CMake/Modules/FindDoxygen.cmake

# Distributed under the OSI-approved BSD 3-Clause License.  See accompanying
# file Copyright.txt or https://cmake.org/licensing for details.

#[=======================================================================[.rst:
FindDoxygen
-----------

Doxygen is a documentation generation tool (see http://www.doxygen.org).
This module looks for Doxygen and some optional tools it supports. These
tools are enabled as components in the :command:`find_package` command:

``dot``
  `Graphviz <http://graphviz.org>`_ ``dot`` utility used to render various
  graphs.
``mscgen``
  `Message Chart Generator <http://www.mcternan.me.uk/mscgen/>`_ utility used
  by Doxygen's ``\msc`` and ``\mscfile`` commands.
``dia``
  `Dia <https://wiki.gnome.org/Apps/Dia>`_ the diagram editor used by Doxygen's
  ``\diafile`` command.

Examples:

.. code-block:: cmake

  # Require dot, treat the other components as optional
  find_package(Doxygen
               REQUIRED dot
               OPTIONAL_COMPONENTS mscgen dia)

The following variables are defined by this module:

.. variable:: DOXYGEN_FOUND

  True if the ``doxygen`` executable was found.

.. variable:: DOXYGEN_VERSION

  The version reported by ``doxygen --version``.

The module defines ``IMPORTED`` targets for Doxygen and each component found.
These can be used as part of custom commands, etc. and should be preferred over
old-style (and now deprecated) variables like ``DOXYGEN_EXECUTABLE``. The
following import targets are defined if their corresponding executable could be
found (the component import targets will only be defined if that component was
requested):

::

  Doxygen::doxygen
  Doxygen::dot
  Doxygen::mscgen
  Doxygen::dia


Functions
^^^^^^^^^

.. command:: doxygen_add_docs

  This function is intended as a convenience for adding a target for generating
  documentation with Doxygen. It aims to provide sensible defaults so that
  projects can generally just provide the input files and directories and that
  will be sufficient to give sensible results. The function supports the
  ability to customize the Doxygen configuration used to build the
  documentation.

  ::

    doxygen_add_docs(targetName
        [filesOrDirs...]
        [ALL]
        [WORKING_DIRECTORY dir]
        [COMMENT comment])

  The function constructs a ``Doxyfile`` and defines a custom target that runs
  Doxygen on that generated file. The listed files and directories are used as
  the ``INPUT`` of the generated ``Doxyfile`` and they can contain wildcards.
  Any files that are listed explicitly will also be added as ``SOURCES`` of the
  custom target so they will show up in an IDE project's source list.

  So that relative input paths work as expected, by default the working
  directory of the Doxygen command will be the current source directory (i.e.
  :variable:`CMAKE_CURRENT_SOURCE_DIR`). This can be overridden with the
  ``WORKING_DIRECTORY`` option to change the directory used as the relative
  base point. Note also that Doxygen's default behavior is to strip the working
  directory from relative paths in the generated documentation (see the
  ``STRIP_FROM_PATH`` `Doxygen config option
  <http://www.doxygen.org/manual/config.html>`_ for details).

  If provided, the optional ``comment`` will be passed as the ``COMMENT`` for
  the :command:`add_custom_target` command used to create the custom target
  internally.

  If ALL is set, the target will be added to the default build target.

  The contents of the generated ``Doxyfile`` can be customized by setting CMake
  variables before calling ``doxygen_add_docs()``. Any variable with a name of
  the form ``DOXYGEN_<tag>`` will have its value substituted for the
  corresponding ``<tag>`` configuration option in the ``Doxyfile``. See the
  `Doxygen documentation <http://www.doxygen.org/manual/config.html>`_ for the
  full list of supported configuration options.

  Some of Doxygen's defaults are overridden to provide more appropriate
  behavior for a CMake project. Each of the following will be explicitly set
  unless the variable already has a value before ``doxygen_add_docs()`` is
  called (with some exceptions noted):

  .. variable:: DOXYGEN_HAVE_DOT

    Set to ``YES`` if the ``dot`` component was requested and it was found,
    ``NO`` otherwise. Any existing value of ``DOXYGEN_HAVE_DOT`` is ignored.

  .. variable:: DOXYGEN_DOT_MULTI_TARGETS

    Set to ``YES`` by this module (note that this requires a ``dot`` version
    newer than 1.8.10). This option is only meaningful if ``DOXYGEN_HAVE_DOT``
    is also set to ``YES``.

  .. variable:: DOXYGEN_GENERATE_LATEX

    Set to ``NO`` by this module.

  .. variable:: DOXYGEN_WARN_FORMAT

    For Visual Studio based generators, this is set to the form recognized by
    the Visual Studio IDE: ``$file($line) : $text``. For all other generators,
    Doxygen's default value is not overridden.

  .. variable:: DOXYGEN_PROJECT_NAME

    Populated with the name of the current project (i.e.
    :variable:`PROJECT_NAME`).

  .. variable:: DOXYGEN_PROJECT_NUMBER

    Populated with the version of the current project (i.e.
    :variable:`PROJECT_VERSION`).

  .. variable:: DOXYGEN_PROJECT_BRIEF

    Populated with the description of the current project (i.e.
    :variable:`PROJECT_DESCRIPTION`).

  .. variable:: DOXYGEN_INPUT

    Projects should not set this variable. It will be populated with the set of
    files and directories passed to ``doxygen_add_docs()``, thereby providing
    consistent behavior with the other built-in commands like
    :command:`add_executable`, :command:`add_library` and
    :command:`add_custom_target`. If a variable named ``DOXYGEN_INPUT`` is set
    by the project, it will be ignored and a warning will be issued.

