cmake-packages(7)¶
Contents
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
.
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(_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 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:
$<INSTALL_INTERFACE:$<$<CONFIG:Debug>:$<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
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:
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 theFoo_LIBRARIES
with justfoo
to ask the linker to search for the library instead of hard-coding a path.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:
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:
The
export(PACKAGE)
command does not populate the user package registry whenCMP0090
is set toNEW
unless theCMAKE_EXPORT_PACKAGE_REGISTRY
variable explicitly enables it. WhenCMP0090
is not set toNEW
thenexport(PACKAGE)
populates the user package registry unless theCMAKE_EXPORT_NO_PACKAGE_REGISTRY
variable explicitly disables it.CMAKE_FIND_USE_PACKAGE_REGISTRY
disables the User Package Registry in all thefind_package()
calls when set toFALSE
.Deprecated
CMAKE_FIND_PACKAGE_NO_PACKAGE_REGISTRY
disables the User Package Registry in all thefind_package()
calls when set toTRUE
. This variable is ignored whenCMAKE_FIND_USE_PACKAGE_REGISTRY
has been set.CMAKE_FIND_PACKAGE_NO_SYSTEM_PACKAGE_REGISTRY
disables the System Package Registry in all thefind_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.