source_group
------------

Define a grouping for source files in IDE project generation.
There are two different signatures to create source groups.

::

  source_group(<name> [FILES <src>...] [REGULAR_EXPRESSION <regex>])
  source_group(TREE <root> [PREFIX <prefix>] [FILES <src>...])

Defines a group into which sources will be placed in project files.
This is intended to set up file tabs in Visual Studio.
The options are:

``TREE``
 CMake will automatically detect, from ``<src>`` files paths, source groups
 it needs to create, to keep structure of source groups analogically to the
 actual files and directories structure in the project. Paths of ``<src>``
 files will be cut to be relative to ``<root>``.

``PREFIX``
 Source group and files located directly in ``<root>`` path, will be placed
 in ``<prefix>`` source groups.

``FILES``
 Any source file specified explicitly will be placed in group
 ``<name>``.  Relative paths are interpreted with respect to the
 current source directory.

``REGULAR_EXPRESSION``
 Any source file whose name matches the regular expression will
 be placed in group ``<name>``.

If a source file matches multiple groups, the *last* group that
explicitly lists the file with ``FILES`` will be favored, if any.
If no group explicitly lists the file, the *last* group whose
regular expression matches the file will be favored.

The ``<name>`` of the group and ``<prefix>`` argument may contain backslashes
to specify subgroups:

.. code-block:: cmake

  source_group(outer\\inner ...)
  source_group(TREE <root> PREFIX sources\\inc ...)

For backwards compatibility, the short-hand signature

.. code-block:: cmake

  source_group(<name> <regex>)

is equivalent to

.. code-block:: cmake

  source_group(<name> REGULAR_EXPRESSION <regex>)