  .. variable:: DOXYGEN_RECURSIVE

    Set to ``YES`` by this module.

  .. variable:: DOXYGEN_EXCLUDE_PATTERNS

    If the set of inputs includes directories, this variable will specify
    patterns used to exclude files from them. The following patterns are added
    by ``doxygen_add_docs()`` to ensure CMake-specific files and directories
    are not included in the input. If the project sets
    ``DOXYGEN_EXCLUDE_PATTERNS``, those contents are merged with these
    additional patterns rather than replacing them:

    ::

      */.git/*
      */.svn/*
      */.hg/*
      */CMakeFiles/*
      */_CPack_Packages/*
      DartConfiguration.tcl
      CMakeLists.txt
      CMakeCache.txt

  .. variable:: DOXYGEN_OUTPUT_DIRECTORY

    Set to :variable:`CMAKE_CURRENT_BINARY_DIR` by this module. Note that if
    the project provides its own value for this and it is a relative path, it
    will be converted to an absolute path relative to the current binary
    directory. This is necessary because doxygen will normally be run from a
    directory within the source tree so that relative source paths work as
    expected. If this directory does not exist, it will be recursively created
    prior to executing the doxygen commands.

To change any of these defaults or override any other Doxygen config option,
set relevant variables before calling ``doxygen_add_docs()``. For example:

  .. code-block:: cmake

    set(DOXYGEN_GENERATE_HTML NO)
    set(DOXYGEN_GENERATE_MAN YES)

    doxygen_add_docs(
        doxygen
        ${PROJECT_SOURCE_DIR}
        COMMENT "Generate man pages"
    )

A number of Doxygen config options accept lists of values, but Doxygen requires
them to be separated by whitespace. CMake variables hold lists as a string with
items separated by semi-colons, so a conversion needs to be performed. The
``doxygen_add_docs()`` command specifically checks the following Doxygen config
options and will convert their associated CMake variable's contents into the
required form if set.

::

  ABBREVIATE_BRIEF
  ALIASES
  CITE_BIB_FILES
  DIAFILE_DIRS
  DOTFILE_DIRS
  DOT_FONTPATH
  ENABLED_SECTIONS
  EXAMPLE_PATH
  EXAMPLE_PATTERNS
  EXCLUDE
  EXCLUDE_PATTERNS
  EXCLUDE_SYMBOLS
  EXPAND_AS_DEFINED
  EXTENSION_MAPPING
  EXTRA_PACKAGES
  EXTRA_SEARCH_MAPPINGS
  FILE_PATTERNS
  FILTER_PATTERNS
  FILTER_SOURCE_PATTERNS
  HTML_EXTRA_FILES
  HTML_EXTRA_STYLESHEET
  IGNORE_PREFIX
  IMAGE_PATH
  INCLUDE_FILE_PATTERNS
  INCLUDE_PATH
  INPUT
  LATEX_EXTRA_FILES
  LATEX_EXTRA_STYLESHEET
  MATHJAX_EXTENSIONS
  MSCFILE_DIRS
  PLANTUML_INCLUDE_PATH
  PREDEFINED
  QHP_CUST_FILTER_ATTRS
  QHP_SECT_FILTER_ATTRS
  STRIP_FROM_INC_PATH
  STRIP_FROM_PATH
  TAGFILES
  TCL_SUBST

The following single value Doxygen options will be quoted automatically
if they contain at least one space:

::

  CHM_FILE
  DIA_PATH
  DOCBOOK_OUTPUT
  DOCSET_FEEDNAME
  DOCSET_PUBLISHER_NAME
  DOT_FONTNAME
  DOT_PATH
  EXTERNAL_SEARCH_ID
  FILE_VERSION_FILTER
  GENERATE_TAGFILE
  HHC_LOCATION
  HTML_FOOTER
  HTML_HEADER
  HTML_OUTPUT
  HTML_STYLESHEET
  INPUT_FILTER
  LATEX_FOOTER
  LATEX_HEADER
  LATEX_OUTPUT
  LAYOUT_FILE
  MAN_OUTPUT
  MAN_SUBDIR
  MATHJAX_CODEFILE
  MSCGEN_PATH
  OUTPUT_DIRECTORY
  PERL_PATH
  PLANTUML_JAR_PATH
  PROJECT_BRIEF
  PROJECT_LOGO
  PROJECT_NAME
  QCH_FILE
  QHG_LOCATION
  QHP_CUST_FILTER_NAME
  QHP_VIRTUAL_FOLDER
  RTF_EXTENSIONS_FILE
  RTF_OUTPUT
  RTF_STYLESHEET_FILE
  SEARCHDATA_FILE
  USE_MDFILE_AS_MAINPAGE
  WARN_FORMAT
  WARN_LOGFILE
  XML_OUTPUT

There are situations where it may be undesirable for a particular config option
to be automatically quoted by ``doxygen_add_docs()``, such as ``ALIASES`` which
may need to include its own embedded quoting.  The ``DOXYGEN_VERBATIM_VARS``
variable can be used to specify a list of Doxygen variables (including the
leading ``DOXYGEN_`` prefix) which should not be quoted.  The project is then
responsible for ensuring that those variables' values make sense when placed
directly in the Doxygen input file.  In the case of list variables, list items
are still separated by spaces, it is only the automatic quoting that is
skipped.  For example, the following allows ``doxygen_add_docs()`` to apply
quoting to ``DOXYGEN_PROJECT_BRIEF``, but not each item in the
``DOXYGEN_ALIASES`` list (:ref:`bracket syntax <Bracket Argument>` can also
be used to make working with embedded quotes easier):

.. code-block:: cmake

  set(DOXYGEN_PROJECT_BRIEF "String with spaces")
  set(DOXYGEN_ALIASES
      [[somealias="@some_command param"]]
      "anotherAlias=@foobar"
  )
  set(DOXYGEN_VERBATIM_VARS DOXYGEN_ALIASES)

The resultant ``Doxyfile`` will contain the following lines:

.. code-block:: text

  PROJECT_BRIEF = "String with spaces"
  ALIASES       = somealias="@some_command param" anotherAlias=@foobar


Deprecated Result Variables
^^^^^^^^^^^^^^^^^^^^^^^^^^^

For compatibility with previous versions of CMake, the following variables
are also defined but they are deprecated and should no longer be used:

.. variable:: DOXYGEN_EXECUTABLE

  The path to the ``doxygen`` command. If projects need to refer to the
  ``doxygen`` executable directly, they should use the ``Doxygen::doxygen``
  import target instead.

