poky/documentation/contributor-guide/recipe-style-guide.rst - mdmillerii/openbmc - Gitiles

 .. SPDX-License-Identifier: CC-BY-SA-2.0-UK

 Recipe Style Guide
 ******************

 Recipe Naming Conventions
 =========================

 In general, most recipes should follow the naming convention
 ``recipes-category/package/packagename_version.bb``. Recipes for related
 projects may share the same package directory. ``packagename``, ``category``,
 and ``package`` may contain hyphens, but hyphens are not allowed in ``version``.

 If the recipe is tracking a Git revision that does not correspond to a released
 version of the software, ``version`` may be ``git`` (e.g. ``packagename_git.bb``)

 Version Policy
 ==============

 Our versions follow the form ``<package epoch>:<package version>-<package revision>``
 or in BitBake variable terms ${:term:`PE`}:${:term:`PV`}-${:term:`PR`}. We
 generally follow the `Debian <https://www.debian.org/doc/debian-policy/ch-controlfields.html#version>`__
 version policy which defines these terms.

 In most cases the version :term:`PV` will be set automatically from the recipe
 file name. It is recommended to use released versions of software as these are
 revisions that upstream are expecting people to use.

 Package versions should always compare and sort correctly so that upgrades work
 as expected. With conventional versions such as ``1.4`` upgrading ``to 1.5``
 this happens naturally, but some versions don't sort. For example,
 ``1.5 Release Candidate 2`` could be written as ``1.5rc2`` but this sorts after
 ``1.5``, so upgrades from feeds won't happen correctly.

 Instead the tilde (``~``) operator can be used, which sorts before the empty
 string so ``1.5~rc2`` comes before ``1.5``. There is a historical syntax which
 may be found where :term:`PV` is set as a combination of the prior version
 ``+`` the pre-release version, for example ``PV=1.4+1.5rc2``. This is a valid
 syntax but the tilde form is preferred.

 For version comparisons, the ``opkg-compare-versions`` program from
 ``opkg-utils`` can be useful when attempting to determine how two version
 numbers compare to each other. Our definitive version comparison algorithm is
 the one within bitbake which aims to match those of the package managers and
 Debian policy closely.

 When a recipe references a git revision that does not correspond to a released
 version of software (e.g. is not a tagged version), the :term:`PV` variable
 should include the Git revision using the following to make the
 version clear::

     PV = "<version>+git${SRCPV}"

 In this case, ``<version>`` should be the most recently released version of the
 software from the current source revision (``git describe`` can be useful for
 determining this). Whilst not recommended for published layers, this format is
 also useful when using :term:`AUTOREV` to set the recipe to increment source
 control revisions automatically, which can be useful during local development.

 Version Number Changes
 ======================

 The :term:`PR` variable is used to indicate different revisions of a recipe
 that reference the same upstream source version. It can be used to force a
 new version of a package to be installed onto a device from a package feed.
 These once had to be set manually but in most cases these can now be set and
 incremented automatically by a PR Server connected with a package feed.

 When :term:`PV` increases, any existing :term:`PR` value can and should be
 removed.

 If :term:`PV` changes in such a way that it does not increase with respect to
 the previous value, you need to increase :term:`PE` to ensure package managers
 will upgrade it correctly. If unset you should set :term:`PE` to "1" since
 the default of empty is easily confused with "0" depending on the package
 manager. :term:`PE` can only have an integer value.

 Recipe formatting
 =================

 Variable Formatting
 -------------------

 -  Variable assignment should a space around each side of the operator, e.g.
    ``FOO = "bar"``, not ``FOO="bar"``.

 -  Double quotes should be used on the right-hand side of the assignment,
    e.g. ``FOO = "bar"`` not ``FOO = 'bar'``

 -  Spaces should be used for indenting variables, with 4 spaces per tab

 -  Long variables should be split over multiple lines when possible by using
    the continuation character (``\``)

 -  When splitting a long variable over multiple lines, all continuation lines
    should be indented (with spaces) to align with the start of the quote on the
    first line::

        FOO = "this line is \
               long \
               "

    Instead of::

        FOO = "this line is \
        long \
        "

 Python Function formatting
 --------------------------

 -  Spaces must be used for indenting Python code, with 4 spaces per tab

 Shell Function formatting
 -------------------------

 -  The formatting of shell functions should be consistent within layers.
    Some use tabs, some use spaces.

 Recipe metadata
 ===============

 Required Variables
 ------------------

 The following variables should be included in all recipes:

 -  :term:`SUMMARY`: a one line description of the upstream project

 -  :term:`DESCRIPTION`: an extended description of the upstream project,
    possibly with multiple lines. If no reasonable description can be written,
    this may be omitted as it defaults to :term:`SUMMARY`.

