Working with gerrit (very old article)

Note: This article is very, very old. I’m publishing it mostly for fun :)

Before start: in later of this document I assume that you have a basics of git knowledge. In our development team we use git a lot, but git not solve every problem - it’s only a source control software. We need more, we employe new people who at an start point often make mistakes - and write ugly code. We decided to make code review, and for this propose we choose gerrit.

Gerrit is nothing more then git repository and tool that can approve and comment commits. Whole workflow involves of create commit, push it to gist, wait for approval - and boom - everything work. But because we often make mistakes and everyone in company work (or should work) asynchronous - this workflow is a little more complicated. Grate picture I found on Android developers site that present workflow on gerrit:

You’d better look at this diagram before continue for better understanding of commands bellow.

Lets starts

When using gerrit your repo usually looks like: ssh://<username>@review.<your-domain>:29418/<your project>.git. Part that can create problems is <username>, especially when you are using submodules because you will have to put: git submodule add ssh://<username>@review.<your-domain>:29418/<your project>.git <your directory>, and everyone who download your repo will have to replace <username> with his/her username. Instead I suggest to add two lines to your ~/.ssh/config file:

Host review.assembla.com
  User jacek.marchwicki
  Port 29418

and use clone, submodule add, remote add omitting the <username> part. For testing proposes I suggest to use assembla.com with gerrit - but if you rather want to use some other tool you are free to go. I assume you already have gerrit repo url, in my case: ssh://review.assembla.com/gerrit-example.git than create project:

mkdir gerrit-example
git init
touch README.md
git add -A
git commit
git remote add origin ssh://review.assembla.com/gerrit-example.git
git push origin HEAD:refs/heads/master

Now your project should be on gerrit repo, now everyone can pull it as usual:

git clone ssh://rgit.assembla.com/gerrit-example.git

And what is most important you have to install hook for commits after clone and import:

scp review.assembla.com:hooks/commit-msg .git/hooks/

To avoid screwing something up is better to remove master on your local repository and use origin/master instead

git remote update
git checkout origin/master
git brach -d master

Making changes

Before making some changes, lets do it:

echo > file1.txt << EOF
some text of file1
and mre text of file1
EOF
echo > file2.txt << EOF
some text of file2
and more text of file2
EOF
git add file1.txt
git commit

this time I specially forgot of file2.txt in commit and done a typo in file1.txt for learning propose. You can ensure that in your last commit was "Change-Id: ***" looking in git log. If not you did not installed commit-msg hook, so:

scp review.assembla.com:hooks/commit-msg .git/hooks/
git add file1.txt
git commit --amend

This command append fixes tu current commit. If "Change-Id" now appears in log you can submit your commit for review:

git push origin HEAD:refs/for/master

Reviewing code

Now you have too look on your gerrit site: i.e.: https://review.assembla.com/ and in “All->Open” section you should see a your commit to approve. Normally you wouldn’t do yourself, but for test proposes we you can ;). One code reviewer should checkout this code and test it, and two of code reviewers should only check for changes that you made i.e.: Two of your friends look in to code on commit site, commenting your code and click one button on “Code review” +1 if is look ok, -1 if its not look ok - i.e. some bug. Third friend download code and verify it.

Verifying

Let become third friend. Clone your project to some other directory to simulate third friend:

git clone ssh://review.assembla.com:/gerrit-example.git gerrit-example2
cd gerrit-example2
scp review.assembla.com:hooks/commit-msg .git/hooks/

Ok.. look for some commits to verify on “All->Open” get some and copy url from its page and type it in command line: git fetch ssh://review.assembla.com:/gerrit-example refs/changes/73/6673/1 && git checkout -b c6673 FETCH_HEAD Compile it and test it - I know it is hard do compile text files but you can imagine it ;) Now you should use “Review” button on commit site and type your vote in “Verified” section and fill a comment if needed.

Code review

Let become one of your first and second friend. They no need to download code, they only need to check your code on the web site. They check code, comment it if they find something to comment, and approve or not (+1, -1 or 0). Suppose that first friend looked at your code and +1 LGTM (Look good to me), but second noticed that you filled a typo in file1.txt. He should give -1 and fill a comment.

Repairing

No you return and look for reviews and you see that your code was not approved, now you should fix it.

cd ../gerrit-example
git fetch ssh://review.assembla.com/gerrit-example refs/changes/73/6673/1 && git checkout -b c6673 FETCH_HEAD
sed -i '' "s/mre/more/" file1.txt
git add file1.txt
git commit --amend
git push origin HEAD:refs/for/master

Now your code is corrected an sendend second time to code review

Merging

Now everyone of your friend approved you commit but you have bad luck - some other commit was approved before and there are conflict. You have to resolve you commit and sand changes back go gerrit.

git checkout master
git pull
ssh://review.assembla.com/gerrit-example refs/changes/73/6673/1 && git checkout -b c6673 FETCH_HEAD
git remote update
git rebase origin/master

resolve conflicts

git add -A
git rebase --commit
git push origin HEAD:refs/for/master

Now you code with fresh base was sent to review. And this time your friends approved and verified your code - your code will be automatically merged.

Fixing order

Sometimes you can observer that you commit have OUTDATED dependency. This mean that commit which was parent from your have never version. Now you have to get rid of outdated commit. You will use cherry-pick which inserts you commit at top of another commit. You have to choose a commit which you would like to be the parent of your commit. Usually is a newer version of outdated commit. You have to check it out:

ssh://review.assembla.com/gerrit-example refs/changes/73/6673/3 && git checkout FETCH_HEAD

and cherry pick your commit to remove outdated dependency:

ssh://review.assembla.com/gerrit-example refs/changes/74/234/1 && git cherry-pick FETCH_HEAD

resolve conflicts

git add -A
git commit
git push origin HEAD:refs/for/master

Now you should observer that on gerrit you do not have OUTDATED reference.

Abandoned

If your commit is abandoned it means it will never be merged to repository. But if you have dependency from ABANDONED you have to get rid of this dependency. You have to choose some commit as a parent of your commit - usually origin/master and cherry-pick your commit:

git remote update
git checkout origin/master
ssh://review.assembla.com/gerrit-example refs/changes/74/234/1 && git cherry-pick FETCH_HEAD

resolve conflicts

git add -A
git commit
git push origin HEAD:refs/for/master

Now you should observe that in gerrit you do not have dependency from ABANDONED commit.

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