cmake/Help/command/find_package.rst

find_package
------------

Load settings for an external project.

::

  find_package(<package> [version] [EXACT] [QUIET] [MODULE]
               [REQUIRED] [[COMPONENTS] [components...]]
               [OPTIONAL_COMPONENTS components...]
               [NO_POLICY_SCOPE])

Finds and loads settings from an external project.  ``<package>_FOUND``
will be set to indicate whether the package was found.  When the
package is found package-specific information is provided through
variables and :ref:`Imported Targets` documented by the package itself.  The
``QUIET`` option disables messages if the package cannot be found.  The
``MODULE`` option disables the second signature documented below.  The
``REQUIRED`` option stops processing with an error message if the package
cannot be found.

A package-specific list of required components may be listed after the
``COMPONENTS`` option (or after the ``REQUIRED`` option if present).
Additional optional components may be listed after
``OPTIONAL_COMPONENTS``.  Available components and their influence on
whether a package is considered to be found are defined by the target
package.

The ``[version]`` argument requests a version with which the package found
should be compatible (format is ``major[.minor[.patch[.tweak]]]``).  The
``EXACT`` option requests that the version be matched exactly.  If no
``[version]`` and/or component list is given to a recursive invocation
inside a find-module, the corresponding arguments are forwarded
automatically from the outer call (including the ``EXACT`` flag for
``[version]``).  Version support is currently provided only on a
package-by-package basis (details below).

User code should generally look for packages using the above simple
signature.  The remainder of this command documentation specifies the
full command signature and details of the search process.  Project
maintainers wishing to provide a package to be found by this command
are encouraged to read on.

The command has two modes by which it searches for packages: "Module"
mode and "Config" mode.  Module mode is available when the command is
invoked with the above reduced signature.  CMake searches for a file
called ``Find<package>.cmake`` in the :variable:`CMAKE_MODULE_PATH`
followed by the CMake installation.  If the file is found, it is read
and processed by CMake.  It is responsible for finding the package,
checking the version, and producing any needed messages.  Many
find-modules provide limited or no support for versioning; check
the module documentation.  If no module is found and the ``MODULE``
option is not given the command proceeds to Config mode.

The complete Config mode command signature is::

  find_package(<package> [version] [EXACT] [QUIET]
               [REQUIRED] [[COMPONENTS] [components...]]
               [CONFIG|NO_MODULE]
               [NO_POLICY_SCOPE]
               [NAMES name1 [name2 ...]]
               [CONFIGS config1 [config2 ...]]
               [HINTS path1 [path2 ... ]]
               [PATHS path1 [path2 ... ]]
               [PATH_SUFFIXES suffix1 [suffix2 ...]]
               [NO_DEFAULT_PATH]
               [NO_CMAKE_ENVIRONMENT_PATH]
               [NO_CMAKE_PATH]
               [NO_SYSTEM_ENVIRONMENT_PATH]
               [NO_CMAKE_PACKAGE_REGISTRY]
               [NO_CMAKE_BUILDS_PATH]
               [NO_CMAKE_SYSTEM_PATH]
               [NO_CMAKE_SYSTEM_PACKAGE_REGISTRY]
               [CMAKE_FIND_ROOT_PATH_BOTH |
                ONLY_CMAKE_FIND_ROOT_PATH |
                NO_CMAKE_FIND_ROOT_PATH])

The ``CONFIG`` option may be used to skip Module mode explicitly and
switch to Config mode.  It is synonymous to using ``NO_MODULE``.  Config
mode is also implied by use of options not specified in the reduced
signature.

Config mode attempts to locate a configuration file provided by the
package to be found.  A cache entry called ``<package>_DIR`` is created to
hold the directory containing the file.  By default the command
searches for a package with the name ``<package>``.  If the ``NAMES`` option
is given the names following it are used instead of ``<package>``.  The
command searches for a file called ``<name>Config.cmake`` or
``<lower-case-name>-config.cmake`` for each name specified.  A
replacement set of possible configuration file names may be given
using the ``CONFIGS`` option.  The search procedure is specified below.
Once found, the configuration file is read and processed by CMake.
Since the file is provided by the package it already knows the
location of package contents.  The full path to the configuration file
is stored in the cmake variable ``<package>_CONFIG``.

All configuration files which have been considered by CMake while
searching for an installation of the package with an appropriate
version are stored in the cmake variable ``<package>_CONSIDERED_CONFIGS``,
the associated versions in ``<package>_CONSIDERED_VERSIONS``.

If the package configuration file cannot be found CMake will generate
an error describing the problem unless the ``QUIET`` argument is
specified.  If ``REQUIRED`` is specified and the package is not found a
fatal error is generated and the configure step stops executing.  If
``<package>_DIR`` has been set to a directory not containing a
configuration file CMake will ignore it and search from scratch.