.. variable:: DOXYGEN_DOT_FOUND

  True if the ``dot`` executable was found.

.. variable:: DOXYGEN_DOT_EXECUTABLE

  The path to the ``dot`` command. If projects need to refer to the ``dot``
  executable directly, they should use the ``Doxygen::dot`` import target
  instead.

.. variable:: DOXYGEN_DOT_PATH

  The path to the directory containing the ``dot`` executable as reported in
  ``DOXYGEN_DOT_EXECUTABLE``. The path may have forward slashes even on Windows
  and is not suitable for direct substitution into a ``Doxyfile.in`` template.
  If you need this value, get the :prop_tgt:`IMPORTED_LOCATION` property of the
  ``Doxygen::dot`` target and use :command:`get_filename_component` to extract
  the directory part of that path. You may also want to consider using
  :command:`file(TO_NATIVE_PATH)` to prepare the path for a Doxygen
  configuration file.


Deprecated Hint Variables
^^^^^^^^^^^^^^^^^^^^^^^^^

.. variable:: DOXYGEN_SKIP_DOT

  This variable has no effect for the component form of ``find_package``.
  In backward compatibility mode (i.e. without components list) it prevents
  the finder module from searching for Graphviz's ``dot`` utility.

#]=======================================================================]

cmake_policy(PUSH)
cmake_policy(SET CMP0057 NEW) # if IN_LIST

# For backwards compatibility support
if(Doxygen_FIND_QUIETLY)
    set(DOXYGEN_FIND_QUIETLY TRUE)
endif()

# ===== Rationale for OS X AppBundle mods below =====
#  With the OS X GUI version, Doxygen likes to be installed to /Applications
#  and it contains the doxygen executable in the bundle. In the versions I've
#  seen, it is located in Resources, but in general, more often binaries are
#  located in MacOS.
#
#  NOTE: The official Doxygen.app distributed for OS X uses non-standard
#  conventions. Instead of the command-line "doxygen" tool being placed in
#  Doxygen.app/Contents/MacOS, "Doxywizard" is placed there instead and
#  "doxygen" is placed in Contents/Resources.  This is most likely done
#  so that something happens when people double-click on the Doxygen.app
#  package. Unfortunately, CMake gets confused by this as when it sees the
#  bundle it uses "Doxywizard" as the executable to use instead of
#  "doxygen". Therefore to work-around this issue we temporarily disable
#  the app-bundle feature, just for this CMake module:
#
if(APPLE)
    # Save the old setting
    set(TEMP_DOXYGEN_SAVE_CMAKE_FIND_APPBUNDLE ${CMAKE_FIND_APPBUNDLE})
    # Disable the App-bundle detection feature
    set(CMAKE_FIND_APPBUNDLE "NEVER")
endif()
# FYI:
# In older versions of OS X Doxygen, dot was included with the Doxygen bundle,
# but newer versions require you to download Graphviz.app which contains "dot"
# or use something like homebrew.
# ============== End OSX stuff ================

#
# Find Doxygen...
#
macro(_Doxygen_find_doxygen)
    find_program(
        DOXYGEN_EXECUTABLE
        NAMES doxygen
        PATHS
            "[HKEY_LOCAL_MACHINE\\SOFTWARE\\Microsoft\\Windows\\CurrentVersion\\Uninstall\\doxygen_is1;Inno Setup: App Path]/bin"
            /Applications/Doxygen.app/Contents/Resources
            /Applications/Doxygen.app/Contents/MacOS
            /Applications/Utilities/Doxygen.app/Contents/Resources
            /Applications/Utilities/Doxygen.app/Contents/MacOS
        DOC "Doxygen documentation generation tool (http://www.doxygen.org)"
    )
    mark_as_advanced(DOXYGEN_EXECUTABLE)

    if(DOXYGEN_EXECUTABLE)
        execute_process(
            COMMAND "${DOXYGEN_EXECUTABLE}" --version
            OUTPUT_VARIABLE DOXYGEN_VERSION
            OUTPUT_STRIP_TRAILING_WHITESPACE
            RESULT_VARIABLE _Doxygen_version_result
        )
        if(_Doxygen_version_result)
            message(WARNING "Unable to determine doxygen version: ${_Doxygen_version_result}")
        endif()

        # Create an imported target for Doxygen
        if(NOT TARGET Doxygen::doxygen)
            add_executable(Doxygen::doxygen IMPORTED GLOBAL)
            set_target_properties(Doxygen::doxygen PROPERTIES
                IMPORTED_LOCATION "${DOXYGEN_EXECUTABLE}"
            )
        endif()
    endif()
endmacro()

