Using git in eclipse by Chris Aniszczyk

Using Git in Eclipse http://eclipse.org/egit Chris Aniszczyk (Red Hat) zx@redhat.com http://aniszczyk.org

About Me I've been using and hacking Eclipse for nearly a decade Eclipse Board of Directors, Committer Representative Member in the Eclipse Architecture Council I like to run! (just finished Chicago marathon in 3:20) Co-author of RCP Book (www.eclipsercp.org) Using Git in Eclipse | © 2010 by C. Aniszczyk and M. Sohn

Software Trends and Revolution Most major open source projects use some form of DVCS Git, Hg, Bazaar Linux X.org MySQL OpenJDK Android JQuery Gnome Fedora Bugzilla and so on... Using Git in Eclipse | © 2010 by C. Aniszczyk and M. Sohn

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

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

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

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

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

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

Centralized VCS Examples? CVS and SVN There is one Master repository where code is shared Everyone checks out their code (or branch) from that repository, and checks changes back in Two major problems • You need to be on-line to perform actions • Patches go stale They are generally terrible, antiquated Understanding and Using Git at Eclipse | © 2010 by C. Aniszczyk, S. Pearce, R. Rosenberg and M. Sohn

Distributed VCS Examples? Git and Hg Each user has a full local copy of the repository Forks happen, deal with it There is no real master repository like in a CVCS Understanding and Using Git at Eclipse | © 2010 by C. Aniszczyk, S. Pearce, R. Rosenberg and M. Sohn

How does it work? A DVCS like Git generally operates at the level of a changeset Logically, a repository is made up from an initial empty state, followed by many changesets Changesets are identified by a SHA-1 hash value e.g., 0878a8189e6a3ae1ded86d9e9c7cbe3f Understanding and Using Git at Eclipse | © 2010 by C. Aniszczyk, S. Pearce, R. Rosenberg and M. Sohn

It's all about the changesets Changesets contain pointers to the previous changeset previous: 48b2179994d494485b79504e8b5a6b23ce24a026 --- a/README.txt +++ b/README.txt @@ -1 +1 @@ -SVN is great +Git is great previous: 6ff60e964245816221414736d7e5fe6972246ead --- a/README.txt +++ b/README.txt @@ -1 +1 @@ -Git is great +SVN is great Understanding and Using Git at Eclipse | © 2010 by C. Aniszczyk, S. Pearce, R. Rosenberg and M. Sohn

Branches The current version of your repository is simply a pointer to the end of the tree The default "trunk" in Git is called "master" The tip of the current branch is called "HEAD" Any branch can be referred to by its hash id Creating branches in a DVCS is fast, you simply point to a different element in the tree on disk already Understanding and Using Git at Eclipse | © 2010 by C. Aniszczyk, S. Pearce, R. Rosenberg and M. Sohn

Merging DVCS are all about merging Merges are just the weaving together of two (or more) local branches into one However, unlike CVCS, you don't have to specify anything about where you're merging from and to; the trees automatically know what their split point was in the past, and can work it out from there. Merging is much easier in a DVCS like Git Understanding and Using Git at Eclipse | © 2010 by C. Aniszczyk, S. Pearce, R. Rosenberg and M. Sohn

Pulling and Pushing We've not talked about the distributed nature of DVCS Changes flow between repositories by push and pull Since a DVCS tree is merely a pointer to a branch... There's three cases to consider for comparing two trees: • Your tip is an ancestor of my tip • My tip is an ancestor of your tip • Neither of our tips are direct ancestors; however, we both share a common ancestor Understanding and Using Git at Eclipse | © 2010 by C. Aniszczyk, S. Pearce, R. Rosenberg and M. Sohn

Cloning and Remotes git clone git://egit.eclipse.org/egit.git Where you can push or pull to is configured on a per (local) repository basis git remote add github http://github.com/zx/myegit.git origin is the default remote; you can have many remotes Understanding and Using Git at Eclipse | © 2010 by C. Aniszczyk, S. Pearce, R. Rosenberg and M. Sohn

What is Peer Code Review? Guido van Rossum [1] 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 [1] http://code.google.com/p/rietveld/downloads/detail?name=Mondrian2006.pdf Using Git in Eclipse | © 2010 by C. Aniszczyk and M. Sohn

Code Review – Benefits Guido van Rossum [1] 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 [1] http://code.google.com/p/rietveld/downloads/detail?name=Mondrian2006.pdf Using Git in Eclipse | © 2010 by C. Aniszczyk and M. Sohn

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

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

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

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

History: Google and 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

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

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

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

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

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

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 Open source has embraced the way of DVCS Using Git in Eclipse | © 2010 by C. Aniszczyk and M. Sohn

Using git in eclipse by Chris Aniszczyk

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