A guide to getting the hg-git Mercurial plugin to work on a Windows machine

When you’re developing a Ruby on Rails application on Windows, you have to learn to deal with a lot of minor issues. I used Mercurial (Hg) initially as my source control. However when time came to deploy my application, I found out that Git would have been a much better choice. Both Heroku and Engine Yard make Ruby on Rails so easy to deploy that it would be crazy not to use them. However they integrate with Git and Mercurial support seems a long way off.

So I decided to convert my Mercurial repository to Git using the hg-git Mercurial plugin and ran into a lot of issues along the way. Here is a guide to successfully getting the hg-git plugin to work on a Windows machine:

Install TortoiseHg if you haven’t already

If you’re developing on Windows and using Hg, you probably already have TortoiseHg installed. If not, go ahead and download and install TortoiseHg. Make a note of where you install TortoiseHg, since you need to make some modifications in this directory.

Install the prerequisites for the hg-git plugin

We’re going to use the hg-git Mercurial plugin to allow us to pull from and push to any Git repository. This has a dependence on Mercurial (which is handled by installing TortoiseHg in the previous step) and dulwich which is a library that provides an interface to git repos using pure Python code.

However since you most probably don’t have Python installed on your Windows machine, follow these steps to “install” the dulwich library for use by the hg-git plugin:

1. Download the latest source code for dulwich (version 0.4.0 or above) and unzip it to a temporary directory
2. IMPORTANT: Read the note at the bottom of the post for troubleshooting. You might need to make a change to a file in the dulwich folder in order for it to work on Windows.
3. Under the newly unzipped folder, you should see a directory called “dulwich” which contains all the Python code (you should see a bunch of files with the .py extension)
4. In the installation directory for your TortoiseHg installation, you should see a zip file called library.zip. Copy the dulwich folder into this zip file in the root of the zip file.

Download the source code for the hg-git Mercurial plugin

Clone the repository at http://bitbucket.org/durin42/hg-git/ to a location on your hard drive, say C:\hg\hg-git

Setup .hgrc to use the hg-git plugin

Navigate to the hg repository on your hard drive that you want to convert to Git. Under the .hg directory, edit the hgrc file to contain the following three lines:

[extensions]
hgext.bookmarks =
hggit = C:\hg\hg-git\hggit

You need to point hggit in your hgrc file to point to the subdirectory called “hggit” located in the cloned repository (see step 3 above). This folder usually only contains Python code files (with a .py extension)

Pull and push from a Git repository

That’s it! Provided your current working directory is inside the hg repository that you set up, you should be able to pull from and push to any Git repository.

Troubleshooting

1. If you’re getting a error about a function called build_tree in index.py, you need to add the line  to the very top of the build_tree(path) method as follows. Once you’ve added this line, you can add the dulwich folder to zip file as in step 2:

def build_tree(path)
    path = path.replace ("\\", "/")

2. If you’re getting an error like “abort: The system cannot find the file specified”

• Dulwich most probably cannot find ssh in your PATH. You need to make sure to install Cygwin’s OpenSSH and that you can run “ssh” from the command line.
• Make sure that you are using the Git Bash shell as you work through this guide (Credit goes to SPR in the comments for this tip)

3. If you get “Permission denied (publickey)”, it just means that the public key required to access and push to the server cannot be found. To get around this we’re going to run the following commands:

ssh-agent
ssh-add <full path to your key file>