ExternalProject¶
Contents
External Project Definition¶
-
ExternalProject_Add
¶ The
ExternalProject_Add()
function creates a custom target to drive download, update/patch, configure, build, install and test steps of an external project:ExternalProject_Add(<name> [<option>...])
The individual steps within the process can be driven independently if required (e.g. for CDash submission) and extra custom steps can be defined, along with the ability to control the step dependencies. The directory structure used for the management of the external project can also be customized. The function supports a large number of options which can be used to tailor the external project behavior.
- Directory Options:
Most of the time, the default directory layout is sufficient. It is largely an implementation detail that the main project usually doesn’t need to change. In some circumstances, however, control over the directory layout can be useful or necessary. The directory options are potentially more useful from the point of view that the main build can use the
ExternalProject_Get_Property()
command to retrieve their values, thereby allowing the main project to refer to build artifacts of the external project.PREFIX <dir>
Root directory for the external project. Unless otherwise noted below, all other directories associated with the external project will be created under here.
TMP_DIR <dir>
Directory in which to store temporary files.
STAMP_DIR <dir>
Directory in which to store the timestamps of each step. Log files from individual steps are also created in here (see Logging Options below).
DOWNLOAD_DIR <dir>
Directory in which to store downloaded files before unpacking them. This directory is only used by the URL download method, all other download methods use
SOURCE_DIR
directly instead.SOURCE_DIR <dir>
Source directory into which downloaded contents will be unpacked, or for non-URL download methods, the directory in which the repository should be checked out, cloned, etc. If no download method is specified, this must point to an existing directory where the external project has already been unpacked or cloned/checked out.
Note
If a download method is specified, any existing contents of the source directory may be deleted. Only the URL download method checks whether this directory is either missing or empty before initiating the download, stopping with an error if it is not empty. All other download methods silently discard any previous contents of the source directory.
BINARY_DIR <dir>
Specify the build directory location. This option is ignored if
BUILD_IN_SOURCE
is enabled.INSTALL_DIR <dir>
Installation prefix to be placed in the
<INSTALL_DIR>
placeholder. This does not actually configure the external project to install to the given prefix. That must be done by passing appropriate arguments to the external project configuration step, e.g. using<INSTALL_DIR>
.
If any of the above
..._DIR
options are not specified, their defaults are computed as follows. If thePREFIX
option is given or theEP_PREFIX
directory property is set, then an external project is built and installed under the specified prefix:TMP_DIR = <prefix>/tmp STAMP_DIR = <prefix>/src/<name>-stamp DOWNLOAD_DIR = <prefix>/src SOURCE_DIR = <prefix>/src/<name> BINARY_DIR = <prefix>/src/<name>-build INSTALL_DIR = <prefix>
Otherwise, if the
EP_BASE
directory property is set then components of an external project are stored under the specified base:TMP_DIR = <base>/tmp/<name> STAMP_DIR = <base>/Stamp/<name> DOWNLOAD_DIR = <base>/Download/<name> SOURCE_DIR = <base>/Source/<name> BINARY_DIR = <base>/Build/<name> INSTALL_DIR = <base>/Install/<name>
If no
PREFIX
,EP_PREFIX
, orEP_BASE
is specified, then the default is to setPREFIX
to<name>-prefix
. Relative paths are interpreted with respect toCMAKE_CURRENT_BINARY_DIR
at the point whereExternalProject_Add()
is called.- Download Step Options:
A download method can be omitted if the
SOURCE_DIR
option is used to point to an existing non-empty directory. Otherwise, one of the download methods below must be specified (multiple download methods should not be given) or a customDOWNLOAD_COMMAND
provided.DOWNLOAD_COMMAND <cmd>...
Overrides the command used for the download step (
generator expressions
are supported). If this option is specified, all other download options will be ignored. Providing an empty string for<cmd>
effectively disables the download step.- URL Download
URL <url1> [<url2>...]
