CMake/Modules/FindPkgConfig.cmake

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

#[========================================[.rst:
FindPkgConfig
-------------

A ``pkg-config`` module for CMake.

Finds the ``pkg-config`` executable and provides commands to use it in
CMake:

.. code-block:: cmake

  find_package(PkgConfig [<version>] [QUIET] [REQUIRED] [...])

``pkg-config`` is a command-line program for configuring build dependency
information.  Initially developed by FreeDesktop, it is also available in
several implementations, such as pkgconf, u-config, and similar.  It reads
package data from the so-called PC metadata files (``<module-name>.pc``)
that may come installed with packages.  This module is a wrapper around the
``pkg-config`` command-line executable.

Result Variables
^^^^^^^^^^^^^^^^

This module defines the following variables:

``PkgConfig_FOUND``
  .. versionadded:: 3.3

  Boolean indicating whether the (requested version of) ``pkg-config``
  executable is found.

``PkgConfig_VERSION``
  .. versionadded:: 4.2

  The version of ``pkg-config`` that was found.

``PKG_CONFIG_EXECUTABLE``
  The pathname of the ``pkg-config`` program.

``PKG_CONFIG_ARGN``
  .. versionadded:: 3.22

  A list of arguments to pass to ``pkg-config``.

Both ``PKG_CONFIG_EXECUTABLE`` and ``PKG_CONFIG_ARGN`` are initialized by the
module, but may be overridden by the user.  See `Hints`_ for how these
variables are initialized.

Commands
^^^^^^^^

This module provides the following commands, if ``pkg-config`` is found:

* :command:`pkg_check_modules`
* :command:`pkg_search_module`
* :command:`pkg_get_variable`

.. command:: pkg_check_modules

  Checks for all the given modules, setting a variety of result variables
  in the calling scope:

  .. code-block:: cmake

    pkg_check_modules(
      <prefix>
      [QUIET]
      [REQUIRED]
      [NO_CMAKE_PATH]
      [NO_CMAKE_ENVIRONMENT_PATH]
      [IMPORTED_TARGET [GLOBAL]]
      <module-spec> [<module-spec>...]
    )

  .. rubric:: The arguments are:

  ``<prefix>``
    Prefix string prepended to result variables for the specified modules.

  ``QUIET``
    When this argument is given, no status messages will be printed.

  ``REQUIRED``
    When this argument is given, the command will fail with an error if any
    of the specified module(s) could not be found.

  ``NO_CMAKE_PATH``, ``NO_CMAKE_ENVIRONMENT_PATH``
    .. versionadded:: 3.3

    The :variable:`CMAKE_PREFIX_PATH`,
    :variable:`CMAKE_FRAMEWORK_PATH`, and :variable:`CMAKE_APPBUNDLE_PATH` cache
    and environment variables will be added to the ``pkg-config`` search path.
    The ``NO_CMAKE_PATH`` and ``NO_CMAKE_ENVIRONMENT_PATH`` arguments
    disable this behavior for the cache variables and environment variables
    respectively.
    The ``PKG_CONFIG_USE_CMAKE_PREFIX_PATH`` variable set to ``FALSE``
    disables this behavior globally.

    .. This was actually added in 3.1, but didn't work until 3.3.

  ``IMPORTED_TARGET [GLOBAL]``
    .. versionadded:: 3.7

    This argument will create an :ref:`imported target <Imported Targets>`
    named ``PkgConfig::<prefix>`` that can be passed directly as an argument
    to :command:`target_link_libraries`.  It will encapsulate usage
    requirements for all specified modules ``<module-spec>...`` at once.

    .. This was actually added in 3.6, but didn't work until 3.7.

    ``GLOBAL``
      .. versionadded:: 3.13

      This argument is used together with ``IMPORTED_TARGET`` and will make
      the imported target available in global scope.

    .. versionadded:: 3.15
      Non-library linker options reported by ``pkg-config`` are stored in the
      :prop_tgt:`INTERFACE_LINK_OPTIONS` target property.

    .. versionchanged:: 3.18
      Include directories specified with ``-isystem`` are stored in the
      :prop_tgt:`INTERFACE_INCLUDE_DIRECTORIES` target property.  Previous
      versions of CMake left them in the :prop_tgt:`INTERFACE_COMPILE_OPTIONS`
      property.

  ``<module-spec>``
    Each ``<module-spec>`` can be either a bare module name (as defined in
    its PC metadata file name ``<module-name>.pc``) or it can be a module
    name with a version constraint (operators ``=``, ``<``, ``>``, ``<=``
    and ``>=`` are supported).  The following are examples for a module
    named ``foo`` with various constraints:

    - ``foo`` matches any version.
    - ``foo<2`` only matches versions before 2.
    - ``foo>=3.1`` matches any version from 3.1 or later.
    - ``foo=1.2.3`` requires that foo must be exactly version 1.2.3.

  .. rubric:: Result Variables

  The following variables may be set upon return.  Two sets of values exist:
  One for the common case (``<XXX> = <prefix>``) and another for the
  information ``pkg-config`` provides when called with the ``--static``
  option (``<XXX> = <prefix>_STATIC``).

  ``<XXX>_FOUND``
    Boolean variable set to 1 if module(s) exist.
  ``<XXX>_LIBRARIES``
    A list of only the libraries (without the ``-l``).
  ``<XXX>_LINK_LIBRARIES``
    The libraries and their absolute paths.
  ``<XXX>_LIBRARY_DIRS``
    The paths of the libraries (without the ``-L``).
  ``<XXX>_LDFLAGS``
    All required linker flags.
  ``<XXX>_LDFLAGS_OTHER``
    All other linker flags.
  ``<XXX>_INCLUDE_DIRS``
    The ``-I`` preprocessor flags (without the ``-I``).
  ``<XXX>_CFLAGS``
    All required cflags.
  ``<XXX>_CFLAGS_OTHER``
    The other compiler flags.

  All but ``<XXX>_FOUND`` may be a :ref:`semicolon-separated list
  <CMake Language Lists>` if the
  associated variable returned from ``pkg-config`` has multiple values.

  .. versionchanged:: 3.18
    Include directories specified with ``-isystem`` are stored in the
    ``<XXX>_INCLUDE_DIRS`` variable.  Previous versions of CMake left them
    in ``<XXX>_CFLAGS_OTHER``.

  There are some special variables whose prefix depends on the number of
  ``<module-spec>`` given.  When there is only one ``<module-spec>``,
  ``<YYY>`` will simply be ``<prefix>``, but if two or more ``<module-spec>``
  items are given, ``<YYY>`` will be ``<prefix>_<module-name>``.

  ``<YYY>_VERSION``
    The version of the module.
  ``<YYY>_PREFIX``
    The prefix directory of the module.
  ``<YYY>_INCLUDEDIR``
    The include directory of the module.
  ``<YYY>_LIBDIR``
    The lib directory of the module.

  .. versionchanged:: 3.8
    For any given ``<prefix>``, ``pkg_check_modules()`` can be called multiple
    times with different parameters.  Previous versions of CMake cached and
    returned the first successful result.

  .. versionchanged:: 3.16
    If a full path to the found library can't be determined, but it's still
    visible to the linker, pass it through as ``-l<name>``.  Previous versions
    of CMake failed in this case.

.. command:: pkg_search_module

  Searches for the first successful match from one or more provided module
  specifications:

  .. code-block:: cmake

    pkg_search_module(
      <prefix>
      [QUIET]
      [REQUIRED]
      [NO_CMAKE_PATH]
      [NO_CMAKE_ENVIRONMENT_PATH]
      [IMPORTED_TARGET [GLOBAL]]
      <module-spec> [<module-spec>...]
    )

  The behavior and arguments of this command are the same as
  :command:`pkg_check_modules`, except that rather than checking for all
  the specified modules, it searches for just the first successful match.

  This command can be used, for example, when some package is known to have
  possible multiple ``<module-spec>`` on different platforms or versions for
  the same package.

  .. rubric:: Result Variables

  This command defines the same variables as described above with addition
  to:

  ``<prefix>_MODULE_NAME``
    .. versionadded:: 3.16

    If a module is found, the ``<prefix>_MODULE_NAME`` variable will contain
    the name of the matching module. This variable can be used if the
    :command:`pkg_get_variable` command needs to be called with the
    ``<module-name>`` argument that was found by the
    :command:`pkg_search_module`.

.. command:: pkg_get_variable

  .. versionadded:: 3.4

  Retrieves the value of a ``pkg-config`` variable and stores it in the
  result variable in the calling scope:

  .. code-block:: cmake

    pkg_get_variable(
      <result-var>
      <module-name>
      <var-name>
      [DEFINE_VARIABLES <key>=<value>...]
    )

  .. rubric:: The arguments are:

  ``<result-var>``
    Name of the result variable that will contain the value of ``pkg-config``
    variable.  If ``pkg-config`` returns multiple values for the specified
    variable ``<var-name>``, ``<result-var>`` will contain a
    :ref:`semicolon-separated list <CMake Language Lists>`.

  ``<module-name>``
    Name of the module as defined in its PC metadata file name
    (``<module-name>.pc``).

  ``<var-name>``
    The ``pkg-config`` variable name from the PC metadata file
    ``<module-name>.pc``.

  ``DEFINE_VARIABLES <key>=<value>...``
    .. versionadded:: 3.28

    Specify key-value pairs to redefine variables affecting the variable
    retrieved with ``pkg-config``.

Hints
^^^^^

This module accepts the following variables before calling
``find_package(PkgConfig)`` to influence this module's behavior:

``ENV{PKG_CONFIG_PATH}``
  Environment variable that specifies additional paths in which
  ``pkg-config`` will search for its ``.pc`` files.  The ``pkg-config``
  tool by default uses this variable, while CMake also provides more common
  :variable:`CMAKE_PREFIX_PATH` variable to specify additional paths where
  to look for packages and their ``.pc`` files.

``ENV{PKG_CONFIG}``
  .. versionadded:: 3.1

  Environment variable that can be set to the path of the ``pkg-config``
  executable and can be used to initialize the ``PKG_CONFIG_EXECUTABLE``
  variable, if it has not yet been set.

``PKG_CONFIG_EXECUTABLE``

  This cache variable can be set to the path of the ``pkg-config``
  executable.  :command:`find_program` is called internally by the module
  with this variable.

  .. versionchanged:: 3.22
    If the ``PKG_CONFIG`` environment variable is set, only the first
    argument is taken from it when using it as a hint.

``PKG_CONFIG_ARGN``

  .. versionadded:: 3.22

  This cache variable can be set to a list of arguments to additionally pass
  to ``pkg-config`` if needed. If not provided, it will be initialized from
  the ``PKG_CONFIG`` environment variable, if set. The first argument in that
  environment variable is assumed to be the ``pkg-config`` program, while all
  remaining arguments after that are used to initialize ``PKG_CONFIG_ARGN``.
  If no such environment variable is defined, ``PKG_CONFIG_ARGN`` is
  initialized to an empty string. The module does not update the variable once
  it has been set in the cache.

``PKG_CONFIG_USE_CMAKE_PREFIX_PATH``

  .. versionadded:: 3.1

  Specifies whether :command:`pkg_check_modules` and
  :command:`pkg_search_module` should add the paths in the
  :variable:`CMAKE_PREFIX_PATH`, :variable:`CMAKE_FRAMEWORK_PATH` and
  :variable:`CMAKE_APPBUNDLE_PATH` cache and environment variables to the
  ``pkg-config`` search path.

  If this variable is not set, this behavior is enabled by default if
  :variable:`CMAKE_MINIMUM_REQUIRED_VERSION` is 3.1 or later, disabled
  otherwise.

Deprecated Variables
^^^^^^^^^^^^^^^^^^^^

The following variables are provided for backward compatibility:

``PKG_CONFIG_FOUND``
  .. deprecated:: 4.2
    Use ``PkgConfig_FOUND``, which has the same value.

  Boolean indicating whether the (requested version of) ``pkg-config``
  executable is found.

``PKG_CONFIG_VERSION_STRING``
  .. deprecated:: 4.2
    Use ``PkgConfig_VERSION``, which has the same value.

  The version of ``pkg-config`` that was found.

Examples
^^^^^^^^

Examples: Finding pkg-config
""""""""""""""""""""""""""""

Finding ``pkg-config``:

.. code-block:: cmake

  find_package(PkgConfig)

Finding ``pkg-config`` and making it required (if not found, processing stops
with an error message):

.. code-block:: cmake

  find_package(PkgConfig REQUIRED)

Finding ``pkg-config`` quietly without printing status message as commonly
used in find modules:

.. code-block:: cmake

  find_package(PkgConfig QUIET)

Examples: Using ``pkg_check_modules()``
"""""""""""""""""""""""""""""""""""""""

Checking for any version of glib2.  If found, the output variable
``GLIB2_VERSION`` will hold the actual version found:

.. code-block:: cmake

  find_package(PkgConfig QUIET)

  if(PkgConfig_FOUND)
    pkg_check_modules(GLIB2 glib-2.0)
  endif()

The following example looks for at least version 2.10 of glib2.  If found,
the output variable ``GLIB2_VERSION`` will hold the actual version found:

.. code-block:: cmake

  find_package(PkgConfig QUIET)

  if(PkgConfig_FOUND)
    pkg_check_modules(GLIB2 glib-2.0>=2.10)
  endif()

The following example looks for both glib2-2.0 (at least version 2.10) and
any version of gtk2+-2.0.  Only if both are found will ``FOO`` be considered
found.  The ``FOO_glib-2.0_VERSION`` and ``FOO_gtk+-2.0_VERSION`` variables
will be set to their respective found module versions.

