[openstack-dev] [git-review] Supporting development in local branches

Yuriy Taraday yorik.sar at gmail.com
Mon Aug 4 23:18:07 UTC 2014

Hello, git-review users!

I'd like to gather feedback on a feature I want to implement that might
turn out useful for you.

I like using Git for development. It allows me to keep track of current
development process, it remembers everything I ever did with the code (and
I also really like using Gerrit for code review. It provides clean
interfaces, forces clean histories (who needs to know that I changed one
line of code in 3am on Monday?) and allows productive collaboration.
What I really hate is having to throw away my (local, precious for me)
history for all change requests because I need to upload a change to Gerrit.

That's why I want to propose making git-review to support the workflow that
will make me happy. Imagine you could do smth like this:

0. create new local branch;

master: M--....
feature:  *

1. start hacking, doing small local meaningful (to you) commits;

master: M--....
feature:  A-B-...-C

2. since hacking takes tremendous amount of time (you're doing a Cool
Feature (tm), nothing less) you need to update some code from master, so
you're just merging master in to your branch (i.e. using Git as you'd use
it normally);

master: M--....-N-O-...
         \    \    \
feature:  A-B-...-C-D-...

3. and now you get the first version that deserves to be seen by community,
so you run 'git review', it asks you for desired commit message, and <poof,
magic-magic> all changes from your branch is uploaded to Gerrit as _one_
change request;

master: M--....-N-O-...
         \    \    \----E* <= uploaded
feature:  A-B-...-C-D-...-E

4. you repeat steps 1 and 2 as much as you like;
5. and all consecutive calls to 'git review' will show you last commit
message you used for upload and use it to upload new state of your local
branch to Gerrit, as one change request.

Note that during this process git-review will never run rebase or merge
operations. All such operations are done by user in local branch instead.

Now, to the dirty implementations details.

- Since suggested feature changes default behavior of git-review, it'll
have to be explicitly turned on in config (review.shadow_branches?
review.local_branches?). It should also be implicitly disabled on master
branch (or whatever is in .gitreview config).
- Last uploaded commit for branch <branch-name> will be kept in
- For every call of 'git review' it will find latest commit in
gerrit/master (or remote and branch from .gitreview), create a new one that
will have that commit as its parent and a tree of current commit from local
branch as its tree.
- While creating new commit, it'll open an editor to fix commit message for
that new commit taking it's initial contents from
refs/review-branches/<branch-name> if it exists.
- Creating this new commit might involve generating a temporary bare repo
(maybe even with shared objects dir) to prevent changes to current index
and HEAD while using bare 'git commit' to do most of the work instead of
loads of plumbing commands.

Note that such approach won't work for uploading multiple change request
without some complex tweaks, but I imagine later we can improve it and
support uploading several interdependent change requests from several local
branches. We can resolve dependencies between them by tracking latest
merges (if branch myfeature-a has been merged to myfeature-b then change
request from myfeature-b will depend on change request from myfeature-a):

master:    M--....-N-O-...
            \    \    \---------E*
myfeature-a: A-B-...-C-D-...-E   \
                      \       \   J* <= uploaded
myfeature-b:           F-...-G-I-J

This improvement would be implemented later if needed.

I hope such feature seams to be useful not just for me and I'm looking
forward to some comments on it.


Kind regards, Yuriy.
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