List of paths and/or URL(s) of the external project’s source. When more than one URL is given, they are tried in turn until one succeeds. A URL may be an ordinary path in the local file system (in which case it must be the only URL provided) or any downloadable URL supported by the
file(DOWNLOAD)
command. A local filesystem path may refer to either an existing directory or to an archive file, whereas a URL is expected to point to a file which can be treated as an archive. When an archive is used, it will be unpacked automatically unless theDOWNLOAD_NO_EXTRACT
option is set to prevent it. The archive type is determined by inspecting the actual content rather than using logic based on the file extension.URL_HASH <algo>=<hashValue>
Hash of the archive file to be downloaded. The argument should be of the form
<algo>=<hashValue>
wherealgo
can be any of the hashing algorithms supported by thefile()
command. Specifying this option is strongly recommended for URL downloads, as it ensures the integrity of the downloaded content. It is also used as a check for a previously downloaded file, allowing connection to the remote location to be avoided altogether if the local directory already has a file from an earlier download that matches the specified hash.URL_MD5 <md5>
Equivalent to
URL_HASH MD5=<md5>
.DOWNLOAD_NAME <fname>
File name to use for the downloaded file. If not given, the end of the URL is used to determine the file name. This option is rarely needed, the default name is generally suitable and is not normally used outside of code internal to the
ExternalProject
module.DOWNLOAD_NO_EXTRACT <bool>
Allows the extraction part of the download step to be disabled by passing a boolean true value for this option. If this option is not given, the downloaded contents will be unpacked automatically if required. If extraction has been disabled, the full path to the downloaded file is available as
<DOWNLOADED_FILE>
in subsequent steps or as the propertyDOWNLOADED_FILE
with theExternalProject_Get_Property()
command.DOWNLOAD_NO_PROGRESS <bool>
Can be used to disable logging the download progress. If this option is not given, download progress messages will be logged.
TIMEOUT <seconds>
Maximum time allowed for file download operations.
HTTP_USERNAME <username>
Username for the download operation if authentication is required.
HTTP_PASSWORD <password>
Password for the download operation if authentication is required.
HTTP_HEADER <header1> [<header2>...]
Provides an arbitrary list of HTTP headers for the download operation. This can be useful for accessing content in systems like AWS, etc.
TLS_VERIFY <bool>
Specifies whether certificate verification should be performed for https URLs. If this option is not provided, the default behavior is determined by the
CMAKE_TLS_VERIFY
variable (seefile(DOWNLOAD)
). If that is also not set, certificate verification will not be performed. In situations whereURL_HASH
cannot be provided, this option can be an alternative verification measure.TLS_CAINFO <file>
Specify a custom certificate authority file to use if
TLS_VERIFY
is enabled. If this option is not specified, the value of theCMAKE_TLS_CAINFO
variable will be used instead (seefile(DOWNLOAD)
)NETRC <level>
Specify whether the .netrc file is to be used for operation. If this option is not specified, the value of the
CMAKE_NETRC
variable will be used instead (seefile(DOWNLOAD)
) Valid levels are:IGNORED
The .netrc file is ignored. This is the default.
OPTIONAL
The .netrc file is optional, and information in the URL is preferred. The file will be scanned to find which ever information is not specified in the URL.
REQUIRED
The .netrc file is required, and information in the URL is ignored.
NETRC_FILE <file>
Specify an alternative .netrc file to the one in your home directory if the
NETRC
level isOPTIONAL
orREQUIRED
. If this option is not specified, the value of theCMAKE_NETRC_FILE
variable will be used instead (seefile(DOWNLOAD)
)
- Git
NOTE: A git version of 1.6.5 or later is required if this download method is used.