 -  :term:`HOMEPAGE`: the URL to the upstream projects homepage.

 -  :term:`BUGTRACKER`: the URL upstream projects bug tracking website,
    if applicable.

 Recipe Ordering
 ---------------

 When a variable is defined in recipes and classes, variables should follow the
 general order when possible:

 -  :term:`SUMMARY`
 -  :term:`DESCRIPTION`
 -  :term:`HOMEPAGE`
 -  :term:`BUGTRACKER`
 -  :term:`SECTION`
 -  :term:`LICENSE`
 -  :term:`LIC_FILES_CHKSUM`
 -  :term:`DEPENDS`
 -  :term:`PROVIDES`
 -  :term:`PV`
 -  :term:`SRC_URI`
 -  :term:`SRCREV`
 -  :term:`S`
 -  ``inherit ...``
 -  :term:`PACKAGECONFIG`
 -  Build class specific variables such as ``EXTRA_QMAKEVARS_POST`` and :term:`EXTRA_OECONF`
 -  Tasks such as :ref:`ref-tasks-configure`
 -  :term:`PACKAGE_ARCH`
 -  :term:`PACKAGES`
 -  :term:`FILES`
 -  :term:`RDEPENDS`
 -  :term:`RRECOMMENDS`
 -  :term:`RSUGGESTS`
 -  :term:`RPROVIDES`
 -  :term:`RCONFLICTS`
 -  :term:`BBCLASSEXTEND`

 There are some cases where ordering is important and these cases would override
 this default order. Examples include:

 -  :term:`PACKAGE_ARCH` needing to be set before ``inherit packagegroup``

 Tasks should be ordered based on the order they generally execute. For commonly
 used tasks this would be:

 -  :ref:`ref-tasks-fetch`
 -  :ref:`ref-tasks-unpack`
 -  :ref:`ref-tasks-patch`
 -  :ref:`ref-tasks-prepare_recipe_sysroot`
 -  :ref:`ref-tasks-configure`
 -  :ref:`ref-tasks-compile`
 -  :ref:`ref-tasks-install`
 -  :ref:`ref-tasks-populate_sysroot`
 -  :ref:`ref-tasks-package`

 Custom tasks should be sorted similarly.

 Package specific variables are typically grouped together, e.g.::

     RDEPENDS:${PN} = “foo”
     RDEPENDS:${PN}-libs = “bar”

     RRECOMMENDS:${PN} = “one”
     RRECOMMENDS:${PN}-libs = “two”

 Recipe License Fields
 ---------------------

 Recipes need to define both the :term:`LICENSE` and
 :term:`LIC_FILES_CHKSUM` variables:

 -  :term:`LICENSE`: This variable specifies the license for the software.
    If you do not know the license under which the software you are
    building is distributed, you should go to the source code and look
    for that information. Typical files containing this information
    include ``COPYING``, :term:`LICENSE`, and ``README`` files. You could
    also find the information near the top of a source file. For example,
    given a piece of software licensed under the GNU General Public
    License version 2, you would set :term:`LICENSE` as follows::

       LICENSE = "GPL-2.0-only"

    The licenses you specify within :term:`LICENSE` can have any name as long
    as you do not use spaces, since spaces are used as separators between
    license names. For standard licenses, use the names of the files in
    ``meta/files/common-licenses/`` or the :term:`SPDXLICENSEMAP` flag names
    defined in ``meta/conf/licenses.conf``.

 -  :term:`LIC_FILES_CHKSUM`: The OpenEmbedded build system uses this
    variable to make sure the license text has not changed. If it has,
    the build produces an error and it affords you the chance to figure
    it out and correct the problem.

    You need to specify all applicable licensing files for the software.
    At the end of the configuration step, the build process will compare
    the checksums of the files to be sure the text has not changed. Any
    differences result in an error with the message containing the
    current checksum. For more explanation and examples of how to set the
    :term:`LIC_FILES_CHKSUM` variable, see the
    ":ref:`dev-manual/licenses:tracking license changes`" section.

    To determine the correct checksum string, you can list the
    appropriate files in the :term:`LIC_FILES_CHKSUM` variable with incorrect
    md5 strings, attempt to build the software, and then note the
    resulting error messages that will report the correct md5 strings.
    See the ":ref:`dev-manual/new-recipe:fetching code`" section for
    additional information.

    Here is an example that assumes the software has a ``COPYING`` file::

       LIC_FILES_CHKSUM = "file://COPYING;md5=xxx"

    When you try to build the
    software, the build system will produce an error and give you the
    correct string that you can substitute into the recipe file for a
    subsequent build.