#
# Find Diagram Editor...
#
macro(_Doxygen_find_dia)
    set(_x86 "(x86)")
    find_program(
        DOXYGEN_DIA_EXECUTABLE
        NAMES dia
        PATHS
            "$ENV{ProgramFiles}/Dia"
            "$ENV{ProgramFiles${_x86}}/Dia"
        DOC "Diagram Editor tool for use with Doxygen"
    )
    mark_as_advanced(DOXYGEN_DIA_EXECUTABLE)

    if(DOXYGEN_DIA_EXECUTABLE)
        # The Doxyfile wants the path to the utility, not the entire path
        # including file name
        get_filename_component(DOXYGEN_DIA_PATH
                              "${DOXYGEN_DIA_EXECUTABLE}"
                              DIRECTORY)
        if(WIN32)
            file(TO_NATIVE_PATH "${DOXYGEN_DIA_PATH}" DOXYGEN_DIA_PATH)
        endif()

        # Create an imported target for component
        if(NOT TARGET Doxygen::dia)
            add_executable(Doxygen::dia IMPORTED GLOBAL)
            set_target_properties(Doxygen::dia PROPERTIES
                IMPORTED_LOCATION "${DOXYGEN_DIA_EXECUTABLE}"
            )
        endif()
    endif()

    unset(_x86)
endmacro()

#
# Find Graphviz Dot...
#
macro(_Doxygen_find_dot)
    if(WIN32)
        set(_x86 "(x86)")
        file(
            GLOB _Doxygen_GRAPHVIZ_BIN_DIRS
            "$ENV{ProgramFiles}/Graphviz*/bin"
            "$ENV{ProgramFiles${_x86}}/Graphviz*/bin"
        )
        unset(_x86)
    else()
        set(_Doxygen_GRAPHVIZ_BIN_DIRS "")
    endif()

    find_program(
        DOXYGEN_DOT_EXECUTABLE
        NAMES dot
        PATHS
            ${_Doxygen_GRAPHVIZ_BIN_DIRS}
            "$ENV{ProgramFiles}/ATT/Graphviz/bin"
            "C:/Program Files/ATT/Graphviz/bin"
            [HKEY_LOCAL_MACHINE\\SOFTWARE\\ATT\\Graphviz;InstallPath]/bin
            /Applications/Graphviz.app/Contents/MacOS
            /Applications/Utilities/Graphviz.app/Contents/MacOS
            /Applications/Doxygen.app/Contents/Resources
            /Applications/Doxygen.app/Contents/MacOS
            /Applications/Utilities/Doxygen.app/Contents/Resources
            /Applications/Utilities/Doxygen.app/Contents/MacOS
        DOC "Dot tool for use with Doxygen"
    )
    mark_as_advanced(DOXYGEN_DOT_EXECUTABLE)

    if(DOXYGEN_DOT_EXECUTABLE)
        # The Doxyfile wants the path to the utility, not the entire path
        # including file name
        get_filename_component(DOXYGEN_DOT_PATH
                               "${DOXYGEN_DOT_EXECUTABLE}"
                               DIRECTORY)
        if(WIN32)
            file(TO_NATIVE_PATH "${DOXYGEN_DOT_PATH}" DOXYGEN_DOT_PATH)
        endif()

        # Create an imported target for component
        if(NOT TARGET Doxygen::dot)
            add_executable(Doxygen::dot IMPORTED GLOBAL)
            set_target_properties(Doxygen::dot PROPERTIES
                IMPORTED_LOCATION "${DOXYGEN_DOT_EXECUTABLE}"
            )
        endif()
    endif()

    unset(_Doxygen_GRAPHVIZ_BIN_DIRS)
endmacro()

#
# Find Message Sequence Chart...
#
macro(_Doxygen_find_mscgen)
    set(_x86 "(x86)")
    find_program(
        DOXYGEN_MSCGEN_EXECUTABLE
        NAMES mscgen
        PATHS
            "$ENV{ProgramFiles}/Mscgen"
            "$ENV{ProgramFiles${_x86}}/Mscgen"
        DOC "Message sequence chart tool for use with Doxygen"
    )
    mark_as_advanced(DOXYGEN_MSCGEN_EXECUTABLE)

    if(DOXYGEN_MSCGEN_EXECUTABLE)
        # The Doxyfile wants the path to the utility, not the entire path
        # including file name
        get_filename_component(DOXYGEN_MSCGEN_PATH
                               "${DOXYGEN_MSCGEN_EXECUTABLE}"
                               DIRECTORY)
        if(WIN32)
            file(TO_NATIVE_PATH "${DOXYGEN_MSCGEN_PATH}" DOXYGEN_MSCGEN_PATH)
        endif()

        # Create an imported target for component
        if(NOT TARGET Doxygen::mscgen)
            add_executable(Doxygen::mscgen IMPORTED GLOBAL)
            set_target_properties(Doxygen::mscgen PROPERTIES
                IMPORTED_LOCATION "${DOXYGEN_MSCGEN_EXECUTABLE}"
            )
        endif()
    endif()

    unset(_x86)
endmacro()

# Make sure `doxygen` is one of the components to find
set(_Doxygen_keep_backward_compat FALSE)
if(NOT Doxygen_FIND_COMPONENTS)
    # Search at least for `doxygen` executable
    set(Doxygen_FIND_COMPONENTS doxygen)
    # Preserve backward compatibility:
    # search for `dot` also if `DOXYGEN_SKIP_DOT` is not explicitly disable this.
    if(NOT DOXYGEN_SKIP_DOT)
        list(APPEND Doxygen_FIND_COMPONENTS dot)
    endif()
    set(_Doxygen_keep_backward_compat TRUE)
elseif(NOT doxygen IN_LIST Doxygen_FIND_COMPONENTS)
    list(INSERT Doxygen_FIND_COMPONENTS 0 doxygen)
endif()

