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 Projects --> List --> SELECT-PROJECT --> Branches. Select the branch that interests you, click on gitweb located on the right-hand side. Now, gitweb loads your selection on the Git web interface and redirects appropriately.

Watching a Project

Visit Gerrit, then select Settings, located on the top right corner. Select 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:

Brief (no more than 50 chars) one line description.

Elaborate summary of the changes made referencing why (motivation), what was changed and how it was tested. Note also any changes to documentation made to remain consistent with the code changes, wrapping text at 72 chars/line.

Jira: FAB-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.

Recommended reading: How to Write a Git Commit Message

Avoid Pushing Untested Work to a Gerrit Server

To avoid pushing untested work to Gerrit.

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.

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 REMOTE/master tree to Gerrit for being reviewed as a topic in TopicName use the following command as an example:

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

The topic will show up in the review UI and in the 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:

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

git commit ...
git commit ...
git commit ...

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

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:

git rebase -i HEAD~#Commits

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

Finding Available Topics

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

• gerrit.hyperledger.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 fabric.
• 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.

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

git review -d CHANGEID

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

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):

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 refs/drafts/master/TopicName

The next command ensures a local branch is created:

git checkout -b BRANCHNAME

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

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 refs/sandbox/USERNAME/BRANCHNAME location.

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

git checkout -b sandbox/USERNAME/BRANCHNAME
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:

git push REMOTE sandbox/USERNAME/BRANCHNAME

You can also push forcibly with review:

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:

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 rebasing section for more information. However, you must keep the same Change-Id and push the changes again:

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 review UI section, for each change.

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

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.

Rebasing During a Pull

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

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

git log --oneline REMOTE/master..master

a0
a1
a2
a3
a4
c0
c1
...
c7

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

git pull --rebase REMOTE master

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

$ 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:

git config log.abbrevCommit true

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

git config log.abbrev 5

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

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 --global to config as follows: