doc/source/projectconf.rst - buildstream - Git at Google

 :orphan:

 .. _projectconf:


 Project Configuration
 =====================
 The project configuration file should be named ``project.conf`` and
 be located at the project root. It holds information such as Source
 aliases relevant for the sources used in the given project as well as
 overrides for the configuration of element types used in the project.

 Values specified in the project configuration override any of the
 default BuildStream project configuration, which is included
 :ref:`here <project_defaults>` for reference.


 .. _project_essentials:

 Essentials
 ----------


 Project Name
 ~~~~~~~~~~~~
 The first thing to setup in your ``project.conf`` should be the name
 of your project.

 .. code:: yaml

    name: my-project-name

 The project name will be used in user configuration and anywhere
 that a project needs to be specified.


 .. _project_format_version:

 Format Version
 ~~~~~~~~~~~~~~
 The BuildStream format is guaranteed to be backwards compatible
 with any earlier releases. The project's minimum required format
 version of BuildStream can be specified in ``project.conf`` with
 the ``format-version`` field, e.g.:

 .. code:: yaml

   # The minimum base BuildStream format
   format-version: 0

 BuildStream will increment it's core YAML format version at least once
 in any given minor point release where the format has been extended
 to support a new feature.

 .. note::

    :mod:`Element <buildstream.element>` and :mod:`Source <buildstream.source>`
    plugins also implement their own YAML configuration fragments and as
    such are revisioned separately from the core format. See :ref:`project_plugins`
    for details on specifying a minimum version of a specific plugin.


 Element Path
 ~~~~~~~~~~~~
 To allow the user to structure their project nicely, BuildStream
 allows the user to specify a project subdirectory where element
 ``.bst`` files are stored.

 .. code:: yaml

    element-path: elements

 Note that elements are referred to by their relative paths, whenever
 elements are referred to in a ``.bst`` file or on the command line.


 Source Aliases
 ~~~~~~~~~~~~~~
 In order to abstract the download location of source code and
 any assets which need to be downloaded, and also as a matter of
 convenience, BuildStream allows one to create named aliases for
 URLs which are to be used in the individual ``.bst`` files.

 .. code:: yaml

    aliases:
      foo: git://git.foo.org/
      bar: http://bar.com/downloads/


 .. _project_essentials_artifacts:

 Artifact Server
 ~~~~~~~~~~~~~~~
 If you have setup an :ref:`artifact server <artifacts>` for your
 project then it is convenient to configure this in your ``project.conf``
 so that users need not have any additional configuration to communicate
 with an artifact share.

 .. code:: yaml

   artifacts:

     # A url from which to download prebuilt artifacts
     url: https://foo.com/artifacts

 You can also specify a list of caches here; earlier entries in the list
 will have higher priority than later ones.


 Fail on Overlaps
 ~~~~~~~~~~~~~~~~
 When multiple elements are staged, there's a possibility that different
 elements will try and stage different versions of the same file.

 When ``fail-on-overlap`` is true, if an overlap is detected
 that hasn't been allowed by the element's
 :ref:`overlap whitelist<public_overlap_whitelist>`,
 then an error will be raised and the build will fail.

 otherwise, a warning will be raised indicating which files had overlaps,
 and the order that the elements were overlapped.

 .. code:: yaml

   fail-on-overlap: true


 .. _project_shell:

 Customizing the shell
 ---------------------
 Since BuildStream cannot know intimate details about your host or about
 the nature of the runtime and software that you are building, the shell
 environment for debugging and testing applications may need some help.

 The ``shell`` section allows some customization of the shell environment.

 .. note::

    The ``shell`` section is available since :ref:`format version 1 <project_format_version>`


 Interactive Shell Command
 ~~~~~~~~~~~~~~~~~~~~~~~~~
 By default, BuildStream will use ``sh -i`` when running an interactive
 shell, unless a specific command is given to the ``bst shell`` command.

 BuildStream will automatically set a convenient prompt via the ``PS1``
 environment variable for interactive shells; which might be overwritten
 depending on the shell you use in your runtime.

 If you are using ``bash``, we recommend the following configuration to
 ensure that the customized prompt is not overwritten:

 .. code:: yaml

    shell:

      # Specify the command to run by default for interactive shells
      command: [ 'bash', '--noprofile', '--norc', '-i' ]


 Environment Inheritance
 ~~~~~~~~~~~~~~~~~~~~~~~
 In order to cooperate with your host environment, a debugging shell
 sometimes needs to know some of your host environment variables in
 order to be more useful.