GIT_REPOSITORY <url>
URL of the git repository. Any URL understood by the
git
command may be used.GIT_TAG <tag>
Git branch name, tag or commit hash. Note that branch names and tags should generally be specified as remote names (i.e.
origin/myBranch
rather than simplymyBranch
). This ensures that if the remote end has its tag moved or branch rebased or history rewritten, the local clone will still be updated correctly. In general, however, specifying a commit hash should be preferred for a number of reasons:If the local clone already has the commit corresponding to the hash, no
git fetch
needs to be performed to check for changes each time CMake is re-run. This can result in a significant speed up if many external projects are being used.Using a specific git hash ensures that the main project’s own history is fully traceable to a specific point in the external project’s evolution. If a branch or tag name is used instead, then checking out a specific commit of the main project doesn’t necessarily pin the whole build to a specific point in the life of the external project. The lack of such deterministic behavior makes the main project lose traceability and repeatability.
GIT_REMOTE_NAME <name>
The optional name of the remote. If this option is not specified, it defaults to
origin
.GIT_SUBMODULES <module>...
Specific git submodules that should also be updated. If this option is not provided, all git submodules will be updated.
GIT_SHALLOW <bool>
When this option is enabled, the
git clone
operation will be given the--depth 1
option. This performs a shallow clone, which avoids downloading the whole history and instead retrieves just the commit denoted by theGIT_TAG
option.GIT_PROGRESS <bool>
When enabled, this option instructs the
git clone
operation to report its progress by passing it the--progress
option. Without this option, the clone step for large projects may appear to make the build stall, since nothing will be logged until the clone operation finishes. While this option can be used to provide progress to prevent the appearance of the build having stalled, it may also make the build overly noisy if lots of external projects are used.GIT_CONFIG <option1> [<option2>...]
Specify a list of config options to pass to
git clone
. Each option listed will be transformed into its own--config <option>
on thegit clone
command line, with each option required to be in the formkey=value
.
- Subversion
SVN_REPOSITORY <url>
URL of the Subversion repository.
SVN_REVISION -r<rev>
Revision to checkout from the Subversion repository.
SVN_USERNAME <username>
Username for the Subversion checkout and update.
SVN_PASSWORD <password>
Password for the Subversion checkout and update.
SVN_TRUST_CERT <bool>
Specifies whether to trust the Subversion server site certificate. If enabled, the
--trust-server-cert
option is passed to thesvn
checkout and update commands.
- Mercurial
HG_REPOSITORY <url>
URL of the mercurial repository.
HG_TAG <tag>
Mercurial branch name, tag or commit id.
- CVS
CVS_REPOSITORY <cvsroot>
CVSROOT of the CVS repository.
CVS_MODULE <mod>
Module to checkout from the CVS repository.
CVS_TAG <tag>
Tag to checkout from the CVS repository.
- Update/Patch Step Options:
Whenever CMake is re-run, by default the external project’s sources will be updated if the download method supports updates (e.g. a git repository would be checked if the
GIT_TAG
does not refer to a specific commit).UPDATE_COMMAND <cmd>...
Overrides the download method’s update step with a custom command. The command may use
generator expressions
.UPDATE_DISCONNECTED <bool>
When enabled, this option causes the update step to be skipped. It does not, however, prevent the download step. The update step can still be added as a step target (see
ExternalProject_Add_StepTargets()
) and called manually. This is useful if you want to allow developers to build the project when disconnected from the network (the network may still be needed for the download step though).When this option is present, it is generally advisable to make the value a cache variable under the developer’s control rather than hard-coding it. If this option is not present, the default value is taken from the
EP_UPDATE_DISCONNECTED
directory property. If that is also not defined, updates are performed as normal. TheEP_UPDATE_DISCONNECTED
directory property is intended as a convenience for controlling theUPDATE_DISCONNECTED
behavior for an entire section of a project’s directory hierarchy and may be a more convenient method of giving developers control over whether or not to perform updates (assuming the project also provides a cache variable or some other convenient method for setting the directory property).PATCH_COMMAND <cmd>...
Specifies a custom command to patch the sources after an update. By default, no patch command is defined. Note that it can be quite difficult to define an appropriate patch command that performs robustly, especially for download methods such as git where changing the
GIT_TAG
will not discard changes from a previous patch, but the patch command will be called again after updating to the new tag.
