# CPack External Generator

CPack provides many generators to create packages for a variety of platforms and packaging systems. The intention is for CMake/CPack to be a complete end-to-end solution for building and packaging a software project. However, it may not always be possible to use CPack for the entire packaging process, due to either technical limitations or policies that require the use of certain tools. For this reason, CPack provides the “External” generator, which allows external packaging software to take advantage of some of the functionality provided by CPack, such as component installation and the dependency graph.

## Integration with External Packaging Tools

The CPack External generator generates a .json file containing the CPack internal metadata, which gives external software information on how to package the software. External packaging software may itself invoke CPack, consume the generated metadata, install and package files as required.

Alternatively CPack can invoke an external packaging software through an optional custom CMake script in `CPACK_EXTERNAL_PACKAGE_SCRIPT` instead.

Staging of installation files may also optionally be taken care of by the generator when enabled through the `CPACK_EXTERNAL_ENABLE_STAGING` variable.

## JSON Format

The JSON metadata file contains a list of CPack components and component groups, the various options passed to `cpack_add_component()` and `cpack_add_component_group()`, the dependencies between the components and component groups, and various other options passed to CPack.

The JSON’s root object will always provide two fields: `formatVersionMajor` and `formatVersionMinor`, which are always integers that describe the output format of the generator. Backwards-compatible changes to the output format (for example, adding a new field that didn’t exist before) cause the minor version to be incremented, and backwards-incompatible changes (for example, deleting a field or changing its meaning) cause the major version to be incremented and the minor version reset to 0. The format version is always of the format `major.minor`. In other words, it always has exactly two parts, separated by a period.

You can request one or more specific versions of the output format as described below with `CPACK_EXTERNAL_REQUESTED_VERSIONS`. The output format will have a major version that exactly matches the requested major version, and a minor version that is greater than or equal to the requested minor version. If no version is requested with `CPACK_EXTERNAL_REQUESTED_VERSIONS`, the latest known major version is used by default. Currently, the only supported format is 1.0, which is described below.

### Version 1.0

In addition to the standard format fields, format version 1.0 provides the following fields in the root:

`components`

  The `components` field is an object with component names as the keys and objects describing the components as the values. The component objects have the following fields:

  `name`
    The name of the component. This is always the same as the key in the `components` object.
  `displayName`
    The value of the `DISPLAY_NAME` field passed to `cpack_add_component()`.
  `description`
    The value of the `DESCRIPTION` field passed to `cpack_add_component()`.
  `isHidden`
    True if `HIDDEN` was passed to `cpack_add_component()`, false if it was not.
  `isRequired`
    True if `REQUIRED` was passed to `cpack_add_component()`, false if it was not.
  `isDisabledByDefault`
    True if `DISABLED` was passed to `cpack_add_component()`, false if it was not.
  `group`
    Only present if `GROUP` was passed to `cpack_add_component()`. If so, this field is a string value containing the component’s group.
  `dependencies`
    An array of components the component depends on. This contains the values in the `DEPENDS` argument passed to `cpack_add_component()`. If no `DEPENDS` argument was passed, this is an empty list.
  `installationTypes`
    An array of installation types the component is part of. This contains the values in the `INSTALL_TYPES` argument passed to `cpack_add_component()`. If no `INSTALL_TYPES` argument was passed, this is an empty list.
  `isDownloaded`
    True if `DOWNLOADED` was passed to `cpack_add_component()`, false if it was not.
  `archiveFile`
    The name of the archive file passed with the `ARCHIVE_FILE` argument to `cpack_add_component()`. If no `ARCHIVE_FILE` argument was passed, this is an empty string.
`componentGroups`

  The `componentGroups` field is an object with component group names as the keys and objects describing the component groups as the values. The component group objects have the following fields:

  `name`
    The name of the component group. This is always the same as the key in the `componentGroups` object.
  `displayName`
    The value of the `DISPLAY_NAME` field passed to `cpack_add_component_group()`.
  `description`
    The value of the `DESCRIPTION` field passed to `cpack_add_component_group()`.
  `parentGroup`
    Only present if `PARENT_GROUP` was passed to `cpack_add_component_group()`. If so, this field is a string value containing the component group’s parent group.
  `isExpandedByDefault`
    True if `EXPANDED` was passed to `cpack_add_component_group()`, false if it was not.
  `isBold`
    True if `BOLD_TITLE` was passed to `cpack_add_component_group()`, false if it was not.
  `components`
    An array of names of components that are direct members of the group (components that have this group as their `GROUP`). Components of subgroups are not included.
  `subgroups`
    An array of names of component groups that are subgroups of the group (groups that have this group as their `PARENT_GROUP`).
`installationTypes`

