doc/contribute/gerrit_practices.rst

.. _gerrit_practices:

Gerrit Recommended Practices
############################

This document presents some best practices to help you use Gerrit more
effectively.  The intent is to show how content can be submitted easily. Use the
recommended practices to reduce your troubleshooting time and improve
participation in the community.

Browsing the Git Tree
*********************

Visit `Gerrit`_, then select
:menuselection:`Projects --> List --> SELECT-PROJECT --> Branches`.  Select
the branch that interests you, click on :guilabel:`gitweb` located on the
right-hand side.  Now, :program:`gitweb` loads your selection on the Git web
interface and redirects appropriately.

Watching a Project
******************

Visit `Gerrit`_, select :guilabel:`Settings`, located on the top right corner.
Select :guilabel:`Watched Projects` and then add any projects that interest you.


Commit Messages
***************

Gerrit follows the Git commit message format. Ensure the headers are at the
bottom and don't contain blank lines between one another. The following example
shows the format and content expected in a commit message:::

   Subsystem: Brief one line description.

   Summary of the changes made referencing why, what and how.
   For documented code reference what part of the code the change is applied.

   Jira: ZEP-100
   Change-Id: LONGHEXHASH
   Signed-off-by: Your Name your.email@example.org
   AnotherExampleHeader: An Example of another Value

The Gerrit server provides a precommit hook to autogenerate the Change-Id which
is one time use.  Use the following command as an example:

.. code-block:: console

   $ scp -p -P 29418 <LFID>@gerrit.zephyrproject.org:hooks/commit-msg LOCALREPODIR/.git/hooks/

.. note::

   replace <LFID> with your Linux Foundation ID.
   replace LOCALREPODIR with the directory where you cloned the project.

The command above needs to be entered only once.


Avoid Pushing Untested Work to a Gerrit Server
**********************************************

To avoid pushing untested work to Gerrit, we recommend you follow these steps:

1. Rename your tree:

   - Change the name of the remote Git tree from *origin* to *another name*.
     This prevents complications when work is unintentionally pushed to Gerrit.

     .. code-block:: console

        $ git remote rename origin another-name

   - Use `precommit hooks`_ to scan for problematic words in your commit.
     Follow the installation instructions in the :file:`README.rst` for
     checkpatch.
     Update the :literal:`checkarray` with keywords that might signal danger in
     your commits.

   .. _precommit hooks: https://github.com/niden/Git-Pre-Commit-Hook-for-certain-words

2. Think before you act:

   - Check your work at least three times before pushing your change to Gerrit.
     Be mindful of what information you are publishing.

Keeping Track of Changes
************************

* Set Gerrit to send you emails:

  - Gerrit will add you to the email distribution list for a change if a
    developer adds you as a reviewer, or if you comment on a specific Patch
    Set.

* Opening a change in Gerrit's review interface is a quick way to follow that
  change.

* Watch projects in the Gerrit projects section at `Gerrit`_, select at least
   *New Changes, New Patch Sets, All Comments* and *Submitted Changes*.


Emails contain some helpful headers for filtering:

* **In-Reply-To:** used for threading.
   The following platforms may or may not use this header for filtering:

   - iPhone - OK.
   - Evolution - OK.
   - Thunderbird - OK.
   - Outlook - Not supported.

* **X-Gerrit-MessageType:** comment, newpatchset, etc.
* **Reply-To:** Replies to whom actions caused the email to be sent.

  - Autobuilders usually look like ``sys_EXAMPLE@intel.com``

Always track the projects you are working on; also see the feedback/comments
mailing list to learn and help others ramp up.


Topic branches
**************

Topic branches are temporary branches that you push to commit a set of
logically-grouped dependent commits:

To push changes from :file:`REMOTE/master` tree to Gerrit for being reviewed as
a topic in  **TopicName** use the following command as an example:

.. code-block:: console

   $ git push REMOTE HEAD:refs/for/master/TopicName

The topic will show up in the review :abbr:`UI` and in the
:guilabel:`Open Changes List`.  Topic branches will disappear from the master
tree when its content is merged.


Creating a Cover Letter for a Topic
===================================

You may decide whether or not you'd like the cover letter to appear in the
history.

1. To make a cover letter that appears in the history, use this command:

   .. code-block:: console

      $ git commit --allow-empty

   Edit the commit message, this message then becomes the cover letter.
   The command used doesn't change any files in the source tree.

2. To make a cover letter that doesn't appear in the history follow these steps:

   * Put the empty commit at the end of your commits list so it can be ignored  without having to rebase.

   * Now add your commits

     .. code-block:: console

        $ git commit ...
        $ git commit ...
        $ git commit ...

   * Finally, push the commits to a topic branch.  The following command is an
     example:

     .. code-block:: console

        $ git push REMOTE HEAD:refs/for/master/TopicName

If you already have commits but you want to set a cover letter, create an empty
commit for the cover letter and move the commit so it becomes the last commit
on the list. Use the following command as an example:

.. code-block:: console

   $ git rebase -i HEAD~#Commits

Be careful to uncomment the commit before moving it.
:makevar:`#Commits` is the sum of the commits plus your new cover letter.


Finding Available Topics
========================

.. code-block:: console

   $ ssh -p 29418 gerrit.zephyrproject.org gerrit query \ status:open project:zephyr branch:master \
   | grep topic: | sort -u

* *gerrit.zephyrproject.org* Is the current URL where the project is hosted.
* *status* Indicates the topic's current status: open , merged, abandoned, draft, merge conflict.
* *project* Refers to the current name of the project, in this case zephyr.
* *branch* The topic is searched at this branch.
* *topic* The name of an specific topic, leave it blank to include them all.
* *sort* Sorts the found topics, in this case by update (-u).