When the ``[version]`` argument is given Config mode will only find a
version of the package that claims compatibility with the requested
version (format is ``major[.minor[.patch[.tweak]]]``).  If the ``EXACT``
option is given only a version of the package claiming an exact match
of the requested version may be found.  CMake does not establish any
convention for the meaning of version numbers.  Package version
numbers are checked by "version" files provided by the packages
themselves.  For a candidate package configuration file
``<config-file>.cmake`` the corresponding version file is located next
to it and named either ``<config-file>-version.cmake`` or
``<config-file>Version.cmake``.  If no such version file is available
then the configuration file is assumed to not be compatible with any
requested version.  A basic version file containing generic version
matching code can be created using the
:module:`CMakePackageConfigHelpers` module.  When a version file
is found it is loaded to check the requested version number.  The
version file is loaded in a nested scope in which the following
variables have been defined:

``PACKAGE_FIND_NAME``
  the ``<package>`` name
``PACKAGE_FIND_VERSION``
  full requested version string
``PACKAGE_FIND_VERSION_MAJOR``
  major version if requested, else 0
``PACKAGE_FIND_VERSION_MINOR``
  minor version if requested, else 0
``PACKAGE_FIND_VERSION_PATCH``
  patch version if requested, else 0
``PACKAGE_FIND_VERSION_TWEAK``
  tweak version if requested, else 0
``PACKAGE_FIND_VERSION_COUNT``
  number of version components, 0 to 4

The version file checks whether it satisfies the requested version and
sets these variables:

``PACKAGE_VERSION``
  full provided version string
``PACKAGE_VERSION_EXACT``
  true if version is exact match
``PACKAGE_VERSION_COMPATIBLE``
  true if version is compatible
``PACKAGE_VERSION_UNSUITABLE``
  true if unsuitable as any version

These variables are checked by the ``find_package`` command to determine
whether the configuration file provides an acceptable version.  They
are not available after the find_package call returns.  If the version
is acceptable the following variables are set:

``<package>_VERSION``
  full provided version string
``<package>_VERSION_MAJOR``
  major version if provided, else 0
``<package>_VERSION_MINOR``
  minor version if provided, else 0
``<package>_VERSION_PATCH``
  patch version if provided, else 0
``<package>_VERSION_TWEAK``
  tweak version if provided, else 0
``<package>_VERSION_COUNT``
  number of version components, 0 to 4

and the corresponding package configuration file is loaded.  When
multiple package configuration files are available whose version files
claim compatibility with the version requested it is unspecified which
one is chosen.  No attempt is made to choose a highest or closest
version number.

Config mode provides an elaborate interface and search procedure.
Much of the interface is provided for completeness and for use
internally by find-modules loaded by Module mode.  Most user code
should simply call::

  find_package(<package> [major[.minor]] [EXACT] [REQUIRED|QUIET])

in order to find a package.  Package maintainers providing CMake
package configuration files are encouraged to name and install them
such that the procedure outlined below will find them without
requiring use of additional options.

CMake constructs a set of possible installation prefixes for the
package.  Under each prefix several directories are searched for a
configuration file.  The tables below show the directories searched.
Each entry is meant for installation trees following Windows (W), UNIX
(U), or Apple (A) conventions::

  <prefix>/                                               (W)
  <prefix>/(cmake|CMake)/                                 (W)
  <prefix>/<name>*/                                       (W)
  <prefix>/<name>*/(cmake|CMake)/                         (W)
  <prefix>/(lib/<arch>|lib|share)/cmake/<name>*/          (U)
  <prefix>/(lib/<arch>|lib|share)/<name>*/                (U)
  <prefix>/(lib/<arch>|lib|share)/<name>*/(cmake|CMake)/  (U)

On systems supporting OS X Frameworks and Application Bundles the
following directories are searched for frameworks or bundles
containing a configuration file::

  <prefix>/<name>.framework/Resources/                    (A)
  <prefix>/<name>.framework/Resources/CMake/              (A)
  <prefix>/<name>.framework/Versions/*/Resources/         (A)
  <prefix>/<name>.framework/Versions/*/Resources/CMake/   (A)
  <prefix>/<name>.app/Contents/Resources/                 (A)
  <prefix>/<name>.app/Contents/Resources/CMake/           (A)

In all cases the ``<name>`` is treated as case-insensitive and corresponds
to any of the names specified (``<package>`` or names given by ``NAMES``).
Paths with ``lib/<arch>`` are enabled if the
:variable:`CMAKE_LIBRARY_ARCHITECTURE` variable is set.  If ``PATH_SUFFIXES``
is specified the suffixes are appended to each (W) or (U) directory entry
one-by-one.

This set of directories is intended to work in cooperation with
projects that provide configuration files in their installation trees.
Directories above marked with (W) are intended for installations on
Windows where the prefix may point at the top of an application's
installation directory.  Those marked with (U) are intended for
installations on UNIX platforms where the prefix is shared by multiple
packages.  This is merely a convention, so all (W) and (U) directories
are still searched on all platforms.  Directories marked with (A) are
intended for installations on Apple platforms.  The cmake variables
``CMAKE_FIND_FRAMEWORK`` and ``CMAKE_FIND_APPBUNDLE``
determine the order of preference as specified below.

