A talk given at Eclipse Summit Europe 2010 on using Git in Eclipse.

1. Using Git in Eclipse
http://eclipse.org/egit
Matthias Sohn (SAP)
matthias.sohn@sap.com
+ =
Chris Aniszczyk (Red Hat)
zx@redhat.com

2. Learning Git – There's no free lunch!
Using Git in Eclipse | © 2010 by C. Aniszczyk and M. Sohn
… the purpose of this presentation isn't to teach you Git,
you have to do that yourself!

3. 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

4. Git, EGit and JGit
- Demo and Tour of EGit
Code Review at Eclipse
Gerrit
- Demo of Gerrit
Conclusion
Outline
Using Git in Eclipse | © 2010 by C. Aniszczyk and M. Sohn

5. 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

6. Projects using Git
… Git is widely used and is the most popular
distributed version control system
Git
Linux
Perl
Gnome
Qt
Ruby on Rails
Android
PostgreSQL
Wine
Fedora
Debian
X.org and so on...
Using Git in Eclipse | © 2010 by C. Aniszczyk and M. Sohn

7. 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

8. Git at Eclipse
EGit and JGit developed at http://egit.eclipse.org
http://git.eclipse.org/
hosts live Eclipse Git repos
Virgo, Mylyn Review, ECF, SWTBot …
http://dev.eclipse.org/git/index.html
git mirrors for CVS
Read-only copies kept up-to-date
Can clone with git:// or http://
Using Git in Eclipse | © 2010 by C. Aniszczyk and M. Sohn

9. 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
SAP joins JGit/EGit
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

10. Features EGit 0.10
git-addgit-add git-format-patchgit-format-patch git-shortloggit-shortlog git-relinkgit-relink git-rev-parsegit-rev-parse
git-amgit-am git-gcgit-gc git-showgit-show git-remotegit-remote git-show-branchgit-show-branch
git-archivegit-archive git-grepgit-grep git-stashgit-stash git-repackgit-repack git-verify-taggit-verify-tag
git-bisectgit-bisect git-initgit-init git-statusgit-status git-replacegit-replace git-whatchangedgit-whatchanged
git-branchgit-branch git-loggit-log git-submodulegit-submodule git-annotategit-annotate
git-bundlegit-bundle * git-merge* git-merge * git-tag* git-tag * git-blame* git-blame .gitignore.gitignore
git-checkoutgit-checkout git-mvgit-mv git-configgit-config git-cherrygit-cherry git daemongit daemon
git-cherry-pickgit-cherry-pick git-notesgit-notes git-fast-exportgit-fast-export git-count-objectsgit-count-objects Visual merge toolVisual merge tool
git-cleangit-clean git-pull git-pull git-fast-importgit-fast-import git-difftoolgit-difftool ** HTTP support** HTTP support
git-clonegit-clone git-pushgit-push git-filter-branchgit-filter-branch git-fsckgit-fsck * Mylyn integration* Mylyn integration
git-commitgit-commit ** git-rebase** git-rebase git-mergetoolgit-mergetool git-get-tar-commit-idgit-get-tar-commit-id * Staging View* Staging View
git-describegit-describe git-resetgit-reset git-pack-refsgit-pack-refs git-helpgit-help * Synchronize View* Synchronize View
git-diffgit-diff git-revertgit-revert git-prunegit-prune git-merge-treegit-merge-tree History ViewHistory View
git-fetchgit-fetch git-rmgit-rm git-refloggit-reflog git-rereregit-rerere Repositories ViewRepositories View
** planned for 0.10, * planned for 0.11
supported, partial, missing, irrelevant for EGit

11. Demo: A tour of EGit
Using Git in Eclipse | © 2010 by C. Aniszczyk and M. Sohn

12. Git, EGit and JGit
Code Review and Eclipse
Gerrit
Conclusion
Outline
Using Git in Eclipse | © 2010 by C. Aniszczyk and M. Sohn

13. 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
Often an integral part of coding process
Debugging someone else's broken code
– Involuntary code review: Not so good; emotions may flare
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

14. Code Review – Benefits
Four eyes catch more bugs
 Catch bugs early to save hours of debugging
Enforce coding standards
 Keep overall readability & code quality high
Mentoring of new developers
 Learn from mistakes without breaking stuff
Establish trust relationships
 Prepare for more delegation
Good alternative to pair programming
 asynchronous and across locations
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