#
# Find all requested components of Doxygen...
#
foreach(_comp IN LISTS Doxygen_FIND_COMPONENTS)
    if(_comp STREQUAL "doxygen")
        _Doxygen_find_doxygen()
    elseif(_comp STREQUAL "dia")
        _Doxygen_find_dia()
    elseif(_comp STREQUAL "dot")
        _Doxygen_find_dot()
    elseif(_comp STREQUAL "mscgen")
        _Doxygen_find_mscgen()
    else()
        message(WARNING "${_comp} is not a valid Doxygen component")
        set(Doxygen_${_comp}_FOUND FALSE)
        continue()
    endif()

    if(TARGET Doxygen::${_comp})
        set(Doxygen_${_comp}_FOUND TRUE)
    else()
        set(Doxygen_${_comp}_FOUND FALSE)
    endif()
endforeach()
unset(_comp)

# Verify find results
include(${CMAKE_CURRENT_LIST_DIR}/FindPackageHandleStandardArgs.cmake)
find_package_handle_standard_args(
    Doxygen
    REQUIRED_VARS DOXYGEN_EXECUTABLE
    VERSION_VAR DOXYGEN_VERSION
    HANDLE_COMPONENTS
)

#
# Backwards compatibility...
#
if(APPLE)
    # Restore the old app-bundle setting
    set(CMAKE_FIND_APPBUNDLE ${TEMP_DOXYGEN_SAVE_CMAKE_FIND_APPBUNDLE})
endif()

# Maintain the _FOUND variables as "YES" or "NO" for backwards
# compatibility. This allows people to substitute them directly into
# Doxyfile with configure_file().
if(DOXYGEN_FOUND)
    set(DOXYGEN_FOUND "YES")
else()
    set(DOXYGEN_FOUND "NO")
endif()
if(_Doxygen_keep_backward_compat)
    if(Doxygen_dot_FOUND)
        set(DOXYGEN_DOT_FOUND "YES")
    else()
        set(DOXYGEN_DOT_FOUND "NO")
    endif()

    # For backwards compatibility support for even older CMake versions
    set(DOXYGEN ${DOXYGEN_EXECUTABLE})
    set(DOT ${DOXYGEN_DOT_EXECUTABLE})

    # No need to keep any backward compatibility for `DOXYGEN_MSCGEN_XXX`
    # and `DOXYGEN_DIA_XXX` since they were not supported before component
    # support was added
endif()
unset(_Doxygen_keep_backward_compat)

#
# Allow full control of Doxygen from CMakeLists.txt
#

# Prepare a template Doxyfile and Doxygen's default values CMake file
if(TARGET Doxygen::doxygen)
    # If doxygen was found, use it to generate a minimal default Doxyfile.
    # We will delete this file after we have finished using it below to
    # generate the other files that doxygen_add_docs() will use.
    set(_Doxygen_tpl "${CMAKE_BINARY_DIR}/CMakeDoxyfile.tpl")
    execute_process(
        COMMAND "${DOXYGEN_EXECUTABLE}" -s -g "${_Doxygen_tpl}"
        OUTPUT_QUIET
        RESULT_VARIABLE _Doxygen_tpl_result
    )
    if(_Doxygen_tpl_result)
        message(FATAL_ERROR
                "Unable to generate Doxyfile template: ${_Doxygen_tpl_result}")
    elseif(NOT EXISTS "${_Doxygen_tpl}")
        message(FATAL_ERROR
                "Doxygen has failed to generate a Doxyfile template")
    endif()

    # Write a do-not-edit header to files we are going to generate...
    set(_Doxygen_dne_header
[[
#
# DO NOT EDIT! THIS FILE WAS GENERATED BY CMAKE!
#

]]
    )
    # We only need one copy of these across the whole build, since their
    # content is only dependent on the version of Doxygen being used. Therefore
    # we always put them at the top of the build tree so that they are in a
    # predictable location.
    set(_doxyfile_in       "${CMAKE_BINARY_DIR}/CMakeDoxyfile.in")
    set(_doxyfile_defaults "${CMAKE_BINARY_DIR}/CMakeDoxygenDefaults.cmake")

    file(WRITE "${_doxyfile_in}"       ${_Doxygen_dne_header})
    file(WRITE "${_doxyfile_defaults}" ${_Doxygen_dne_header})

    # Get strings containing a configuration key from the template Doxyfile
    # we obtained from this version of Doxygen. Because some options are split
    # across multiple lines by ending lines with backslashes, we cannot just
    # use file(STRINGS...) with a REGEX. Instead, read lines without a REGEX
    # so that file(STRINGS...) handles the trailing backslash as a line
    # continuation. It stores multi-lines as lists, so we then have to replace
    # the ";" list separator with backslashed newlines again so that we get the
    # original content stored back as the value part.
    file(STRINGS "${_Doxygen_tpl}" _file_lines)
    unset(_Doxygen_tpl_params)
    foreach(_line IN LISTS _file_lines)
        if(_line MATCHES "([A-Z][A-Z0-9_]+)( *=)(.*)")
            set(_key "${CMAKE_MATCH_1}")
            set(_eql "${CMAKE_MATCH_2}")
            set(_value "${CMAKE_MATCH_3}")
            string(REPLACE "\\" "\\\\" _value "${_value}")
            string(REPLACE ";" "\\\n" _value "${_value}")
            list(APPEND _Doxygen_tpl_params "${_key}${_eql}${_value}")
        endif()
    endforeach()