 Tips and Guidelines for Writing Recipes
 ---------------------------------------

 -  Use :term:`BBCLASSEXTEND` instead of creating separate recipes such as ``-native``
    and ``-nativesdk`` ones, whenever possible. This avoids having to maintain multiple
    recipe files at the same time.
	.. SPDX-License-Identifier: CC-BY-SA-2.0-UK

	Recipe Style Guide
	******************

	Recipe Naming Conventions
	=========================

	In general, most recipes should follow the naming convention
	``recipes-category/package/packagename_version.bb``. Recipes for related
	projects may share the same package directory. ``packagename``, ``category``,
	and ``package`` may contain hyphens, but hyphens are not allowed in ``version``.

	If the recipe is tracking a Git revision that does not correspond to a released
	version of the software, ``version`` may be ``git`` (e.g. ``packagename_git.bb``)

	Version Policy
	==============

	Our versions follow the form ``<package epoch>:<package version>-<package revision>``
	or in BitBake variable terms ${:term:`PE`}:${:term:`PV`}-${:term:`PR`}. We
	generally follow the `Debian <https://www.debian.org/doc/debian-policy/ch-controlfields.html#version>`__
	version policy which defines these terms.

	In most cases the version :term:`PV` will be set automatically from the recipe
	file name. It is recommended to use released versions of software as these are
	revisions that upstream are expecting people to use.

	Package versions should always compare and sort correctly so that upgrades work
	as expected. With conventional versions such as ``1.4`` upgrading ``to 1.5``
	this happens naturally, but some versions don't sort. For example,
	``1.5 Release Candidate 2`` could be written as ``1.5rc2`` but this sorts after
	``1.5``, so upgrades from feeds won't happen correctly.

	Instead the tilde (``~``) operator can be used, which sorts before the empty
	string so ``1.5~rc2`` comes before ``1.5``. There is a historical syntax which
	may be found where :term:`PV` is set as a combination of the prior version
	``+`` the pre-release version, for example ``PV=1.4+1.5rc2``. This is a valid
	syntax but the tilde form is preferred.

	For version comparisons, the ``opkg-compare-versions`` program from
	``opkg-utils`` can be useful when attempting to determine how two version
	numbers compare to each other. Our definitive version comparison algorithm is
	the one within bitbake which aims to match those of the package managers and
	Debian policy closely.

	When a recipe references a git revision that does not correspond to a released
	version of software (e.g. is not a tagged version), the :term:`PV` variable
	should include the Git revision using the following to make the
	version clear::

	PV = "<version>+git${SRCPV}"

	In this case, ``<version>`` should be the most recently released version of the
	software from the current source revision (``git describe`` can be useful for
	determining this). Whilst not recommended for published layers, this format is
	also useful when using :term:`AUTOREV` to set the recipe to increment source
	control revisions automatically, which can be useful during local development.

	Version Number Changes
	======================

	The :term:`PR` variable is used to indicate different revisions of a recipe
	that reference the same upstream source version. It can be used to force a
	new version of a package to be installed onto a device from a package feed.
	These once had to be set manually but in most cases these can now be set and
	incremented automatically by a PR Server connected with a package feed.

	When :term:`PV` increases, any existing :term:`PR` value can and should be
	removed.

	If :term:`PV` changes in such a way that it does not increase with respect to
	the previous value, you need to increase :term:`PE` to ensure package managers
	will upgrade it correctly. If unset you should set :term:`PE` to "1" since
	the default of empty is easily confused with "0" depending on the package
	manager. :term:`PE` can only have an integer value.

	Recipe formatting
	=================

	Variable Formatting
	-------------------

	- Variable assignment should a space around each side of the operator, e.g.
	``FOO = "bar"``, not ``FOO="bar"``.

	- Double quotes should be used on the right-hand side of the assignment,
	e.g. ``FOO = "bar"`` not ``FOO = 'bar'``

	- Spaces should be used for indenting variables, with 4 spaces per tab

	- Long variables should be split over multiple lines when possible by using
	the continuation character (``\``)

	- When splitting a long variable over multiple lines, all continuation lines
	should be indented (with spaces) to align with the start of the quote on the
	first line::

	FOO = "this line is \
	long \
	"

	Instead of::

	FOO = "this line is \
	long \
	"

	Python Function formatting
	--------------------------

	- Spaces must be used for indenting Python code, with 4 spaces per tab

	Shell Function formatting
	-------------------------

	- The formatting of shell functions should be consistent within layers.
	Some use tabs, some use spaces.

	Recipe metadata
	===============

	Required Variables
	------------------

	The following variables should be included in all recipes:

	- :term:`SUMMARY`: a one line description of the upstream project

	- :term:`DESCRIPTION`: an extended description of the upstream project,
	possibly with multiple lines. If no reasonable description can be written,
	this may be omitted as it defaults to :term:`SUMMARY`.