- Configure Step Options:
The configure step is run after the download and update steps. By default, the external project is assumed to be a CMake project, but this can be overridden if required.
CONFIGURE_COMMAND <cmd>...
The default configure command runs CMake with options based on the main project. For non-CMake external projects, the
CONFIGURE_COMMAND
option must be used to override this behavior (generator expressions
are supported). For projects that require no configure step, specify this option with an empty string as the command to execute.CMAKE_COMMAND /.../cmake
Specify an alternative cmake executable for the configure step (use an absolute path). This is generally not recommended, since it is usually desirable to use the same CMake version throughout the whole build. This option is ignored if a custom configure command has been specified with
CONFIGURE_COMMAND
.CMAKE_GENERATOR <gen>
Override the CMake generator used for the configure step. Without this option, the same generator as the main build will be used. This option is ignored if a custom configure command has been specified with the
CONFIGURE_COMMAND
option.CMAKE_GENERATOR_PLATFORM <platform>
Pass a generator-specific platform name to the CMake command (see
CMAKE_GENERATOR_PLATFORM
). It is an error to provide this option without theCMAKE_GENERATOR
option.CMAKE_GENERATOR_TOOLSET <toolset>
Pass a generator-specific toolset name to the CMake command (see
CMAKE_GENERATOR_TOOLSET
). It is an error to provide this option without theCMAKE_GENERATOR
option.CMAKE_GENERATOR_INSTANCE <instance>
Pass a generator-specific instance selection to the CMake command (see
CMAKE_GENERATOR_INSTANCE
). It is an error to provide this option without theCMAKE_GENERATOR
option.CMAKE_ARGS <arg>...
The specified arguments are passed to the
cmake
command line. They can be any argument thecmake
command understands, not just cache values defined by-D...
arguments (see alsoCMake Options
). In addition, arguments may usegenerator expressions
.CMAKE_CACHE_ARGS <arg>...
This is an alternate way of specifying cache variables where command line length issues may become a problem. The arguments are expected to be in the form
-Dvar:STRING=value
, which are then transformed into CMakeset()
commands with theFORCE
option used. Theseset()
commands are written to a pre-load script which is then applied using thecmake -C
command line option. Arguments may usegenerator expressions
.CMAKE_CACHE_DEFAULT_ARGS <arg>...
This is the same as the
CMAKE_CACHE_ARGS
option except theset()
commands do not include theFORCE
keyword. This means the values act as initial defaults only and will not override any variables already set from a previous run. Use this option with care, as it can lead to different behavior depending on whether the build starts from a fresh build directory or re-uses previous build contents.SOURCE_SUBDIR <dir>
When no
CONFIGURE_COMMAND
option is specified, the configure step assumes the external project has aCMakeLists.txt
file at the top of its source tree (i.e. inSOURCE_DIR
). TheSOURCE_SUBDIR
option can be used to point to an alternative directory within the source tree to use as the top of the CMake source tree instead. This must be a relative path and it will be interpreted as being relative toSOURCE_DIR
.
- Build Step Options:
If the configure step assumed the external project uses CMake as its build system, the build step will also. Otherwise, the build step will assume a Makefile-based build and simply run
make
with no arguments as the default build step. This can be overridden with custom build commands if required.BUILD_COMMAND <cmd>...
Overrides the default build command (
generator expressions
are supported). If this option is not given, the default build command will be chosen to integrate with the main build in the most appropriate way (e.g. using recursivemake
for Makefile generators orcmake --build
if the project uses a CMake build). This option can be specified with an empty string as the command to make the build step do nothing.BUILD_IN_SOURCE <bool>
When this option is enabled, the build will be done directly within the external project’s source tree. This should generally be avoided, the use of a separate build directory is usually preferred, but it can be useful when the external project assumes an in-source build. The
BINARY_DIR
option should not be specified if building in-source.BUILD_ALWAYS <bool>
Enabling this option forces the build step to always be run. This can be the easiest way to robustly ensure that the external project’s own build dependencies are evaluated rather than relying on the default success timestamp-based method. This option is not normally needed unless developers are expected to modify something the external project’s build depends on in a way that is not detectable via the step target dependencies (e.g.
