cmTarget: add support for C++ module fileset types

C++ modules have two variants which are of importance to CMake:

  - `CXX_MODULES`: interface modules (those using `export module M;`,
    `export module M:part;`, or `module M:internal_part;`)
  - `CXX_MODULE_HEADER_UNITS`: importable header units

Creating C++ modules or partitions are *not* supported in any other
source listing. This is because the source files must be installed (so
their scope matters), but not part of usage requirements (what it means
for a module source to be injected into a consumer is not clear at this
moment). Due to the way `FILE_SET` works with scopes, they are a perfect
fit as long as `INTERFACE` is not allowed (which it is not).

12 files changed, 209 insertions, 0 deletions

diff --git a/Help/prop_tgt/CXX_MODULE_DIRS.rst b/Help/prop_tgt/CXX_MODULE_DIRS.rst
new file mode 100644
index 0000000000..fdf383196c
--- /dev/null
+++ b/Help/prop_tgt/CXX_MODULE_DIRS.rst
@@ -0,0 +1,17 @@
+CXX_MODULE_DIRS
+---------------
+
+.. note ::
+
+  Experimental. Gated by ``CMAKE_EXPERIMENTAL_CXX_MODULE_CMAKE_API``
+
+Semicolon-separated list of base directories of the target's default
+C++ module set (i.e. the file set with name and type ``CXX_MODULES``). The
+property supports
+:manual:`generator expressions <cmake-generator-expressions(7)>`.
+
+This property is normally only set by :command:`target_sources(FILE_SET)`
+rather than being manipulated directly.
+
+See :prop_tgt:`CXX_MODULE_DIRS_<NAME>` for the list of base directories in
+other C++ module sets.
diff --git a/Help/prop_tgt/CXX_MODULE_DIRS_NAME.rst b/Help/prop_tgt/CXX_MODULE_DIRS_NAME.rst
new file mode 100644
index 0000000000..8c27d4573e
--- /dev/null
+++ b/Help/prop_tgt/CXX_MODULE_DIRS_NAME.rst
@@ -0,0 +1,17 @@
+CXX_MODULE_DIRS_<NAME>
+----------------------
+
+.. note ::
+
+  Experimental. Gated by ``CMAKE_EXPERIMENTAL_CXX_MODULE_CMAKE_API``
+
+Semicolon-separated list of base directories of the target's ``<NAME>`` C++
+module set, which has the set type ``CXX_MODULES``. The property supports
+:manual:`generator expressions <cmake-generator-expressions(7)>`.
+
+This property is normally only set by :command:`target_sources(FILE_SET)`
+rather than being manipulated directly.
+
+See :prop_tgt:`CXX_MODULE_DIRS` for the list of base directories in the
+default C++ module set. See :prop_tgt:`CXX_MODULE_SETS` for the file set names
+of all C++ module sets.
diff --git a/Help/prop_tgt/CXX_MODULE_HEADER_UNIT_DIRS.rst b/Help/prop_tgt/CXX_MODULE_HEADER_UNIT_DIRS.rst
new file mode 100644
index 0000000000..17e5cf0ed7
--- /dev/null
+++ b/Help/prop_tgt/CXX_MODULE_HEADER_UNIT_DIRS.rst
@@ -0,0 +1,17 @@
+CXX_MODULE_HEADER_UNIT_DIRS
+---------------------------
+
+.. note ::
+
+  Experimental. Gated by ``CMAKE_EXPERIMENTAL_CXX_MODULE_CMAKE_API``
+
+Semicolon-separated list of base directories of the target's default C++
+module header set (i.e. the file set with name and type
+``CXX_MODULE_HEADER_UNITS``). The property supports
+:manual:`generator expressions <cmake-generator-expressions(7)>`.
+
+This property is normally only set by :command:`target_sources(FILE_SET)`
+rather than being manipulated directly.
+
+See :prop_tgt:`CXX_MODULE_HEADER_UNIT_DIRS_<NAME>` for the list of base directories
+in other C++ module header sets.
diff --git a/Help/prop_tgt/CXX_MODULE_HEADER_UNIT_DIRS_NAME.rst b/Help/prop_tgt/CXX_MODULE_HEADER_UNIT_DIRS_NAME.rst
new file mode 100644
index 0000000000..ca30f23cd4
--- /dev/null
+++ b/Help/prop_tgt/CXX_MODULE_HEADER_UNIT_DIRS_NAME.rst
@@ -0,0 +1,19 @@
+CXX_MODULE_HEADER_UNIT_DIRS_<NAME>
+----------------------------------
+
+.. note ::
+
+  Experimental. Gated by ``CMAKE_EXPERIMENTAL_CXX_MODULE_CMAKE_API``
+
+Semicolon-separated list of base directories of the target's ``<NAME>`` C++
+module header set, which has the set type ``CXX_MODULE_HEADER_UNITS``. The
