Edgewall Software

Version 100 (modified by Christian Boos, 9 years ago) ( diff )

new version, compatible with Mercurial 3.2

Mercurial Plugin for Trac (#1847)

This a plugin for Trac which enables Mercurial to be used instead of Subversion as the VersionControlSystem for Trac.

Please take care to use a recent version of the plugin before reporting issues. See the version table below.

The mercurial plugin for Trac is now hosted in its own Mercurial repository, mercurial-plugin (it was about time!)

hg clone https://hg.edgewall.org/trac/mercurial-plugin

Detailed Change Logs:

Download and Installation

Releases and compatibility matrix

Version mercurial-plugin Trac Compatible with hg mercurial-plugin@c91c42e (1.0 branch) branches/1.0-stable (1.0.x), trunk (1.1.x) 1.1.x to 3.2 mercurial-plugin@28d2535 (1.0 branch) branches/1.0-stable (1.0.x), trunk (1.1.x) 1.1.x to 2.2.2, 2.3? tip? plugins/0.13/mercurial-plugin@10900 trunk (0.13dev) 1.1.x to 2.0.2, tip? plugins/0.13/mercurial-plugin@10880 trunk (0.13dev) 1.1.x to 1.7.5, tip? plugins/0.13/mercurial-plugin@10620 trunk (0.13dev) 1.1.x to 1.7.5, tip? plugins/0.13/mercurial-plugin@10527 trunk (0.13dev) 1.1.x to 1.7.5, tip? mercurial-plugin@a97b17f1bac7 (0.12 branch) branches/0.12-stable (0.12.x) 1.1.x to 2.0.2, tip? plugins/0.12/mercurial-plugin@10878 branches/0.12-stable (0.12.x) 1.1.x to 1.7.5, tip? plugins/0.12/mercurial-plugin@10619 branches/0.12-stable (0.12.x) 1.1.x to 1.7.5, tip? plugins/0.12/mercurial-plugin@10524 branches/0.12-stable (0.12.x) 1.1.x to 1.7.5, tip?


Consult the version table below to check which precise version you need for your version of Trac. If you want to get a specific revision, add an svn up -rxxx step to the instructions below, after the checkout.

Installation of the plugin:

hg clone http://hg.edgewall.org/trac/mercurial-plugin#0.12


hg clone http://hg.edgewall.org/trac/mercurial-plugin#1.0

depending on the version of Trac you're using (0.12 or 1.0) (also use 1.0 for trunk).

Then from the checkout (cd mercurial-plugin), you have various installation options:

  • create an "egg" which you can copy to your $TRACENV/plugins, for example:
    $ python setup.py bdist_egg
  • install it in the current Python (or virtualenv) installation:
    $ python setup.py install
  • similar to the above, but directly use the code from the checkout (ideal for hacking):
    $ python setup.py develop


You can download Mercurial itself from Hg:Download.

We try to maintain backward compatibility with versions of Mercurial as old as 1.1, up to the latest. Better use a recent version however.


On Windows, it looks like it's possible to re-use the Mercurial library coming from the installer, see this mail (though to my knowledge, it is not possible to achieve this using PYTHONPATH and PATH: it fails with ImportError: No module named handlers due to library.zip coming in the sys.path before the standard library).

Note! Mercurial's library.zip contains pyd-files, which normal python import can't use (py2exe uses a special importer that allows that), but if you unzip library.zip somewhere and add that directory, it will work on Windows (tested with tracd).

Alternatively you can install the pre-built Mercurial Python modules from http://bitbucket.org/tortoisehg/thg-winbuild/downloads/

You may also want to experiment with the newly introduced Mercurial:HackableMercurial distribution.


The configuration has to be done on the Trac side, there's nothing to do on the Mercurial repository side, except for the fact that the repository should be made accessible as a local repository. Thanks to the distributed nature of Mercurial, that's always possible (if the repository is not already local, simply hg clone it).

Setting up the mercurial plugin

The TracMercurial plugin egg should be added to the plugins folder of the environment, or it can be globally installed (python setup.py install or a python setup.py develop).

For general instructions about plugins, see also TracPlugins.