 For example, to share your host ``DISPLAY`` and ``DBUS_SESSION_BUS_ADDRESS``
 environments with debugging shells for your project, specify the following:

 .. code:: yaml

    shell:

      # Environment variables to inherit from the host environment
      environment-inherit:
      - DISPLAY
      - DBUS_SESSION_BUS_ADDRESS


 Host Files
 ~~~~~~~~~~
 It can be useful to share some files on the host with a shell so that
 it can integrate better with the host environment.

 The ``host-files`` configuration allows one to specify files on
 the host to be bind mounted into the sandbox. If a file listed here
 is found to be a directory on the host, or if the file does not exist
 on the host at all; then a warning message will be printed and the shell
 will still be launched.

 The ``host-files`` configuration can be specified as a list
 of filenames to be mirrored into the sandbox at the same location:

 .. code:: yaml

    shell:

      # Specify a list of files to mount in the sandbox
      # directory from the host.
      host-files:
      - '/etc/resolv.conf'
      - '/etc/passwd'

 Alternatively, one can specify a dictionary with the ``host`` and ``sandbox``
 attributes for a bit more flexibility, allowing one to mount a file
 from the host to an alternative location in the sandbox:

 .. code:: yaml

    shell:

      # Mount the host's resolv.conf in a different location
      host-files:
      - host: '/etc/resolv.conf'
        sandbox: '/usr/local/etc/resolv.conf'

 .. note::

    The ``host-files`` configuration is available since :ref:`format version 2 <project_format_version>`


 .. _project_plugins:

 External Plugins
 ----------------
 If your project makes use of any custom :mod:`Element <buildstream.element>` or
 :mod:`Source <buildstream.source>` plugins, then the project must inform BuildStream
 of the plugins it means to make use of and the origin from which it can be loaded.

 Note that plugins with the same name from different origins are not permitted.


 Core plugins
 ~~~~~~~~~~~~
 Plugins provided by the BuildStream core need not be explicitly specified
 here, but you may use this section to specify a minimal format version
 to ensure that they provide the features which your project requires.

 .. code:: yaml

    plugins:
    - origin: core

      # We require a new feature of the `git` source plugin, and
      # a new feature introduced in version 2 of the `patch` plugin.
      sources:
        git: 1
        patch: 2

      # ... And a new feature of the `script` element, added
      # in version 2 of it's own format version.
      elements:
        script: 2


 Local Plugins
 ~~~~~~~~~~~~~
 Local plugins are expected to be found in a subdirectory of the actual
 BuildStream project. :mod:`Element <buildstream.element>` and
 :mod:`Source <buildstream.source>` plugins should be stored in separate
 directories to avoid namespace collisions.

 The versions of local plugins are largely immaterial since they are
 revisioned along with the project by the user, usually in a VCS like git.
 However, for the sake of consistency with other plugin loading origins
 we require that you specify a version, this can always be ``0`` for a local
 plugin.


 .. code:: yaml

    plugins:

    - origin: local
      path: plugins/sources

      # We want to use the `mysource` source plugin located in our
      # project's `plugins/sources` subdirectory.
      sources:
        mysource: 0


 Pip Plugins
 ~~~~~~~~~~~
 Plugins loaded from the ``pip`` origin are expected to be installed
 separately on the host operating system using python's package management
 system.

 .. code:: yaml

    plugins:

    - origin: pip

      # Specify the name of the python package containing
      # the plugins we want to load. The name one would use
      # on the `pip install` command line.
      #
      package-name: potato

      # We again must specify a minimal format version for the
      # external plugin, it is allowed to be `0`.
      #
      elements:
        potato: 0


 .. _project_options:

 Options
 -------
 Options are how BuildStream projects can define parameters which
 can be configured by users invoking BuildStream to build your project.

 Options are declared in the ``project.conf`` in the main ``options``
 dictionary.

