.. _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. For upstream Zephyr, the installation looks
like this:

.. code-block:: none

   zephyrproject
   ├── .west
   │   └── config
   ├── 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>`.

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.

Topologies supported
********************

The following three source code topologies supported by west:

* **T1**: Star topology with zephyr as the manifest repository:

  - The zephyr repository acts as the central repository and includes a
    complete list of projects used upstream
  - Default (upstream) configuration
  - Analogy with existing mechanisms: Git sub-modules with zephyr as the
    super-project
  - See :ref:`west-installation` for how mainline Zephyr is an example
    of this topology

* **T2**: Star topology with an application repository as the manifest
  repository:

  - A repository containing a Zephyr application acts as the central repository
    and includes a complete list of other projects, including the zephyr
    repository, required to build it
  - Useful for those focused on a single application
  - Analogy with existing mechanisms: Git sub-modules with the application as
    the super-project, zephyr and other projects as sub-modules
  - An installation using this topology could look like this:

    .. code-block:: none

       app-manifest-installation
       ├── application
       │   ├── CMakeLists.txt
       │   ├── prj.conf
       │   ├── src
       │   │   └── main.c
       │   └── west.yml
       ├── modules
       │   └── lib
       │       └── tinycbor
       └── zephyr

* **T3**: Forest topology:

  - A dedicated manifest repository which contains no Zephyr source code,
    and specifies a list of projects all at the same "level"
  - Useful for downstream distributions with no "central" repository
  - Analogy with existing mechanisms: Google repo-based source distribution
  - An installation using this topology could look like this:

    .. code-block:: none

       forest
       ├── app1
       │   ├── CMakeLists.txt
       │   ├── prj.conf
       │   └── src
       │       └── main.c
       ├── app2
       │   ├── CMakeLists.txt
       │   ├── prj.conf
       │   └── src
       │       └── main.c
       ├── manifest-repo
       │   └── west.yml
       ├── modules
       │   └── lib
       │       └── tinycbor
       └── zephyr

.. _west-struct:

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

West's code is distributed via PyPI in a `namespace package`_ named ``west``.
See :ref:`west-apis` for API documentation.

This distribution also includes a launcher executable, also named ``west``. When
west is installed, the launcher is placed by :file:`pip3` somewhere in the
user's ``PATH``. This is the command-line entry point.

.. _west-manifest-rev:

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 (as
fallback) paths to them. Omitting project arguments to commands which accept a
list of projects (such as ``west list``, ``west forall``, etc.) usually
defaults to using all projects in the manifest file plus the manifest
repository itself.

For help on individual commands, run ``west <command> -h`` (e.g. ``west diff
-h``).

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``. This is
     the only reason to use ``-l``.

  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
     the ``-mr`` default is overridden to ``v1.15.0``).

- ``west update [--fetch {always,smart}] [--rebase] [--keep-descendants]
  [PROJECT ...]``: clone and update the specified projects based
  on the current :term:`west manifest`.

  By default, this command:

  #. Parses the manifest file, :file:`west.yml`
  #. Clones any project repositories that are not already present locally
  #. Fetches any project revisions in the manifest file which are not already
     pulled from the remote
  #. Sets each project's :ref:`manifest-rev <west-manifest-rev>` branch to the
     current manifest revision
  #. Checks out those revisions in local working trees

  To operate on a subset of projects only, specify them using the ``PROJECT``
  positional arguments, which can be either project names as given in the
  manifest file, or paths to the local project clones.

  To force this command to fetch from project remotes even if the revisions
  appear to be available locally, either use ``--fetch always`` or set the
  ``update.fetch`` :ref:`configuration option <west-config>` to ``"always"``.

  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.

.. _west-multi-repo-misc:

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

West has a few more commands for managing the multi-repo, which are briefly
discussed here. Run ``west <command> -h`` for detailed help.

- ``west list [-f FORMAT] [PROJECT ...]``: Lists project information from the
  manifest file, such as URL, revision, path, etc. The printed information can
  be controlled using the ``-f`` option.

- ``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 manifest --validate``: Ensure the current manifest file is
  well-formed. Print information about what's wrong and fail the process in
  case of error.

- ``west diff [PROJECT ...]``: Runs a multi-repo ``git diff``
  for the specified 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 help <command>``: this is equivalent to ``west <command> -h``.

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

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

.. _namespace package:
   https://www.python.org/dev/peps/pep-0420/