.. code-block:: cmake

  find_package(PkgConfig QUIET)

  if(PkgConfig_FOUND)
    pkg_check_modules(FOO glib-2.0>=2.10 gtk+-2.0)
  endif()

The following example requires any version of ``xrender``:

.. code-block:: cmake

  find_package(PkgConfig QUIET REQUIRED)
  pkg_check_modules(XRENDER REQUIRED xrender)

Example output variables set by a successful call::

  XRENDER_LIBRARIES=Xrender;X11
  XRENDER_STATIC_LIBRARIES=Xrender;X11;pthread;Xau;Xdmcp

Example: Using ``pkg_search_module()``
""""""""""""""""""""""""""""""""""""""

Searching for LibXml2 package, which might be provided with different
module specifications (``libxml-2.0`` or ``libxml2``):

.. code-block:: cmake

  find_package(PkgConfig QUIET)

  if(PkgConfig_FOUND)
    pkg_search_module(BAR libxml-2.0 libxml2 libxml>=2)
  endif()

Example: Creating Imported Target
"""""""""""""""""""""""""""""""""

In the following example an imported target is created from the module
specifications to use in the project directly without using a find module.
These imported targets can be used, for example, in cases, where package is
known to support ``pkg-config`` on all supported platforms:

.. code-block:: cmake

  find_package(PkgConfig QUIET REQUIRED)
  pkg_check_modules(GTK REQUIRED IMPORTED_TARGET gtk4>=4.14)
  target_link_libraries(example PRIVATE PkgConfig::GTK)

Example: Using ``pkg_get_variable()``
"""""""""""""""""""""""""""""""""""""

Retrieving the value of ``pkg-config`` variable ``girdir`` from the package
Gobject:

.. code-block:: cmake

  find_package(PkgConfig QUIET)

  if(PkgConfig_FOUND)
    pkg_get_variable(GI_GIRDIR gobject-introspection-1.0 girdir)
  endif()

  message(STATUS "${GI_GIRDIR}")

See Also
^^^^^^^^

* The :command:`cmake_pkg_config` command for a modern and more advanced
  way to work with ``pkg-config`` in CMake without requiring ``pkg-config``
  executable to be installed.
* :ref:`Find Modules` for details how to write a find module.
#]========================================]

### Common stuff ####
set(PKG_CONFIG_VERSION 1)

# find pkg-config, use PKG_CONFIG if set
if((NOT PKG_CONFIG_EXECUTABLE) AND (NOT "$ENV{PKG_CONFIG}" STREQUAL ""))
  separate_arguments(PKG_CONFIG_FROM_ENV_SPLIT NATIVE_COMMAND PROGRAM SEPARATE_ARGS "$ENV{PKG_CONFIG}")
  list(LENGTH PKG_CONFIG_FROM_ENV_SPLIT PKG_CONFIG_FROM_ENV_SPLIT_ARGC)
  if(PKG_CONFIG_FROM_ENV_SPLIT_ARGC GREATER 0)
    list(GET PKG_CONFIG_FROM_ENV_SPLIT 0 PKG_CONFIG_FROM_ENV_ARGV0)
    if(PKG_CONFIG_FROM_ENV_SPLIT_ARGC GREATER 1)
      list(SUBLIST PKG_CONFIG_FROM_ENV_SPLIT 1 -1 PKG_CONFIG_ARGN)
    endif()
    set(PKG_CONFIG_EXECUTABLE "${PKG_CONFIG_FROM_ENV_ARGV0}" CACHE FILEPATH "pkg-config executable")
  endif()
endif()

set(PKG_CONFIG_NAMES "pkg-config")
if(CMAKE_HOST_WIN32)
  list(PREPEND PKG_CONFIG_NAMES "pkg-config.bat")
  set(_PKG_CONFIG_VALIDATOR VALIDATOR __FindPkgConfig_EXECUTABLE_VALIDATOR)
  function(__FindPkgConfig_EXECUTABLE_VALIDATOR result_var candidate)
    if(candidate MATCHES "\\.[Ee][Xx][Ee]$")
      return()
    endif()
    # Exclude the pkg-config distributed with Strawberry Perl.
    execute_process(COMMAND "${candidate}" --help OUTPUT_VARIABLE _output ERROR_VARIABLE  _output RESULT_VARIABLE _result)
    if(NOT _result EQUAL 0 OR _output MATCHES "Pure-Perl")
      set("${result_var}" FALSE PARENT_SCOPE)
    endif()
  endfunction()
else()
  set(_PKG_CONFIG_VALIDATOR "")
endif()
list(APPEND PKG_CONFIG_NAMES "pkgconf")

find_program(PKG_CONFIG_EXECUTABLE
  NAMES ${PKG_CONFIG_NAMES}
  NAMES_PER_DIR
  DOC "pkg-config executable"
  ${_PKG_CONFIG_VALIDATOR})
mark_as_advanced(PKG_CONFIG_EXECUTABLE)
unset(_PKG_CONFIG_VALIDATOR)

set(PKG_CONFIG_ARGN "${PKG_CONFIG_ARGN}" CACHE STRING "Arguments to supply to pkg-config")
mark_as_advanced(PKG_CONFIG_ARGN)

set(_PKG_CONFIG_FAILURE_MESSAGE "")
if (PKG_CONFIG_EXECUTABLE)
  execute_process(COMMAND ${PKG_CONFIG_EXECUTABLE} ${PKG_CONFIG_ARGN} --version
    OUTPUT_VARIABLE PkgConfig_VERSION OUTPUT_STRIP_TRAILING_WHITESPACE
    ERROR_VARIABLE _PKG_CONFIG_VERSION_ERROR ERROR_STRIP_TRAILING_WHITESPACE
    RESULT_VARIABLE _PKG_CONFIG_VERSION_RESULT
    )

  if (NOT _PKG_CONFIG_VERSION_RESULT EQUAL 0)
    string(REPLACE "\n" "\n    " _PKG_CONFIG_VERSION_ERROR "      ${_PKG_CONFIG_VERSION_ERROR}")
    if(PKG_CONFIG_ARGN)
      string(REPLACE ";" " " PKG_CONFIG_ARGN " ${PKG_CONFIG_ARGN}")
    endif()
    string(APPEND _PKG_CONFIG_FAILURE_MESSAGE
      "The command\n"
      "      \"${PKG_CONFIG_EXECUTABLE}\"${PKG_CONFIG_ARGN} --version\n"
      "    failed with output:\n${PkgConfig_VERSION}\n"
      "    stderr: \n${_PKG_CONFIG_VERSION_ERROR}\n"
      "    result: \n${_PKG_CONFIG_VERSION_RESULT}"
      )
    set(PKG_CONFIG_EXECUTABLE "")
    set(PKG_CONFIG_ARGN "")
    unset(PkgConfig_VERSION)
  endif ()
  unset(_PKG_CONFIG_VERSION_RESULT)
endif ()