 .. code:: yaml

    options:
      debug:
        type: bool
        description: Whether to enable debugging
        default: False

 Users can configure those options when invoking BuildStream with the
 ``--option`` argument::

     $ bst --option debug True ...


 Common Properties
 ~~~~~~~~~~~~~~~~~
 All option types accept the following common attributes

 * ``type``

   Indicates the type of option to declare

 * ``description``

   A description of the meaning of the option

 * ``variable``

   Optionally indicate a :ref:`variable <format_variables>` name to
   export the option to. A string form of the selected option will
   be used to set the exported value.

   If used, this value will override any existing value for the
   variable declared in ``project.conf``, and will be overridden in
   the regular :ref:`composition order <format_composition>`.


 Boolean
 ~~~~~~~
 The ``bool`` option type allows specifying boolean values which
 can be cased in conditional expressions.


 **Declaring**

 .. code:: yaml

    options:
      debug:
        type: bool
        description: Whether to enable debugging
        default: False


 **Evaluating**

 Boolean options can be tested in expressions with equality tests:

 .. code:: yaml

    variables:
      enable-debug: False
      (?):
      - debug == True:
          enable-debug: True

 Or simply treated as truthy values:

 .. code:: yaml

    variables:
      enable-debug: False
      (?):
      - debug:
          enable-debug: True


 **Exporting**

 When exporting boolean options as variables, a ``True`` option value
 will be exported as ``1`` and a ``False`` option as ``0``


 Enumeration
 ~~~~~~~~~~~
 The ``enum`` option type allows specifying a string value
 with a restricted set of possible values.


 **Declaring**

 .. code:: yaml

    options:
      loglevel:
        type: enum
        description: The logging level
        values:
        - debug
        - info
        - warning
        default: info


 **Evaluating**

 Enumeration options must be tested as strings in conditional
 expressions:

 .. code:: yaml

    variables:
      enable-debug: False
      (?):
      - loglevel == "debug":
          enable-debug: True


 **Exporting**

 When exporting enumeration options as variables, the value is
 exported as a variable directly, as it is a simple string.


 Flags
 ~~~~~
 The ``flags`` option type allows specifying a list of string
 values with a restricted set of possible values.

 In contrast with the ``enum`` option type, the *default* value
 need not be specified and will default to an empty set.


 **Declaring**

 .. code:: yaml

    options:
      logmask:
        type: flags
        description: The logging mask
        values:
        - debug
        - info
        - warning
        default:
        - info


 **Evaluating**

 Options of type ``flags`` can be tested in conditional expressions using
 a pythonic *in* syntax to test if an element is present in a set:

 .. code:: yaml

    variables:
      enable-debug: False
      (?):
      - ("debug" in logmask):
          enable-debug: True


 **Exporting**

 When exporting flags options as variables, the value is
 exported as a comma separated list of selected value strings.


 Architecture
 ~~~~~~~~~~~~
 The ``arch`` option type is special enumeration option which
 defaults to the result of `uname -m`, and does not support
 assigning any default in the project configuration.

 .. code:: yaml

    options:
      machine_arch:
        type: arch
        description: The machine architecture
        values:
        - arm
        - aarch64
        - i386
        - x86_64


 Architecture options can be tested with the same expressions
 as other Enumeration options.


 Element Mask
 ~~~~~~~~~~~~
 The ``element-mask`` option type is a special Flags option
 which automatically allows only element names as values.

 .. code:: yaml

    options:
      debug_elements:
        type: element-mask
        description: The elements to build in debug mode

 This can be convenient for automatically declaring an option
 which might apply to any element, and can be tested with the
 same syntax as other Flag options.


 .. code:: yaml

    variables:
      enable-debug: False
      (?):
      - ("element.bst" in debug_elements):
          enable-debug: True


 .. _project_defaults:

 Specifying Defaults
 --------------------
 The ``project.conf`` plays a role in defining elements by
 providing default values and also by overriding values declared
 by plugins on a plugin wide basis.

 See the :ref:`composition <format_composition>` documentation for
 more detail on how elements are composed.


 Variables
 ~~~~~~~~~
 The defaults for :ref:`Variables <format_variables>` used in your
 project is defined here.

 .. code:: yaml

    variables:
      prefix: "/usr"


 Environment
 ~~~~~~~~~~~
 The defaults environment for the build sandbox is defined here.

