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CMAKE-PACKAGES(7)		     CMake		     CMAKE-PACKAGES(7)

NAME
       cmake-packages -	CMake Packages Reference

INTRODUCTION
       Packages	 provide  dependency  information to CMake based buildsystems.
       Packages	are found with the find_package() command.  The	result of  us-
       ing  find_package()  is	either	a set of IMPORTED targets, or a	set of
       variables corresponding to build-relevant information.

USING PACKAGES
       CMake provides direct support for two forms  of	packages,  Config-file
       Packages	 and  Find-module  Packages.   Indirect	support	for pkg-config
       packages	is also	provided via the FindPkgConfig module.	In all	cases,
       the basic form of find_package()	calls is the same:

	  find_package(Qt4 4.7.0 REQUIRED) # CMake provides a Qt4 find-module
	  find_package(Qt5Core 5.1.0 REQUIRED) # Qt provides a Qt5 package config file.
	  find_package(LibXml2 REQUIRED) # Use pkg-config via the LibXml2 find-module

       In  cases  where	 it is known that a package configuration file is pro-
       vided by	upstream, and only that	should be used,	the CONFIG keyword may
       be passed to find_package():

	  find_package(Qt5Core 5.1.0 CONFIG REQUIRED)
	  find_package(Qt5Gui 5.1.0 CONFIG)

       Similarly, the MODULE keyword says to use only a	find-module:

	  find_package(Qt4 4.7.0 MODULE	REQUIRED)

       Specifying  the	type  of package explicitly improves the error message
       shown to	the user if it is not found.

       Both types of packages also support specifying components of a package,
       either after the	REQUIRED keyword:

	  find_package(Qt5 5.1.0 CONFIG	REQUIRED Widgets Xml Sql)

       or as a separate	COMPONENTS list:

	  find_package(Qt5 5.1.0 COMPONENTS Widgets Xml	Sql)

       or as a separate	OPTIONAL_COMPONENTS list:

	  find_package(Qt5 5.1.0 COMPONENTS Widgets
				 OPTIONAL_COMPONENTS Xml Sql
	  )

       Handling	 of COMPONENTS and OPTIONAL_COMPONENTS is defined by the pack-
       age.

       By setting  the	CMAKE_DISABLE_FIND_PACKAGE_<PackageName>  variable  to
       TRUE,  the  <PackageName> package will not be searched, and will	always
       be NOTFOUND.

   Config-file Packages
       A config-file package is	a set of files provided	by upstreams for down-
       streams	to  use.  CMake	 searches in a number of locations for package
       configuration files, as described in the	find_package()	documentation.
       The  most  simple  way for a CMake user to tell cmake(1)	to search in a
       non-standard prefix for a package is to set the CMAKE_PREFIX_PATH cache
       variable.

       Config-file packages are	provided by upstream vendors as	part of	devel-
       opment packages,	that is, they belong with the  header  files  and  any
       other files provided to assist downstreams in using the package.

       A  set  of  variables which provide package status information are also
       set automatically when using  a	config-file  package.	The  <Package-
       Name>_FOUND  variable is	set to true or false, depending	on whether the
       package was found.  The <PackageName>_DIR cache variable	is set to  the
       location	of the package configuration file.

   Find-module Packages
       A  find	module	is a file with a set of	rules for finding the required
       pieces of a dependency, primarily header	files  and  libraries.	 Typi-
       cally,  a  find	module	is  needed when	the upstream is	not built with
       CMake, or is not	CMake-aware enough to otherwise	provide	a package con-
       figuration  file.   Unlike  a  package  configuration  file,  it	is not
       shipped with upstream, but is used by downstream	to find	the  files  by
       guessing	locations of files with	platform-specific hints.

       Unlike  the case	of an upstream-provided	package	configuration file, no
       single point of reference identifies the	package	as being found,	so the
       <PackageName>_FOUND variable is not automatically set by	the find_pack-
       age() command.  It can still be expected	to be set by  convention  how-
       ever  and  should  be  set by the author	of the Find-module.  Similarly
       there is	no <PackageName>_DIR variable, but each	of the artifacts  such
       as library locations and	header file locations provide a	separate cache
       variable.