# For backward compatibility.
unset(PKG_CONFIG_VERSION_STRING)
if(DEFINED PkgConfig_VERSION)
  set(PKG_CONFIG_VERSION_STRING "${PkgConfig_VERSION}")
endif()

include(FindPackageHandleStandardArgs)
find_package_handle_standard_args(PkgConfig
                                  REQUIRED_VARS PKG_CONFIG_EXECUTABLE
                                  REASON_FAILURE_MESSAGE "${_PKG_CONFIG_FAILURE_MESSAGE}"
                                  VERSION_VAR PkgConfig_VERSION)

# This is needed because the module name is "PkgConfig" but the name of
# this variable has always been PKG_CONFIG_FOUND so this isn't automatically
# handled by FPHSA.
set(PKG_CONFIG_FOUND "${PkgConfig_FOUND}")

# Unsets the given variables
macro(_pkgconfig_unset var)
  # Clear normal variable (possibly set by project code).
  unset(${var})
  # Store as cache variable.
  # FIXME: Add a policy to switch to a normal variable.
  set(${var} "" CACHE INTERNAL "")
endmacro()

macro(_pkgconfig_set var value)
  # Clear normal variable (possibly set by project code).
  unset(${var})
  # Store as cache variable.
  # FIXME: Add a policy to switch to a normal variable.
  set(${var} ${value} CACHE INTERNAL "")
endmacro()

# Invokes pkgconfig, cleans up the result and sets variables
macro(_pkgconfig_invoke _pkglist _prefix _varname _regexp)
  set(_pkgconfig_invoke_result)

  execute_process(
    COMMAND ${PKG_CONFIG_EXECUTABLE} ${PKG_CONFIG_ARGN} ${ARGN} ${_pkglist}
    OUTPUT_VARIABLE _pkgconfig_invoke_result
    RESULT_VARIABLE _pkgconfig_failed
    OUTPUT_STRIP_TRAILING_WHITESPACE)

  if (_pkgconfig_failed)
    set(_pkgconfig_${_varname} "")
    _pkgconfig_unset(${_prefix}_${_varname})
  else()
    string(REGEX REPLACE "[\r\n]"       " " _pkgconfig_invoke_result "${_pkgconfig_invoke_result}")

    if (NOT ${_regexp} STREQUAL "")
      string(REGEX REPLACE "${_regexp}" " " _pkgconfig_invoke_result "${_pkgconfig_invoke_result}")
    endif()

    # pkg-config <0.29.1 and pkgconf <1.5.1 prints quoted variables without unquoting
    # unquote only if quotes are first and last characters
    if((PkgConfig_VERSION VERSION_LESS 0.29.1) OR
        (PkgConfig_VERSION VERSION_GREATER_EQUAL 1.0 AND PkgConfig_VERSION VERSION_LESS 1.5.1))
      if (_pkgconfig_invoke_result MATCHES "^\"(.*)\"$")
        set(_pkgconfig_invoke_result "${CMAKE_MATCH_1}")
      elseif(_pkgconfig_invoke_result MATCHES "^'(.*)'$")
        set(_pkgconfig_invoke_result "${CMAKE_MATCH_1}")
      endif()
    endif()

    # pkg-config can represent "spaces within an argument" by backslash-escaping the space.
    # UNIX_COMMAND mode treats backslash-escaped spaces as "not a space that delimits arguments".
    separate_arguments(_pkgconfig_invoke_result UNIX_COMMAND "${_pkgconfig_invoke_result}")

    #message(STATUS "  ${_varname} ... ${_pkgconfig_invoke_result}")
    set(_pkgconfig_${_varname} ${_pkgconfig_invoke_result})
    _pkgconfig_set(${_prefix}_${_varname} "${_pkgconfig_invoke_result}")
  endif()
endmacro()

# Internal version of pkg_get_variable; expects PKG_CONFIG_PATH to already be set
function (_pkg_get_variable result pkg variable)
  _pkgconfig_invoke("${pkg}" "prefix" "result" "" "--variable=${variable}")
  set("${result}"
    "${prefix_result}"
    PARENT_SCOPE)
endfunction ()

# Invokes pkgconfig two times; once without '--static' and once with
# '--static'
macro(_pkgconfig_invoke_dyn _pkglist _prefix _varname cleanup_regexp)
  _pkgconfig_invoke("${_pkglist}" ${_prefix}        ${_varname} "${cleanup_regexp}" ${ARGN})
  _pkgconfig_invoke("${_pkglist}" ${_prefix} STATIC_${_varname} "${cleanup_regexp}" --static  ${ARGN})
endmacro()

# Splits given arguments into options and a package list
macro(_pkgconfig_parse_options _result _is_req _is_silent _no_cmake_path _no_cmake_environment_path _imp_target _imp_target_global)
  set(${_is_req} 0)
  set(${_is_silent} 0)
  set(${_no_cmake_path} 0)
  set(${_no_cmake_environment_path} 0)
  set(${_imp_target} 0)
  set(${_imp_target_global} 0)
  if(DEFINED PKG_CONFIG_USE_CMAKE_PREFIX_PATH)
    if(NOT PKG_CONFIG_USE_CMAKE_PREFIX_PATH)
      set(${_no_cmake_path} 1)
      set(${_no_cmake_environment_path} 1)
    endif()
  elseif(CMAKE_MINIMUM_REQUIRED_VERSION VERSION_LESS 3.1)
    set(${_no_cmake_path} 1)
    set(${_no_cmake_environment_path} 1)
  endif()

  foreach(_pkg ${ARGN})
    if (_pkg STREQUAL "REQUIRED")
      set(${_is_req} 1)
    endif ()
    if (_pkg STREQUAL "QUIET")
      set(${_is_silent} 1)
    endif ()
    if (_pkg STREQUAL "NO_CMAKE_PATH")
      set(${_no_cmake_path} 1)
    endif()
    if (_pkg STREQUAL "NO_CMAKE_ENVIRONMENT_PATH")
      set(${_no_cmake_environment_path} 1)
    endif()
    if (_pkg STREQUAL "IMPORTED_TARGET")
      set(${_imp_target} 1)
    endif()
    if (_pkg STREQUAL "GLOBAL")
      set(${_imp_target_global} 1)
    endif()
  endforeach()

  if (${_imp_target_global} AND NOT ${_imp_target})
    message(SEND_ERROR "the argument GLOBAL may only be used together with IMPORTED_TARGET")
  endif()

  set(${_result} ${ARGN})
  list(REMOVE_ITEM ${_result} "REQUIRED")
  list(REMOVE_ITEM ${_result} "QUIET")
  list(REMOVE_ITEM ${_result} "NO_CMAKE_PATH")
  list(REMOVE_ITEM ${_result} "NO_CMAKE_ENVIRONMENT_PATH")
  list(REMOVE_ITEM ${_result} "IMPORTED_TARGET")
  list(REMOVE_ITEM ${_result} "GLOBAL")
endmacro()

