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.

The rationale for this is that EVM and Damien Cassou's PPA have had various issues in my usage of them, and the latter is now unmaintained.

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 images, no window-system
• Allow easy local testing

Status

• Official release versions from 23.4 onwards are supported (MacOS: 24.3 onwards, see issue #4)
• An Emacs development snapshot build is also available
• Binary caching via Cachix is enabled, and working
• A Github Action is available for easy integration with your workflows
• Early Travis integration is tested and in use elsewhere (e.g. my emacs config and various other github projects) but see notes below.

Travis usage

Here's some example usage: caution that this early method may change. Early adopters should watch issue #6 to be kept up to date with changes to the recommended usage method.

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-27-1
  - 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 ...

Github Actions usage

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

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

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

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.

Using newer snapshot builds

snapshot builds aim to be a relatively recent commit on the Emacs master branch, and do not automatically give you the very latest Emacs revision available via Git. That would defeat binary caching, so the current plan is to periodically update the -snapshot builds manually. Send me a pull request to do this:

• Update the commit named in default.nix
• Try nix-build -A emacs-snapshot.
• This will fail due to SHA256 checksum mismatch of the downloaded archive, so now update that too, and rebuild.
• Now submit the change as a pull request.
• Once merged, we'll all be testing against a newer snapshot build.

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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