SOURCE_DIR
is used without a download method and developers might modify the sources inSOURCE_DIR
).BUILD_BYPRODUCTS <file>...
Specifies files that will be generated by the build command but which might or might not have their modification time updated by subsequent builds. These ultimately get passed through as
BYPRODUCTS
to the build step’s own underlying call toadd_custom_command()
.
- Install Step Options:
If the configure step assumed the external project uses CMake as its build system, the install step will also. Otherwise, the install step will assume a Makefile-based build and simply run
make install
as the default build step. This can be overridden with custom install commands if required.INSTALL_COMMAND <cmd>...
The external project’s own install step is invoked as part of the main project’s build. It is done after the external project’s build step and may be before or after the external project’s test step (see the
TEST_BEFORE_INSTALL
option below). The external project’s install rules are not part of the main project’s install rules, so if anything from the external project should be installed as part of the main build, these need to be specified in the main build as additionalinstall()
commands. The default install step builds theinstall
target of the external project, but this can be overridden with a custom command using this option (generator expressions
are supported). Passing an empty string as the<cmd>
makes the install step do nothing.
- Test Step Options:
The test step is only defined if at least one of the following
TEST_...
options are provided.TEST_COMMAND <cmd>...
Overrides the default test command (
generator expressions
are supported). If this option is not given, the default behavior of the test step is to build the external project’s owntest
target. This option can be specified with<cmd>
as an empty string, which allows the test step to still be defined, but it will do nothing. Do not specify any of the otherTEST_...
options if providing an empty string as the test command, but prefer to omit allTEST_...
options altogether if the test step target is not needed.TEST_BEFORE_INSTALL <bool>
When this option is enabled, the test step will be executed before the install step. The default behavior is for the test step to run after the install step.
TEST_AFTER_INSTALL <bool>
This option is mainly useful as a way to indicate that the test step is desired but all default behavior is sufficient. Specifying this option with a boolean true value ensures the test step is defined and that it comes after the install step. If both
TEST_BEFORE_INSTALL
andTEST_AFTER_INSTALL
are enabled, the latter is silently ignored.TEST_EXCLUDE_FROM_MAIN <bool>
If enabled, the main build’s default ALL target will not depend on the test step. This can be a useful way of ensuring the test step is defined but only gets invoked when manually requested.
- Output Logging Options:
Each of the following
LOG_...
options can be used to wrap the relevant step in a script to capture its output to files. The log files will be created in theSTAMP_DIR
directory with step-specific file names.LOG_DOWNLOAD <bool>
When enabled, the output of the download step is logged to files.
LOG_UPDATE <bool>
When enabled, the output of the update step is logged to files.
LOG_CONFIGURE <bool>
When enabled, the output of the configure step is logged to files.
LOG_BUILD <bool>
When enabled, the output of the build step is logged to files.
LOG_INSTALL <bool>
When enabled, the output of the install step is logged to files.
LOG_TEST <bool>
When enabled, the output of the test step is logged to files.
- Terminal Access Options:
Steps can be given direct access to the terminal in some cases. Giving a step access to the terminal may allow it to receive terminal input if required, such as for authentication details not provided by other options. With the
Ninja
generator, these options place the steps in theconsole
job pool
. Each step can be given access to the terminal individually via the following options:USES_TERMINAL_DOWNLOAD <bool>
Give the download step access to the terminal.
USES_TERMINAL_UPDATE <bool>
Give the update step access to the terminal.
USES_TERMINAL_CONFIGURE <bool>
Give the configure step access to the terminal.
USES_TERMINAL_BUILD <bool>
Give the build step access to the terminal.