       See the cmake-developer(7) manual for more information  about  creating
       Find-module files.

PACKAGE	LAYOUT
       A  config-file package consists of a Package Configuration File and op-
       tionally	a Package Version File provided	with the project distribution.

   Package Configuration File
       Consider	a project Foo that installs the	following files:

	  <prefix>/include/foo-1.2/foo.h
	  <prefix>/lib/foo-1.2/libfoo.a

       It may also provide a CMake package configuration file:

	  <prefix>/lib/cmake/foo-1.2/FooConfig.cmake

       with content defining IMPORTED targets, or defining variables, such as:

	  # ...
	  # (compute PREFIX relative to	file location)
	  # ...
	  set(Foo_INCLUDE_DIRS ${PREFIX}/include/foo-1.2)
	  set(Foo_LIBRARIES ${PREFIX}/lib/foo-1.2/libfoo.a)

       If another project wishes to use	Foo it need only to locate the FooCon-
       fig.cmake  file	and  load it to	get all	the information	it needs about
       package content locations.  Since the  package  configuration  file  is
       provided	 by the	package	installation it	already	knows all the file lo-
       cations.

       The find_package() command may be used to search	for the	 package  con-
       figuration  file.   This	 command constructs a set of installation pre-
       fixes and searches under	each prefix in several locations.   Given  the
       name  Foo,  it  looks  for  a  file  called FooConfig.cmake or foo-con-
       fig.cmake.  The full set	of locations is	specified  in  the  find_pack-
       age() command documentation. One	place it looks is:

	  <prefix>/lib/cmake/Foo*/

       where  Foo*  is a case-insensitive globbing expression.	In our example
       the globbing expression will match <prefix>/lib/cmake/foo-1.2  and  the
       package configuration file will be found.

       Once  found,  a	package	configuration file is immediately loaded.  It,
       together	with a package version file, contains all the information  the
       project needs to	use the	package.

   Package Version File
       When the	find_package() command finds a candidate package configuration
       file it looks next to it	for a version file. The	version	file is	loaded
       to test whether the package version is an acceptable match for the ver-
       sion requested.	If the version file claims compatibility the  configu-
       ration file is accepted.	 Otherwise it is ignored.

       The  name  of  the  package version file	must match that	of the package
       configuration file but has either -version or Version appended  to  the
       name before the .cmake extension.  For example, the files:

	  <prefix>/lib/cmake/foo-1.3/foo-config.cmake
	  <prefix>/lib/cmake/foo-1.3/foo-config-version.cmake

       and:

	  <prefix>/lib/cmake/bar-4.2/BarConfig.cmake
	  <prefix>/lib/cmake/bar-4.2/BarConfigVersion.cmake

       are each	pairs of package configuration files and corresponding package
       version files.

       When the	find_package() command loads a version file it first sets  the
       following variables:

       PACKAGE_FIND_NAME
	      The <PackageName>

       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 must use these variables to check whether it is com-
       patible or an exact match for the requested version and set the follow-
       ing variables with results:

       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

       Version	files are loaded in a nested scope so they are free to set any
       variables they wish as part of their computation. The find_package com-
       mand wipes out the scope	when the version file has completed and	it has
       checked the output variables. When the version file claims to be	an ac-
       ceptable	 match for the requested version the find_package command sets
       the following variables for use by the project:

       <PackageName>_VERSION
	      Full provided version string

       <PackageName>_VERSION_MAJOR
	      Major version if provided, else 0

       <PackageName>_VERSION_MINOR
	      Minor version if provided, else 0

       <PackageName>_VERSION_PATCH
	      Patch version if provided, else 0

       <PackageName>_VERSION_TWEAK
	      Tweak version if provided, else 0

       <PackageName>_VERSION_COUNT
	      Number of	version	components, 0 to 4

       The variables report the	version	 of  the  package  that	 was  actually
       found.  The <PackageName> part of their name matches the	argument given
       to the find_package() command.

