1. History 2. Structure 3. Git Comparison 4. File Storage 5. File Tracking 6. Staging 7. Queues (MQ) 8. Merge Tools 9. Interfaces

Transcription

1 1 Hg 1. History 2. Structure 3. Git Comparison 4. File Storage 5. File Tracking 6. Staging 7. Queues (MQ) 8. Merge Tools 9. Interfaces

2 2 Mercurial / Git History Bitmover's BitKeeper Proprietary distributed revision control system Used by Linux Kernel project for three years until April 2005 Bitmover CEO Larry McVoy pulls the free version of BitKeeper completely. Linus Torvalds Leaves kernel project to create the next kernel RVS Two months later Git is born and hosts the kernel project Matt Mackall simultaneously creates Mercurial "Mercurial is very good, but Git is better. Linus Torvalds It largely comes down to taste. I guess some people just have no taste, but if Git makes them happy, I won't try to stop them. Matt Mackall

3 3 Mercurial Project named Mercurial Application named Hg (Mercury) Open Source (GPL2) Mercurial is written in Python Some machine language components Notable users: Mozilla, Python, NetBeans, OpenOffice, OpenJDK, rpm Free hosting: bitbucket.org, code.google.com, sourceforge.net

4 4 Mercurial Structure - Filesystem / Working directory Represents one revision Refreshed by 'hg update' /.hg/ Repository store File snapshots Manifest of files Changesets of file deltas Logs of all revisions /.hgignore List of ignored files /.hgtags Tags are global pointers to changesets, like Git Repository folder /.hg/ /.hgignore /.hgtags.hgignore and.hgtags kept in the working directory for version control. A tag will always point to a revision older than the one that committed the tag. Cloning from a tag will retrieve a repository that doesn't have the tag you cloned from.

5 5 Mercurial Structure Repository b1 b2 branch v1 v2 v3 v4 main Revisions form a directed acyclic graph Revisions stored as keyframed deltas A revision is a snapshot of a commit. The last revision in the chain is a head There can be any number of heads Heads can be merged two at a time into new revisions.

6 6 Mercurial vs. Git Largely equivalent to Git Most functionality identical between systems Differences in implementation and approach Discrepancies resolved by extensions hg-git Mercurial plugin two-way bridge between Mercurial and Git Allows Mercurial repository to push/pull with Git repositories Full command comparison at

7 7 Mercurial vs. Git Extensions Extensions provide feature parity between Git and Hg Git Stash / Mercurial Attic or Shelve Set aside working environment for later Side commit of working directory Git Index / Mercurial Queue[s]

8 8 Mercurial vs. Git Staging Git Repo git commit Index git add Working Directory Hg Repo hg commit Working Directory Git explicitly identifies what files to commit through an Index, or staging area Mercurial treats the working directory as a snapshot of the commit, automatically managing which files are modified and need to be included. Mercurial Queues extension can be used for more atomic control over commits, as well as the ability to push and pop patches in a system similar to Quilt.

9 9 Mercurial File Storage File Storage Stores a snapshot (instance) of the current heads Stores changesets containing commit deltas Conflates deltas into keyframes Compress deltas Increase random access performance Compression Files stored via compress (zip) Algorithm balances compression with performance Files stored raw if already compressed Hg always does the right thing when storing files. HTTP transfers use bzip2 SSH connections use SSH built in stream compression

10 10 Mercurial File Tracking Track files not folders Empty folders not allowed Only files are tracked File path is created with the file and torn down after if empty Tracking Files hg add Add file[s] to the repository, and to the next commit hg addremove Add all new files, removes missing files hg remove Stop tracking history, file is deleted from working directory. The complete history of the file is still stored, forever. No garbage collection Mercurial will track a new file with the same name as a separate entity.

11 11 Mercurial History What is past stays in the past, history moves forward. Mercurial an append-only philosophy and makes it difficult to alter the history of commits Avoids pitfalls of allowing history rewriting Trades off flexibility Guaranteed atomicity of transactions Repository unlocked for reading at all times

12 12 Mercurial vs. Git Rebasing Git is designed to allow the graph to be modified freely. Mercurial is designed to keep the graph moving forward. Rewriting the commit graph is not allowed in Mercurial. Mercurial Rebase Extension Allows rebasing uncommitted changes hg pull a new head. hg rebase your changes onto the head. Fails if conflicts detected Can also be done as part of a pull hg pull rebase Hg's Rebase will not allow rebasing to your own ancestor rebasing to merge revision with external parents.