If you installed the egg globally and you're modifying an existing Trac environment to use the Mercurial backend, then you have to explicitly enable the plugin in TracIni.

Since the version 0.11 of the plugin, the package has been renamed to tracext:

tracext.hg.* = enabled

Setting up a Trac environment

You can either reuse an existing Trac environment, or create a brand new one.

For general instructions, see TracInstall.

When creating a new environment with TracAdmin initenv command,

  • for the repository type, specify hg instead of the default svn.
  • for the repository directory, specify the location of the Mercurial repository (without the ending .hg).

Your <trac_environment>/conf/trac.ini configuration file should have a [trac] section similar to the following:

repository_type = hg
repository_dir = /path/to/my/hg/repository

There's also a few Mercurial specific settings in TracIni:

# -- Show revision number in addition to the changeset hash (defaults to yes)
show_rev = yes

# -- Changeset hash format
node_format = short
# hex:   Show the full SHA1 hash 
# short: Show a shortened hash for the changesets (default)

Setting up post-commit hooks

For 0.12 and later:

If you want to enable post-commit hook functionality on your repository, add the following to your repository's .hg/hgrc file (since [10728]):

; If mercurial-plugin is installed globally
commit = python:tracext.hg.hooks.add_changesets
changegroup = python:tracext.hg.hooks.add_changesets

; If mercurial-plugin is installed in a Trac plugins directory
commit = python:/path/to/hooks.py:add_changesets
changegroup = python:/path/to/hooks.py:add_changesets

env = /path/to/env
trac-admin = /path/to/trac-admin

Remember to change /path/to/env and /path/to/trac-admin to reflect your environment. If TracMercurial is installed in a Trac plugins directory, you will also have to download hooks.py and place it somewhere accessible.

You must also enable the CommitTicketUpdater functionality in your trac.ini by adding

tracopt.ticket.commit_updater.* = enabled

to the [components] section.


The Mercurial support is pretty basic, but works well. I've tested that on the Mercurial repository itself and the performance is acceptable, even if there's currently no caching in the database (this is what I'm going to work on next, with a very loose definition of next, see #8417).

For those used to Subversion in general and Subversion repository browsing in Trac in particular, there are a few differences worth noting.

Mercurial Changesets

Changeset Navigation

In Mercurial, the Previous Changeset/Next Changeset navigation is not purely sequential, as it is in Subversion. Instead of a flat history of successive changesets, we actually navigate a DAG of changesets. This means a changeset can have multiple parents (0, 1 or 2) and multiple children as well (0 to n).

Therefore, Previous Changeset is a link to the first parent, and Next Changeset is a link to the first child. In case there are additional parents or children, these are shown as additional changeset properties (Parents or Children), placed below the Author property and above the Message property.

Changeset view, showing multiple parents. Note that the diffs are providing against each parent.

Another additional changeset property is the list of Tags that might be associated with a changeset.

Wiki syntax

The Wiki syntax has been extended a bit, to cope with the hexadecimal notation of hg changesets. E.g. [8ef2] would link to the changeset 8ef2ba892518c115170398ec754bd1c27cab271f … Plain changeset numbers are also recognized, provided they are long enough (12 to 40). Also, it is possible to refer to changesets using the changeset: prefix (or cset: or chgset:, for hgweb compatibility). The tag: prefix can be used to refer to symbolic tags, although this is not a requirement (using. e.g. cset:tip would work too). Finally, the branch: prefix has a special meaning, as this will not select the specified revision, but the head which is reachable from that revision.

TracBrowser changes in 0.11

The TracBrowser View revision form has been extended with pulldown menus for jumping to a given tag or branch (in Mercurial, a branch within a repository corresponds to a head, i.e. a changeset without children):

Browser view, showing the pulldown menu of tags

There's also support for visual blame annotations:

Screen shot of the annotate / blame feature of Trac 0.11, on the .hgtags file of the Mercurial repository

Mercurial Queue

Since r6443, the MQ extension is supported. If you happen to have applied mq patches in your repository, Trac will show the corresponding patch names as Tags: in the changeset view.