 .. code:: yaml

    environment:
      PATH: /usr/bin:/bin:/usr/sbin:/sbin

 Additionally, the special ``environment-nocache`` list which specifies
 which environment variables do not effect build output, and are thus
 not considered in the calculation of artifact keys can be defined here.

 .. code:: yaml

    environment-nocache:
    - MAXJOBS

 Note that the ``environment-nocache`` list only exists so that we can
 control parameters such as ``make -j ${MAXJOBS}``, allowing us to control
 the number of jobs for a given build without effecting the resulting
 cache key.


 Split Rules
 ~~~~~~~~~~~
 The project wide :ref:`split rules <public_split_rules>` defaults can
 be specified here.

 .. code:: yaml

    split-rules:
      devel:
      - |
        %{includedir}
      - |
        %{includedir}/**
      - |
        %{libdir}/lib*.a
      - |
        %{libdir}/lib*.la


 .. _project_element_overrides:

 Element Overrides
 ~~~~~~~~~~~~~~~~~
 Base attributes declared by element default yaml files can be overridden
 on a project wide basis. The elements dictionary can be used to override
 variables, environments or plugin specific configuration data as shown below.


 .. code:: yaml

    elements:

      # Override default values for all autotools elements
      autotools:

        variables:
          bindir: "%{prefix}/bin"

        config:
          configure-commands: ...

        environment:
          PKG_CONFIG_PATH=%{libdir}/pkgconfig


 .. _project_source_overrides:

 Source Overrides
 ~~~~~~~~~~~~~~~~
 Default values (overriding built-in defaults) can be set on a project
 wide basis. The sources dictionary can be used to override plugin specific
 configuration data as shown below.


 .. code:: yaml

    sources:

      # Override default values for all git sources
      git:

        config:
          checkout-submodules: False


 .. _project_builtin_defaults:

 Builtin Defaults
 ----------------
 BuildStream defines some default values for convenience, the default
 values overridden by your project's ``project.conf`` are presented here:

   .. literalinclude:: ../../buildstream/data/projectconfig.yaml
      :language: yaml
	:orphan:

	.. _projectconf:


	Project Configuration
	=====================
	The project configuration file should be named ``project.conf`` and
	be located at the project root. It holds information such as Source
	aliases relevant for the sources used in the given project as well as
	overrides for the configuration of element types used in the project.

	Values specified in the project configuration override any of the
	default BuildStream project configuration, which is included
	:ref:`here <project_defaults>` for reference.


	.. _project_essentials:

	Essentials
	----------


	Project Name
	~~~~~~~~~~~~
	The first thing to setup in your ``project.conf`` should be the name
	of your project.

	.. code:: yaml

	name: my-project-name

	The project name will be used in user configuration and anywhere
	that a project needs to be specified.


	.. _project_format_version:

	Format Version
	~~~~~~~~~~~~~~
	The BuildStream format is guaranteed to be backwards compatible
	with any earlier releases. The project's minimum required format
	version of BuildStream can be specified in ``project.conf`` with
	the ``format-version`` field, e.g.:

	.. code:: yaml

	# The minimum base BuildStream format
	format-version: 0

	BuildStream will increment it's core YAML format version at least once
	in any given minor point release where the format has been extended
	to support a new feature.

	.. note::

	:mod:`Element <buildstream.element>` and :mod:`Source <buildstream.source>`
	plugins also implement their own YAML configuration fragments and as
	such are revisioned separately from the core format. See :ref:`project_plugins`
	for details on specifying a minimum version of a specific plugin.


	Element Path
	~~~~~~~~~~~~
	To allow the user to structure their project nicely, BuildStream
	allows the user to specify a project subdirectory where element
	``.bst`` files are stored.

	.. code:: yaml

	element-path: elements

	Note that elements are referred to by their relative paths, whenever
	elements are referred to in a ``.bst`` file or on the command line.