The set of installation prefixes is constructed using the following
steps.  If ``NO_DEFAULT_PATH`` is specified all ``NO_*`` options are
enabled.

1. Search paths specified in cmake-specific cache variables.  These
   are intended to be used on the command line with a ``-DVAR=value``.
   This can be skipped if ``NO_CMAKE_PATH`` is passed::

     CMAKE_PREFIX_PATH
     CMAKE_FRAMEWORK_PATH
     CMAKE_APPBUNDLE_PATH

2. Search paths specified in cmake-specific environment variables.
   These are intended to be set in the user's shell configuration.
   This can be skipped if ``NO_CMAKE_ENVIRONMENT_PATH`` is passed::

     <package>_DIR
     CMAKE_PREFIX_PATH
     CMAKE_FRAMEWORK_PATH
     CMAKE_APPBUNDLE_PATH

3. Search paths specified by the ``HINTS`` option.  These should be paths
   computed by system introspection, such as a hint provided by the
   location of another item already found.  Hard-coded guesses should
   be specified with the ``PATHS`` option.

4. Search the standard system environment variables.  This can be
   skipped if ``NO_SYSTEM_ENVIRONMENT_PATH`` is passed.  Path entries
   ending in ``/bin`` or ``/sbin`` are automatically converted to their
   parent directories::

     PATH

5. Search project build trees recently configured in a :manual:`cmake-gui(1)`.
   This can be skipped if ``NO_CMAKE_BUILDS_PATH`` is passed.  It is intended
   for the case when a user is building multiple dependent projects one
   after another.
   (This step is implemented only on Windows.)

6. Search paths stored in the CMake :ref:`User Package Registry`.
   This can be skipped if ``NO_CMAKE_PACKAGE_REGISTRY`` is passed.
   See the :manual:`cmake-packages(7)` manual for details on the user
   package registry.

7. Search cmake variables defined in the Platform files for the
   current system.  This can be skipped if ``NO_CMAKE_SYSTEM_PATH`` is
   passed::

     CMAKE_SYSTEM_PREFIX_PATH
     CMAKE_SYSTEM_FRAMEWORK_PATH
     CMAKE_SYSTEM_APPBUNDLE_PATH

8. Search paths stored in the CMake :ref:`System Package Registry`.
   This can be skipped if ``NO_CMAKE_SYSTEM_PACKAGE_REGISTRY`` is passed.
   See the :manual:`cmake-packages(7)` manual for details on the system
   package registry.

9. Search paths specified by the ``PATHS`` option.  These are typically
   hard-coded guesses.

.. |FIND_XXX| replace:: find_package
.. |FIND_ARGS_XXX| replace:: <package>
.. |CMAKE_FIND_ROOT_PATH_MODE_XXX| replace::
   :variable:`CMAKE_FIND_ROOT_PATH_MODE_PACKAGE`

.. include:: FIND_XXX_MAC.txt
.. include:: FIND_XXX_ROOT.txt
.. include:: FIND_XXX_ORDER.txt

Every non-REQUIRED ``find_package`` call can be disabled by setting the
:variable:`CMAKE_DISABLE_FIND_PACKAGE_<PackageName>` variable to ``TRUE``.

When loading a find module or package configuration file ``find_package``
defines variables to provide information about the call arguments (and
restores their original state before returning):

``<package>_FIND_REQUIRED``
  true if ``REQUIRED`` option was given
``<package>_FIND_QUIETLY``
  true if ``QUIET`` option was given
``<package>_FIND_VERSION``
  full requested version string
``<package>_FIND_VERSION_MAJOR``
  major version if requested, else 0
``<package>_FIND_VERSION_MINOR``
  minor version if requested, else 0
``<package>_FIND_VERSION_PATCH``
  patch version if requested, else 0
``<package>_FIND_VERSION_TWEAK``
  tweak version if requested, else 0
``<package>_FIND_VERSION_COUNT``
  number of version components, 0 to 4
``<package>_FIND_VERSION_EXACT``
  true if ``EXACT`` option was given
``<package>_FIND_COMPONENTS``
  list of requested components
``<package>_FIND_REQUIRED_<c>``
  true if component ``<c>`` is required,
  false if component ``<c>`` is optional

In Module mode the loaded find module is responsible to honor the
request detailed by these variables; see the find module for details.
In Config mode ``find_package`` handles ``REQUIRED``, ``QUIET``, and
``[version]`` options automatically but leaves it to the package
configuration file to handle components in a way that makes sense
for the package.  The package configuration file may set
``<package>_FOUND`` to false to tell ``find_package`` that component
requirements are not satisfied.

See the :command:`cmake_policy` command documentation for discussion
of the ``NO_POLICY_SCOPE`` option.