Emacs installations for continuous integration

This project aims to provide a method for Emacs Lisp authors to easily test their code against a wide variety of Emacs versions. It is used most widely as the basis of the popular setup-emacs GitHub Action.

Goals:

• Usable without Nix knowledge
• Clear, simple docs and setup, initially primarily for Travis and Github Actions
• Binary caching, ie. pre-built executables, via Cachix (a wonderful service!)
• Both Linux and MacOS support
• Minimal installations by default, for download speed: no image support, no window-system
• Allow easy local testing

Status

• Works for Linux and MacOS (but no binary cache for ARM on either yet, sorry)
• Official release versions from 23.4 onwards are supported (though not necessarily on all platforms)
• Emacs development and pre-release snapshot builds are also available
• Binary caching via Cachix is enabled, and working
• A Github Action is available for easy integration with your workflows
• Travis integration is presumably still working but see notes below.

Github Actions usage

The purcell/setup-emacs Github Action is available for easy integration with your Github workflows.

Travis usage

While people were still using Travis for open source, integration worked like this:

language: nix

os:
  - linux
  - osx

env:
  - EMACS_CI=emacs-24-1
  - EMACS_CI=emacs-24-5
  - EMACS_CI=emacs-25-3
  - EMACS_CI=emacs-26-3
  - EMACS_CI=emacs-27-2
  - EMACS_CI=emacs-snapshot

install:
  # The default "emacs" executable on the $PATH will now be the version named by $EMACS_CI
  - bash <(curl https://raw.githubusercontent.com/purcell/nix-emacs-ci/master/travis-install)

script:
  - ... your commands go here ...

This repo no longer actively aims to support Travis.

Low-level Nix usage, e.g. for local testing

With Flakes

There's a flake definition in this repo so (assuming you have flakes enabled in your nix installation) you can easily run any given Emacs, e.g. using:

nix run 'github:purcell/nix-emacs-ci#emacs-28-2' -- -Q

The flake contains the necessary binary cache config, which you may be prompted to authorise.

On MacOS with Apple Silicon and Rosetta installed, you can run the pre-built cached x86_64 Emacsen like this:

nix run --system x86_64-darwin 'github:purcell/nix-emacs-ci#emacs-28-2' -- -Q

Without Flakes

First, ensure you have cachix enabled, to obtain cached binaries:

nix-env -iA cachix -f https://cachix.org/api/v1/install
cachix use emacs-ci

If you want to add the cache address and key to your substituters system-wide, use the details on the cache page.

Then, evaluate one of the emacs-* expressions in default.nix. You can do this without first downloading the contents of this repo, e.g. here's how you would add a specific version to your Nix profile:

nix-env -iA emacs-25-2 -f https://github.com/purcell/nix-emacs-ci/archive/master.tar.gz

The above command mutates your user-level profile, so you probably don't want to do that when testing locally. There'll be a nix-shell equivalent of this, in order to run a command inside a transient environment containing a specific Emacs, but I haven't figured that out yet.

About snapshot builds

snapshot builds aim to be a relatively recent commit on the Emacs master branch, and does not automatically give you the very latest Emacs revision available via Git. That would defeat binary caching.

Instead, a scheduled Action runs every week to speculatively update the version: it requires me to click a couple of things, but most weeks this should happen.

What patches are applied to these binaries, and why?

There's a tension between having a CI binary that is easily usable for the majority of testing purposes, and one that faithfully reproduces the known broken behaviour of that version in certain circumstances. Binaries for old Emacs versions "in the wild" will have been built with various old versions of GNUTLS and other libraries, and there is no single way to reproduce all their quirks.

For this project, we are doing the least patching that will allow the older Emacsen to install packages from ELPA over HTTPS using a recent version of GNUTLS. (While older versions used the http ELPA URL anyway, cask uses https unconditionally.) This involves applying patches for the E_AGAIN issue that was fixed in 26.3, plus a patch to let old Emacsen find the system cert store on recent OSX versions.

Additionally, the ELPA package signing key has changed and no longer matches the public key that was bundled with older Emacs releases (25.x), which meant that those releases could not now install ELPA packages with stock settings: package-check-signatures needed to be disabled, or the new public key imported into the user's keychain. To avoid this issue, we bundle the latest public keys into all builds.

Finally, minor patches are applied as necessary to allow very old Emacs versions to compile against newer glibc versions.

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