Presentation on EGit and Gerrit Code Review held at Eclipse DemoCamp Bonn Nov 16, 2010

1. EGit & Gerrit Code Review
Towards Contributor's Heaven
http://eclipse.org/egit
http://code.google.com/p/gerrit/
Matthias Sohn (SAP)
matthias.sohn@sap.com
+ =

2. Git
… a distributed revision control system built by the
Linux project to automate patch workflow
Distributed means no central repository
• No central authority!
• Easy offline usage
• Easy to fork a project
• Protected against manipulation by cryptographic hashes
Really good at merging
• Coordination only needed "after the fact”
• Easier to rejoin (or refresh) forked projects
Structured around commits (i.e. patches)
• Integrates with email channel
• Tools for identifying problem commits (git bisect)
• Tools for restructuring branches w/ specific commits
Using Git in Eclipse | © 2010 by C. Aniszczyk and M. Sohn

3. Git at Eclipse
Eclipse defined a roadmap to move to Git in 2009
CVS is deprecated; SVN will be deprecated in the future
EGit is an Eclipse Team provider for Git
http://www.eclipse.org/egit/
JGit is a lightweight Java library implementing Git
http://www.eclipse.org/jgit/
The goal is to build an Eclipse community around Git
EGit and JGit are still beta and we want to establish
a feedback loop to improve the tooling
Using Git in Eclipse | © 2010 by C. Aniszczyk and M. Sohn

4. History of JGit and EGit
2005 Linus Torvalds starts Git
2006 Shawn Pearce starts JGit
2009 Eclipse decides for Git Roadmap
JGit/EGit move to eclipse.org
3/2010 Released 0.7 (first release at Eclipse)
Diff/Merge Algorithms, Automatic IP Logs
6/2010 Released 0.8 (Helios)
Usability Improvements, Git Repositories View, Tagging
9/2010 Released 0.9 (Helios SR1)
Merge, Synchronize View, .gitignore
Planned: 12/2010 0.10 (Helios SR2) 3/2011 0.11 6/2011 1.0 (Indigo)
Using Git in Eclipse | © 2010 by C. Aniszczyk and M. Sohn

5. What is Peer Code Review?
When one developer writes code,
another developer is asked to review that code
… a careful line-by-line critique
… happens in a non-threatening context
… goal is cooperation, not fault-finding
… best an integral part of coding process
Debugging someone else's broken code
... involuntary code review, not so good
Guido van Rossum [1]
[1] http://code.google.com/p/rietveld/downloads/detail?name=Mondrian2006.pdf
Using Git in Eclipse | © 2010 by C. Aniszczyk and M. Sohn

6. Code Review – Benefits
Four eyes catch more bugs
Coding standards help readability → better code
Mentoring of new developers
Establish trust relationships
Good alternative to pair programming
Guido van Rossum [1]
[1] http://code.google.com/p/rietveld/downloads/detail?name=Mondrian2006.pdf
Using Git in Eclipse | © 2010 by C. Aniszczyk and M. Sohn

7. Code Review @ Eclipse in Bugzilla
Using Git in Eclipse | © 2010 by C. Aniszczyk and M. Sohn

8. Eclipse – Review Process
Contributors
• create patch using CVS, SVN, Git
• attach patch to bug in Bugzilla
Committers
• do code and IP review in Bugzilla
• initiate IP review for changes > 250 loc
• commit accepted changes
IP Team
• does IP reviews
Using Git in Eclipse | © 2010 by C. Aniszczyk and M. Sohn

9. Gerrit Code Review
Gerrit is a Code Review system based on JGit
http://code.google.com/p/gerrit/
Also serves as a git server
adding access control and workflow
Used by
• Android https://review.source.android.com/
• JGit, EGit http://egit.eclipse.org/r/
• Google, SAP, …
Eclipse wants to use it …
Using Git in Eclipse | © 2010 by C. Aniszczyk and M. Sohn

10. Gerrit
http://egit.eclipse.org/r/ - change,825
Using Git in Eclipse | © 2010 by C. Aniszczyk and M. Sohn

11. Gerrit Workflow
Using Git in Eclipse | © 2010 by C. Aniszczyk and M. Sohn

12. Code Review – Our Experience
• Review all changes!
• Review takes time (1 day … weeks)
• Implies parallel workflow
• Every team member should do reviews regularly
• Authors have to wait for the review to happen
• Git & Gerrit help a lot here
Code Review | © 2010 by M. Sohn

13. Demo: Using EGit and Gerrit Code Review
Using Git in Eclipse | © 2010 by C. Aniszczyk and M. Sohn

14. Conclusion
EGit and JGit are evolving quickly
Gerrit enables a nice code review workflow
Git supports convenient branching and merging
Git is very fast and scales well
Eclipse and major other OS projects are moving to Git
Git and Gerrit kick ass!
Using Git in Eclipse | © 2010 by C. Aniszczyk and M. Sohn

15. Git Resources
http://git-scm.com/documentation is your friend
Watch Linus' talk at Google
http://www.youtube.com/watch?v=4XpnKHJAok8
Read the Pro Git book - http://progit.org/book/
Using Git in Eclipse | © 2010 by C. Aniszczyk and M. Sohn

16. Features EGit 0.10
git-add git-format-patch git-shortlog git-relink git-rev-parse
git-am git-gc git-show git-remote git-show-branch
git-archive git-grep git-stash git-repack git-verify-tag
git-bisect git-init git-status git-replace git-whatchanged
git-branch git-log git-submodule git-annotate
git-bundle * git-merge * git-tag * git-blame .gitignore
git-checkout git-mv git-config git-cherry git daemon
git-cherry-pick git-notes git-fast-export git-count-objects Visual merge tool
git-clean git-pull git-fast-import git-difftool ** HTTP support
git-clone git-push git-filter-branch git-fsck * Mylyn integration
git-commit ** git-rebase git-mergetool git-get-tar-commit-id * Staging View
git-describe git-reset git-pack-refs git-help * Synchronize View
git-diff git-revert git-prune git-merge-tree History View
git-fetch git-rm git-reflog git-rerere Repositories View
** planned for 0.10, * planned for 0.11
supported, partial, missing, irrelevant for EGit

17. Git at Eclipse
EGit and JGit developed at http://egit.eclipse.org
http://git.eclipse.org/
hosts live Eclipse Git repos
http://dev.eclipse.org/git/index.html
git mirrors for CVS
Read-only copies kept up-to-date
Using Git in Eclipse | © 2010 by C. Aniszczyk and M. Sohn