New in Emacs 25.1: Archive priorities and downgrading packages

This is the feature I’ve been wanting to show off the most. Anyone who’s configured Emacs to use more than one package archive knows this problem. The package menu displays countless redundant entries, as it must list a package once for each archive that offers it. Even worse, if you install a package from one archive, the package menu will gladly upgrade it to a newer version on another archive, clueless to the fact that it may be giving you unstable code.

All of this has been addressed now, with the package-archive-priorities variable. It is an alist where you can assign a priority number to each archive you use. Thanks to Jorgen Schaefer, the first thing it does is change the package-install command to download the package from the highest priority archive instead of just choosing the highest version.

Here’s an example configuration.

(setq package-archive-priorities
      '(("melpa-stable" . 20)
        ("marmalade" . 20)
        ("gnu" . 10)
        ("melpa" . 0)))

Since you all know I’m a bit of a menu fanatic, I took my time extending that functionality to the package menu. Now, instead of listing all entries for a given package, the menu will only list the package that’s offered by the highest priority archive. With the above configuration, you will only see Melpa packages if they are not also available from another archive. More importantly, after installing a stable version you will never be inadvertently upgraded to an unstable version.

This behaviour can be permanently configured with the package-menu-hide-low-priority variable, and you can temporarily toggle it on and off with (. Therefore, if a package has stable version available but you prefer the Melpa version, you can display it with ( and then install it as usual. And what’s more, package.el will identify that situation and will keep upgrading you on the bleeding-edge for that specific package, even though Melpa is the lowest priority archive.

Furthermore, the ( key is now a general key for displaying possibly unwanted packages (much like it hides/displays details in dired buffers). In addition to the behaviour above, this key will also display packages that are considered obsolete. That is, those whose version is lower than something you already have installed. This was not previously possible, and it can be used to downgrade a package. As long as the older version is available from some archive, you can mark it for installation and mark the current version for deletion.

This concludes our series on package.el. There are other small improvements here and there, but it’s time we go back to our weekly code snippets and productivity tips. Hopefully, this was enough to inspire some of you to clone the Emacs repo and start building the master branch.