HJKLPlugin
A plugin for vim key bindings in Mac OS X Mail
Mac OS X 10.10/10.9 (Yosemite/Mavericks) Compatibility Note
Last version tested: Mail Version 8.0 (1988) / OS X Version 10.10 (14A386b)
This is currently compatible with 10.9+ provided you're willing to sign the plugin yourself. This is because Apple now requires code signatures (you can, however, use a self-signed certificate).
So what does this do?
It's a simple plugin that lets you use vim keybindings in Mac OS X's Mail.app (up to and including version 6.6, which ships with 10.8.5, 7.3, which ships with 10.9.4, and 8.0, which ships with 10.10)
At the moment, it only works on the message view pane (to navigate all messages in a given thread) and in the message list (to move the selection up or down and to expand/collapse threads).
It also allows you to hit x to delete a message and v to open the first URL in an HTML message in the browser (useful if, like me, you miss Google Reader)
How do I install it?
If you're brave enough, you can try out a pre-built bundle from the releases page - just drop the .bundle to your ~/Library/Mail/Bundles folder and restart Mail.
Before installing
Before installing the plug-in, you'll need to make sure that Mail.app's plug-in support is turned on by running the following two commands in Terminal.app:
defaults write com.apple.mail EnableBundles -bool true
defaults write com.apple.mail BundleCompatibilityVersion 3
Doing it from source
If you're running an older version of Mac OS X, run sh install.sh under your own account (i.e., do not use sudo, under any circumstances!).
For installing in Mavericks (10.9) or Yosemite (10.10), you'll also need to have a self-signed certificate in your login keychain. To create one, follow this Mac Developer Library article.
Then run sh install_signed.sh "<certificate name>" under your own account.
That will build, codesign and deploy the .bundle to your ~/Library/Mail/Bundles folder.
What manner of dark magic is this?
It's a bit of Python that swizzles Objective-C methods and handles keypresses, mapping them to the codes Mail.app expects. The whole codebase fits in a screenful, and you can tweak it to your liking with minimal effort.
References
In case of Mac OS X Upgrades
Whenever Apple updates Mail.app, you need to update the compatibility UUIDs in setup.py and rebuild the plugin. To figure out the required UUIDs, you need to issue these commands:
# For Mac OS X 10.8.x
defaults read /Applications/Mail.app/Contents/Info PluginCompatibilityUUID
defaults read /System/Library/Frameworks/Message.framework/Resources/Info PluginCompatibilityUUID
# For Mac OS X 10.9.x/10.10.x
defaults find UUID | grep MailCompatibility
defaults find UUID | grep MessageCompatibility
Add the new UUIDs to setup.py and reinstall.
Of course, Apple can change Mail.app's UI as they please. In that case, you'll need to figure out which Cocoa views are involved and refactor the method swizzling.
In either case, feel free to fork this project and send me a pull request. I am unlikely to upgrade all my machines to bleeding edge versions, so you'll likely be ahead of me and able to help out others.