	Source Aliases
	~~~~~~~~~~~~~~
	In order to abstract the download location of source code and
	any assets which need to be downloaded, and also as a matter of
	convenience, BuildStream allows one to create named aliases for
	URLs which are to be used in the individual ``.bst`` files.

	.. code:: yaml

	aliases:
	foo: git://git.foo.org/
	bar: http://bar.com/downloads/


	.. _project_essentials_artifacts:

	Artifact Server
	~~~~~~~~~~~~~~~
	If you have setup an :ref:`artifact server <artifacts>` for your
	project then it is convenient to configure this in your ``project.conf``
	so that users need not have any additional configuration to communicate
	with an artifact share.

	.. code:: yaml

	artifacts:

	# A url from which to download prebuilt artifacts
	url: https://foo.com/artifacts

	You can also specify a list of caches here; earlier entries in the list
	will have higher priority than later ones.


	Fail on Overlaps
	~~~~~~~~~~~~~~~~
	When multiple elements are staged, there's a possibility that different
	elements will try and stage different versions of the same file.

	When ``fail-on-overlap`` is true, if an overlap is detected
	that hasn't been allowed by the element's
	:ref:`overlap whitelist<public_overlap_whitelist>`,
	then an error will be raised and the build will fail.

	otherwise, a warning will be raised indicating which files had overlaps,
	and the order that the elements were overlapped.

	.. code:: yaml

	fail-on-overlap: true


	.. _project_shell:

	Customizing the shell
	---------------------
	Since BuildStream cannot know intimate details about your host or about
	the nature of the runtime and software that you are building, the shell
	environment for debugging and testing applications may need some help.

	The ``shell`` section allows some customization of the shell environment.

	.. note::

	The ``shell`` section is available since :ref:`format version 1 <project_format_version>`


	Interactive Shell Command
	~~~~~~~~~~~~~~~~~~~~~~~~~
	By default, BuildStream will use ``sh -i`` when running an interactive
	shell, unless a specific command is given to the ``bst shell`` command.

	BuildStream will automatically set a convenient prompt via the ``PS1``
	environment variable for interactive shells; which might be overwritten
	depending on the shell you use in your runtime.

	If you are using ``bash``, we recommend the following configuration to
	ensure that the customized prompt is not overwritten:

	.. code:: yaml

	shell:

	# Specify the command to run by default for interactive shells
	command: [ 'bash', '--noprofile', '--norc', '-i' ]


	Environment Inheritance
	~~~~~~~~~~~~~~~~~~~~~~~
	In order to cooperate with your host environment, a debugging shell
	sometimes needs to know some of your host environment variables in
	order to be more useful.

	For example, to share your host ``DISPLAY`` and ``DBUS_SESSION_BUS_ADDRESS``
	environments with debugging shells for your project, specify the following:

	.. code:: yaml

	shell:

	# Environment variables to inherit from the host environment
	environment-inherit:
	- DISPLAY
	- DBUS_SESSION_BUS_ADDRESS


	Host Files
	~~~~~~~~~~
	It can be useful to share some files on the host with a shell so that
	it can integrate better with the host environment.

	The ``host-files`` configuration allows one to specify files on
	the host to be bind mounted into the sandbox. If a file listed here
	is found to be a directory on the host, or if the file does not exist
	on the host at all; then a warning message will be printed and the shell
	will still be launched.

	The ``host-files`` configuration can be specified as a list
	of filenames to be mirrored into the sandbox at the same location:

	.. code:: yaml

	shell:

	# Specify a list of files to mount in the sandbox
	# directory from the host.
	host-files:
	- '/etc/resolv.conf'
	- '/etc/passwd'

	Alternatively, one can specify a dictionary with the ``host`` and ``sandbox``
	attributes for a bit more flexibility, allowing one to mount a file
	from the host to an alternative location in the sandbox:

	.. code:: yaml

	shell:

	# Mount the host's resolv.conf in a different location
	host-files:
	- host: '/etc/resolv.conf'
	sandbox: '/usr/local/etc/resolv.conf'

	.. note::

	The ``host-files`` configuration is available since :ref:`format version 2 <project_format_version>`


	.. _project_plugins:

	External Plugins
	----------------
	If your project makes use of any custom :mod:`Element <buildstream.element>` or
	:mod:`Source <buildstream.source>` plugins, then the project must inform BuildStream
	of the plugins it means to make use of and the origin from which it can be loaded.