USES_TERMINAL_INSTALL <bool>
Give the install step access to the terminal.
USES_TERMINAL_TEST <bool>
Give the test step access to the terminal.
- Target Options:
DEPENDS <targets>...
Specify other targets on which the external project depends. The other targets will be brought up to date before any of the external project’s steps are executed. Because the external project uses additional custom targets internally for each step, the
DEPENDS
option is the most convenient way to ensure all of those steps depend on the other targets. Simply doingadd_dependencies(<name> <targets>)
will not make any of the steps dependent on<targets>
.EXCLUDE_FROM_ALL <bool>
When enabled, this option excludes the external project from the default ALL target of the main build.
STEP_TARGETS <step-target>...
Generate custom targets for the specified steps. This is required if the steps need to be triggered manually or if they need to be used as dependencies of other targets. If this option is not specified, the default value is taken from the
EP_STEP_TARGETS
directory property. SeeExternalProject_Add_Step()
below for further discussion of the effects of this option.INDEPENDENT_STEP_TARGETS <step-target>...
Generate custom targets for the specified steps and prevent these targets from having the usual dependencies applied to them. If this option is not specified, the default value is taken from the
EP_INDEPENDENT_STEP_TARGETS
directory property. This option is mostly useful for allowing individual steps to be driven independently, such as for a CDash setup where each step should be initiated and reported individually rather than as one whole build. SeeExternalProject_Add_Step()
below for further discussion of the effects of this option.
- Miscellaneous Options:
LIST_SEPARATOR <sep>
For any of the various
..._COMMAND
options, replace;
with<sep>
in the specified command lines. This can be useful where list variables may be given in commands where they should end up as space-separated arguments (<sep>
would be a single space character string in this case).COMMAND <cmd>...
Any of the other
..._COMMAND
options can have additional commands appended to them by following them with as manyCOMMAND ...
options as needed (generator expressions
are supported). For example:ExternalProject_Add(example ... # Download options, etc. BUILD_COMMAND ${CMAKE_COMMAND} -E echo "Starting $<CONFIG> build" COMMAND ${CMAKE_COMMAND} --build <BINARY_DIR> --config $<CONFIG> COMMAND ${CMAKE_COMMAND} -E echo "$<CONFIG> build complete" )
It should also be noted that each build step is created via a call to
ExternalProject_Add_Step()
. See that command’s documentation for the automatic substitutions that are supported for some options.
Obtaining Project Properties¶
-
ExternalProject_Get_Property
¶ The
ExternalProject_Get_Property()
function retrieves external project target properties:ExternalProject_Get_Property(<name> <prop1> [<prop2>...])
The function stores property values in variables of the same name. Property names correspond to the keyword argument names of
ExternalProject_Add()
. For example, the source directory might be retrieved like so:ExternalProject_Get_property(myExtProj SOURCE_DIR) message("Source dir of myExtProj = ${SOURCE_DIR}")
Explicit Step Management¶
The ExternalProject_Add()
function on its own is often sufficient for
incorporating an external project into the main build. Certain scenarios
require additional work to implement desired behavior, such as adding in a
custom step or making steps available as manually triggerable targets. The
ExternalProject_Add_Step()
, ExternalProject_Add_StepTargets()
and
ExternalProject_Add_StepDependencies
functions provide the lower level
control needed to implement such step-level capabilities.
-
ExternalProject_Add_Step
¶ The
ExternalProject_Add_Step()
function specifies an additional custom step for an external project defined by an earlier call toExternalProject_Add()
:ExternalProject_Add_Step(<name> <step> [<option>...])
<name>
is the same as the name passed to the original call toExternalProject_Add()
. The specified<step>
must not be one of the pre-defined steps (mkdir
,download
,update
,skip-update
,patch
,configure
,build
,install
ortest
). The supported options are:COMMAND <cmd>...
The command line to be executed by this custom step (
generator expressions
are supported). This option can be repeated multiple times to specify multiple commands to be executed in order.COMMENT "<text>..."
