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As of April, 2004, the Launchpad code has been placed under mandatory pre-merge review. Read this document carefully for a description of the review process and what it entails.
As of 2009, we use Launchpad Code Merge Proposals to manage the queue of work.
What are Pre-Merge Reviews?
Pre-merge reviews are peer reviews of source code modifications. They are a great tool for ensuring quality of the resulting product, and also for communicating technique and style between team members. A good review process ensures that everybody learns at a much faster rate, and creates a valuable technical relationship between reviewer and coder.
As of June 2006, we encourage all developers to arrange pre-implementation design reviews with another developer, preferably by phone call. IRC can be used if a phone call is not possible, but voice contact is more desirable.
Pre-implementation calls should be used before starting to implement any feature or bug. For more details on the work flow and what is expected from both callers and callees, see DesignPhoneCall.
The PendingReviews template has been updated to include a line where you will be expected to add your pre-implementation call buddy's name, and your reviewer will ask you whether you've had a pre-implementation review. The expected answer is "yes".
Working with PreMergeReviews
For pre-merge reviews to be effective, however, small modifications to the development workflow are required. The main modification is, of course, requesting peer review of your code changes before merging your code into RocketFuel. The sections below go into the details of how this is best performed. There is a crib sheet for getting a branch merged on the WorkingWithReviews page.
Branch size limits
As of 12-Dec-2007 a limit of 800 lines per branch diff has been set as a maximum. If your branch grows above this limit you must negotiate with a reviewer to accept the oversized branch. Note that very large branches are not recommended for on-call reviews as they slow down the work of the reviewer who is trying interactively review a high volume of branches during the shift.
What are reviewers looking for ?
Reviewers are checking both the design of your branch and the quality of the code in it. The best way to understand what a review is looking for is to read TipsForReviewers. (You can also use the CodeReviewChecklist cheat-sheet to do a self-review.)
If in doubt, use a branch
Any non-trivial changes for review must be on a branch. The goal is to make it easy to look at which changes have been made without spurious diffs, and without having to worry about RocketFuel changing from under your feet. A good rule of thumb is:
If what you're working on is complex enough that you'll likely be making several commits, you definitely need a branch.
If the changes are simple, it may be appropriate to request a review by sending a diff directly to a reviewer. If you do this:
- arrange with the reviewer first, perhaps on IRC
use the -p option to diff to get reasonable amounts of context
You are responsible for your branch
The central rule that is used in the Launchpad review process is:
The coder is responsible for getting his branch through the review process
This means that you, as a coder, are reponsible for
- writing the code
requesting review (and editing PendingReviews)
- finding a reviewer (if the process breaks down - normally this is managed by the review team lead)
- reminding/nagging/pursuing/coordinating with your reviewer
- dealing with review comments / requests
landing your change (cleaning up PendingReviews once that is done).
The reviewer, conversely, is responsible only for two important things:
- Reviewing requests in a timely manner.
- Participating in follow-up discussion once a review is sent.
The reviewer is the obvious bottleneck in the process, and if you can make his life easier, please do. This includes making smaller changes, coordinating with other developers to order reviews to minimize conflicts, and reminding of forgotten branches periodically.
Before you request a review, you should make sure that make check_merge reports no errors after having first merged rocketfuel, as fixing any broken tests after a review might involve an unnecessary additional review which could have been avoided.
Reviews should be requested by adding a tagged and dated branch name to the PendingReviews page, under the section for your favorite reviewer.
The entry in the reviews page and the email sent should contain a summary of the changes, the name of the branch they're on, and URLs of any bugs that they fix.
 As of 2007-03-15 it's been confirmed that only PQM gets through all the tests unscathed. This could be because PQM runs on Dapper, and most developers are running Edgy or Feisty, and the test suite hasn't been fixed to accommodate these.
Dealing with reviews
A thorough guide to dealing with reviews and finally merging your changes is available at WorkingWithReviews.
The Launchpad-Reviews mailing list
We have a review-specific mailing list: firstname.lastname@example.org. The mailman page for it is at http://lists.canonical.com/mailman/listinfo/launchpad-reviews
This mailing list should concentrate review activity on the mailing list, including both review requests (see below) and reviewer comments and replies. The following guidelines apply to it:
- The launchpad-reviews mailing list is open to any team member that would like to subscribe to it.
Reviewers /must/ subscribe to the mailing list (in order to receive notifications, for one).
There is no need to send email to launchpad-reviews with your review request if you add your branch to PendingReviews.
- Keep replies to launchpad-reviews mail CCed to launchpad-reviews. You should only move the thread to launchpad-list if you:
- Identify a topic that is worthy of launchpad attention (setting new policy is included in this group)
- Change the subject to a meaningful indication of the topic
- The reviewers team will make a summary of the important review issues of the week and send this out to the launchpad mailing list.
Currently, the official review team is:
RobertCollins (team lead)
MatthewPaulThomas (User Interface)
For smaller patches, you _may_ at your discretion seek out another peer to serve as your reviewer. Use your judgement in determining whether the patch you are working on is small enough to not require an official reviewer. Patches that are not reviewed by an official review must be rubber-stamp or trivial patches.
- This section is for documenting future plans that are not well formed enough for specs yet.
21:08 < spiv> I like it, although I'm starting to itch for slightly more workflow, so that we'd show "days since last touched" or something ; 21:09 < lifeless> I'd love to have stats on average time to merge a branch 21:09 < lifeless> time to review 21:09 < lifeless> time to reply 21:10 < BjornT> lifeless, jamesh: it would be nice to have a quick way of getting the description of the branch as well.
- When reviewing a diff of a very large change that presumably developed over many revisions, I find myself wondering "why did they change this?" In some cases, a comment could be added to the code that was added or changed. But that doesn't make sense for all modifications -- for instance, deleting files or code isn't something you can sensibly leave comments in for.
If the HTML of the diff had something like the output of "bzr annotate" for the changed lines, that might help. Ideally I'd want to see what revision deleted a line, as well as which one added it, and what the commit message was. Tooltips would be a tolerable way to display this information. (I don't want the ability to trivially cut-and-paste diffs into my review mails impeded.)
Better display of moved code?
In a plain diff, moved code shows up as a large delete and add (or a large add and delete). It would make the reviewer's life a bit simpler if somehow large chunks of code that are both removed and added were obviously shown as moves, so the reviewer knows they don't need to pay as much attention to it as new code. Perhaps this is more in the realm of a graphical tool like meld than a diff on a web page.
Tests/documentation first in diffs
Additions and changes to tests and documentation help explain what the code changes in a patch are for. It would be nice if, say files with "ftests", "tests", or "doc" in their paths appeared before others in a diff, so that reviewers can easily read them first.
-- AndrewBennetts 2006-05-01 11:51:27