	Note that plugins with the same name from different origins are not permitted.


	Core plugins
	~~~~~~~~~~~~
	Plugins provided by the BuildStream core need not be explicitly specified
	here, but you may use this section to specify a minimal format version
	to ensure that they provide the features which your project requires.

	.. code:: yaml

	plugins:
	- origin: core

	# We require a new feature of the `git` source plugin, and
	# a new feature introduced in version 2 of the `patch` plugin.
	sources:
	git: 1
	patch: 2

	# ... And a new feature of the `script` element, added
	# in version 2 of it's own format version.
	elements:
	script: 2


	Local Plugins
	~~~~~~~~~~~~~
	Local plugins are expected to be found in a subdirectory of the actual
	BuildStream project. :mod:`Element <buildstream.element>` and
	:mod:`Source <buildstream.source>` plugins should be stored in separate
	directories to avoid namespace collisions.

	The versions of local plugins are largely immaterial since they are
	revisioned along with the project by the user, usually in a VCS like git.
	However, for the sake of consistency with other plugin loading origins
	we require that you specify a version, this can always be ``0`` for a local
	plugin.


	.. code:: yaml

	plugins:

	- origin: local
	path: plugins/sources

	# We want to use the `mysource` source plugin located in our
	# project's `plugins/sources` subdirectory.
	sources:
	mysource: 0


	Pip Plugins
	~~~~~~~~~~~
	Plugins loaded from the ``pip`` origin are expected to be installed
	separately on the host operating system using python's package management
	system.

	.. code:: yaml

	plugins:

	- origin: pip

	# Specify the name of the python package containing
	# the plugins we want to load. The name one would use
	# on the `pip install` command line.
	#
	package-name: potato

	# We again must specify a minimal format version for the
	# external plugin, it is allowed to be `0`.
	#
	elements:
	potato: 0


	.. _project_options:

	Options
	-------
	Options are how BuildStream projects can define parameters which
	can be configured by users invoking BuildStream to build your project.

	Options are declared in the ``project.conf`` in the main ``options``
	dictionary.

	.. code:: yaml

	options:
	debug:
	type: bool
	description: Whether to enable debugging
	default: False

	Users can configure those options when invoking BuildStream with the
	``--option`` argument::

	$ bst --option debug True ...


	Common Properties
	~~~~~~~~~~~~~~~~~
	All option types accept the following common attributes

	* ``type``

	Indicates the type of option to declare

	* ``description``

	A description of the meaning of the option

	* ``variable``

	Optionally indicate a :ref:`variable <format_variables>` name to
	export the option to. A string form of the selected option will
	be used to set the exported value.

	If used, this value will override any existing value for the
	variable declared in ``project.conf``, and will be overridden in
	the regular :ref:`composition order <format_composition>`.


	Boolean
	~~~~~~~
	The ``bool`` option type allows specifying boolean values which
	can be cased in conditional expressions.


	Declaring

	.. code:: yaml

	options:
	debug:
	type: bool
	description: Whether to enable debugging
	default: False


	Evaluating

	Boolean options can be tested in expressions with equality tests:

	.. code:: yaml

	variables:
	enable-debug: False
	(?):
	- debug == True:
	enable-debug: True

	Or simply treated as truthy values:

	.. code:: yaml

	variables:
	enable-debug: False
	(?):
	- debug:
	enable-debug: True


	Exporting

	When exporting boolean options as variables, a ``True`` option value
	will be exported as ``1`` and a ``False`` option as ``0``


	Enumeration
	~~~~~~~~~~~
	The ``enum`` option type allows specifying a string value
	with a restricted set of possible values.


	Declaring

	.. code:: yaml

	options:
	loglevel:
	type: enum
	description: The logging level
	values:
	- debug
	- info
	- warning
	default: info


	Evaluating

	Enumeration options must be tested as strings in conditional
	expressions:

	.. code:: yaml

	variables:
	enable-debug: False
	(?):
	- loglevel == "debug":
	enable-debug: True


	Exporting

	When exporting enumeration options as variables, the value is
	exported as a variable directly, as it is a simple string.