Text to be printed when the custom step executes.
DEPENDEES <step>...
Other steps (custom or pre-defined) on which this step depends.
DEPENDERS <step>...
Other steps (custom or pre-defined) that depend on this new custom step.
DEPENDS <file>...
Files on which this custom step depends.
BYPRODUCTS <file>...
Files that will be generated by this custom step but which might or might not have their modification time updated by subsequent builds. This list of files will ultimately be passed through as the
BYPRODUCTS
option to theadd_custom_command()
used to implement the custom step internally.ALWAYS <bool>
When enabled, this option specifies that the custom step should always be run (i.e. that it is always considered out of date).
EXCLUDE_FROM_MAIN <bool>
When enabled, this option specifies that the external project’s main target does not depend on the custom step.
WORKING_DIRECTORY <dir>
Specifies the working directory to set before running the custom step’s command. If this option is not specified, the directory will be the value of the
CMAKE_CURRENT_BINARY_DIR
at the point whereExternalProject_Add_Step()
was called.LOG <bool>
If set, this causes the output from the custom step to be captured to files in the external project’s
STAMP_DIR
.USES_TERMINAL <bool>
If enabled, this gives the custom step direct access to the terminal if possible.
The command line, comment, working directory and byproducts of every standard and custom step are processed to replace the tokens
<SOURCE_DIR>
,<SOURCE_SUBDIR>
,<BINARY_DIR>
,<INSTALL_DIR>
<TMP_DIR>
,<DOWNLOAD_DIR>
and<DOWNLOADED_FILE>
with their corresponding property values defined in the original call toExternalProject_Add()
.
-
ExternalProject_Add_StepTargets
¶ The
ExternalProject_Add_StepTargets()
function generates targets for the steps listed. The name of each created target will be of the form<name>-<step>
:ExternalProject_Add_StepTargets(<name> [NO_DEPENDS] <step1> [<step2>...])
Creating a target for a step allows it to be used as a dependency of another target or to be triggered manually. Having targets for specific steps also allows them to be driven independently of each other by specifying targets on build command lines. For example, you may be submitting to a sub-project based dashboard where you want to drive the configure portion of the build, then submit to the dashboard, followed by the build portion, followed by tests. If you invoke a custom target that depends on a step halfway through the step dependency chain, then all the previous steps will also run to ensure everything is up to date.
If the
NO_DEPENDS
option is specified, the step target will not depend on the dependencies of the external project (i.e. on any dependencies of the<name>
custom target created byExternalProject_Add()
). This is usually safe for thedownload
,update
andpatch
steps, since they do not typically require that the dependencies are updated and built. UsingNO_DEPENDS
for any of the other pre-defined steps, however, may break parallel builds. Only useNO_DEPENDS
where it is certain that the named steps genuinely do not have dependencies. For custom steps, consider whether or not the custom commands require the dependencies to be configured, built and installed.Internally,
ExternalProject_Add()
callsExternalProject_Add_Step()
to create each step. If anySTEP_TARGETS
orINDEPENDENT_STEP_TARGETS
were specified, thenExternalProject_Add_StepTargets()
will also be called afterExternalProject_Add_Step()
.INDEPENDENT_STEP_TARGETS
have theNO_DEPENDS
option set, whereasSTEP_TARGETS
do not. Other than that, the two options result inExternalProject_Add_StepTargets()
being called in the same way. Even if a step is not mentioned in either of those two options,ExternalProject_Add_StepTargets()
can still be called later to manually define a target for the step.The
STEP_TARGETS
andINDEPENDENT_STEP_TARGETS
options forExternalProject_Add()
are generally the easiest way to ensure targets are created for specific steps of interest. For custom steps,ExternalProject_Add_StepTargets()
must be called explicitly if a target should also be created for that custom step. An alternative to these two options is to populate theEP_STEP_TARGETS
andEP_INDEPENDENT_STEP_TARGETS
directory properties. These act as defaults for the step target options and can save having to repeatedly specify the same set of step targets when multiple external projects are being defined.
