.. _west-multi-repo:

Multiple Repository Management
##############################

This page introduces basic concepts related to West and its multiple repository
management features, and gives an overview of the associated commands. See
:ref:`west-history` and `Zephyr issue #6770`_ for additional discussion,
rationale, and motivation.

.. note::

   West's multi-repo commands are meant to augment Git in minor ways for
   multi-repo work, not to replace it. For tasks that only operate on one
   repository, just use plain Git commands.

.. _west-installation:

Introduction
************

West's built-in commands allow you to work with projects composed of multiple
Git repositories installed under a common parent directory, which we call a
*west installation*. This works similarly to `Git Submodules
<https://git-scm.com/book/en/v2/Git-Tools-Submodules>`_ and Google's `repo
<https://gerrit.googlesource.com/git-repo/>`_.

A west installation is the result of running the ``west init`` command, which
is described in more detail below. This command can either create a new
installation, or convert a standalone "mono-repo" zephyr repository into a full
west installation. For upstream Zephyr, the installation looks like this:

.. code-block:: none

   zephyrproject
   ├── .west
   │   ├── config
   │   └── west
   ├── zephyr
   │   ├── west.yml
   │   └── [... other files ...]
   ├── modules
   │   └── lib
   │       └── tinycbor
   ├── net-tools
   └── [ ... other projects ...]

Above, :file:`zephyrproject` is the name of the west installation's root
directory. This name is just an example -- it could be anything, like ``z``,
``my-zephyr-installation``, etc.  The file :file:`.west/config` is the
installation's :ref:`local configuration file <west-config>`. The directory
:file:`.west/west` is a clone of the west repository itself; more details on
why that is currently needed are given in the next section.

Every west installation contains exactly one *manifest repository*, which is a
Git repository containing a file named :file:`west.yml`, which is the *west
manifest*. The location of the manifest repository is given by the
:ref:`manifest.path configuration option <west-config-index>` in the local
configuration file. The manifest file, along with west's configuration files,
controls the installation's behavior. For upstream Zephyr, :file:`zephyr` is
the manifest repository, but you can configure west to use any Git repository
in the installation as the manifest repository. The only requirement is that it
contains a valid manifest file. See :ref:`west-manifests` for more details on
what this means.

Both of the :file:`tinycbor` and :file:`net-tools` directories are *projects*
managed by west, and configured in the manifest file. A west installation can
contain arbitrarily many projects. As shown above, projects can be located
anywhere in the installation. They don't have to be subdirectories of the
manifest directory, and they can be inside of arbitrary subdirectories inside
the installation's root directory. By default, the Zephyr build system uses
west to get the locations of all the projects in the installation, so any code
they contain can be used by applications. This behavior can be overridden using
the ``ZEPHYR_MODULES`` CMake variable; see
:zephyr_file:`cmake/zephyr_module.cmake` for details.

Finally, any repository managed by a west installation can contain
:ref:`extension commands <west-extensions>`, which are extra west commands
provided by that project. This includes the manifest repository and any project
repository.

.. _west-struct:

West Structure
**************

West is currently split in two:

* Bootstrapper: Installed by ``pip3 install west``, which provides the ``west``
  binary and the ``west init`` command.
* Per-installation clone: this is the west repository cloned into each
  installation, which provides the built-in commands.

.. note::

   This "bootstrapper" / "everything else" separation is similar to the model
   used by Google's ``repo`` tool, but unfortunately in retrospect was not a
   good strategy for west.

   In future versions, the ``west`` binary and all built-in commands (including
   ``init``) will be installed by ``pip3 install west``. Besides eliminating
   complexity, this will also make it possible to use :ref:`West's APIs
   <west-apis-west>` from any Python file, not just extension
   commands.

   Updating west will still be possible manually, e.g. with ``pip3
   install --upgrade west``. If necessary, it will also still be possible to
   use different versions of west on the same computer through Python virtual
   environments.

Bootstrapper
============

The bootstrapper module is distributed using `PyPI`_ and installed using
:file:`pip3`. A launcher named ``west`` is placed by :file:`pip3` in the user's
``PATH``. This the only entry point to west.  It implements a single command:
``west init``. This command needs to be run first to use the rest of
functionality included in ``west``, by creating a west installation. The
command ``west init`` does the following:

* Clones west itself in a :file:`.west/west` folder in the installation.
* Clones the manifest repository in the folder specified by the manifest file's
  ``self.path`` section.
* Creates an initial local configuration file.

Once ``west init`` has been run, the bootstrapper will delegate the handling of
any west commands other than ``init`` to the cloned west repository. This means
that there is a single bootstrapper instance installed at any time (unless you
use virtual environments), which can then be used to initialize as many
installations as needed, each of which can have a different version of west.

.. _west-struct-installation:

Per-Installation Clone
======================

A west installation, as described above, contains a clone of the west
repository in :file:`.west/west`. This is where the built-in command
implementations are currently provided. The rest of :ref:`West's APIs
<west-apis-west>` are also currently provided to extension commands by this
repository. So that west can update itself, the built-in ``west update`` and
``west selfupdate`` commands fetch and update the :file:`.west/west` repository.

