Emacs buildpack for Heroku

This is a Heroku buildpack which installs GNU Emacs for use on server applications such as GNU ELPA Mirror.

Usage

To install Emacs for your Heroku app called <myapp>, run:

$ heroku buildpacks:add                                        \
    https://github.com/radian-software/heroku-buildpack-emacs  \
    -a <myapp>

After the next time you deploy your app, emacs will be available on the PATH.

Configuration

Supported versions of Emacs are:

• 25.2 (for heroku-20 and below)
• 25.3 (for heroku-20 and below)
• 26.1 (for heroku-20 and below)
• 26.2 (for heroku-20 and below)
• 26.3 (for heroku-20 and below)
• 27.1 (for heroku-20 and below)
• 27.2 (for heroku-20 and below)
• 28.1

By default the latest supported version will be selected. You can force a specific version to be selected by setting EMACS_VERSION appropriately in the app config (e.g. heroku config:set EMACS_VERSION 27.2).

Supported versions of the Heroku runtime are:

• heroku-18
• heroku-20
• heroku-22

This is detected automatically during buildpack processing and cannot be overridden.

How does it work?

We have a script build.bash in this repository which does the following things:

• Pull the latest version of the Heroku runtime base Docker image.
  • Run using --security-opt seccomp=unconfined to support pre-27.1 versions of Emacs that use some very sketchy OS features as part of the build process.
• Download the Emacs source code into it.
• Compile and install it with a prefix of /app/emacs.
• Create a tarball of that installation and export it outside the container.

Then I manually do the following:

• Create an empty tag in this repo named heroku-VER-emacs-VER (where the versions are for the Heroku stack and Emacs respectively).
• Upload the tarball to that tag as a GitHub Release. Provided I follow the existing naming convention, this is picked up automatically by the buildpack.

Why not...?

• Install using heroku-buildpack-apt: Because it doesn't work, which is because Emacs installations are not relocatable.
• Build from source at deployment time: Because we can't use Docker when executing a buildpack.

Why is only Emacs 28 supported in heroku-22?

Because this:

sysdep.c:1821:22: error: variably modified 'sigsegv_stack' at file scope
 1821 | static unsigned char sigsegv_stack[SIGSTKSZ];
      |                      ^~~~~~~~~~~~~

If you know how to resolve the compilation error, let me know and I'd be happy to compile prior versions of Emacs for heroku-22.

History

This repository was originally forked from kosh04/heroku-buildpack-emacs, but today literally none of the original code or documentation remains, so I marked it as a source repository and added a license.