Downloading or Checking Out a Change
************************************

In the review UI, on the top right corner, the **Download** link provides a
list of commands and hyperlinks to checkout or download diffs or files.

We recommend the use of the *git review* plugin.
The steps to install git review are beyond the scope of this document.
Refer to the `git review documentation`_ for the installation process.

.. _git review documentation: https://wiki.openstack.org/wiki/Documentation/HowTo/FirstTimers

To check out a specific change using Git, the following command usually works:

.. code-block:: console

   $ git review -d CHANGEID

If you don't have Git-review installed, the following commands will do the same
thing:

.. code-block:: console

   $ git fetch REMOTE refs/changes/NN/CHANGEIDNN/VERSION \ && git checkout FETCH_HEAD

For example, for the 4th version of change 2464, NN is the first two digits
(24):

.. code-block:: console

   $ git fetch REMOTE refs/changes/24/2464/4 \ && git checkout FETCH_HEAD


Using Draft Branches
********************

You can use draft branches to add specific reviewers before you publishing your
change.  The Draft Branches are pushed to :file:`refs/drafts/master/TopicName`

The next command ensures a local branch is created:

.. code-block:: console

   $ git checkout -b BRANCHNAME


The next command pushes your change to the drafts branch under **TopicName**:

.. code-block:: console

   $ git push REMOTE HEAD:refs/drafts/master/TopicName



Using Sandbox Branches
**********************

You can create your own branches to develop features. The branches are pushed to
the :file:`refs/sandbox/USERNAME/BRANCHNAME` location.

These commands ensure the branch is created in Gerrit's server.

.. code-block:: console

   $ git checkout -b sandbox/USERNAME/BRANCHNAME

.. code-block:: console

   $ git push --set-upstream REMOTE HEAD:refs/heads/sandbox/USERNAME/BRANCHNAME

Usually, the process to create content is:

* develop the code,
* break the information into small commits,
* submit changes,
* apply feedback,
* rebase.

The next command pushes forcibly without review

.. code-block:: console

   $ git push REMOTE sandbox/USERNAME/BRANCHNAME

You can also push forcibly with review

.. code-block:: console

   $ git push REMOTE HEAD:ref/for/sandbox/USERNAME/BRANCHNAME


Updating the Version of a Change
********************************

During the review process, you might be asked to update your change. It is
possible to submit multiple versions of the same change. Each version of the
change is called a patch set.

Always maintain the **Change-Id** that was assigned.
For example, there is a list of commits, **c0...c7**, which were submitted as a
topic branch:

.. code-block:: console

   $ git log REMOTE/master..master

   c0
   ...
   c7

   $ git push REMOTE HEAD:refs/for/master/SOMETOPIC

After you get reviewers' feedback, there are changes in **c3** and **c4** that
must be fixed.  If the fix requires rebasing, rebasing changes the commit Ids,
see the :ref:`rebasing` section for more information. However, you must keep
the same Change-Id and push the changes again:

.. code-block:: console

   $ git push REMOTE HEAD:refs/for/master/SOMETOPIC

This new push creates a patches revision, your local history is then cleared.
However you can still access the history of your changes in Gerrit on the
:guilabel:`review UI` section, for each change.

It is also permitted to add more commits when pushing new versions.

.. _rebasing:

Rebasing
********

Rebasing is usually the last step before pushing changes to Gerrit; this allows
you to make the necessary *Change-Ids*.  The *Change-Ids* must be kept the same.

* **squash:** mixes two or more commits into a single one.
* **reword:** changes the commit message.
* **edit:** changes the commit content.
* **reorder:** allows you to interchange the order of the commits.
* **rebase:** stacks the commits on top of the master.

For more information you can visit `Atlasian`_ , `git book`_  and `git rebase`_.

.. _Atlasian: https://www.atlassian.com/git/tutorials/rewriting-history/
.. _git book: http://git-scm.com/book/en/v2/Git-Branching-Rebasing
.. _git rebase: http://www.slideshare.net/forvaidya/git-rebase-howto

Rebasing During a Pull
**********************

Before pushing a rebase to your master, ensure that the history has a
consecutive order.

For example, your :file:`REMOTE/master` has the list of commits from **a0** to
**a4**; Then, your changes **c0...c7** are on top of **a4**; thus:

.. code-block:: console

   $ git log --oneline REMOTE/master..master

   a0
   a1
   a2
   a3
   a4
   c0
   c1
   ...
   c7

If :file:`REMOTE/master` receives commits **a5**, **a6** and **a7**. Pull with a
rebase as follows:

.. code-block:: console

   $ git pull --rebase REMOTE master

This pulls **a5-a7** and re-apply **c0-c7** on top of them:


.. code-block:: console

   $ git log --oneline REMOTE/master..master
   a0
   ...
   a7
   c0
   c1
   ...
   c7

Getting Better Logs from Git
****************************

Use these commands to change the configuration of Git in order to produce better
logs:

.. code-block:: console

   $ git config log.abbrevCommit true

The command above sets the log to abbreviate the commits' hash.

.. code-block:: console

   $ git config log.abbrev 5

The command above sets the abbreviation length to the last 5 characters of the
hash.

.. code-block:: console

   $ git config format.pretty oneline

The command above avoids the insertion of an unnecessary line before the Author
line.

To make these configuration changes specifically for the current Git user,
you must add the path option :option:`--global` to :command:`config` as follows:

.. code-block:: console

   $ git config –-global log.abbrevCommit true
   $ git config –-global log.abbrev 5
   $ git config –-global format.pretty oneline

.. _Gerrit: http://gerrit.zephyrproject.org