Selectively converting Subversion repository to Mercurial


Intro


I've hosted many of my projects on my under subversion for a while(Berry4All, FantomIDE and many more)

Some of them on my own server, some others on sourceforge.

I've now decided it was time to move to a Distributed SCM and I picked Mercurial.

Why not git ?
Nothing against git but I liked BitBucket over GitHub, my work firewall does not like gitHub and I use Netbeans which as builtin Mercurial support - end of story

Existing setup


So anyway my current projects where on subversion but my existing repository was far from perfect because:
  • I had put all my projects in one repo (creating repos in SVN is too much work - I'm lazy)
  • I had committed a lot of binaries and other files that should not belong in the repo (ignoring files is annoying and I'm lazy)
  • Some of my projects have the proper "tag/branch/trunk" structure and some didn't - I'm lazy and didn't know any better early on.

Goals


So because of the existing setup I wanted to accomplish the following:
  • Keep the SVN history (obviously)
  • Convert each project in my single SVN repo to individual Mercurial projects (Cause that's the proper way)
  • Filter out the stuff I should not have committed (binaries etc..) because it does not belong there and it would take too much space on BitBucket
  • Push the new projects to BitBucket

Let's do it


I choose to use the "hg convert" tool because: It's built-in Mercurial and it allows some filtering.

Cloning the repo


Unless your repo is really tiny (mine was about 1GB wit about 1700 commits), using 'hg convert' from a remote repo will be extremely slow so, it will be much better to have a local mirror of the repo to work with.

You probably don't want people to commit stuff while you are doing this to keep your mirror in sync.

To create a mirror we will use 'svnsync'
Local mirror of the SVN repo
# Lets' ceate the mirror somewhere
cd /tmp
svnadmin create myrepo-mirror
echo '#!/bin/sh' > myrepo-mirror/hooks/pre-revprop-change
chmod +x myrepo-mirror/hooks/pre-revprop-change

# Now let's synchronize our mirror from the svn server root
svnsync init file://`pwd`/myrepo-mirror http://your.svn.server/svn/
svnsync sync file://`pwd`/myrepo-mirror


Converting Part of the SVN repo into a mercurial project


If you had a "perfect" svn repo, ou can just convert the whole thing like this:

hg convert colar-mirror myrepo.hg (myrepo.hg folder will contain your Mercurial project)

But in my case with my 'bad' SVN repo I wanted to convert separate "parts" of my existing repo into individual project, and also filter out some files.

So for this I will use two options of 'hg convert'

  • --config convert.svn.trunk=somePath
This allow to specify what is the project root, can be any subfolder of the repo.

  • --filemap filemap.txt
This allows filtering some files (completely from any version of the history)

So first I created my filter: filemap.txt file:
Example filemap filter
# Those files/folders should never have been commited
exclude dist
exclude javadoc
exclude resources/doclet/NetBeansProjects


Now I can convert the project like this
hg convert --config convert.svn.trunk=Project1 --filemap filemap.txt colar-mirror Project1.hg

or for a project that had the proper branch/tag/trunk structure:

hg convert --config convert.svn.trunk=Project2/trunk --filemap filemap.txt colar-mirror Project2.hg

Pushing the new mercurial project to a repo (BitBucket)


Now we can push the converted project to a Mercurial repo:
Publishing the project to a repo
cd Project1.hg
hg push http://bitbucket.org/myuser/project1


Mercurial basics for Subversion user


Because Mercurial is distributed it works a bit differently than SVN, while most command are the same for example:
  • svn add -> hg add
Commit and Updates are a two step process:
  • svn commit -> hg commit then hg push
  • svn update -> hg pull then hg update OR SHORTCUT hg pull -u

Anyway here is a nice page for users switching from SVN to HG:
http://nedbatchelder.com/text/hgsvn.html

Links


hg convert: http://mercurial.selenic.com/wiki/ConvertExtension

Guides for users switching from SVN to HG:
http://nedbatchelder.com/text/hgsvn.html

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