About the 'elpa-devel' package archive (Emacs)

2022-05-13

Overview of GNU ELPA

The official package archive of Emacs is GNU ELPA. It is maintained as part of Emacs: those with write access to emacs.git can commit changes to elpa.git.

The “ELPA” acronym stands for “Emacs Lisp Package Archive”. GNU ELPA is enabled by default in recent stable versions of Emacs per the value of the variable package-archives. This means that the user can install lots of useful, free/libre packages without setting up another package archive.

One might read in various fora references to “ELPA” without a qualifier. These typically mean “GNU ELPA”.

The “devel” version of GNU ELPA

GNU ELPA provides the latest tagged release of a package. There is, however, the option to fetch packages that are built periodically from source using the most recent commit in the main branch. This is the “development” version of GNU ELPA, hereinafter referred to as elpa-devel, which can be added to the list of archives thus:

(add-to-list 'package-archives '("elpa-devel" . "https://elpa.gnu.org/devel/"))

Or declare the entire list outright:

(setq package-archives
      '(("elpa" . "https://elpa.gnu.org/packages/")
        ("elpa-devel" . "https://elpa.gnu.org/devel/")
        ("nongnu" . "https://elpa.nongnu.org/nongnu/")
        ("melpa" . "https://melpa.org/packages/")))

[ Remember to use M-x package-refresh-contents to update the list of packages. ]

elpa-devel is useful for those who (i) want to live on the bleeding edge, (ii) understand that packages may break from time-to-time, and (iii) may want to help the developer test their program.

Setting up elpa-devel does not mean opting in to it indiscriminately. The user can pick which version of a package they prefer, such as by specifying the one to download in the buffer of M-x list-packages. More on this in the next section.

M-x describe-package (C-h P by default) shows which versions are available. If the package is already installed, the Help buffer will mention which version is in use. Example:

     Status: Installed in ‘vertico-0.23.0.20220511.61449/’. [Delete]
    Version: 0.23.0.20220511.61449
     Commit: d5d6e312af7c2525c8e6be3397373929a28dd421
    Summary: VERTical Interactive COmpletion
   Requires: emacs-27.1
    Website: https://github.com/minad/vertico
 Maintainer: Daniel Mendler <mail@daniel-mendler.de>
     Author: Daniel Mendler <mail@daniel-mendler.de>
Other versions: 0.23.0.20220511.61449 (elpa-devel), 0.23 (elpa).

Notice the difference in notation. elpa will get the value of the Version header specified in the package’s metadata: 0.23 in this case. Whereas elpa-devel follows a more descriptive pattern of VERSION.DATE.IDENTIFIER, as in 0.23.0.20220511.61449.

Prioritise archives and pin packages to archives

By default, package archives are not prioritised. The Emacs package manager (package.el) will fetch the highest version it finds. Users can control this behaviour by configuring the user option package-archive-priorities.

;; Assuming a `package-archives' like this:
(setq package-archives
      '(("elpa" . "https://elpa.gnu.org/packages/")
        ("elpa-devel" . "https://elpa.gnu.org/devel/")
        ("nongnu" . "https://elpa.nongnu.org/nongnu/")
        ("melpa" . "https://melpa.org/packages/")))

;; Highest number gets priority (what is not mentioned gets priority 0)
(setq package-archive-priorities
      '(("elpa" . 2)
        ("nongnu" . 1)))

[ Remember M-x package-refresh-contents to propagate changes. ]

In this example, the Emacs package manager will prefer the elpa version of a package, even if it is found in other archives.

Notwithstanding such prioritisation, the Emacs package manager has the power to choose versions of individual packages by associating them with a particular archive. The user option is package-pinned-packages. It is only needed for packages that should deviate from the norm of package-archive-priorities.

;; Do it like this:
(setq package-pinned-packages
      '((fontaine . "elpa-devel")
        (logos . "elpa-devel")
        (vertico . "elpa-devel")))

;; Or perhaps:
(defvar my-elpa-devel-packages
  '(fontaine logos vertico)
  "List of packages I want to pin to elpa-devel.")

(dolist (package my-elpa-devel-packages)
  (add-to-list 'package-pinned-packages (cons package "elpa-devel")))

Help test packages

GNU ELPA is “stable” though “stability” here refers to the cadence of updates, not the inherent features of the respective package’s code base. A stable package can still have bugs!

From my perspective as a maintainer of several Emacs packages, the elpa-devel option is very helpful to identify misfeatures or errors and iterate on them in a timely fashion. Feedback is valuable.

I often receive emails pertaining to my packages which start with a statement along the lines of “sorry to bother you about PACKAGE”. Don’t worry about it: the duty of a maintainer is to consider information of this sort and act on it accordingly.

On this note, I encourage you to report actual or even perceived problems to package maintainers, while consulting the official documentation (asking folks on some forum is okay, but don’t expect the maintainer to keep track of such exchanges). Emacs is one of those programs that encourages you to introspect it and, in the process of learning, blur the line between user and developer.

Do your part to improve packages, however minor you may think your contribution is.