CREATING PACKAGES
       Usually,	the upstream depends on	CMake itself and can  use  some	 CMake
       facilities  for	creating the package files. Consider an	upstream which
       provides	a single shared	library:

	  project(UpstreamLib)

	  set(CMAKE_INCLUDE_CURRENT_DIR	ON)
	  set(CMAKE_INCLUDE_CURRENT_DIR_IN_INTERFACE ON)

	  set(Upstream_VERSION 3.4.1)

	  include(GenerateExportHeader)

	  add_library(ClimbingStats SHARED climbingstats.cpp)
	  generate_export_header(ClimbingStats)
	  set_property(TARGET ClimbingStats PROPERTY VERSION ${Upstream_VERSION})
	  set_property(TARGET ClimbingStats PROPERTY SOVERSION 3)
	  set_property(TARGET ClimbingStats PROPERTY
	    INTERFACE_ClimbingStats_MAJOR_VERSION 3)
	  set_property(TARGET ClimbingStats APPEND PROPERTY
	    COMPATIBLE_INTERFACE_STRING	ClimbingStats_MAJOR_VERSION
	  )

	  install(TARGETS ClimbingStats	EXPORT ClimbingStatsTargets
	    LIBRARY DESTINATION	lib
	    ARCHIVE DESTINATION	lib
	    RUNTIME DESTINATION	bin
	    INCLUDES DESTINATION include
	  )
	  install(
	    FILES
	      climbingstats.h
	      "${CMAKE_CURRENT_BINARY_DIR}/climbingstats_export.h"
	    DESTINATION
	      include
	    COMPONENT
	      Devel
	  )

	  include(CMakePackageConfigHelpers)
	  write_basic_package_version_file(
	    "${CMAKE_CURRENT_BINARY_DIR}/ClimbingStats/ClimbingStatsConfigVersion.cmake"
	    VERSION ${Upstream_VERSION}
	    COMPATIBILITY AnyNewerVersion
	  )

	  export(EXPORT	ClimbingStatsTargets
	    FILE "${CMAKE_CURRENT_BINARY_DIR}/ClimbingStats/ClimbingStatsTargets.cmake"
	    NAMESPACE Upstream::
	  )
	  configure_file(cmake/ClimbingStatsConfig.cmake
	    "${CMAKE_CURRENT_BINARY_DIR}/ClimbingStats/ClimbingStatsConfig.cmake"
	    COPYONLY
	  )

	  set(ConfigPackageLocation lib/cmake/ClimbingStats)
	  install(EXPORT ClimbingStatsTargets
	    FILE
	      ClimbingStatsTargets.cmake
	    NAMESPACE
	      Upstream::
	    DESTINATION
	      ${ConfigPackageLocation}
	  )
	  install(
	    FILES
	      cmake/ClimbingStatsConfig.cmake
	      "${CMAKE_CURRENT_BINARY_DIR}/ClimbingStats/ClimbingStatsConfigVersion.cmake"
	    DESTINATION
	      ${ConfigPackageLocation}
	    COMPONENT
	      Devel
	  )

       The CMakePackageConfigHelpers module provides a macro  for  creating  a
       simple  ConfigVersion.cmake  file.   This  file sets the	version	of the
       package.	 It is read by CMake when find_package() is called  to	deter-
       mine the	compatibility with the requested version, and to set some ver-
       sion-specific   variables   <PackageName>_VERSION,   <PackageName>_VER-
       SION_MAJOR,  <PackageName>_VERSION_MINOR	etc.  The install(EXPORT) com-
       mand is used to export the  targets  in	the  ClimbingStatsTargets  ex-
       port-set, defined previously by the install(TARGETS) command. This com-
       mand generates the ClimbingStatsTargets.cmake file to contain  IMPORTED
       targets,	 suitable for use by downstreams and arranges to install it to
       lib/cmake/ClimbingStats.	   The	  generated    ClimbingStatsConfigVer-
       sion.cmake  and	a cmake/ClimbingStatsConfig.cmake are installed	to the
       same location, completing the package.

