Up to this point my Learn Emacs series has been all about how to do cool stuff in emacs. One of my personal favorites is align-regexp. A while back that stopped working for me. Now I get an error: Wrong type argument: markerp, 0. Emacs doesn't always do what I mean.

First Remove your Config

Whether you use a single .emacs file or a ~/.emacs.d/ directory it is time to remove it. Personally I keep ~/.emacs.d/ symlinked to my emacs.d github repo so it iss quite easy to remove the symlink. Alternatively you can start emacs with the --no-init-file option, to skip loading your files. The rationale for removing your config is simply that it reduces the number of variables you are dealing with. Is the problem with your config or with emacs itself?

Then Check your Emacs Version

After I removed my config and tried M-x align-regexp again, I got the same error. So its not my config. If you find you have a problem with a particular version of emacs M-x emacs-version will tell you what version you have. In my case it was

GNU Emacs 24.0.92.1 (x86_64-apple-darwin, NS apple-appkit-1038.36) of 2011-12-02 on bob.porkrind.org

As I get my emacs builds from EmacsForMacOSX or brew install them myself. At this point I'm fairly certain I'm getting the error as a result of running a nightly build. A quick google leads me to bug#10249: 24.0.92. I installed a pretest version, and align-regexp works fine like it used to.. I would prefer to be running the stable version, but I'm using emacs-starter-kit for my config, which requires emacs 24.

Version your Config

When functionality like this breaks it is really awesome to have an emacs configuration that is under version control. I can walk backwards through any recent changes to find what is causing breakage. So if your config isn't already versioned, version it right now.

PS: I'm interested to know any emacs topics you'd like to see a blogpost on. I haven't been hacking my emacs config much lately, so I'm short on ideas for emacs posts.