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 * Installation instructions and example usage can be found at http://mercurial.aragost.com/kick-start/en/hgsubversion/
 * Sources and additional examples of usage can be found at http://www.bitbucket.org/durin42/hgsubversion/.

As an example of HgSubversion usage, let's say you want to contribute to CPython. You first clone the repository.

{{{
$ hg clone svn+http://svn.python.org/projects/python python-hg
}}}
This way you get a folder named "python-hg" containing both a hg repo with each changeset mirroring an SVN revision.

When you want to produce a patch to the maintainers, it's simple:

{{{
$ hg di -b -r last_svn_revision:your_tip > mybugfix.patch
}}}
When you want to push the changes directly into svn, you first pull the latest changes from svn, then rebase your changes to the svn HEAD and push them back.

{{{
$ hg pull # pull the changes from svn
$ hg up your_head # update the repo to the head of the changes you want to push to svn
$ hg rebase --svn # rebase your_head onto svn
$ hg push --svn
}}}
You can also first pull from svn and then generate a patch. This works just like pushing back, with the exception that you create the patch instead of pushing.

{{{
$ hg pull
$ hg up your_head
$ hg rebase --svn
$ hg di -b -r last_svn_revision:tip > mybugfix.patch
}}}
Naturally you can use any of the various possible workflows to get the changes into the Mercurial repository you created with hgsubversion, including seperate feature or bugfix clones, but remember that you rebase the hgsubversion repository.
See the HgSubversion extension page for installation instructions and example usage.
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 * Uses standard hg commands, so learning curve is relatively short.

Working with Subversion (SVN)

Interoperating with SVN is possible with third-party tools or existing extensions. This page will detail the options and discuss their pros and cons.

1. With hgsubversion

HgSubversion is a third-party tool dedicated to convenient SVN interoperability, using standard hg commands.

See the HgSubversion extension page for installation instructions and example usage.

1.1. Pros

  • Simple and fast to setup.
  • Can pull new revisions, using svn replay protocol if available which is the fastest way to grab svn revisions.
  • Can directly push back changes, so it's a full subversion bridge.
  • Uses standard hg commands, so learning curve is relatively short.

1.2. Cons

  • For huge svn repositories the first clone is slow.
  • Depends on svn python bindings. There are plans to use ctypes instead, nothing done yet.
  • May fail to import repositories with strange history elements
    • If you encounter this on a public OSS repository, please file a bug so the developers can look into the problem

2. With MQ only

If we don't really care about existing history, and only want to hack an existing Subversion codebase with Mercurial and push changes back, we can start with an svn checkout and track it into Mercurial. For this example, assume we have a repository at svn://repo.org/subversion with a wanted module trunk.

$ svn co svn://repo.org/subversion/trunk trunk
A    trunk/a
Checked out revision 1.
$ cd trunk
$ hg init
$ cat > .hgignore <<EOF
> \.svn/
> \.hgignore$
> EOF
$ hg st
? a
$ hg ci -Am "Initializing from subversion checkout"
adding a

Now we hack the sources. The trick is not to commit in Mercurial but to store all the changes as MQ patches.

$ echo b >> a
$ hg st
M a
$ hg qnew -f changea

If you want to have versioning on your patches, do:

$ hg qinit -c

Use MQ in the normal way, doing qrefresh (and qcommit if using versioning).

Once we are ready to push the patches, first resync with svn:

$ hg qpop -a
$ svn up
U    a
A    b
Updated to revision 3.
$ hg st
M a
? b
$ hg addre -s 75
adding b
$ hg ci -m upstream

Then apply the patch queue again.

$ hg qpush -a
applying changea
patching file a
Hunk #1 FAILED at 0
1 out of 1 hunk FAILED -- saving rejects to file a.rej
patch failed, unable to continue (try -v)
patch failed, rejects left in working dir
Errors during apply, please fix and refresh changea

Oups, our changes do not apply any longer, we have to rebase:

$ hg up -C .^
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg qpush -a
applying changea
Now at: changea
$ hg qsave -c -e
copy .hg/patches to .hg/patches.1
$ hg heads
changeset:   4:ace2da3ad857
tag:         tip
user:        Patrick Mezard <pmezard@gmail.com>
date:        Sun Feb 17 15:39:11 2008 +0100
summary:     hg patches saved state

changeset:   2:6e35211ce252
user:        Patrick Mezard <pmezard@gmail.com>
date:        Sun Feb 17 15:38:11 2008 +0100
summary:     upstream

$ hg up -C 2
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg qpush -am
merging with queue at: .hg/patches.1
applying changea
patching file a
Hunk #1 FAILED at 0
1 out of 1 hunk FAILED -- saving rejects to file a.rej
patch failed, unable to continue (try -v)
patch failed, rejects left in working dir
patch didn't work out, merging changea
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
merging a
0 files updated, 1 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
Now at: changea

In most case, you won't have to do that, the patch queue will apply cleanly. Now, we can apply one patch after another and push them into Subversion.

$ hg qpop -a
Patch queue now empty
$ hg qpush
applying changea
Now at: changea
$ svn st
?      .hgignore
?      .hg
M      a
$ svn ci -m "change a"
Sending        a
Transmitting file data .
Committed revision 5.
$ hg qdel -r qbase:qtip

At this point, our changes are in Subversion and in our local Mercurial mirror as real revisions. Large chunks of this process can be automated.