-
ExternalProject_Add_StepDependencies
¶ The
ExternalProject_Add_StepDependencies()
function can be used to add dependencies to a step. The dependencies added must be targets CMake already knows about (these can be ordinary executable or library targets, custom targets or even step targets of another external project):ExternalProject_Add_StepDependencies(<name> <step> <target1> [<target2>...])
This function takes care to set both target and file level dependencies and will ensure that parallel builds will not break. It should be used instead of
add_dependencies()
whenever adding a dependency for some of the step targets generated by theExternalProject
module.
Examples¶
The following example shows how to download and build a hypothetical project called FooBar from github:
include(ExternalProject)
ExternalProject_Add(foobar
GIT_REPOSITORY git@github.com:FooCo/FooBar.git
GIT_TAG origin/release/1.2.3
)
For the sake of the example, also define a second hypothetical external project
called SecretSauce, which is downloaded from a web server. Two URLs are given
to take advantage of a faster internal network if available, with a fallback to
a slower external server. The project is a typical Makefile
project with no
configure step, so some of the default commands are overridden. The build is
only required to build the sauce target:
find_program(MAKE_EXE NAMES gmake nmake make)
ExternalProject_Add(secretsauce
URL http://intranet.somecompany.com/artifacts/sauce-2.7.tgz
https://www.somecompany.com/downloads/sauce-2.7.zip
URL_HASH MD5=d41d8cd98f00b204e9800998ecf8427e
CONFIGURE_COMMAND ""
BUILD_COMMAND ${MAKE_EXE} sauce
)
Suppose the build step of secretsauce
requires that foobar
must already
be built. This could be enforced like so:
ExternalProject_Add_StepDependencies(secretsauce build foobar)
Another alternative would be to create a custom target for foobar
’s build
step and make secretsauce
depend on that rather than the whole foobar
project. This would mean foobar
only needs to be built, it doesn’t need to
run its install or test steps before secretsauce
can be built. The
dependency can also be defined along with the secretsauce
project:
ExternalProject_Add_StepTargets(foobar build)
ExternalProject_Add(secretsauce
URL http://intranet.somecompany.com/artifacts/sauce-2.7.tgz
https://www.somecompany.com/downloads/sauce-2.7.zip
URL_HASH MD5=d41d8cd98f00b204e9800998ecf8427e
CONFIGURE_COMMAND ""
BUILD_COMMAND ${MAKE_EXE} sauce
DEPENDS foobar-build
)
Instead of calling ExternalProject_Add_StepTargets()
, the target could
be defined along with the foobar
project itself:
ExternalProject_Add(foobar
GIT_REPOSITORY git@github.com:FooCo/FooBar.git
GIT_TAG origin/release/1.2.3
STEP_TARGETS build
)
If many external projects should have the same set of step targets, setting a
directory property may be more convenient. The build
step target could be
created automatically by setting the EP_STEP_TARGETS
directory property
before creating the external projects with ExternalProject_Add()
:
set_property(DIRECTORY PROPERTY EP_STEP_TARGETS build)
Lastly, suppose that secretsauce
provides a script called makedoc
which
can be used to generate its own documentation. Further suppose that the script
expects the output directory to be provided as the only parameter and that it
should be run from the secretsauce
source directory. A custom step and a
custom target to trigger the script can be defined like so:
ExternalProject_Add_Step(secretsauce docs
COMMAND <SOURCE_DIR>/makedoc <BINARY_DIR>
WORKING_DIRECTORY <SOURCE_DIR>
COMMENT "Building secretsauce docs"
ALWAYS TRUE
EXCLUDE_FROM_MAIN TRUE
)
ExternalProject_Add_StepTargets(secretsauce docs)
The custom step could then be triggered from the main build like so:
cmake --build . --target secretsauce-docs