	Flags
	~~~~~
	The ``flags`` option type allows specifying a list of string
	values with a restricted set of possible values.

	In contrast with the ``enum`` option type, the default value
	need not be specified and will default to an empty set.


	Declaring

	.. code:: yaml

	options:
	logmask:
	type: flags
	description: The logging mask
	values:
	- debug
	- info
	- warning
	default:
	- info


	Evaluating

	Options of type ``flags`` can be tested in conditional expressions using
	a pythonic in syntax to test if an element is present in a set:

	.. code:: yaml

	variables:
	enable-debug: False
	(?):
	- ("debug" in logmask):
	enable-debug: True


	Exporting

	When exporting flags options as variables, the value is
	exported as a comma separated list of selected value strings.


	Architecture
	~~~~~~~~~~~~
	The ``arch`` option type is special enumeration option which
	defaults to the result of `uname -m`, and does not support
	assigning any default in the project configuration.

	.. code:: yaml

	options:
	machine_arch:
	type: arch
	description: The machine architecture
	values:
	- arm
	- aarch64
	- i386
	- x86_64


	Architecture options can be tested with the same expressions
	as other Enumeration options.


	Element Mask
	~~~~~~~~~~~~
	The ``element-mask`` option type is a special Flags option
	which automatically allows only element names as values.

	.. code:: yaml

	options:
	debug_elements:
	type: element-mask
	description: The elements to build in debug mode

	This can be convenient for automatically declaring an option
	which might apply to any element, and can be tested with the
	same syntax as other Flag options.


	.. code:: yaml

	variables:
	enable-debug: False
	(?):
	- ("element.bst" in debug_elements):
	enable-debug: True



	.. _project_defaults:

	Specifying Defaults
	--------------------
	The ``project.conf`` plays a role in defining elements by
	providing default values and also by overriding values declared
	by plugins on a plugin wide basis.

	See the :ref:`composition <format_composition>` documentation for
	more detail on how elements are composed.


	Variables
	~~~~~~~~~
	The defaults for :ref:`Variables <format_variables>` used in your
	project is defined here.

	.. code:: yaml

	variables:
	prefix: "/usr"


	Environment
	~~~~~~~~~~~
	The defaults environment for the build sandbox is defined here.

	.. code:: yaml

	environment:
	PATH: /usr/bin:/bin:/usr/sbin:/sbin

	Additionally, the special ``environment-nocache`` list which specifies
	which environment variables do not effect build output, and are thus
	not considered in the calculation of artifact keys can be defined here.

	.. code:: yaml

	environment-nocache:
	- MAXJOBS

	Note that the ``environment-nocache`` list only exists so that we can
	control parameters such as ``make -j ${MAXJOBS}``, allowing us to control
	the number of jobs for a given build without effecting the resulting
	cache key.


	Split Rules
	~~~~~~~~~~~
	The project wide :ref:`split rules <public_split_rules>` defaults can
	be specified here.

	.. code:: yaml

	split-rules:
	devel:
	- \|
	%{includedir}
	- \|
	%{includedir}/**
	- \|
	%{libdir}/lib*.a
	- \|
	%{libdir}/lib*.la


	.. _project_element_overrides:

	Element Overrides
	~~~~~~~~~~~~~~~~~
	Base attributes declared by element default yaml files can be overridden
	on a project wide basis. The elements dictionary can be used to override
	variables, environments or plugin specific configuration data as shown below.


	.. code:: yaml

	elements:

	# Override default values for all autotools elements
	autotools:

	variables:
	bindir: "%{prefix}/bin"

	config:
	configure-commands: ...

	environment:
	PKG_CONFIG_PATH=%{libdir}/pkgconfig


	.. _project_source_overrides:

	Source Overrides
	~~~~~~~~~~~~~~~~
	Default values (overriding built-in defaults) can be set on a project
	wide basis. The sources dictionary can be used to override plugin specific
	configuration data as shown below.


	.. code:: yaml

	sources:

	# Override default values for all git sources
	git:

	config:
	checkout-submodules: False


	.. _project_builtin_defaults:

	Builtin Defaults
	----------------
	BuildStream defines some default values for convenience, the default
	values overridden by your project's ``project.conf`` are presented here:

	.. literalinclude:: ../../buildstream/data/projectconfig.yaml
	:language: yaml