Mercurial Distributed Version Control

Mercurial Distributed Source Control Presented by David Stockton for Front Range PHP User Group April 28, 2010

“If debugging is the process of removing bugs, then programming must be the process of putting them in.” - Anonymous

Source Control in a Nutshell A great way to avoid catastrophic mistakes with your code Essential - If your code is more than a few lines long and you’re not using source control, you must not think very highly of your work. If you’re not using source control, start now. Even CVS is better than no source control. (Not sure about VSS though)

Source Control in a Nutshell If you are working with a team (read, one or more other people) source control is essential If you’re working by yourself and you’ve ever made a mistake, source control is essential If you ever wished you could undo something you just did, source control is essential If you need to maintain different versions of the same code, source control is essential.

I could go on, but...

I could go on, but... The bottom line is...

I could go on, but... The bottom line is... Source control is absolutely essential!

Questions? Questions about source control in general?

Goals of Source Control Keep your source code safe Allow you to look at different versions of your code Allow multiple developers to work simultaneously Allow multiple “branches” of code to be worked on at the same time

Common/Popular Source Control Tools CVS SVN (Subversion) ClearCase Perforce Microsoft Visual SourceSafe Git Mercurial

Common/Popular Source Control Tools BitKeeper Telelogic Synergy Visual Studio Team System StarTeam RCS Tons of others...

Types of Source Control Client Server Model (CVS, SVN, etc) Distributed (Git, Mercurial)

Mercurial Distributed Version Control System Works the way you want it instead of forcing you to use it in a certain way Used by lots of big projects

Who uses Mercurial? Adium Audacious BitBucket Growl Linux HA LinuxTV

Who uses Mercurial? Mozilla Netbeans Mutt OpenOfﬁce OpenJDK OpenSolaris

How does it work? Probably not the way you’d think if you’ve used CVS or SVN or other client server VCS (Version Control System)

How it’s different No central server ... or at least not one that’s required Works on changesets, not ﬁle or repository versions Changesets allow merges (shudder) to be simple This is a good thing since you’ll be merging a lot Learn to not be afraid of the merge

What else? Doing a checkout gives you a full copy of the repository Including all changes, etc Lose a server? Just clone another copy of the repository

What can you do with it? Pretty much anything Clone a repository to try out some experimental code If it works, keep it If not, delete it, no harm done And no evidence of your failed attempt

What can you do with it? Work on a plane (and still check in code) Collaborate with a colleague in a coffee shop Pick and choose what you want in your repository Push, pull and clone from other repositories

Make your VCS work how you do! Work on the road Work from home Work from work Work from a plane Work from a train Work in an automobile (if you’re not driving)

#1 Awesome Thing Branches are easy ... But they’re pretty easy in CVS and SVN too

Branches If you’re working on Feature A and I am working on Feature B, we’ve essentially branched Two or more people working on code based on the same thing creates branches Named branches Unnamed branches Branches by cloning

#2 Awesome Thing Branches being easy is great, but only if... Merges are super easy! Most merges handled automatically Merge conﬂicts can be handled by a tool of your choice I like kdiff3

#3 Awesome Thing No network? No problem Work from anywhere Collaborate with a colleague in the middle of nowhere

Installation Mercurial is cross platform with excellent support on Windows, Linux and Mac http://mercurial.selenic.com/ Download binary for Windows or Mac ... or apt-get install mercurial yum install mercurial ermerge mercurial pkg install SUNWmercurial

Create a new Repository

What’d that do?

You now have a working repository If you don’t do command line there are other ways IDE Integration - Eclipse, NetBeans, IntelliJ, Emacs, Vim, TextMate, Visual Studio Windows integration with TortoiseHg Build/Management tools with Hg support: CruiseControl, JIRA, Trac, Maven, Redmine, Hudson, ant, etc

Add some code Use ‘hg add’ to tell Mercurial about the ﬁles you want it to track Use ‘hg commit’ to tell Mercurial to check in code hg ci hg com

Adding and Committing

Look at the repository

Make some more changes

Easy peasy...

Enter developer #2

Developer 2 Commits

What does that commit look like? Pretty much the same Why? Luke Skywalker has his own repository

How can I get Luke’s Change? Use ‘hg push’ from Luke’s instance Use ‘hg pull’ on my instance to Luke’s instance

What’d that do?

What does it do to me? Where are the changes? Pushes do not affect the working copy Why? Updating the workspace could make me lose my work

How to see those changes? Use ‘hg up’ Update your own workspace

Let’s mix it up Dave makes a change to cookie to specify ﬂour amount Luke makes a change to cookie to add eggs

A matter of timing...

Dave commits changes

Luke commits changes

But then... Don’t use -f to force... Don’t do it...

Let’s merge

Quick recap First check-in goes in Second check-in based on same code needs merge ‘hg pull’ + ‘hg merge’ took a fraction of a second Merge was correct Luke now needs to commit the merge and push back to Dave’s server

Merge Check-in

And it now looks like...

Still too easy... Let’s try a merge conflict... Dave needs more flour in the recipe Also, Dave hasn’t updated his workspace with the merge results Luke wants to use cake flour

Merge conﬂict in the making

Now the fun part Luke uses the force and does a check in and push before Dave does a check-in

Here comes trouble... Dave tries to commit ... And it works ...

But... it created a new head

To get Luke’s changes...

Merge 2 heads into 1 All that junk is kdiff3 launching. I should ﬁx that...

Merge in kdiff3 Notice that the eggs part was automatically resolved

Merge completed

Commit the merge

What’d that do?

Crazy branch/merges The example to the right was done with just 5 users but I was purposely trying to make lots of weird branch merge situations occur.

Command overview hg clone - clone a repository hg merge - merge changes together hg add - tell Mercurial to start caring about some ﬁles hg commit - commit a new changeset hg push - send your changesets to another server hg pull - retrieve changesets from another server

Command overview cont... hg update - Update your local workspace with the stuff from hg pull hg annotate - show which changeset is responsible for each line in a file hg diff - show the differences between files in your workspace and the committed file hg export - dump the header and diffs for one or more changesets

Command overview cont... hg forget - Forget the specified files (remove from repository, not from workspace) when you commit hg log - show revision history hg remove - delete file and remove from repository when you commit hg serve - simple http server to show the repository (useful for coffee shop working)

hg addremove - add all new files, remove deleted files hg backout - reverse effect of earlier changeset hg bisect - search changesets (DEMO) hg branch - set or show branch names hg branches - list all branches hg copy - mark file as copied for next commit (DEMO) hg heads - show repository or branch heads

hg help - Where I’m getting this list of commands hg identify - identify the working copy hg incoming - show new changesets in source hg init - create a new repository hg outgoing - show changesets not in destination hg parents - show parents of working directory or revision

Command overview cont... hg status - Show what’s going to happen when you commit hg summary - Summarize state of working directory hg paths - show aliases for remote repositories hg rename - rename a ﬁle (same as hg copy + hg remove) (DEMO) hg tag - tag a revision hg tags - show tags in repository

Holy crap... That wasn’t even all the commands Or all the coolness

As time permits... hg bisect demo hg copy demo hg rename demo hg mq - Patching, orthogonal mutable changesets

Other sweet awesomeness Hooks Attic ACL

Excellent Resources Quick and easy overview: http://hginit.com - Joel Spolsky’s explanation of Mercurial Mercurial: The Deﬁnitive Guide Available online at http://hgbook.red-bean.com/read/ Or buy from Amazon.com or O’Reilly Media

Questions?

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Mercurial Distributed Version Control

by David Stockton on Apr 16, 2010

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Mercurial Distributed Version Control — Presentation Transcript