2.1. Pros

  • Simple, fast and cheap to setup
  • No heavy dependencies, only requires an SVN client and MQ extension.

2.2. Cons

  • Renames cannot be handled that way because they cannot be recorded in Subversion after they happened. You have to perform them directly in SVN, outside of this workflow.
  • No SVN history. It means no "hg grep", "hg annotate", "hg bisect" and dumb merges.
  • May be tedious

3. With Convert extension

First use convert extension to create a local reference mirror. For this example, assume the SVN repository is at svn://repo.org/subversion with a wanted module trunk.

$ hg --config convert.hg.tagsbranch=0 convert svn://repo.org/subversion/trunk trunk-mirror
initializing destination trunk-mirror repository
scanning source...
sorting...
converting...
4 Repository initialization
3 append c to a
2 add b
1 change a
0 change a

Mercurial versions from 1.0 support shallow conversions like:

$ hg --config convert.svn.startrev=3 --config convert.hg.tagsbranch=0 convert svn://repo.org/subversion/trunk trunk-mirror
initializing destination trunk-mirror repository
scanning source...
sorting...
converting...
2 add b
1 change a
0 change a

Prepare the working copy. Instead of cloning the mirror, we checkout a working copy, make it a Mercurial repository, pull from the mirror and synchronize both. This way we end with an hybrid Subversion and Mercurial working copy.

$ svn co svn://repo.org/subversion/trunk trunk
A    trunk/a
A    trunk/b
Checked out revision 5.
$ cd trunk
$ hg init
$ cat > .hgignore <<EOF
> \.svn/
> \.hgignore$
> EOF
$ hg pull ../trunk-mirror
pulling from ../trunk-mirror
requesting all changes
adding changesets
adding manifests
adding file changes
added 5 changesets with 5 changes to 2 files
(run 'hg update' to get a working copy)
$ hg up -C
2 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg st
$ svn st
?      .hgignore
?      .hg

We hack it and end with an collection of patches in MQ. The situation is very similar to the one in "With MQ only" section. The difference is we do not change the patches into Mercurial revisions, we push them and get rid of them when done. Synchronize with Subversion first:

$ hg qpop -a
$ cd ..
$ hg --config convert.hg.tagsbranch=0 convert svn://repo.org/subversion/trunk trunk-mirror
scanning source...
sorting...
converting...
0 add c
$ cd trunk
$ svn up
A    c
Updated to revision 6.
$ hg pull -u ../trunk-mirror
pulling from ../trunk-mirror
searching for changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 1 changes to 1 files
1 files updated, 0 files merged, 0 files removed, 0 files unresolved

Then apply the patches:

$ hg qpush
applying changea
Now at: changea
$ svn st
?      .hgignore
?      .hg
M      a
$ svn ci -m "change a"
Sending        a
Transmitting file data .
Committed revision 7.
$ hg qpop
Patch queue now empty
$ hg qdel changea

Synchronize with Subversion again:

$ cd ..
$ hg --config convert.hg.tagsbranch=0 convert svn://repo.org/subversion/trunk trunk-mirror
scanning source...
sorting...
converting...
0 change a
$ cd trunk
$ svn up
At revision 7.
$ hg pull -u ../trunk-mirror
pulling from ../trunk-mirror
searching for changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 1 changes to 1 files
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
[16:14:55][pmezard:~/dev/mercurial/svn/trunk]$ hg tip
changeset:   6:2fba38614917
tag:         tip
user:        pmezard
date:        Sun Feb 17 15:13:55 2008 +0000
summary:     change a

Again, large parts of this process can be scripted.

3.1. Pros

  • Full SVN history. It means "hg grep", "hg annotate", "hg bisect" and good merges.

3.2. Cons

  • Renames cannot be handled that way because they cannot be recorded in Subversion after they happened. You have to perform them directly in SVN, outside of this workflow.
  • Pushing changes may still be tedious.
  • Requires a recent Mercurial version, Subversion python bindings may be tricky to setup. Hint for Windows users: TortoiseHg includes them.

Improvement Discussion

Mercurial interoperability with Subversion is clearly not as good as Git or Bazaar-NG one, and this is a real showstopper for massive adoption. The question is what can be improved and in which order so we move from "existing but tedious" to "usable".

  • (./) Shallow conversions. Convert extension inability to convert partially makes it unusable with most of remote repositories. Imperfect suggestions were made in this direction, see "convert: add --startrev option" development mailing thread for more details (http://selenic.com/pipermail/mercurial-devel/2008-January/004004.html).

  • Pushing back to Subversion. A functional svn sink is implemented in Convert extension but it is very basic and lack documentation. There is a test-convert-hg-svn test using it though.

    • (./) This is a native feature of hgsubversion.

  • Rebasing. There is not simple native branch rebasing support in Mercurial. This feature is very useful to update the branch being worked on on top of the latest Subversion revision. In the meantime, it can be done with MQ. What about RebaseExtension?

    • (./) This is provided in hgsubversion as hg rebase --svn.


CategoryHowTo

WorkingWithSubversion (last edited 2013-05-17 06:26:53 by rcl)