       The generated IMPORTED targets have appropriate properties set  to  de-
       fine  their  usage requirements,	such as	INTERFACE_INCLUDE_DIRECTORIES,
       INTERFACE_COMPILE_DEFINITIONS and other	relevant  built-in  INTERFACE_
       properties.  The	INTERFACE variant of user-defined properties listed in
       COMPATIBLE_INTERFACE_STRING and other Compatible	 Interface  Properties
       are  also  propagated  to the generated IMPORTED	targets.  In the above
       case, ClimbingStats_MAJOR_VERSION is defined as a string	which must  be
       compatible  among  the  dependencies  of	any depender.  By setting this
       custom defined user property in this version and	in the next version of
       ClimbingStats,  cmake(1)	will issue a diagnostic	if there is an attempt
       to use version 3	together with version 4.  Packages can choose  to  em-
       ploy  such a pattern if different major versions	of the package are de-
       signed to be incompatible.

       A NAMESPACE with	double-colons is specified when	exporting the  targets
       for  installation.  This	convention of double-colons gives CMake	a hint
       that the	name is	an IMPORTED target when	it is used by downstreams with
       the target_link_libraries() command.  This way, CMake can issue a diag-
       nostic if the package providing it has not yet been found.

       In this case, when using	install(TARGETS) the INCLUDES DESTINATION  was
       specified.   This  causes  the  IMPORTED	 targets  to have their	INTER-
       FACE_INCLUDE_DIRECTORIES	populated with the include  directory  in  the
       CMAKE_INSTALL_PREFIX.   When the	IMPORTED target	is used	by downstream,
       it automatically	consumes the entries from that property.

   Creating a Package Configuration File
       In this case, the ClimbingStatsConfig.cmake file	could be as simple as:

	  include("${CMAKE_CURRENT_LIST_DIR}/ClimbingStatsTargets.cmake")

       As this allows downstreams to use the IMPORTED targets.	If any	macros
       should  be  provided  by	the ClimbingStats package, they	should be in a
       separate	file which is installed	to the same  location  as  the	Climb-
       ingStatsConfig.cmake file, and included from there.

       This can	also be	extended to cover dependencies:

	  # ...
	  add_library(ClimbingStats SHARED climbingstats.cpp)
	  generate_export_header(ClimbingStats)

	  find_package(Stats 2.6.4 REQUIRED)
	  target_link_libraries(ClimbingStats PUBLIC Stats::Types)

       As  the	Stats::Types  target  is a PUBLIC dependency of	ClimbingStats,
       downstreams  must  also	find  the  Stats  package  and	link  to   the
       Stats::Types  library.  The Stats package should	be found in the	Climb-
       ingStatsConfig.cmake file to ensure this.   The	find_dependency	 macro
       from  the  CMakeFindDependencyMacro  helps  with	 this  by  propagating
       whether the package is REQUIRED,	or QUIET etc.  All REQUIRED  dependen-
       cies of a package should	be found in the	Config.cmake file:

	  include(CMakeFindDependencyMacro)
	  find_dependency(Stats	2.6.4)

	  include("${CMAKE_CURRENT_LIST_DIR}/ClimbingStatsTargets.cmake")
	  include("${CMAKE_CURRENT_LIST_DIR}/ClimbingStatsMacros.cmake")

       The find_dependency macro also sets ClimbingStats_FOUND to False	if the
       dependency is not found,	along with a diagnostic	that the ClimbingStats
       package can not be used without the Stats package.