+property supports
+:manual:`generator expressions <cmake-generator-expressions(7)>`.
+
+This property is normally only set by :command:`target_sources(FILE_SET)`
+rather than being manipulated directly.
+
+See :prop_tgt:`CXX_MODULE_HEADER_UNIT_DIRS` for the list of base directories
+in the default C++ module header set. See
+:prop_tgt:`CXX_MODULE_HEADER_UNIT_SETS` for the file set names of all C++
+module header sets.
diff --git a/Help/prop_tgt/CXX_MODULE_HEADER_UNIT_SET.rst b/Help/prop_tgt/CXX_MODULE_HEADER_UNIT_SET.rst
new file mode 100644
index 0000000000..f67a84886d
--- /dev/null
+++ b/Help/prop_tgt/CXX_MODULE_HEADER_UNIT_SET.rst
@@ -0,0 +1,18 @@
+CXX_MODULE_HEADER_UNIT_SET
+--------------------------
+
+.. note ::
+
+  Experimental. Gated by ``CMAKE_EXPERIMENTAL_CXX_MODULE_CMAKE_API``
+
+Semicolon-separated list of files in the target's default C++ module header
+set, (i.e. the file set with name and type ``CXX_MODULE_HEADER_UNITS``). If
+any of the paths are relative, they are computed relative to the target's
+source directory. The property supports
+:manual:`generator expressions <cmake-generator-expressions(7)>`.
+
+This property is normally only set by :command:`target_sources(FILE_SET)`
+rather than being manipulated directly.
+
+See :prop_tgt:`CXX_MODULE_HEADER_UNIT_SET_<NAME>` for the list of files in
+other C++ module header sets.
diff --git a/Help/prop_tgt/CXX_MODULE_HEADER_UNIT_SETS.rst b/Help/prop_tgt/CXX_MODULE_HEADER_UNIT_SETS.rst
new file mode 100644
index 0000000000..7b4bd3fb2a
--- /dev/null
+++ b/Help/prop_tgt/CXX_MODULE_HEADER_UNIT_SETS.rst
@@ -0,0 +1,18 @@
+CXX_MODULE_HEADER_UNIT_SETS
+---------------------------
+
+.. note ::
+
+  Experimental. Gated by ``CMAKE_EXPERIMENTAL_CXX_MODULE_CMAKE_API``
+
+Read-only list of the target's ``PRIVATE`` and ``PUBLIC`` C++ module header
+sets (i.e. all file sets with the type ``CXX_MODULE_HEADER_UNITS``). Files
+listed in these file sets are treated as source files for the purpose of IDE
+integration.
+
+C++ module header sets may be defined using the :command:`target_sources`
+command ``FILE_SET`` option with type ``CXX_MODULE_HEADER_UNITS``.
+
+See also :prop_tgt:`CXX_MODULE_HEADER_UNIT_SET_<NAME>`,
+:prop_tgt:`CXX_MODULE_HEADER_UNIT_SET` and
+:prop_tgt:`INTERFACE_CXX_MODULE_HEADER_UNIT_SETS`.
diff --git a/Help/prop_tgt/CXX_MODULE_HEADER_UNIT_SET_NAME.rst b/Help/prop_tgt/CXX_MODULE_HEADER_UNIT_SET_NAME.rst
new file mode 100644
index 0000000000..d328950324
--- /dev/null
+++ b/Help/prop_tgt/CXX_MODULE_HEADER_UNIT_SET_NAME.rst
@@ -0,0 +1,19 @@
+CXX_MODULE_HEADER_UNIT_SET_<NAME>
+---------------------------------
+
+.. note ::
+
+  Experimental. Gated by ``CMAKE_EXPERIMENTAL_CXX_MODULE_CMAKE_API``
+
+Semicolon-separated list of files in the target's ``<NAME>`` C++ module header
+set, which has the set type ``CXX_MODULE_HEADER_UNITS``. If any of the paths
+are relative, they are computed relative to the target's source directory. The
+property supports
+:manual:`generator expressions <cmake-generator-expressions(7)>`.
+
+This property is normally only set by :command:`target_sources(FILE_SET)`
+rather than being manipulated directly.
+
+See :prop_tgt:`CXX_MODULE_HEADER_UNIT_SET` for the list of files in the
+default C++ module header set. See :prop_tgt:`CXX_MODULE_HEADER_UNIT_SETS` for
+the file set names of all C++ module header sets.
diff --git a/Help/prop_tgt/CXX_MODULE_SET.rst b/Help/prop_tgt/CXX_MODULE_SET.rst
new file mode 100644
index 0000000000..ae9000e9e4
--- /dev/null
+++ b/Help/prop_tgt/CXX_MODULE_SET.rst
@@ -0,0 +1,18 @@
+CXX_MODULE_SET
+--------------
+
+.. note ::
+
+  Experimental. Gated by ``CMAKE_EXPERIMENTAL_CXX_MODULE_CMAKE_API``
+
+Semicolon-separated list of files in the target's default C++ module set,
+(i.e. the file set with name and type ``CXX_MODULES``). If any of the paths