# Add the content of a variable or an environment variable to a list of
# paths
# Usage:
#  - _pkgconfig_add_extra_path(_extra_paths VAR)
#  - _pkgconfig_add_extra_path(_extra_paths ENV VAR)
function(_pkgconfig_add_extra_path _extra_paths_var _var)
  set(_is_env 0)
  if(ARGC GREATER 2 AND _var STREQUAL "ENV")
    set(_var ${ARGV2})
    set(_is_env 1)
  endif()
  if(NOT _is_env)
    if(NOT "${${_var}}" STREQUAL "")
      list(APPEND ${_extra_paths_var} ${${_var}})
    endif()
  else()
    if(NOT "$ENV{${_var}}" STREQUAL "")
      file(TO_CMAKE_PATH "$ENV{${_var}}" _path)
      list(APPEND ${_extra_paths_var} ${_path})
      unset(_path)
    endif()
  endif()
  set(${_extra_paths_var} ${${_extra_paths_var}} PARENT_SCOPE)
endfunction()

# scan the LDFLAGS returned by pkg-config for library directories and
# libraries, figure out the absolute paths of that libraries in the
# given directories
function(_pkg_find_libs _prefix _no_cmake_path _no_cmake_environment_path)
  unset(_libs)
  unset(_find_opts)

  # set the options that are used as long as the .pc file does not provide a library
  # path to look into
  if(_no_cmake_path)
    list(APPEND _find_opts "NO_CMAKE_PATH")
  endif()
  if(_no_cmake_environment_path)
    list(APPEND _find_opts "NO_CMAKE_ENVIRONMENT_PATH")
  endif()

  unset(_search_paths)
  unset(_next_is_framework)
  foreach (flag IN LISTS ${_prefix}_LDFLAGS)
    if (_next_is_framework)
      list(APPEND _libs "-framework ${flag}")
      unset(_next_is_framework)
      continue()
    endif ()
    if (flag MATCHES "^-L(.*)")
      list(APPEND _search_paths ${CMAKE_MATCH_1})
      continue()
    endif()
    if (flag MATCHES "^-l(.*)")
      set(_pkg_search "${CMAKE_MATCH_1}")
    else()
      if (flag STREQUAL "-framework")
        set(_next_is_framework TRUE)
      endif ()
      continue()
    endif()

    if(_search_paths)
        # Firstly search in -L paths
        find_library(pkgcfg_lib_${_prefix}_${_pkg_search}
                     NAMES ${_pkg_search}
                     HINTS ${_search_paths} NO_DEFAULT_PATH)
    endif()
    find_library(pkgcfg_lib_${_prefix}_${_pkg_search}
                 NAMES ${_pkg_search}
                 ${_find_opts})
    mark_as_advanced(pkgcfg_lib_${_prefix}_${_pkg_search})
    if(pkgcfg_lib_${_prefix}_${_pkg_search})
      list(APPEND _libs "${pkgcfg_lib_${_prefix}_${_pkg_search}}")
    else()
      list(APPEND _libs ${_pkg_search})
    endif()
  endforeach()

  set(${_prefix}_LINK_LIBRARIES "${_libs}" PARENT_SCOPE)
endfunction()

# create an imported target from all the information returned by pkg-config
function(_pkg_create_imp_target _prefix _imp_target_global)
  if (NOT TARGET PkgConfig::${_prefix})
    if(${_imp_target_global})
      set(_global_opt "GLOBAL")
    else()
      unset(_global_opt)
    endif()
    add_library(PkgConfig::${_prefix} INTERFACE IMPORTED ${_global_opt})

    if(${_prefix}_INCLUDE_DIRS)
      set_property(TARGET PkgConfig::${_prefix} PROPERTY
                   INTERFACE_INCLUDE_DIRECTORIES "${${_prefix}_INCLUDE_DIRS}")
    endif()
    if(${_prefix}_LINK_LIBRARIES)
      set_property(TARGET PkgConfig::${_prefix} PROPERTY
                   INTERFACE_LINK_LIBRARIES "${${_prefix}_LINK_LIBRARIES}")
    endif()
    if(${_prefix}_LDFLAGS_OTHER)
      set_property(TARGET PkgConfig::${_prefix} PROPERTY
                   INTERFACE_LINK_OPTIONS "${${_prefix}_LDFLAGS_OTHER}")
    endif()
    if(${_prefix}_CFLAGS_OTHER)
      set_property(TARGET PkgConfig::${_prefix} PROPERTY
                   INTERFACE_COMPILE_OPTIONS "${${_prefix}_CFLAGS_OTHER}")
    endif()
  endif()
endfunction()

# recalculate the dynamic output
# this is a macro and not a function so the result of _pkg_find_libs is automatically propagated
macro(_pkg_recalculate _prefix _no_cmake_path _no_cmake_environment_path _imp_target _imp_target_global)
  _pkg_find_libs(${_prefix} ${_no_cmake_path} ${_no_cmake_environment_path})
  if(${_imp_target})
    _pkg_create_imp_target(${_prefix} ${_imp_target_global})
  endif()
endmacro()

###
macro(_pkg_set_path_internal)
  set(_extra_paths)

  if(NOT _no_cmake_path)
    _pkgconfig_add_extra_path(_extra_paths CMAKE_PREFIX_PATH)
    _pkgconfig_add_extra_path(_extra_paths CMAKE_FRAMEWORK_PATH)
    _pkgconfig_add_extra_path(_extra_paths CMAKE_APPBUNDLE_PATH)
  endif()

  if(NOT _no_cmake_environment_path)
    _pkgconfig_add_extra_path(_extra_paths ENV CMAKE_PREFIX_PATH)
    _pkgconfig_add_extra_path(_extra_paths ENV CMAKE_FRAMEWORK_PATH)
    _pkgconfig_add_extra_path(_extra_paths ENV CMAKE_APPBUNDLE_PATH)
  endif()

  if(NOT _extra_paths STREQUAL "")
    # Save the PKG_CONFIG_PATH environment variable, and add paths
    # from the CMAKE_PREFIX_PATH variables
    set(_pkgconfig_path_old "$ENV{PKG_CONFIG_PATH}")
    set(_pkgconfig_path "${_pkgconfig_path_old}")
    if(NOT _pkgconfig_path STREQUAL "")
      file(TO_CMAKE_PATH "${_pkgconfig_path}" _pkgconfig_path)
    endif()