    # Build up a Doxyfile that provides @configVar@ substitutions for each
    # Doxygen config option as well as a separate CMake script which provides
    # the default value for each of those options if the project doesn't supply
    # them. Each config option will support substitution of a CMake variable
    # of the same name except with DOXYGEN_ prepended.
    foreach(_Doxygen_param IN LISTS _Doxygen_tpl_params)
        if(_Doxygen_param MATCHES "([A-Z][A-Z0-9_]+)( *)=( (.*))?")
            # Ok, this is a config key with a value
            if(CMAKE_MATCH_COUNT EQUAL 4)
                file(APPEND "${_doxyfile_in}"
                    "${CMAKE_MATCH_1}${CMAKE_MATCH_2}= @DOXYGEN_${CMAKE_MATCH_1}@\n")
                # Remove the backslashes we had to preserve to handle newlines
                string(REPLACE "\\\n" "\n" _value "${CMAKE_MATCH_4}")
                file(APPEND "${_doxyfile_defaults}"
"if(NOT DEFINED DOXYGEN_${CMAKE_MATCH_1})
    set(DOXYGEN_${CMAKE_MATCH_1} ${_value})
endif()
")
            # Ok, this is a config key with empty default value
            elseif(CMAKE_MATCH_COUNT EQUAL 2)
                file(APPEND "${_doxyfile_in}"
                    "${CMAKE_MATCH_1}${CMAKE_MATCH_2}= @DOXYGEN_${CMAKE_MATCH_1}@\n")
            else()
                message(AUTHOR_WARNING
"Unexpected line format! Code review required!\nFault line: ${_Doxygen_param}")
            endif()
        else()
            message(AUTHOR_WARNING
"Unexpected line format! Code review required!\nFault line: ${_Doxygen_param}")
        endif()
    endforeach()

    # Ok, dumped defaults are not needed anymore...
    file(REMOVE "${_Doxygen_tpl}")

    unset(_Doxygen_param)
    unset(_Doxygen_tpl_params)
    unset(_Doxygen_dne_header)
    unset(_Doxygen_tpl)

endif()

function(doxygen_quote_value VARIABLE)
    # Quote a value of the given variable if:
    # - VARIABLE parameter was really given
    # - the variable it names is defined and is not present in the list
    #   specified by DOXYGEN_VERBATIM_VARS (if set)
    # - the value of the named variable isn't already quoted
    # - the value has spaces
    if(VARIABLE AND DEFINED ${VARIABLE} AND
       NOT ${VARIABLE} MATCHES "^\".* .*\"$" AND ${VARIABLE} MATCHES " " AND
       NOT (DEFINED DOXYGEN_VERBATIM_VARS AND
            "${VARIABLE}" IN_LIST DOXYGEN_VERBATIM_VARS))
        set(${VARIABLE} "\"${${VARIABLE}}\"" PARENT_SCOPE)
    endif()
endfunction()

function(doxygen_list_to_quoted_strings LIST_VARIABLE)
    if(LIST_VARIABLE AND DEFINED ${LIST_VARIABLE})
        unset(_inputs)
        unset(_sep)
        unset(_verbatim)
        # Have to test if list items should be treated as verbatim here
        # because we lose the variable name when we pass just one list item
        # to doxygen_quote_value() below
        if(DEFINED DOXYGEN_VERBATIM_VARS AND
           "${LIST_VARIABLE}" IN_LIST DOXYGEN_VERBATIM_VARS)
            set(_verbatim True)
        endif()
        foreach(_in IN LISTS ${LIST_VARIABLE})
            if(NOT _verbatim)
                doxygen_quote_value(_in)
            endif()
            string(APPEND _inputs "${_sep}${_in}")
            set(_sep " ")
        endforeach()
        set(${LIST_VARIABLE} "${_inputs}" PARENT_SCOPE)
    endif()
endfunction()

function(doxygen_add_docs targetName)
    set(_options ALL)
    set(_one_value_args WORKING_DIRECTORY COMMENT)
    set(_multi_value_args)
    cmake_parse_arguments(_args
                          "${_options}"
                          "${_one_value_args}"
                          "${_multi_value_args}"
                          ${ARGN})

    if(NOT _args_COMMENT)
        set(_args_COMMENT "Generate API documentation for ${targetName}")
    endif()

    if(NOT _args_WORKING_DIRECTORY)
        set(_args_WORKING_DIRECTORY "${CMAKE_CURRENT_SOURCE_DIR}")
    endif()

    if(DEFINED DOXYGEN_INPUT)
        message(WARNING
"DOXYGEN_INPUT is set but it will be ignored. Pass the files and directories \
directly to the doxygen_add_docs() command instead.")
    endif()
    set(DOXYGEN_INPUT ${_args_UNPARSED_ARGUMENTS})

    if(NOT TARGET Doxygen::doxygen)
        message(FATAL_ERROR "Doxygen was not found, needed by \
doxygen_add_docs() for target ${targetName}")
    endif()

    # If not already defined, set some relevant defaults based on the
    # assumption that the documentation is for the whole project. Details
    # specified in the project() command will be used to populate a number of
    # these defaults.

    if(NOT DEFINED DOXYGEN_PROJECT_NAME)
        # The PROJECT_NAME tag is a single word (or a sequence of words
        # surrounded by double-quotes, unless you are using Doxywizard) that
        # should identify the project for which the documentation is generated.
        # This name is used in the title of most generated pages and in a few
        # other places. The default value is: My Project.
        set(DOXYGEN_PROJECT_NAME ${PROJECT_NAME})
    endif()

    if(NOT DEFINED DOXYGEN_PROJECT_NUMBER)
        # The PROJECT_NUMBER tag can be used to enter a project or revision
        # number. This could be handy for archiving the generated documentation
        # or if some version control system is used.
        set(DOXYGEN_PROJECT_NUMBER ${PROJECT_VERSION})
    endif()

