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
using 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
provided 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
package.
By setting the CMAKE_DISABLE_FIND_PACKAGE_<PackageName> variable to
TRUE, the <PackageName> package will not be searched, and will always
be NOTFOUND. Likewise, setting the
CMAKE_REQUIRE_FIND_PACKAGE_<PackageName> to TRUE will make the package
REQUIRED.
Config-file Packages
A config-file package is a set of files provided by upstreams for
downstreams 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
development 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
<PackageName>_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.
Typically, a find module is needed when the upstream is not built with
CMake, or is not CMake-aware enough to otherwise provide a package
configuration 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_package() command. It can still be expected to be set by
convention however 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
optionally 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
FooConfig.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
locations.
The find_package() command may be used to search for the package
configuration file. This command constructs a set of installation
prefixes and searches under each prefix in several locations. Given
the name Foo, it looks for a file called FooConfig.cmake or
foo-config.cmake. The full set of locations is specified in the
find_package() 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
version requested. If the version file claims compatibility the
configuration 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
compatible or an exact match for the requested version and set the
following 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
command 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
acceptable 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
determine the compatibility with the requested version, and to set some
version-specific variables <PackageName>_VERSION,
<PackageName>_VERSION_MAJOR, <PackageName>_VERSION_MINOR etc. The
install(EXPORT) command is used to export the targets in the
ClimbingStatsTargets export-set, defined previously by the
install(TARGETS) command. This command 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
ClimbingStatsConfigVersion.cmake and a cmake/ClimbingStatsConfig.cmake
are installed to the same location, completing the package.
The generated IMPORTED targets have appropriate properties set to
define 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
employ such a pattern if different major versions of the package are
designed 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
diagnostic 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
INTERFACE_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
ClimbingStatsConfig.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
ClimbingStatsConfig.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
dependencies 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_REQUIRED_<comp> will be true. This can be tested
with logic in the package 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(_ClimbingStats_supported_components Plot Table)
foreach(_comp ${ClimbingStats_FIND_COMPONENTS})
if (NOT ";${_ClimbingStats_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
specified. 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
package version file to define a package for the build tree which may
be used without installation. Consumers of the build tree can simply
ensure 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,
using paths relative to the location of the package itself. When
defining 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:
$<INSTALL_INTERFACE:$<$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
appropriately. Those imported targets may then be used with the
target_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
IMPORTED 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
corresponding 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
sufficient 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
export(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
desired.
On Windows the system package registry is stored in the Windows
registry 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
allows one to disable them using the following variables:
o The export(PACKAGE) command does not populate the user package
registry when CMP0090 is set to NEW unless the
CMAKE_EXPORT_PACKAGE_REGISTRY 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
content hashes. They are deterministic and unlikely to collide
(export(PACKAGE) uses this approach). The name of an entry referencing
a specific directory is simply the content hash of the directory path
itself.
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
entries 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_package() whether a specific location is suitable for the version
requested.
Package Registry Ownership
Package registry entries are individually owned by the project
installations 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_package() 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
2000-2024 Kitware, Inc. and Contributors
3.29.3 May 15, 2024 cmake-packages(7)
cmake 3.29.3 - Generated Wed May 15 13:18:17 CDT 2024