Also, with the 0.12 branch of the plugin (and the MultipleRepositorySupport branch of Trac), you can browse jointly the main repository and the repository for the associated Mercurial queue, if any (i.e. if you versioned your patch queue using hg qinit -c and hg qcommit). Furthermore, if you declare such a mercurial repository to be a MQ repository, then all the patches will be correctly rendered as patches, regardless of the patch name (see r6462 for details).

Cool Features

Wild ideas section…

Visualize branches and merges

There should be a way to show graphically the branch and merge points within the revision log view. Not something as fancy as hgk, but nonetheless something that will make the changeset relationships immediately obvious.

Starting with Trac 0.13, we show a graphical overview of the branch graph when viewing the log of the repository root (#1492)

Also, there is RevtreePlugin.

Search over the source

A search provider could do the equivalent of an hg grep.

Highlight Conflict Resolution

While visualizing changeset diffs for merge changesets, we already show the changes relative to both parents, which helps to understand how conflicts (if any) were solved. But this can be improved by specifically highlighting lines that differs from both parents.

Repository Management

Trac should allow for creating new repositories or clones of existing repositories. Maybe repository deletion and renaming should be supported, too.

HG Forest Support Subrepositories support

The forest extension has been superseded by support for nested repositories. Replace forest below by subrepository. (#9704)

Support for the Forest extension for Mercurial. Forest extension allows operations on trees with nested Mercurial repositories, called forests. Those to some degree correspond to multi-project CVS/Svn/… repositories.

Already got most of it working, expect that it's pretty much hacked in the Trac 0.10.3 version of the mercurial plugin. Since it needs a bit more flexibile templating (in regards with the lookup/url's) this is hacked around node.path at the moment. Some (small/large?) issues remain but most of it is working.

Note that with the MultipleRepositorySupport branch of Trac, it should be possible to implement an IRepositoryProvider component knowing about the forest extension and adding besides the repository for the forest itself, the managed repositories as well.

Add your cool feature here…

Mercurial bundle attachments should be viewable in readable representation.
CachedRepository support in TracMercurial
Support for subrepositories mercurial extension
Mercurial plugin support for pulling repository description from hgrc
Enhancing TracMercurial plugin to use new server-command protocol
Include Mercurial support in Trac distribution

Bugs and Limitations

There are still a lot of things that can be improved.

Features that Trac+svn has but not currently implemented for Trac+hg

  • No path history mode (i.e. show all create/delete operations that affected a given path)

To cache or not to cache?

Recent versions of the plugin (r7744 for 0.11 or r7757 for 0.12) have a greatly improved browsing speed. It's now possible to navigate on repositories of the size of the Linux kernel repo.

However, producing diffs or even gathering the timeline events for repositories of such size is still too slow. For the diffs, we could reduce the amount diffs generated (see #2591, #7975). For the timeline, we should really have a cache, not only for the performance issue but also because the current heuristic for retrieving the changesets in a given period of time doesn't always work (see r5365).


"unsupported version control system hg"

If you get this message try the following two basic checks first:

  • From a Python console session try to import the Mercurial module, if all goes well it should not complain:
    >>> from mercurial import ui, hg
    >>> repo = hg.repository(ui.ui(), '/path/to/a/mercurial/repo')
    >>> len(repo)
    You can also look at the hg.__file__ attribute to verify you're loading the expected Mercurial library.
  • Log in as an user with TRAC_ADMIN permission, and look in the Admin pages, General / Plugins. Do you see the entry for the TracMercurial plugin there? If yes, is the MercurialConnector component enabled?

Known Issues

Abort: cannot follow file not in parent revision: "tracext/hg/backend.py"
[hg] encoding setting is not used for files in hg
Quickjump dropdown overflows due to Mercurial tags
Unified diff of changeset sometimes include wrong changes?
Changeset with new file links to a different revision

Implementation Notes

Hacking on Mercurial:

I'm interested in feedback concerning the code, in particular concerning Mercurial. I'm pretty sure I did things in a sub-optimal way, as I was discovering the guts of hg while writing the plugin. Therefore, I'll be pleased to get tips for improvements.


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