    if(NOT DEFINED DOXYGEN_PROJECT_BRIEF)
        # Using the PROJECT_BRIEF tag one can provide an optional one line
        # description for a project that appears at the top of each page and
        # should give viewer a quick idea about the purpose of the project.
        # Keep the description short.
        set(DOXYGEN_PROJECT_BRIEF "${PROJECT_DESCRIPTION}")
    endif()

    if(NOT DEFINED DOXYGEN_RECURSIVE)
        # The RECURSIVE tag can be used to specify whether or not
        # subdirectories should be searched for input files as well. CMake
        # projects generally evolve to span multiple directories, so it makes
        # more sense for this to be on by default. Doxygen's default value
        # has this setting turned off, so we override it.
        set(DOXYGEN_RECURSIVE YES)
    endif()

    if(NOT DEFINED DOXYGEN_OUTPUT_DIRECTORY)
        # The OUTPUT_DIRECTORY tag is used to specify the (relative or
        # absolute) path into which the generated documentation will be
        # written. If a relative path is used, Doxygen will interpret it as
        # being relative to the location where doxygen was started, but we need
        # to run Doxygen in the source tree so that relative input paths work
        # intuitively. Therefore, we ensure that the output directory is always
        # an absolute path and if the project provided a relative path, we
        # treat it as relative to the current BINARY directory so that output
        # is not generated inside the source tree.
        set(DOXYGEN_OUTPUT_DIRECTORY "${CMAKE_CURRENT_BINARY_DIR}")
    elseif(NOT IS_ABSOLUTE "${DOXYGEN_OUTPUT_DIRECTORY}")
        get_filename_component(DOXYGEN_OUTPUT_DIRECTORY
                               "${DOXYGEN_OUTPUT_DIRECTORY}"
                               ABSOLUTE
                               BASE_DIR "${CMAKE_CURRENT_BINARY_DIR}")
    endif()

    if(NOT DEFINED DOXYGEN_HAVE_DOT)
        # If you set the HAVE_DOT tag to YES then doxygen will assume the dot
        # tool is available from the path. This tool is part of Graphviz (see:
        # http://www.graphviz.org/), a graph visualization toolkit from AT&T
        # and Lucent Bell Labs. The other options in this section have no
        # effect if this option is set to NO.
        # Doxygen's default value is: NO.
        if(Doxygen_dot_FOUND)
          set(DOXYGEN_HAVE_DOT "YES")
        else()
          set(DOXYGEN_HAVE_DOT "NO")
        endif()
    endif()

    if(NOT DEFINED DOXYGEN_DOT_MULTI_TARGETS)
        # Set the DOT_MULTI_TARGETS tag to YES to allow dot to generate
        # multiple output files in one run (i.e. multiple -o and -T options on
        # the command line). This makes dot run faster, but since only newer
        # versions of dot (>1.8.10) support this, Doxygen disables this feature
        # by default.
        # This tag requires that the tag HAVE_DOT is set to YES.
        set(DOXYGEN_DOT_MULTI_TARGETS YES)
    endif()

    if(NOT DEFINED DOXYGEN_GENERATE_LATEX)
        # If the GENERATE_LATEX tag is set to YES, doxygen will generate LaTeX
        # output. We only want the HTML output enabled by default, so we turn
        # this off if the project hasn't specified it.
        set(DOXYGEN_GENERATE_LATEX NO)
    endif()

    if(NOT DEFINED DOXYGEN_WARN_FORMAT)
        if(CMAKE_VS_MSBUILD_COMMAND OR CMAKE_VS_DEVENV_COMMAND)
            # The WARN_FORMAT tag determines the format of the warning messages
            # that doxygen can produce. The string should contain the $file,
            # $line and $text tags, which will be replaced by the file and line
            # number from which the warning originated and the warning text.
            # Optionally, the format may contain $version, which will be
            # replaced by the version of the file (if it could be obtained via
            # FILE_VERSION_FILTER).
            # Doxygen's default value is: $file:$line: $text
            set(DOXYGEN_WARN_FORMAT "$file($line) : $text ")
        endif()
    endif()

    if(DEFINED DOXYGEN_WARN_LOGFILE AND NOT IS_ABSOLUTE "${DOXYGEN_WARN_LOGFILE}")
        # The WARN_LOGFILE tag can be used to specify a file to which warning and error
        # messages should be written. If left blank the output is written to standard
        # error (stderr).
        get_filename_component(DOXYGEN_WARN_LOGFILE
                               "${DOXYGEN_WARN_LOGFILE}"
                               ABSOLUTE
                               BASE_DIR "${CMAKE_CURRENT_BINARY_DIR}")
    endif()

    # Any files from the INPUT that match any of the EXCLUDE_PATTERNS will be
    # excluded from the set of input files. We provide some additional patterns
    # to prevent commonly unwanted things from CMake builds being pulled in.
    #
    # Note that the wildcards are matched against the file with absolute path,
    # so to exclude all test directories for example use the pattern */test/*
    list(
        APPEND
        DOXYGEN_EXCLUDE_PATTERNS
        "*/.git/*"
        "*/.svn/*"
        "*/.hg/*"
        "*/CMakeFiles/*"
        "*/_CPack_Packages/*"
        "DartConfiguration.tcl"
        "CMakeLists.txt"
        "CMakeCache.txt"
    )

    # Now bring in Doxgen's defaults for those things the project has not
    # already set and we have not provided above
    include("${CMAKE_BINARY_DIR}/CMakeDoxygenDefaults.cmake" OPTIONAL)

    # Cleanup built HTMLs on "make clean"
    # TODO Any other dirs?
    if(DOXYGEN_GENERATE_HTML)
        if(IS_ABSOLUTE "${DOXYGEN_HTML_OUTPUT}")
            set(_args_clean_html_dir "${DOXYGEN_HTML_OUTPUT}")
        else()
            set(_args_clean_html_dir
                "${DOXYGEN_OUTPUT_DIRECTORY}/${DOXYGEN_HTML_OUTPUT}")
        endif()
        set_property(DIRECTORY APPEND PROPERTY
            ADDITIONAL_CLEAN_FILES "${_args_clean_html_dir}")
    endif()

