Switching to the Emacs Lisp Package Archive

For those who are unaware, Emacs 24 was finally released this past June. I had been following the official repository for about a year before the release using what was becoming version 24, very quickly becoming dependent on several of the new features. Now that it’s been officially released I’m back to using a stable version of Emacs, about which I’m quite relieved.

One of the new features that I hadn’t been using until recently was the package manager, package, and the Emacs Lisp Package Archive (ELPA). You can now ask Emacs to download and install new modes and extensions from the Internet. By default, it only uses the official archive. It only hosts packages with copyright assigned to the FSF — quite restrictive. There are alternatives, the most popular of which is Marmalade. Fortunately it’s easy to ask package to use additional repositories, so this is a non-issue.

Because it was still unstable and buggy at the time, I avoided using it when setting up my configuration repository. Instead I opted to gather packages by way of Git submodules. I’d give package a shot once Emacs 24 was released. Once it was released in June it was just a matter of time until I invested into this new system.

The trigger was an e-mail from one of my readers, Rolando. He asked me if I could move my recently updated memoization function into its own repository and touch it up so that it could be turned into a package with MELPA, another alternative package repository. This forced me to finally investigate.

It turns out MELPA is really interesting. Each package is described by a “recipe” file, which is essentially just a tiny s-expression listing the repository URL. In the case of my memoization package,

(memoize :repo "skeeto/emacs-memoize"
         :fetcher github)

From a package maintainer’s point-of-view, this is fantastic. I don’t have to take any extra steps to publish updates to my package. I just keep doing what I do and it happens automatically. However, I need to be more careful about not pushing broken commits — which is why I started unit testing (to be covered in a future post). And I need to be extra careful with my SSH keys, since they’re now used to publish code that other people automatically trust and execute.

Excited about MELPA and wanting to actually use my own package, I started throwing out my submodules, replacing them with their package equivalents. If you follow my configuration repository you probably noticed all the recent disruption, because updating requires manual intervention. Git leaves submodules around (for good reason!) so they need to be manually removed.

I also heavily updated and renamed my web server (now called simple-httpd) to provide it as a package (also to be covered in a future post). Thanks to MELPA, I follow the package rather than my own repository since it follows so closely (< 1 hour).

Another barrier was that I was using an old version of Magit due to a bad interaction of modern versions with Wombat, my preferred color theme. After some face tweaking, I not only fixed it but I made it better than it was before. Sinking a an hour or two into these sorts of annoyances usually works out really well. I need to remind myself of this in the future when I run into annoyance issues.

Surprisingly, package doesn’t seem to be written with managed configuration in mind. The provided functionally is designed to be used interactively rather than programmatically. package-install is only meant to be invoked once, so care needs to be taken in listing packages in a configuration and doing everything in the right order. Here’s how I have it set up at the moment, after after listing the packages to use in my-packages,

(require 'package)
(add-to-list 'package-archives
             '("melpa" . "http://melpa.milkbox.net/packages/") t)
(unless package-archive-contents
(dolist (p my-packages)
  (when (not (package-installed-p p))
    (package-install p)))

Upgrading/updating is currently a manual process. Run package-refresh-contents, list the packages with list-packages, type U to mark updates, then x to execute the upgrade. Sometime I may work that into my configuration to be done automatically once-per-week or something.

I really look forward to making more use of the package manager, especially as packages can more easily become interdependent, reducing duplication of effort.

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Chris Wellons