Monday, March 27, 2017

A New Gerrit User

Recently I had to commit work upstream to the public Open Daylight project. As part of that effort, I had to learn some new tools, particularly Gerrit. This is a code review/management tool that works with Git, which I was already familiar with.

Here are some ad hoc things I learned as part of committing work upstream...

Gerrit has a different workflow that you are likely using in downstream coding with other tools. There is a general tutorial and an ODL coding introduction to working with Gerrit.

We followed our own coding guidelines downstream and those did not match to the Google coding conventions used upstream. Differences we ran into were:

• Lower-case method names, even for JUnit test methods (I won't push back with Spock conventions) • Using the most restrictive visibility for access qualifiers (I won't push back the philosophy of library design)
• Use Java 8 lambdas everywhere possible

Gerrit (plugin) has some non-obvious controls, namely that you can kick off another build by putting "recheck" as your comment. Others are "rerun", "verify" as in here.

Upstream coders usually add the prefix "WIP: " to their bug report to let other developers know things are not ready for prime time reviews yet.

Mechanically you can review the issues by using "Diff against:" drop list to pick a revision to start at then go into the first file and then use the green upper right arrows to navigate between files. (It'd be nice if Gerrit had a "next feedback item" navigation).

The master branch on ODL can and does break, causing lots of down time with broken builds (days even).

Full builds take 10 hours and verifying-before-pushing is an evolving process.

If you are using "git review" and you forgot the "--amend" option on your commit, you will be prompted to squash and will end up with a new branch. You can recover using "git rebase -i HEAD~2" then using the force option and then abandoning the new branch.

Along with master breaking, master can also produce stale artifacts, so don't assume that clearing your m2 cache, creating a subproject repo and building will give you up-to-date code.

You can search jar files using find . -type f -name '*.jar' -print0 | xargs -0 -I '{}' sh -c 'jar tf {} | grep "YourClassHere" && echo {}' for helping verify your m2 has the latest.

The patch workflow is not very good at all for having multiple people working on an item; traditional git branches and management are superior in this respect so expect some pain.

If your patch won't build because master is broken, you can rebase it to pick up a fix temporarily. When you do a "git review" to push it, you will be prompted because there are two commits (your new patch revision and the fix). You do not want to merge that fix into your patch.

Hopefully, some of these tips will find their way to helping someone else along the way.

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