+are relative, they are computed relative to the target's source directory. The
+property supports
+:manual:`generator expressions <cmake-generator-expressions(7)>`.
+
+This property is normally only set by :command:`target_sources(FILE_SET)`
+rather than being manipulated directly.
+
+See :prop_tgt:`CXX_MODULE_SET_<NAME>` for the list of files in other C++
+module sets.
diff --git a/Help/prop_tgt/CXX_MODULE_SETS.rst b/Help/prop_tgt/CXX_MODULE_SETS.rst
new file mode 100644
index 0000000000..c03df391ac
--- /dev/null
+++ b/Help/prop_tgt/CXX_MODULE_SETS.rst
@@ -0,0 +1,16 @@
+CXX_MODULE_SETS
+---------------
+
+.. note ::
+
+  Experimental. Gated by ``CMAKE_EXPERIMENTAL_CXX_MODULE_CMAKE_API``
+
+Read-only list of the target's ``PRIVATE`` and ``PUBLIC`` C++ module sets (i.e.
+all file sets with the type ``CXX_MODULES``). Files listed in these file sets are
+treated as source files for the purpose of IDE integration.
+
+C++ module sets may be defined using the :command:`target_sources` command
+``FILE_SET`` option with type ``CXX_MODULES``.
+
+See also :prop_tgt:`CXX_MODULE_SET_<NAME>`, :prop_tgt:`CXX_MODULE_SET` and
+:prop_tgt:`INTERFACE_CXX_MODULE_SETS`.
diff --git a/Help/prop_tgt/CXX_MODULE_SET_NAME.rst b/Help/prop_tgt/CXX_MODULE_SET_NAME.rst
new file mode 100644
index 0000000000..27c88f319b
--- /dev/null
+++ b/Help/prop_tgt/CXX_MODULE_SET_NAME.rst
@@ -0,0 +1,18 @@
+CXX_MODULE_SET_<NAME>
+---------------------
+
+.. note ::
+
+  Experimental. Gated by ``CMAKE_EXPERIMENTAL_CXX_MODULE_CMAKE_API``
+
+Semicolon-separated list of files in the target's ``<NAME>`` C++ module set,
+which has the set type ``CXX_MODULES``. If any of the paths are relative, they
+are computed relative to the target's source directory. The property supports
+:manual:`generator expressions <cmake-generator-expressions(7)>`.
+
+This property is normally only set by :command:`target_sources(FILE_SET)`
+rather than being manipulated directly.
+
+See :prop_tgt:`CXX_MODULE_SET` for the list of files in the default C++ module
+set. See :prop_tgt:`CXX_MODULE_SETS` for the file set names of all C++ module
+sets.
diff --git a/Help/prop_tgt/INTERFACE_CXX_MODULE_HEADER_UNIT_SETS.rst b/Help/prop_tgt/INTERFACE_CXX_MODULE_HEADER_UNIT_SETS.rst
new file mode 100644
index 0000000000..eb3a9ff809
--- /dev/null
+++ b/Help/prop_tgt/INTERFACE_CXX_MODULE_HEADER_UNIT_SETS.rst
@@ -0,0 +1,16 @@
+INTERFACE_CXX_MODULE_HEADER_UNIT_SETS
+-------------------------------------
+
+.. note ::
+
+  Experimental. Gated by ``CMAKE_EXPERIMENTAL_CXX_MODULE_CMAKE_API``
+
+Read-only list of the target's ``PUBLIC`` C++ module header sets (i.e. all
+file sets with the type ``CXX_MODULE_HEADER_UNITS``). Files listed in these
+C++ module header sets can be installed with :command:`install(TARGETS)` and
+exported with :command:`install(EXPORT)` and :command:`export`.
+
+C++ module header sets may be defined using the :command:`target_sources`
+command ``FILE_SET`` option with type ``CXX_MODULE_HEADER_UNITS``.
+
+See also :prop_tgt:`CXX_MODULE_HEADER_UNIT_SETS`.
diff --git a/Help/prop_tgt/INTERFACE_CXX_MODULE_SETS.rst b/Help/prop_tgt/INTERFACE_CXX_MODULE_SETS.rst
new file mode 100644
index 0000000000..cc30386220
--- /dev/null
+++ b/Help/prop_tgt/INTERFACE_CXX_MODULE_SETS.rst
@@ -0,0 +1,16 @@
+INTERFACE_CXX_MODULE_SETS
+-------------------------
+
+.. note ::
+
+  Experimental. Gated by ``CMAKE_EXPERIMENTAL_CXX_MODULE_CMAKE_API``
+
+Read-only list of the target's ``PUBLIC`` C++ module sets (i.e. all file sets
+with the type ``CXX_MODULES``). Files listed in these C++ module sets can be
+installed with :command:`install(TARGETS)` and exported with
+:command:`install(EXPORT)` and :command:`export`.
+
+C++ module sets may be defined using the :command:`target_sources` command
+``FILE_SET`` option with type ``CXX_MODULES``.
+
+See also :prop_tgt:`CXX_MODULE_SETS`.