    # Create a list of the possible pkgconfig subfolder (depending on
    # the system
    set(_lib_dirs)
    if(NOT DEFINED CMAKE_SYSTEM_NAME
        OR (CMAKE_SYSTEM_NAME MATCHES "^(Linux|GNU)$"
            AND NOT CMAKE_CROSSCOMPILING))
      if(EXISTS "/etc/debian_version") # is this a debian system ?
        if(CMAKE_LIBRARY_ARCHITECTURE)
          list(APPEND _lib_dirs "lib/${CMAKE_LIBRARY_ARCHITECTURE}/pkgconfig")
        endif()
      else()
        # not debian, check the FIND_LIBRARY_USE_LIB32_PATHS and FIND_LIBRARY_USE_LIB64_PATHS properties
        get_property(uselib32 GLOBAL PROPERTY FIND_LIBRARY_USE_LIB32_PATHS)
        if(uselib32 AND CMAKE_SIZEOF_VOID_P EQUAL 4)
          list(APPEND _lib_dirs "lib32/pkgconfig")
        endif()
        get_property(uselib64 GLOBAL PROPERTY FIND_LIBRARY_USE_LIB64_PATHS)
        if(uselib64 AND CMAKE_SIZEOF_VOID_P EQUAL 8)
          list(APPEND _lib_dirs "lib64/pkgconfig")
        endif()
        get_property(uselibx32 GLOBAL PROPERTY FIND_LIBRARY_USE_LIBX32_PATHS)
        if(uselibx32 AND CMAKE_INTERNAL_PLATFORM_ABI STREQUAL "ELF X32")
          list(APPEND _lib_dirs "libx32/pkgconfig")
        endif()
      endif()
    endif()
    if(CMAKE_SYSTEM_NAME STREQUAL "FreeBSD" AND NOT CMAKE_CROSSCOMPILING)
      list(APPEND _lib_dirs "libdata/pkgconfig")
    endif()
    list(APPEND _lib_dirs "lib/pkgconfig")
    list(APPEND _lib_dirs "share/pkgconfig")

    # Check if directories exist and eventually append them to the
    # pkgconfig path list
    foreach(_prefix_dir ${_extra_paths})
      foreach(_lib_dir ${_lib_dirs})
        if(EXISTS "${_prefix_dir}/${_lib_dir}")
          list(APPEND _pkgconfig_path "${_prefix_dir}/${_lib_dir}")
          list(REMOVE_DUPLICATES _pkgconfig_path)
        endif()
      endforeach()
    endforeach()

    # Prepare and set the environment variable
    if(NOT _pkgconfig_path STREQUAL "")
      # remove empty values from the list
      list(REMOVE_ITEM _pkgconfig_path "")
      file(TO_NATIVE_PATH "${_pkgconfig_path}" _pkgconfig_path)
      if(CMAKE_HOST_UNIX)
        string(REPLACE ";" ":" _pkgconfig_path "${_pkgconfig_path}")
        string(REPLACE "\\ " " " _pkgconfig_path "${_pkgconfig_path}")
      endif()
      set(ENV{PKG_CONFIG_PATH} "${_pkgconfig_path}")
    endif()

    # Unset variables
    unset(_lib_dirs)
    unset(_pkgconfig_path)
  endif()

  # Tell pkg-config not to strip any -I or -L paths so we can search them all.
  if(DEFINED ENV{PKG_CONFIG_ALLOW_SYSTEM_LIBS})
    set(_pkgconfig_allow_system_libs_old "$ENV{PKG_CONFIG_ALLOW_SYSTEM_LIBS}")
  else()
    unset(_pkgconfig_allow_system_libs_old)
  endif()
  set(ENV{PKG_CONFIG_ALLOW_SYSTEM_LIBS} 1)
  if(DEFINED ENV{PKG_CONFIG_ALLOW_SYSTEM_CFLAGS})
    set(_pkgconfig_allow_system_cflags_old "$ENV{PKG_CONFIG_ALLOW_SYSTEM_CFLAGS}")
  else()
    unset(_pkgconfig_allow_system_cflags_old)
  endif()
  set(ENV{PKG_CONFIG_ALLOW_SYSTEM_CFLAGS} 1)
endmacro()

macro(_pkg_restore_path_internal)
  if(NOT _extra_paths STREQUAL "")
    # Restore the environment variable
    set(ENV{PKG_CONFIG_PATH} "${_pkgconfig_path_old}")
  endif()
  if(DEFINED _pkgconfig_allow_system_libs_old)
    set(ENV{PKG_CONFIG_ALLOW_SYSTEM_LIBS} "${_pkgconfig_allow_system_libs_old}")
    unset(_pkgconfig_allow_system_libs_old)
  else()
    unset(ENV{PKG_CONFIG_ALLOW_SYSTEM_LIBS})
  endif()
  if(DEFINED _pkgconfig_allow_system_cflags_old)
    set(ENV{PKG_CONFIG_ALLOW_SYSTEM_CFLAGS} "${_pkgconfig_allow_system_cflags_old}")
    unset(_pkgconfig_allow_system_cflags_old)
  else()
    unset(ENV{PKG_CONFIG_ALLOW_SYSTEM_CFLAGS})
  endif()

  unset(_extra_paths)
  unset(_pkgconfig_path_old)
endmacro()

# pkg-config returns frameworks in --libs-only-other
# they need to be in ${_prefix}_LIBRARIES so "-framework a -framework b" does
# not incorrectly be combined to "-framework a b"
function(_pkgconfig_extract_frameworks _prefix)
  set(ldflags "${${_prefix}_LDFLAGS_OTHER}")
  list(FIND ldflags "-framework" FR_POS)
  list(LENGTH ldflags LD_LENGTH)

  # reduce length by 1 as we need "-framework" and the next entry
  math(EXPR LD_LENGTH "${LD_LENGTH} - 1")
  while (FR_POS GREATER -1 AND LD_LENGTH GREATER FR_POS)
    list(REMOVE_AT ldflags ${FR_POS})
    list(GET ldflags ${FR_POS} HEAD)
    list(REMOVE_AT ldflags ${FR_POS})
    math(EXPR LD_LENGTH "${LD_LENGTH} - 2")

    list(APPEND LIBS "-framework ${HEAD}")

    list(FIND ldflags "-framework" FR_POS)
  endwhile ()
  set(${_prefix}_LIBRARIES ${${_prefix}_LIBRARIES} ${LIBS} PARENT_SCOPE)
  set(${_prefix}_LDFLAGS_OTHER "${ldflags}" PARENT_SCOPE)
endfunction()

# pkg-config returns -isystem include directories in --cflags-only-other,
# depending on the version and if there is a space between -isystem and
# the actual path
function(_pkgconfig_extract_isystem _prefix)
  set(cflags "${${_prefix}_CFLAGS_OTHER}")
  set(outflags "")
  set(incdirs "${${_prefix}_INCLUDE_DIRS}")

  set(next_is_isystem FALSE)
  foreach (THING IN LISTS cflags)
    # This may filter "-isystem -isystem". That would not work anyway,
    # so let it happen.
    if (THING STREQUAL "-isystem")
      set(next_is_isystem TRUE)
      continue()
    endif ()
    if (next_is_isystem)
      set(next_is_isystem FALSE)
      list(APPEND incdirs "${THING}")
    elseif (THING MATCHES "^-isystem")
      string(SUBSTRING "${THING}" 8 -1 THING)
      list(APPEND incdirs "${THING}")
    else ()
      list(APPEND outflags "${THING}")
    endif ()
  endforeach ()
  set(${_prefix}_CFLAGS_OTHER "${outflags}" PARENT_SCOPE)
  set(${_prefix}_INCLUDE_DIRS "${incdirs}" PARENT_SCOPE)
endfunction()

