
   include(GNUInstallDirs)
-  install(FILES mylib.h
-          DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}/myproj
+  install(FILES logo.png
+          DESTINATION ${CMAKE_INSTALL_DOCDIR}/myproj
   )
 
 .. versionadded:: 3.4
@@ -587,6 +598,13 @@ Installing Directories
 .. _`install(DIRECTORY)`:
 .. _DIRECTORY:
 
+.. note::
+
+  To install a directory sub-tree of headers, consider using file sets
+  defined by :command:`target_sources(FILE_SET)` instead. File sets not only
+  preserve directory structure, they also associate headers with a target
+  and install as part of the target.
+
 .. code-block:: cmake
 
   install(DIRECTORY dirs...
@@ -638,10 +656,10 @@ any expression.  For example, the code
 
 .. code-block:: cmake
 
-  install(DIRECTORY src/ DESTINATION include/myproj
-          FILES_MATCHING PATTERN "*.h")
+  install(DIRECTORY src/ DESTINATION doc/myproj
+          FILES_MATCHING PATTERN "*.png")
 
-will extract and install header files from a source tree.
+will extract and install images from a source tree.
 
 Some options may follow a ``PATTERN`` or ``REGEX`` expression as described
 under :ref:`string(REGEX) <Regex Specification>` and are applied
diff --git a/Help/command/target_sources.rst b/Help/command/target_sources.rst
index 3f8fdd9..6ad86e3 100644
--- a/Help/command/target_sources.rst
+++ b/Help/command/target_sources.rst
@@ -91,73 +91,59 @@ Each ``target_sources(FILE_SET)`` entry starts with ``INTERFACE``, ``PUBLIC``, o
 
 ``FILE_SET <set>``
 
-  A string representing the name of the file set to create or add to. This must
-  contain only numbers, letters, and underscores, and must not start with a
-  capital letter or underscore, unless its name is ``HEADERS``.
+  The name of the file set to create or add to. It must contain only letters,
+  numbers and underscores. Names starting with a capital letter are reserved
+  for built-in file sets predefined by CMake. The only predefined set name is
+  ``HEADERS``. All other set names must not start with a capital letter or
+  underscore.
 
 ``TYPE <type>``
 
-  A string representing the type of the file set. The only acceptable value is
-  ``HEADERS``. This may be omitted if the name of the file set is ``HEADERS``.
+  Every file set is associated with a particular type of file. ``HEADERS``
+  is currently the only defined type and it is an error to specify anything
+  else. As a special case, if the name of the file set is ``HEADERS``, the
+  type does not need to be specified and the ``TYPE <type>`` arguments can be
+  omitted. For all other file set names, ``TYPE`` is required.
 
-``BASE_DIRS <dirs>``
+``BASE_DIRS <dirs>...``
 
-  An optional list of strings representing the base directories of the file
-  set. This argument supports
-  :manual:`generator expressions <cmake-generator-expressions(7)>`. No two
-  ``BASE_DIRS`` may be sub-directories of each other. If no ``BASE_DIRS`` are
+  An optional list of base directories of the file set. Any relative path
+  is treated as relative to the current source directory
+  (i.e. :variable:`CMAKE_CURRENT_SOURCE_DIR`). If no ``BASE_DIRS`` are
   specified when the file set is first created, the value of
-  :variable:`CMAKE_CURRENT_SOURCE_DIR` is added.
-
-``FILES <files>``
-
-  An optional list of strings representing files in the file set. Each file
-  must be in one of the ``BASE_DIRS``. This argument supports
-  :manual:`generator expressions <cmake-generator-expressions(7)>`. If relative
-  paths are specified, they are considered relative to
-  :variable:`CMAKE_CURRENT_SOURCE_DIR` at the time ``target_sources()`` is
-  called, unless they start with ``$<``, in which case they are computed
-  relative to the target's source directory after genex evaluation.
-
-The following target properties are set by ``target_sources(FILE_SET)``:
-
-:prop_tgt:`HEADER_SETS`
-
-  List of ``PRIVATE`` and ``PUBLIC`` header sets associated with a target.
-  Headers listed in these header sets are treated as source files for the
-  purposes of IDE integration, and have their :prop_sf:`HEADER_FILE_ONLY`
-  property set to ``TRUE``.
-
-:prop_tgt:`INTERFACE_HEADER_SETS`
-
-  List of ``INTERFACE`` and ``PUBLIC`` header sets associated with a target.
-  Headers listed in these header sets can be installed with
-  :command:`install(TARGETS)` and exported with :command:`install(EXPORT)` and
-  :command:`export`.
-
-:prop_tgt:`HEADER_SET`
-
-  Headers in the default header set associated with a target. This property
-  supports :manual:`generator expressions <cmake-generator-expressions(7)>`.
-
-:prop_tgt:`HEADER_SET_<NAME>`
-
-  Headers in the named header set ``<NAME>`` associated with a target. This
-  property supports
+  :variable:`CMAKE_CURRENT_SOURCE_DIR` is added. This argument supports
   :manual:`generator expressions <cmake-generator-expressions(7)>`.
 
-:prop_tgt:`HEADER_DIRS`
+  No two base directories for a file set may be sub-directories of each other.
+  This requirement must be met across all base directories added to a file set,
+  not just those within a single call to ``target_sources()``.
 
-  Base directories of the default header set associated with a target. This
-  property supports
-  :manual:`generator expressions <cmake-generator-expressions(7)>`.
-
-:prop_tgt:`HEADER_DIRS_<NAME>`
+``FILES <files>...``
 
-  Base directories of the header set ``<NAME>`` associated with a target. This
-  property supports
+  An optional list of files to add to the file set. Each file must be in
+  one of the base directories, or a subdirectory of one of the base
+  directories. This argument supports
   :manual:`generator expressions <cmake-generator-expressions(7)>`.
 
+  If relative paths are specified, they are considered relative to
+  :variable:`CMAKE_CURRENT_SOURCE_DIR` at the time ``target_sources()`` is
+  called. An exception to this is a path starting with ``$<``. Such paths
+  are treated as relative to the target's source directory after evaluation
+  of generator expressions.
+
+The following target properties are set by ``target_sources(FILE_SET)``,
+but they should not generally be manipulated directly:
+
+* :prop_tgt:`HEADER_SETS`
+* :prop_tgt:`INTERFACE_HEADER_SETS`
+* :prop_tgt:`HEADER_SET`
+* :prop_tgt:`HEADER_SET_<NAME>`
+* :prop_tgt:`HEADER_DIRS`
+* :prop_tgt:`HEADER_DIRS_<NAME>`
+
+Target properties related to include directories are also modified by
+``target_sources(FILE_SET)`` as follows:
+
 :prop_tgt:`INCLUDE_DIRECTORIES`
 
   If the ``TYPE`` is ``HEADERS``, and the scope of the file set is ``PRIVATE``