       If  COMPONENTS  are  specified when the downstream uses find_package(),
       they are	listed in the  <PackageName>_FIND_COMPONENTS  variable.	 If  a
       particular  component  is non-optional, then the	<PackageName>_FIND_RE-
       QUIRED_<comp> will be true. This	can be tested with logic in the	 pack-
       age configuration file:

	  include(CMakeFindDependencyMacro)
	  find_dependency(Stats	2.6.4)

	  include("${CMAKE_CURRENT_LIST_DIR}/ClimbingStatsTargets.cmake")
	  include("${CMAKE_CURRENT_LIST_DIR}/ClimbingStatsMacros.cmake")

	  set(_supported_components Plot Table)

	  foreach(_comp	${ClimbingStats_FIND_COMPONENTS})
	    if (NOT ";${_supported_components};" MATCHES _comp)
	      set(ClimbingStats_FOUND False)
	      set(ClimbingStats_NOT_FOUND_MESSAGE "Unsupported component: ${_comp}")
	    endif()
	    include("${CMAKE_CURRENT_LIST_DIR}/ClimbingStats${_comp}Targets.cmake")
	  endforeach()

       Here,  the  ClimbingStats_NOT_FOUND_MESSAGE  is set to a	diagnosis that
       the package could not be	found because an invalid component was	speci-
       fied.   This  message variable can be set for any case where the	_FOUND
       variable	is set to False, and will be displayed to the user.

   Creating a Package Configuration File for the Build Tree
       The export(EXPORT) command creates an IMPORTED targets definition  file
       which  is specific to the build-tree, and is not	relocatable.  This can
       similarly be used with a	suitable package configuration file and	 pack-
       age  version  file  to define a package for the build tree which	may be
       used without installation.  Consumers of	the build tree can simply  en-
       sure  that  the	CMAKE_PREFIX_PATH contains the build directory,	or set
       the ClimbingStats_DIR to	<build_dir>/ClimbingStats in the cache.

   Creating Relocatable	Packages
       A relocatable package must not reference	absolute paths of files	on the
       machine	where the package is built that	will not exist on the machines
       where the package may be	installed.

       Packages	created	by install(EXPORT) are designed	to be relocatable, us-
       ing  paths relative to the location of the package itself.  When	defin-
       ing the interface of a target for EXPORT, keep in mind that the include
       directories should be specified as relative paths which are relative to
       the CMAKE_INSTALL_PREFIX:

	  target_include_directories(tgt INTERFACE
	    # Wrong, not relocatable:
	    $<INSTALL_INTERFACE:${CMAKE_INSTALL_PREFIX}/include/TgtName>
	  )

	  target_include_directories(tgt INTERFACE
	    # Ok, relocatable:
	    $<INSTALL_INTERFACE:include/TgtName>
	  )

       The $<INSTALL_PREFIX> generator expression may be used as a placeholder
       for  the	install	prefix without resulting in a non-relocatable package.
       This is necessary if complex generator expressions are used:

	  target_include_directories(tgt INTERFACE
	    # Ok, relocatable:
	    $<INSTALL_INTERFACE:$<$<CONFIG:Debug>:$<INSTALL_PREFIX>/include/TgtName>>
	  )

       This also applies to paths referencing external	dependencies.	It  is
       not  advisable to populate any properties which may contain paths, such
       as  INTERFACE_INCLUDE_DIRECTORIES  and  INTERFACE_LINK_LIBRARIES,  with
       paths  relevant	to  dependencies.  For example,	this code may not work
       well for	a relocatable package:

	  target_link_libraries(ClimbingStats INTERFACE
	    ${Foo_LIBRARIES} ${Bar_LIBRARIES}
	    )
	  target_include_directories(ClimbingStats INTERFACE
	    "$<INSTALL_INTERFACE:${Foo_INCLUDE_DIRS};${Bar_INCLUDE_DIRS}>"
	    )

       The referenced variables	may contain the	absolute  paths	 to  libraries
       and  include  directories  as found on the machine the package was made
       on.  This would create a	package	with hard-coded	paths to  dependencies
       and not suitable	for relocation.