###
macro(_pkg_check_modules_internal _is_required _is_silent _no_cmake_path _no_cmake_environment_path _imp_target _imp_target_global _prefix)
  _pkgconfig_unset(${_prefix}_FOUND)
  _pkgconfig_unset(${_prefix}_VERSION)
  _pkgconfig_unset(${_prefix}_PREFIX)
  _pkgconfig_unset(${_prefix}_INCLUDEDIR)
  _pkgconfig_unset(${_prefix}_LIBDIR)
  _pkgconfig_unset(${_prefix}_MODULE_NAME)
  _pkgconfig_unset(${_prefix}_LIBS)
  _pkgconfig_unset(${_prefix}_LIBS_L)
  _pkgconfig_unset(${_prefix}_LIBS_PATHS)
  _pkgconfig_unset(${_prefix}_LIBS_OTHER)
  _pkgconfig_unset(${_prefix}_CFLAGS)
  _pkgconfig_unset(${_prefix}_CFLAGS_I)
  _pkgconfig_unset(${_prefix}_CFLAGS_OTHER)
  _pkgconfig_unset(${_prefix}_STATIC_LIBDIR)
  _pkgconfig_unset(${_prefix}_STATIC_LIBS)
  _pkgconfig_unset(${_prefix}_STATIC_LIBS_L)
  _pkgconfig_unset(${_prefix}_STATIC_LIBS_PATHS)
  _pkgconfig_unset(${_prefix}_STATIC_LIBS_OTHER)
  _pkgconfig_unset(${_prefix}_STATIC_CFLAGS)
  _pkgconfig_unset(${_prefix}_STATIC_CFLAGS_I)
  _pkgconfig_unset(${_prefix}_STATIC_CFLAGS_OTHER)

  # create a better addressable variable of the modules and calculate its size
  set(_pkg_check_modules_list ${ARGN})
  list(LENGTH _pkg_check_modules_list _pkg_check_modules_cnt)

  if(PKG_CONFIG_EXECUTABLE)
    # give out status message telling checked module
    if (NOT ${_is_silent})
      if (_pkg_check_modules_cnt EQUAL 1)
        message(STATUS "Checking for module '${_pkg_check_modules_list}'")
      else()
        message(STATUS "Checking for modules '${_pkg_check_modules_list}'")
      endif()
    endif()

    set(_pkg_check_modules_packages)
    set(_pkg_check_modules_failed "")

    _pkg_set_path_internal()

    # iterate through module list and check whether they exist and match the required version
    foreach (_pkg_check_modules_pkg ${_pkg_check_modules_list})
      set(_pkg_check_modules_exist_query)

      # check whether version is given while ignoring whitespace
      if (_pkg_check_modules_pkg MATCHES "(.*[^>< \t])[ \t]*(=|[><]=?)[ \t]*(.*)")
        set(_pkg_check_modules_pkg_name "${CMAKE_MATCH_1}")
        set(_pkg_check_modules_pkg_op "${CMAKE_MATCH_2}")
        set(_pkg_check_modules_pkg_ver "${CMAKE_MATCH_3}")
      else()
        set(_pkg_check_modules_pkg_name "${_pkg_check_modules_pkg}")
        set(_pkg_check_modules_pkg_op)
        set(_pkg_check_modules_pkg_ver)
      endif()

      _pkgconfig_unset(${_prefix}_${_pkg_check_modules_pkg_name}_VERSION)
      _pkgconfig_unset(${_prefix}_${_pkg_check_modules_pkg_name}_PREFIX)
      _pkgconfig_unset(${_prefix}_${_pkg_check_modules_pkg_name}_INCLUDEDIR)
      _pkgconfig_unset(${_prefix}_${_pkg_check_modules_pkg_name}_LIBDIR)

      list(APPEND _pkg_check_modules_packages    "${_pkg_check_modules_pkg_name}")

      # create the final query which is of the format:
      # * <pkg-name> > <version>
      # * <pkg-name> >= <version>
      # * <pkg-name> = <version>
      # * <pkg-name> <= <version>
      # * <pkg-name> < <version>
      # * --exists <pkg-name>
      list(APPEND _pkg_check_modules_exist_query --print-errors --short-errors)
      if (_pkg_check_modules_pkg_op)
        list(APPEND _pkg_check_modules_exist_query "${_pkg_check_modules_pkg_name} ${_pkg_check_modules_pkg_op} ${_pkg_check_modules_pkg_ver}")
      else()
        list(APPEND _pkg_check_modules_exist_query --exists)
        list(APPEND _pkg_check_modules_exist_query "${_pkg_check_modules_pkg_name}")
      endif()

      # execute the query
      execute_process(
        COMMAND ${PKG_CONFIG_EXECUTABLE} ${PKG_CONFIG_ARGN} ${_pkg_check_modules_exist_query}
        RESULT_VARIABLE _pkgconfig_retval
        ERROR_VARIABLE _pkgconfig_error
        ERROR_STRIP_TRAILING_WHITESPACE)

      # evaluate result and tell failures
      if (_pkgconfig_retval)
        if(NOT ${_is_silent})
          message(STATUS "  ${_pkgconfig_error}")
        endif()

        string(APPEND _pkg_check_modules_failed " - ${_pkg_check_modules_pkg}\n")
      endif()
    endforeach()

    if(_pkg_check_modules_failed)
      # fail when requested
      if (${_is_required})
        message(FATAL_ERROR "The following required packages were not found:\n${_pkg_check_modules_failed}")
      endif ()
    else()
      # when we are here, we checked whether requested modules
      # exist. Now, go through them and set variables

      _pkgconfig_set(${_prefix}_FOUND 1)
      list(LENGTH _pkg_check_modules_packages pkg_count)

      # iterate through all modules again and set individual variables
      foreach (_pkg_check_modules_pkg ${_pkg_check_modules_packages})
        # handle case when there is only one package required
        if (pkg_count EQUAL 1)
          set(_pkg_check_prefix "${_prefix}")
        else()
          set(_pkg_check_prefix "${_prefix}_${_pkg_check_modules_pkg}")
        endif()

        _pkgconfig_invoke(${_pkg_check_modules_pkg} "${_pkg_check_prefix}" VERSION    ""   --modversion )
        pkg_get_variable("${_pkg_check_prefix}_PREFIX" ${_pkg_check_modules_pkg} "prefix")
        pkg_get_variable("${_pkg_check_prefix}_INCLUDEDIR" ${_pkg_check_modules_pkg} "includedir")
        pkg_get_variable("${_pkg_check_prefix}_LIBDIR" ${_pkg_check_modules_pkg} "libdir")
        foreach (variable IN ITEMS PREFIX INCLUDEDIR LIBDIR)
          _pkgconfig_set("${_pkg_check_prefix}_${variable}" "${${_pkg_check_prefix}_${variable}}")
        endforeach ()
          _pkgconfig_set("${_pkg_check_prefix}_MODULE_NAME" "${_pkg_check_modules_pkg}")

        if (NOT ${_is_silent})
          message(STATUS "  Found ${_pkg_check_modules_pkg}, version ${_pkgconfig_VERSION}")
        endif ()
      endforeach()

