Edgewall Software

Mercurial Plugin for Trac

Mercurial logo

This a plugin for Trac which enables Mercurial to be used as the VersionControlSystem for Trac. It was originally developed under #1847.

Please 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:

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

Detailed Change Logs:

Mercurial itself is released under the GPLv2 license.

Download and Installation

Releases and compatibility matrix

Version mercurial-plugin Trac Compatible with hg mercurial-plugin@b48cfb933370 (1.0 branch) branches/1.0-stable (1.0.x), branches/1.2-stable (1.2.x), branches/1.4-stable (1.4.x), branches/1.6-stable (1.6.x) 1.1.x to 6.7.x mercurial-plugin@3fedb001bed9 (1.0 branch) branches/1.0-stable (1.0.x), branches/1.2-stable (1.2.x), branches/1.4-stable (1.4.x) 1.1.x to 6.1.x mercurial-plugin@ea0d3998e2c7 (1.0 branch) branches/1.0-stable (1.0.x), branches/1.2-stable (1.2.x), branches/1.4-stable (1.4.x) 1.1.x to 5.5.x mercurial-plugin@0417bb5def2e (1.0 branch) branches/1.0-stable (1.0.x), branches/1.2-stable (1.2.x), trunk (1.3.x) 1.1.x to 4.6.1 mercurial-plugin@d9139f9 (1.0 branch) branches/1.0-stable (1.0.x), branches/1.2-stable (1.2.x), trunk (1.3.x) 1.1.x to 3.9 mercurial-plugin@e0c98f9 (1.0 branch) branches/1.0-stable (1.0.x), trunk (1.1.x) 1.1.x to 3.2 mercurial-plugin@bee9c8c (1.0 branch) branches/1.0-stable (1.0.x), trunk (1.1.x) 1.1.x to 3.2 mercurial-plugin@c91c42e (1.0 branch) .egg 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 to check which 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.

The latest stable version is available on PyPI. The simplest method of installation is:

$ pip install TracMercurial

You can also install from a checkout of the source:

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


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

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

  • Create an "egg" which you can copy to your $TRACENV/plugins:
    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 is possible to re-use the Mercurial library coming from the installer, see this mail. However, 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 https://bitbucket.org/tortoisehg/files/downloads/ or https://www.mercurial-scm.org/release/windows/

You may also want to experiment with 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 are modifying an existing Trac environment to use the Mercurial backend, then you have to explicitly enable the plugin in TracIni.

tracext.hg.* = enabled

Setting up a Trac environment

You can either reuse an existing Trac environment or create a 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 are 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:

tracopt.ticket.commit_updater.* = enabled


Mercurial support is basic, but works well and has been tested on the Mercurial repository itself. The performance is acceptable, even if there is currently no caching in the database, 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 in this plugin to handle hexadecimal notation of hg changesets. For example, [8ef2] would link to the changeset 8ef2ba892518c115170398ec754bd1c27cab271f. Other extensions include:

  • Plain changeset numbers are also recognized, provided they are long enough (12 to 40).
  • 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, because using cset:tip would work too.
  • The branch: prefix has a special meaning, as this will not select the specified revision, but the head which is reachable from that revision.


The TracBrowser View revision form has pulldown menus for jumping to a given tag or branch. In Mercurial, a branch within a repository corresponds to a head, ie a changeset without children:

Browser view, showing the pulldown menu of tags

There is 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 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, ie 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).

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 1.0, we show a graphical overview of the branch graph when viewing the log of the repository root (#1492).

Also, there is the 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 differ 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.

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 most of it is working, expect that it's hackish in the Trac 0.10.3 version of the plugin. Since it needs a bit more flexible 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 requested 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

Features in Trac+svn but not in Trac+hg

  • No path history mode, ie 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/mercurial/repo')
    >>> len(repo)
    You can also look at the hg.__file__ attribute to verify you are 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?

"Fatal Python error: PyImport_GetModuleDict: no module dictionary!"

You might get hard crashes on Windows showing up such messages on the console, when running TracStandalone with the autoreload feature (-r / --auto-reload), in combination with recent Mercurial versions (> 3.7-rc).

This is already fixed in the code, so either upgrade the plugin or apply the corresponding fix.

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.


Last modified 5 weeks ago Last modified on Apr 15, 2024, 3:23:34 PM

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