       Ideally	such  dependencies  should  be used through their own IMPORTED
       targets that have their own  IMPORTED_LOCATION  and  usage  requirement
       properties  such	 as  INTERFACE_INCLUDE_DIRECTORIES populated appropri-
       ately.	Those  imported	 targets  may  then  be	 used  with  the  tar-
       get_link_libraries() command for	ClimbingStats:

	  target_link_libraries(ClimbingStats INTERFACE	Foo::Foo Bar::Bar)

       With  this  approach  the  package references its external dependencies
       only through the	names of IMPORTED targets.  When a consumer  uses  the
       installed package, the consumer will run	the appropriate	find_package()
       commands	(via the find_dependency macro described above)	 to  find  the
       dependencies  and  populate the imported	targets	with appropriate paths
       on their	own machine.

       Unfortunately many modules shipped with CMake do	not  yet  provide  IM-
       PORTED targets because their development	pre-dated this approach.  This
       may improve incrementally over time.  Workarounds to create relocatable
       packages	using such modules include:

       o When  building	 the  package, specify each Foo_LIBRARY	cache entry as
	 just a	library	name, e.g. -DFoo_LIBRARY=foo.  This tells  the	corre-
	 sponding  find	 module	to populate the	Foo_LIBRARIES with just	foo to
	 ask the linker	to search for the library  instead  of	hard-coding  a
	 path.

       o Or,  after  installing	 the  package  content but before creating the
	 package installation binary for redistribution, manually replace  the
	 absolute paths	with placeholders for substitution by the installation
	 tool when the package is installed.

PACKAGE	REGISTRY
       CMake provides two central locations to	register  packages  that  have
       been built or installed anywhere	on a system:

       o User Package Registry

       o System	Package	Registry

       The  registries are especially useful to	help projects find packages in
       non-standard install locations or directly in their own build trees.  A
       project	may populate either the	user or	system registry	(using its own
       means, see below) to refer to its location.  In either case the package
       should  store  at  the registered location a Package Configuration File
       (<PackageName>Config.cmake)  and	 optionally  a	Package	 Version  File
       (<PackageName>ConfigVersion.cmake).

       The  find_package()  command searches the two package registries	as two
       of the search steps specified in	its documentation.  If it  has	suffi-
       cient  permissions  it also removes stale package registry entries that
       refer to	directories that do not	exist or do  not  contain  a  matching
       package configuration file.

   User	Package	Registry
       The  User  Package  Registry is stored in a per-user location.  The ex-
       port(PACKAGE) command may be used to register a project build  tree  in
       the  user  package  registry.  CMake currently provides no interface to
       add install trees to the	user package  registry.	  Installers  must  be
       manually	taught to register their packages if desired.

       On  Windows the user package registry is	stored in the Windows registry
       under a key in HKEY_CURRENT_USER.

       A <PackageName> may appear under	registry key:

	  HKEY_CURRENT_USER\Software\Kitware\CMake\Packages\<PackageName>

       as a REG_SZ value, with arbitrary name, that  specifies	the  directory
       containing the package configuration file.

       On  UNIX	platforms the user package registry is stored in the user home
       directory under ~/.cmake/packages.  A <PackageName>  may	 appear	 under
       the directory:

	  ~/.cmake/packages/<PackageName>

       as  a  file, with arbitrary name, whose content specifies the directory
       containing the package configuration file.

   System Package Registry
       The System Package Registry is stored in	a system-wide location.	 CMake
       currently  provides no interface	to add to the system package registry.
       Installers must be manually taught to register their  packages  if  de-
       sired.

       On  Windows  the	 system	package	registry is stored in the Windows reg-
       istry under a key in HKEY_LOCAL_MACHINE.	 A  <PackageName>  may	appear
       under registry key:

	  HKEY_LOCAL_MACHINE\Software\Kitware\CMake\Packages\<PackageName>

       as  a  REG_SZ  value, with arbitrary name, that specifies the directory
       containing the package configuration file.

       There is	no system package registry on non-Windows platforms.