13 13 Mercurial Queues (MQ) To use a Git Index style layer, create a single patch 'hg qnew patchname Create a single patch hg qrefresh Record changes into the patch 'hg qfinish Finalize the patch The Queue can contain multiple patches More flexible than Git's single Index Git is capable of handling patches too: StGIT Guilt These are scripts layered over Git MQ is an integral extension to Hg

14 14 Mercurial Queues - Patches Commit Patch 1 UI Tweak Patch 1 Bugfix Working Directory hg qpop and hg qpush - Navigate up and down the patch chain hg refresh Save changes into current patch Changes in the commit can be separated by feature or section and tracked individually. MQ also supports multiple parallel queues. 'hg qqueue -c [queue name]' creates a queue. 'hg qqueue [queue name]' switches between active queues

15 15 Mercurial Queues Versioning Patches Patches are kept in plaintext in the repository Single queue patches stored in: /.hg/patches/[patchname]/ Multiqueue patches stored in: /.hg/patches-[queuename]/[patchname]/ Creating a Mercurial repository inside these folders expands this intermediate area into a versioned repository. Share queues with other people to allow others to look at your patch in progress before it is committed. Collaborate on components of the code at a more local level before finalizing the overall commit.

16 16 Mercurial Branching Git creates branches by attaching labels to commits and growing the tree. In Mercurial branching can be done internally, but cloning a repository is always preferred. Cloning is safer, more modular, easy to discard. If cloning locally, Mercurial uses hardlinks to files

17 17 Mercurial Branching Mercurial supports named branching Named branches exist in a global namespace. Useful for team and project organization Keep a gold, beta, and alpha head. As QA tests, the heads are moved up the chain. Mercurial still doesn t let you change history, so You can never delete or rename a named branch. (Of course you can, but it's not recommended.)

18 18 Mercurial Branching Mercurial Bookmarks Extension Comes in the box Allows commits to be named less permenantly Bookmarks are pointers into the commit graph Can be renamed, nested and deleted at will Bookmarks may be pushed and pulled between repositories Global namespace still applies.

19 19 Mercurial Merge Tools - Internal internal:merge Traditional merge with conflict markers baked into the file hg resolve needed before hg commit is allowed internal:dump Creates three versions of the files to be merged manually: local, other and base For the file a.txt, the conflict files will named "a.txt.local", "a.txt.other" and "a.txt.base internal:fail Marks unmerged files as unresolved, hg resolve needed internal:local Uses the local version of files as the merged version internal:other Uses the other version of files as the merged version internal:prompt Asks the user to keep local or other as the merged version

20 20 Mercurial Merge Tools - External Merge tools are selected in /.hg/hgrc [merge-tools] mymergetool.priority = 100 mymergetool.premerge = False mymergetool.args = $local $other $base -o $output myimgmerge = [merge-patterns] **.jpg = myimgmerge **.exe = internal:fail

21 21 Mercurial Merge Tools - External Tool Arguments $output Where the merge will end up $local - Unmerged local changes $base - Revision from the merge ancestor $other - Second parent revision Tool Options.args - The arguments to pass the merge tool.premerge=false Don t first attempt internal merge (defaults to True).executable Path of merge tool.binary Does the merge tool support binary files?.symlinks Does the merge tool support symlinks?.gui Requires a GUI, interactive merge.priority - Priority of this merge tool (0-100)

22 22 Mercurial Merge Tools - External Interactive merging tools are plentiful KDiff3 Merge GUI Packaged with Hg Meld Merge GUI Linux/Mac/Win meldmerge.org Diffuse Text based interactive merge tool Python diffuse.sourceforge.net

23 23 Mercurial Interfaces SourceTree Free Git/Hg GUI for Win/Mac sourcetreeapp.com MacHg Free Hg GUI for Mac jasonfharris.com/machg TortoiseHg Free file browser integration, Windows and Gnome/Nautilus tortoisehg.bitbucket.org EasyHg Simple free Hg GUI for Linux/Mac/Win easyhg.org

24 24 Mercurial Integration Eclipse Mercurial Eclipse plugin bitbucket.org/mercurialeclipse/main NetBeans Supported out of the box Visual Studio HgSccPackage extension Ant ANT4HG Maven Integrated via scm:hg namespace

25 25 Hg Benjamin Pitts Computer Science M.S. Student Old Dominion University