      # set variables which are combined for multiple modules
      _pkgconfig_invoke_dyn("${_pkg_check_modules_packages}" "${_prefix}" LIBRARIES     "(^| )-l"             --libs-only-l )
      _pkgconfig_invoke_dyn("${_pkg_check_modules_packages}" "${_prefix}" LIBRARY_DIRS  "(^| )-L"             --libs-only-L )
      _pkgconfig_invoke_dyn("${_pkg_check_modules_packages}" "${_prefix}" LDFLAGS       ""                    --libs )
      _pkgconfig_invoke_dyn("${_pkg_check_modules_packages}" "${_prefix}" LDFLAGS_OTHER ""                    --libs-only-other )

      if (APPLE AND "-framework" IN_LIST ${_prefix}_LDFLAGS_OTHER)
        _pkgconfig_extract_frameworks("${_prefix}")
        # Using _pkgconfig_set in this scope so that a future policy can switch to normal variables
        _pkgconfig_set("${_pkg_check_prefix}_LIBRARIES" "${${_pkg_check_prefix}_LIBRARIES}")
        _pkgconfig_set("${_pkg_check_prefix}_LDFLAGS_OTHER" "${${_pkg_check_prefix}_LDFLAGS_OTHER}")
      endif()

      _pkgconfig_invoke_dyn("${_pkg_check_modules_packages}" "${_prefix}" INCLUDE_DIRS  "(^| )(-I|-isystem ?)" --cflags-only-I )
      _pkgconfig_invoke_dyn("${_pkg_check_modules_packages}" "${_prefix}" CFLAGS        ""                    --cflags )
      _pkgconfig_invoke_dyn("${_pkg_check_modules_packages}" "${_prefix}" CFLAGS_OTHER  ""                    --cflags-only-other )

      if (${_prefix}_CFLAGS_OTHER MATCHES "-isystem")
        _pkgconfig_extract_isystem("${_prefix}")
        # Using _pkgconfig_set in this scope so that a future policy can switch to normal variables
        _pkgconfig_set("${_pkg_check_prefix}_CFLAGS_OTHER" "${${_pkg_check_prefix}_CFLAGS_OTHER}")
        _pkgconfig_set("${_pkg_check_prefix}_INCLUDE_DIRS" "${${_pkg_check_prefix}_INCLUDE_DIRS}")
      endif ()

      _pkg_recalculate("${_prefix}" ${_no_cmake_path} ${_no_cmake_environment_path} ${_imp_target} ${_imp_target_global})
    endif()

    _pkg_restore_path_internal()
  else()
    if (${_is_required})
      message(SEND_ERROR "pkg-config tool not found")
    endif ()
  endif()
endmacro()

macro(pkg_check_modules _prefix _module0)
  _pkgconfig_parse_options(_pkg_modules _pkg_is_required _pkg_is_silent _no_cmake_path _no_cmake_environment_path _imp_target _imp_target_global "${_module0}" ${ARGN})
  # check cached value
  if (NOT DEFINED __pkg_config_checked_${_prefix} OR __pkg_config_checked_${_prefix} LESS ${PKG_CONFIG_VERSION} OR NOT ${_prefix}_FOUND OR
      (NOT "${ARGN}" STREQUAL "" AND NOT "${__pkg_config_arguments_${_prefix}}" STREQUAL "${_module0};${ARGN}") OR
      (    "${ARGN}" STREQUAL "" AND NOT "${__pkg_config_arguments_${_prefix}}" STREQUAL "${_module0}"))
    _pkg_check_modules_internal("${_pkg_is_required}" "${_pkg_is_silent}" ${_no_cmake_path} ${_no_cmake_environment_path} ${_imp_target} ${_imp_target_global} "${_prefix}" ${_pkg_modules})

    _pkgconfig_set(__pkg_config_checked_${_prefix} ${PKG_CONFIG_VERSION})
    if (${_prefix}_FOUND)
      _pkgconfig_set(__pkg_config_arguments_${_prefix} "${_module0};${ARGN}")
    endif()
  else()
    if (${_prefix}_FOUND)
      _pkg_recalculate("${_prefix}" ${_no_cmake_path} ${_no_cmake_environment_path} ${_imp_target} ${_imp_target_global})
    endif()
  endif()
endmacro()

macro(pkg_search_module _prefix _module0)
  _pkgconfig_parse_options(_pkg_modules_alt _pkg_is_required _pkg_is_silent _no_cmake_path _no_cmake_environment_path _imp_target _imp_target_global "${_module0}" ${ARGN})
  # check cached value
  if (NOT DEFINED __pkg_config_checked_${_prefix} OR __pkg_config_checked_${_prefix} LESS ${PKG_CONFIG_VERSION} OR NOT ${_prefix}_FOUND)
    set(_pkg_modules_found 0)

    if (NOT ${_pkg_is_silent})
      message(STATUS "Checking for one of the modules '${_pkg_modules_alt}'")
    endif ()

    # iterate through all modules and stop at the first working one.
    foreach(_pkg_alt ${_pkg_modules_alt})
      if(NOT _pkg_modules_found)
        _pkg_check_modules_internal(0 1 ${_no_cmake_path} ${_no_cmake_environment_path} ${_imp_target} ${_imp_target_global} "${_prefix}" "${_pkg_alt}")
      endif()

      if (${_prefix}_FOUND)
        set(_pkg_modules_found 1)
        break()
      endif()
    endforeach()

    if (NOT ${_prefix}_FOUND)
      if(${_pkg_is_required})
        message(SEND_ERROR "None of the required '${_pkg_modules_alt}' found")
      endif()
    endif()

    _pkgconfig_set(__pkg_config_checked_${_prefix} ${PKG_CONFIG_VERSION})
  elseif (${_prefix}_FOUND)
    _pkg_recalculate("${_prefix}" ${_no_cmake_path} ${_no_cmake_environment_path} ${_imp_target} ${_imp_target_global})
  endif()
endmacro()

function (pkg_get_variable result pkg variable)
  set(_multiValueArgs DEFINE_VARIABLES)

  cmake_parse_arguments(_parsedArguments "" "" "${_multiValueArgs}" ${ARGN})
  set(defined_variables )
  foreach(_def_var ${_parsedArguments_DEFINE_VARIABLES})
    if(NOT _def_var MATCHES "^.+=.*$")
      message(FATAL_ERROR "DEFINE_VARIABLES should contain arguments in the form of key=value")
    endif()

    list(APPEND defined_variables "--define-variable=${_def_var}")
  endforeach()

  _pkg_set_path_internal()
  _pkgconfig_invoke("${pkg}" "prefix" "result" "" "--variable=${variable}" ${defined_variables})
  set("${result}"
    "${prefix_result}"
    PARENT_SCOPE)
  _pkg_restore_path_internal()
endfunction ()