The ``manifest-rev`` branch
***************************

West creates a branch named ``manifest-rev`` in each project, pointing to the
commit the project's revision resolves to. The branch is updated whenever
project data is fetched by ``west update``. Other multi-repo commands also use
``manifest-rev`` as a reference for the upstream revision as of the most recent
update. See :ref:`west-multi-repo-cmds`, below, for more information.

``manifest-rev`` is a normal Git branch, but if you delete or otherwise modify
it, west will recreate and/or reset it as if with ``git reset --hard`` on the
next update (though ``git update-ref`` is used internally). For this reason, it
is normally a **bad idea to modify it yourself**. ``manifest-rev`` was added to
allow SHAs as project revisions in the manifest, and to give a consistent
reference for the current upstream revision regardless of how the manifest
changes over time.

.. note::

   West does not create a ``manifest-rev`` branch in the manifest repository,
   since west does not manage the manifest repository's branches or revisions.

.. _west-multi-repo-cmds:

Multi-Repo Commands
*******************

This section gives a quick overview of the multi-repo commands, split up by
functionality. Some commands loosely mimic the corresponding Git command, but
in a multi-repo context (e.g. ``west diff`` shows local changes on all
repositories).

Project arguments can be the names of projects in the manifest, or their paths
within the installation. Passing no project arguments to commands that accept a
list of projects usually means to use all projects in the manifest.

.. note::

   For detailed help, see each command's ``--help`` output (e.g.  ``west diff
   --help``).

Main Commands
=============

The ``west init`` and ``west update`` multi-repo commands are the most
important to understand.

- ``west init [-l] [-m URL] [--mr REVISION] [PATH]``: create a west
  installation in directory :file:`PATH` (i.e. :file:`.west` etc. will be
  created there). If the ``PATH`` argument is not given, the current working
  directory is used. This command does not clone any of the projects in the
  manifest; that is done the next time ``west update`` is run.

  This command can be invoked in two ways:

  1. If you already have a local clone of the zephyr repository and want to
     create a west installation around it, you can use the ``-l`` switch to
     pass its path to west, as in: ``west init -l path/to/zephyr``.

  2. Otherwise, omit ``-l`` to create a new installation from a remote manifest
     repository. You can give the manifest URL using the ``-m`` switch, and its
     revision using ``--mr``. For example, invoking west with: ``west init -m
     https://github.com/zephyrproject-rtos/zephyr --mr v1.15.0`` would clone
     the upstream official zephyr repository at the tagged release v1.15.0
     (``-m`` defaults to https://github.com/zephyrproject-rtos/zephyr, and
     ``--mr`` defaults to ``master``).

- ``west update [--rebase] [--keep-descendants] [--exclude-west] [PROJECT
  ...]``: clone and update the specified projects (default: all projects) based
  on the current :term:`west manifest`.

  This command parses the manifest, clones any project repositories that are
  not already present locally, and checks out the project revisions specified
  in the manifest file, updating ``manifest-rev`` branches along the way.

  For safety, ``west update`` uses ``git checkout --detach`` to check out a
  detached ``HEAD`` at the manifest revision for each updated project, leaving
  behind any branches which were already checked out. This is typically a safe
  operation that will not modify any of your local branches. See the help for
  the ``--rebase`` / ``-r`` and ``--keep-descendants`` / ``-k`` options for
  ways to influence this.

  By default, ``west update`` also updates the west repository in the
  installation. To prevent this, use ``--exclude-west``.

.. _west-multi-repo-misc:

Miscellaneous Commands
======================

West has a few more commands for managing the multi-repo, which are briefly
discussed here.

- ``west list``: Lists project information from the manifest (URL, revision,
  path, etc.), along with other manifest-related information.

- ``west manifest --freeze [-o outfile]``: Save a "frozen" representation of
  the current manifest; all ``revision`` fields are converted to SHAs based on
  the current ``manifest-rev`` branches.

- ``west diff [PROJECT ...]``: Runs a multi-repo ``git diff``
  for the specified projects (default: all cloned projects).

- ``west status [PROJECT ...]``: Like ``west diff``, for
  running ``git status``.

- ``west forall -c COMMAND [PROJECT ...]``: Runs the shell command ``COMMAND``
  within the top-level repository directory of each of the specified projects
  (default: all cloned projects). If ``COMMAND`` consists of more than one
  word, it must be quoted to prevent it from being split up by the shell.

  To run an arbitrary Git command in each project, use something like ``west
  forall -c 'git <command> --options'``. Note that ``west forall`` can be used
  to run any command, though, not just Git commands.

- ``west selfupdate``: Updates the west repository in the installation.

.. _PyPI:
   https://pypi.org/project/west/

.. _Zephyr issue #6770:
   https://github.com/zephyrproject-rtos/zephyr/issues/6770