   Disabling the Package Registry
       In some cases using the Package Registries is not desirable. CMake  al-
       lows one	to disable them	using the following variables:

       o The  export(PACKAGE)  command does not	populate the user package reg-
	 istry when CMP0090 is set to NEW unless the CMAKE_EXPORT_PACKAGE_REG-
	 ISTRY variable	explicitly enables it.	When CMP0090 is	not set	to NEW
	 then export(PACKAGE) populates	the user package registry  unless  the
	 CMAKE_EXPORT_NO_PACKAGE_REGISTRY variable explicitly disables it.

       o CMAKE_FIND_USE_PACKAGE_REGISTRY disables the User Package Registry in
	 all the find_package()	calls when set to FALSE.

       o Deprecated CMAKE_FIND_PACKAGE_NO_PACKAGE_REGISTRY disables  the  User
	 Package  Registry  in	all the	find_package() calls when set to TRUE.
	 This variable is  ignored  when  CMAKE_FIND_USE_PACKAGE_REGISTRY  has
	 been set.

       o CMAKE_FIND_PACKAGE_NO_SYSTEM_PACKAGE_REGISTRY	 disables  the	System
	 Package Registry in all the find_package() calls.

   Package Registry Example
       A simple	convention for naming package registry entries is to use  con-
       tent  hashes.   They  are  deterministic	 and  unlikely to collide (ex-
       port(PACKAGE) uses this approach).  The name of an entry	referencing  a
       specific	directory is simply the	content	hash of	the directory path it-
       self.

       If a project arranges for package registry entries to exist, such as:

	  > reg	query HKCU\Software\Kitware\CMake\Packages\MyPackage
	  HKEY_CURRENT_USER\Software\Kitware\CMake\Packages\MyPackage
	   45e7d55f13b87179bb12f907c8de6fc4 REG_SZ c:/Users/Me/Work/lib/cmake/MyPackage
	   7b4a9844f681c80ce93190d4e3185db9 REG_SZ c:/Users/Me/Work/MyPackage-build

       or:

	  $ cat	~/.cmake/packages/MyPackage/7d1fb77e07ce59a81bed093bbee945bd
	  /home/me/work/lib/cmake/MyPackage
	  $ cat	~/.cmake/packages/MyPackage/f92c1db873a1937f3100706657c63e07
	  /home/me/work/MyPackage-build

       then the	CMakeLists.txt code:

	  find_package(MyPackage)

       will search the registered locations for	 package  configuration	 files
       (MyPackageConfig.cmake).	  The  search order among package registry en-
       tries for a single package is unspecified and the entry	names  (hashes
       in  this	 example)  have	 no meaning.  Registered locations may contain
       package version files (MyPackageConfigVersion.cmake) to tell find_pack-
       age()  whether  a  specific  location  is  suitable for the version re-
       quested.

   Package Registry Ownership
       Package registry	entries	are individually owned by the project  instal-
       lations	that  they  reference.	A package installer is responsible for
       adding its own entry and	the corresponding uninstaller  is  responsible
       for removing it.

       The  export(PACKAGE)  command  populates	the user package registry with
       the location of a project build tree.  Build trees tend to  be  deleted
       by  developers and have no "uninstall" event that could trigger removal
       of their	entries.  In order to keep the registries clean	the find_pack-
       age()  command  automatically removes stale entries it encounters if it
       has sufficient permissions.  CMake provides no interface	to  remove  an
       entry  referencing an existing build tree once export(PACKAGE) has been
       invoked.	 However, if the project  removes  its	package	 configuration
       file  from  the build tree then the entry referencing the location will
       be considered stale.

COPYRIGHT
       2000-2020 Kitware, Inc. and Contributors

3.18.2				 Aug 27, 2020		     CMAKE-PACKAGES(7)

NAME | INTRODUCTION | USING PACKAGES | PACKAGE LAYOUT | CREATING PACKAGES | PACKAGE REGISTRY | COPYRIGHT

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