15. Code Review at
Eclipse ?
Using Git in Eclipse | © 2010 by C. Aniszczyk and M. Sohn

16. Eclipse - Roles
Committer
Formally elected
Can commit own changes without review
Contributor
Small changes
reviewed by committers
Bigger changes
also formal IP review by legal team
in separate protected Bugzilla (IPZilla)
Review Tool
patches attached to bug in Bugzilla
comments in Bugzilla
Using Git in Eclipse | © 2010 by C. Aniszczyk and M. Sohn

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

18. Eclipse – Review Process
Contributors
• create patch using CVS, SVN, Git (since 2009)
• attach patch to bug in Bugzilla
Committers
• do code and IP review
• comment, vote in Bugzilla
• create CQ for changes needing IP review
• commit accepted changes
IP Team
• does IP review bigger changes from contributors
Using Git in Eclipse | © 2010 by C. Aniszczyk and M. Sohn

19. Eclipse – Review Process
Review not done for all changes
Each Eclipse.org project does it differently
Review tedious for contributors
(and also for committers mentoring contributors)
Using Git in Eclipse | © 2010 by C. Aniszczyk and M. Sohn

20. Git, EGit and JGit
Code Review and Eclipse
Gerrit
Conclusion
Outline
Using Git in Eclipse | © 2010 by C. Aniszczyk and M. Sohn

21. 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

22. History Gerrit Code Review
Gerrit: 4th Generation code review at Google
Google started code review with a Linux like review
process
• patch based
• tooling based on Perforce CLI
Using Git in Eclipse | © 2010 by C. Aniszczyk and M. Sohn

23. Google - Web based code review tools
Mondrian (Guido van Rossum)
• based on Perforce, Google infrastructure
• Google proprietary
Rietvield (Guido van Rossum)
• based on Subversion
• Open Source hosted on GoogleApp Engine
Gerrit (Shawn Pearce)
• started as a fork of Rietvield
• based on JGit and GWT
• Open Source (Android)
• Apache 2 license
Using Git in Eclipse | © 2010 by C. Aniszczyk and M. Sohn

24. One Branch per Feature
Master branch contains only reviewed and approved changes
• master moves from good to better state after each
(approved) change
Each feature branch is based on the Master branch
• stable starting point
A change can really be abandoned because
• no other approved change can depend on a not yet
approved change
• Gerrit will automatically reject a successor change of an
abandoned change
Using Git in Eclipse | © 2010 by C. Aniszczyk and M. Sohn

25. Gerrit – Lifecycle of a Change
a
master
topic
1
•
create local topic
branch
•
commit change
•
push it for review
•
do review
•
automated
verification
Using Git in Eclipse | © 2010 by C. Aniszczyk and M. Sohn

26. Gerrit – Lifecycle of a Change
c
b
a1
2
mastertopic
3
a
master
topic
1
•
create local topic
branch
•
commit change
•
push it for review
•
do review
•
automated
verification
•
refine based on
review
•
push new patchsets
until review votes ok
Using Git in Eclipse | © 2010 by C. Aniszczyk and M. Sohn

27. Gerrit – Lifecycle of a Change
c
b
a1
2
mastertopic
3
a
master
topic
1
•
create local topic
branch
•
commit change
•
push it for review
•
do review
•
automated
verification
•
refine based on
review
•
push new patchsets
until review votes ok
c
b
a1
2
master
topic
3
d
•
Submit may lead to
server-side merge
•
or merge / rebase before
push
Using Git in Eclipse | © 2010 by C. Aniszczyk and M. Sohn

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

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

30. 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

31. Gerrit Code Review - Outlook
Upcoming proposal for Mylyn Gerrit Connector
Port from SQL DB to Cassandra
Store review comments as git notes for offline review
Support for change dependencies across repositories
…
Using Git in Eclipse | © 2010 by C. Aniszczyk and M. Sohn

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

33. Git, EGit and JGit
Code Review and Eclipse
Gerrit
Conclusion
Outline
Using Git in Eclipse | © 2010 by C. Aniszczyk and M. Sohn

34. 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