    # Build up a list of files we can identify from the inputs so we can list
    # them as SOURCES in the custom target (makes them display in IDEs). We
    # must do this before we transform the various DOXYGEN_... variables below
    # because we need to process DOXYGEN_INPUT as a list first.
    unset(_sources)
    foreach(_item IN LISTS DOXYGEN_INPUT)
        get_filename_component(_abs_item "${_item}" ABSOLUTE
                               BASE_DIR "${_args_WORKING_DIRECTORY}")
        if(EXISTS "${_abs_item}" AND
           NOT IS_DIRECTORY "${_abs_item}" AND
           NOT IS_SYMLINK "${_abs_item}")
            list(APPEND _sources "${_abs_item}")
        endif()
    endforeach()
    if(_sources)
        list(INSERT _sources 0 SOURCES)
    endif()

    # Transform known list type options into space separated strings.
    set(_doxygen_list_options
        ABBREVIATE_BRIEF
        ALIASES
        CITE_BIB_FILES
        DIAFILE_DIRS
        DOTFILE_DIRS
        DOT_FONTPATH
        ENABLED_SECTIONS
        EXAMPLE_PATH
        EXAMPLE_PATTERNS
        EXCLUDE
        EXCLUDE_PATTERNS
        EXCLUDE_SYMBOLS
        EXPAND_AS_DEFINED
        EXTENSION_MAPPING
        EXTRA_PACKAGES
        EXTRA_SEARCH_MAPPINGS
        FILE_PATTERNS
        FILTER_PATTERNS
        FILTER_SOURCE_PATTERNS
        HTML_EXTRA_FILES
        HTML_EXTRA_STYLESHEET
        IGNORE_PREFIX
        IMAGE_PATH
        INCLUDE_FILE_PATTERNS
        INCLUDE_PATH
        INPUT
        LATEX_EXTRA_FILES
        LATEX_EXTRA_STYLESHEET
        MATHJAX_EXTENSIONS
        MSCFILE_DIRS
        PLANTUML_INCLUDE_PATH
        PREDEFINED
        QHP_CUST_FILTER_ATTRS
        QHP_SECT_FILTER_ATTRS
        STRIP_FROM_INC_PATH
        STRIP_FROM_PATH
        TAGFILES
        TCL_SUBST
    )
    foreach(_item IN LISTS _doxygen_list_options)
        doxygen_list_to_quoted_strings(DOXYGEN_${_item})
    endforeach()

    # Transform known single value variables which may contain spaces, such as
    # paths or description strings.
    set(_doxygen_quoted_options
        CHM_FILE
        DIA_PATH
        DOCBOOK_OUTPUT
        DOCSET_FEEDNAME
        DOCSET_PUBLISHER_NAME
        DOT_FONTNAME
        DOT_PATH
        EXTERNAL_SEARCH_ID
        FILE_VERSION_FILTER
        GENERATE_TAGFILE
        HHC_LOCATION
        HTML_FOOTER
        HTML_HEADER
        HTML_OUTPUT
        HTML_STYLESHEET
        INPUT_FILTER
        LATEX_FOOTER
        LATEX_HEADER
        LATEX_OUTPUT
        LAYOUT_FILE
        MAN_OUTPUT
        MAN_SUBDIR
        MATHJAX_CODEFILE
        MSCGEN_PATH
        OUTPUT_DIRECTORY
        PERL_PATH
        PLANTUML_JAR_PATH
        PROJECT_BRIEF
        PROJECT_LOGO
        PROJECT_NAME
        QCH_FILE
        QHG_LOCATION
        QHP_CUST_FILTER_NAME
        QHP_VIRTUAL_FOLDER
        RTF_EXTENSIONS_FILE
        RTF_OUTPUT
        RTF_STYLESHEET_FILE
        SEARCHDATA_FILE
        USE_MDFILE_AS_MAINPAGE
        WARN_FORMAT
        WARN_LOGFILE
        XML_OUTPUT
    )

    # Store the unmodified value of DOXYGEN_OUTPUT_DIRECTORY prior to invoking
    # doxygen_quote_value() below. This will mutate the string specifically for
    # consumption by Doxygen's config file, which we do not want when we use it
    # later in the custom target's commands.
    set( _original_doxygen_output_dir ${DOXYGEN_OUTPUT_DIRECTORY} )

    foreach(_item IN LISTS _doxygen_quoted_options)
        doxygen_quote_value(DOXYGEN_${_item})
    endforeach()

    # Prepare doxygen configuration file
    set(_doxyfile_template "${CMAKE_BINARY_DIR}/CMakeDoxyfile.in")
    set(_target_doxyfile "${CMAKE_CURRENT_BINARY_DIR}/Doxyfile.${targetName}")
    configure_file("${_doxyfile_template}" "${_target_doxyfile}")

    unset(_all)
    if(${_args_ALL})
        set(_all ALL)
    endif()

    # Add the target
    add_custom_target( ${targetName} ${_all} VERBATIM
        COMMAND ${CMAKE_COMMAND} -E make_directory ${_original_doxygen_output_dir}
        COMMAND "${DOXYGEN_EXECUTABLE}" "${_target_doxyfile}"
        WORKING_DIRECTORY "${_args_WORKING_DIRECTORY}"
        DEPENDS "${_target_doxyfile}"
        COMMENT "${_args_COMMENT}"
        ${_sources}
    )

endfunction()

cmake_policy(POP)