Emacs native-comp on macOS: A (mostly) automated build script

TL;DR:

Warning: As of today (26th August, 2020), this works on my machine. Your luck may vary. Use at your own risk.

About ten days ago I got native-comp/gccemacs working in my personal build script which produces a self-contained Emacs.app macOS application.

I highly recommend reading the Native Comp section of the README before doing anything, as it gives some context of what’s needed to make this work, why, and also some config tweaks you will need to make.

After that, it’s basically just:

1. Ensure Xcode and Homebrew are installed.
2. Clone the repo: https://github.com/jimeh/build-emacs-for-macos
3. Run: brew bundle
4. Run: ./build-emacs-for-macos feature/native-comp
5. Check builds directory for a *.tbz archive containing the built Emacs.app.

The long version

I have a hacky build script which produces completely self-contained Emacs.app applications. Every few years I dust it off and update it whenever I start toying with and/or using upcoming features not available in a stable release yet.

I had been using Emacs 27.x builds since around February this year, and around two weeks ago I came across a few posts on r/emacs with instructions for building a native-comp/gccemacs capable version of Emacs for macOS. So I decided to try and get my build script working with it.

I’ve now been using macOS Emacs builds with native-comp support since Monday last week (August 17th) without any issues impacting my day job. For reference the Emacs config I use is available here: https://github.com/jimeh/.emacs.d

The Native Comp section of the README contains a decent bit of useful/important information for how to configure native-comp, and how to work around a few issues.

Also expect high CPU usage for a while after initial launch as it’s native compiling and caching all lisp code that’s been loaded by your config. Progress is printed in the *Async-native-compile-log* buffer. Once it’s finished CPU usage will drop down to normal, and Emacs should be more responsive as all loaded elisp code is now compiled natively.

At the moment I see myself keeping the build script up to date and working for some time, probably even until native-comp hits a stable release for macOS.

Native comp, worth it?

Personally I’m getting massive improvements to overall GUI performance, to the point I’m not sure I’d ever be able to go back to not having native-comp.

Emacs 27.x’s native JSON library already improved lsp-mode’s performance by a large margin, and with native-comp it’s even faster for me now. To the point that its suggestions are so instant they’re actually getting in the way when I try to use and expand snippets from yasnippet. I might need to increase my suggestion delay from 0s.

Also scrolling long buffers with a mouse wheel — despite still being text/line based — is actually a pretty nice and performant experience now, compared to a very slow and sluggish experience to the point I typically preferred C-v and M-v as they don’t lag.

So yes, in my experience, native-comp is definitely worth it.

Updates

• 2020–10–04: The patched gcc Homebrew formula is no longer needed, and instead the script uses the newly released libgccjit formula, along with the standard gcc one.