  The `installationTypes` field is an object with installation type names as the keys and objects describing the installation types as the values. The installation type objects have the following fields:

  `name`
    The name of the installation type. This is always the same as the key in the `installationTypes` object.
  `displayName`
    The value of the `DISPLAY_NAME` field passed to `cpack_add_install_type()`.
  `index`
    The integer index of the installation type in the list.
`projects`

  The `projects` field is an array of objects describing CMake projects which comprise the CPack project. The values in this field are derived from `CPACK_INSTALL_CMAKE_PROJECTS`. In most cases, this will be only a single project. The project objects have the following fields:

  `projectName`
    The project name passed to `CPACK_INSTALL_CMAKE_PROJECTS`.
  `component`
    The name of the component or component set which comprises the project.
  `directory`
    The build directory of the CMake project. This is the directory which contains the `cmake_install.cmake` script.
  `subDirectory`
    The subdirectory to install the project into inside the CPack package.
`packageName`
  The package name given in `CPACK_PACKAGE_NAME`. Only present if this option is set.
`packageVersion`
  The package version given in `CPACK_PACKAGE_VERSION`. Only present if this option is set.
`packageDescriptionFile`
  The package description file given in `CPACK_PACKAGE_DESCRIPTION_FILE`. Only present if this option is set.
`packageDescriptionSummary`
  The package description summary given in `CPACK_PACKAGE_DESCRIPTION_SUMMARY`. Only present if this option is set.
`buildConfig`
  The build configuration given to CPack with the `-C` option. Only present if this option is set.
`defaultDirectoryPermissions`
  The default directory permissions given in `CPACK_INSTALL_DEFAULT_DIRECTORY_PERMISSIONS`. Only present if this option is set.
`setDestdir`
  True if `CPACK_SET_DESTDIR` is true, false if it is not.
`packagingInstallPrefix`
  The install prefix given in `CPACK_PACKAGING_INSTALL_PREFIX`. Only present if `CPACK_SET_DESTDIR` is true.
`stripFiles`
  True if `CPACK_STRIP_FILES` is true, false if it is not.
`warnOnAbsoluteInstallDestination`
  True if `CPACK_WARN_ON_ABSOLUTE_INSTALL_DESTINATION` is true, false if it is not.
`errorOnAbsoluteInstallDestination`
  True if `CPACK_ERROR_ON_ABSOLUTE_INSTALL_DESTINATION` is true, false if it is not.

## Variables specific to CPack External generator

`CPACK_EXTERNAL_REQUESTED_VERSIONS`

  This variable is used to request a specific version of the CPack External generator. It is a list of `major.minor` values, separated by semicolons.

  If this variable is set to a non-empty value, the CPack External generator will iterate through each item in the list to search for a version that it knows how to generate. Requested versions should be listed in order of descending preference by the client software, as the first matching version in the list will be generated.

  The generator knows how to generate the version if it has a versioned generator whose major version exactly matches the requested major version, and whose minor version is greater than or equal to the requested minor version. For example, if `CPACK_EXTERNAL_REQUESTED_VERSIONS` contains 1.0, and the CPack External generator knows how to generate 1.1, it will generate 1.1. If the generator doesn’t know how to generate a version in the list, it skips the version and looks at the next one. If it doesn’t know how to generate any of the requested versions, an error is thrown.

  If this variable is not set, or is empty, the CPack External generator will generate the highest major and minor version that it knows how to generate.

  If an invalid version is encountered in `CPACK_EXTERNAL_REQUESTED_VERSIONS` (one that doesn’t match `major.minor`, where `major` and `minor` are integers), it is ignored.

`CPACK_EXTERNAL_ENABLE_STAGING`

  This variable can be set to true to enable optional installation into a temporary staging area which can then be picked up and packaged by an external packaging tool. The top level directory used by CPack for the current packaging task is contained in `CPACK_TOPLEVEL_DIRECTORY`. It is automatically cleaned up on each run before packaging is initiated and can be used for custom temporary files required by the external packaging tool. It also contains the staging area `CPACK_TEMPORARY_DIRECTORY` into which CPack performs the installation when staging is enabled.

`CPACK_EXTERNAL_PACKAGE_SCRIPT`

  This variable can optionally specify the full path to a CMake script file to be run as part of the CPack invocation. It is invoked after (optional) staging took place and may run an external packaging tool. The script has access to the variables defined by the CPack config file.