	- :term:`HOMEPAGE`: the URL to the upstream projects homepage.

	- :term:`BUGTRACKER`: the URL upstream projects bug tracking website,
	if applicable.

	Recipe Ordering
	---------------

	When a variable is defined in recipes and classes, variables should follow the
	general order when possible:

	- :term:`SUMMARY`
	- :term:`DESCRIPTION`
	- :term:`HOMEPAGE`
	- :term:`BUGTRACKER`
	- :term:`SECTION`
	- :term:`LICENSE`
	- :term:`LIC_FILES_CHKSUM`
	- :term:`DEPENDS`
	- :term:`PROVIDES`
	- :term:`PV`
	- :term:`SRC_URI`
	- :term:`SRCREV`
	- :term:`S`
	- ``inherit ...``
	- :term:`PACKAGECONFIG`
	- Build class specific variables such as ``EXTRA_QMAKEVARS_POST`` and :term:`EXTRA_OECONF`
	- Tasks such as :ref:`ref-tasks-configure`
	- :term:`PACKAGE_ARCH`
	- :term:`PACKAGES`
	- :term:`FILES`
	- :term:`RDEPENDS`
	- :term:`RRECOMMENDS`
	- :term:`RSUGGESTS`
	- :term:`RPROVIDES`
	- :term:`RCONFLICTS`
	- :term:`BBCLASSEXTEND`

	There are some cases where ordering is important and these cases would override
	this default order. Examples include:

	- :term:`PACKAGE_ARCH` needing to be set before ``inherit packagegroup``

	Tasks should be ordered based on the order they generally execute. For commonly
	used tasks this would be:

	- :ref:`ref-tasks-fetch`
	- :ref:`ref-tasks-unpack`
	- :ref:`ref-tasks-patch`
	- :ref:`ref-tasks-prepare_recipe_sysroot`
	- :ref:`ref-tasks-configure`
	- :ref:`ref-tasks-compile`
	- :ref:`ref-tasks-install`
	- :ref:`ref-tasks-populate_sysroot`
	- :ref:`ref-tasks-package`

	Custom tasks should be sorted similarly.

	Package specific variables are typically grouped together, e.g.::

	RDEPENDS:${PN} = “foo”
	RDEPENDS:${PN}-libs = “bar”

	RRECOMMENDS:${PN} = “one”
	RRECOMMENDS:${PN}-libs = “two”

	Recipe License Fields
	---------------------

	Recipes need to define both the :term:`LICENSE` and
	:term:`LIC_FILES_CHKSUM` variables:

	- :term:`LICENSE`: This variable specifies the license for the software.
	If you do not know the license under which the software you are
	building is distributed, you should go to the source code and look
	for that information. Typical files containing this information
	include ``COPYING``, :term:`LICENSE`, and ``README`` files. You could
	also find the information near the top of a source file. For example,
	given a piece of software licensed under the GNU General Public
	License version 2, you would set :term:`LICENSE` as follows::

	LICENSE = "GPL-2.0-only"

	The licenses you specify within :term:`LICENSE` can have any name as long
	as you do not use spaces, since spaces are used as separators between
	license names. For standard licenses, use the names of the files in
	``meta/files/common-licenses/`` or the :term:`SPDXLICENSEMAP` flag names
	defined in ``meta/conf/licenses.conf``.

	- :term:`LIC_FILES_CHKSUM`: The OpenEmbedded build system uses this
	variable to make sure the license text has not changed. If it has,
	the build produces an error and it affords you the chance to figure
	it out and correct the problem.

	You need to specify all applicable licensing files for the software.
	At the end of the configuration step, the build process will compare
	the checksums of the files to be sure the text has not changed. Any
	differences result in an error with the message containing the
	current checksum. For more explanation and examples of how to set the
	:term:`LIC_FILES_CHKSUM` variable, see the
	":ref:`dev-manual/licenses:tracking license changes`" section.

	To determine the correct checksum string, you can list the
	appropriate files in the :term:`LIC_FILES_CHKSUM` variable with incorrect
	md5 strings, attempt to build the software, and then note the
	resulting error messages that will report the correct md5 strings.
	See the ":ref:`dev-manual/new-recipe:fetching code`" section for
	additional information.

	Here is an example that assumes the software has a ``COPYING`` file::

	LIC_FILES_CHKSUM = "file://COPYING;md5=xxx"

	When you try to build the
	software, the build system will produce an error and give you the
	correct string that you can substitute into the recipe file for a
	subsequent build.

	Tips and Guidelines for Writing Recipes
	---------------------------------------

	- Use :term:`BBCLASSEXTEND` instead of creating separate recipes such as ``-native``
	and ``-nativesdk`` ones, whenever possible. This avoids having to maintain multiple
	recipe files at the same time.