John Gruber at Daring Fireball talks about a problem in SwiftUI-based macOS and iOS apps where undo is completely broken during text editing:

Basic stuff that’s worked reliably for decades — some things that heretofore had worked forever — are dangerously broken. If you’re running MacOS 26 Tahoe, open Journal and make a new dummy entry. Type something like “The quick brown fox.” Then double-click on the word “brown” and delete it. Now invoke Undo.

What you expect is for the word “brown” to reappear. What happens is ... the whole sentence disappears. Gone. Invoke Redo and you only get back to “The quick fox.” The word “brown” is just gone forever. It’s nowhere in the Undo stack. That’s just profoundly fucked up.

I couldn’t believe it, but I reproduced it myself just now on my phone (my backup Tahoe-running Mac is in a closet not responding to pings, I am now assuming out of embarrassment):

Gruber adds:

Apple’s developer message used to be that it was not just easy to develop apps for their platforms, but that it was easy to develop good idiomatically native apps. You got the correct complex behavior — for things like Undo/​Redo — out of the box. That’s still true for AppKit and UIKit, but it’s never been true for SwiftUI, and SwiftUI is now seven years old. That’s too long for any excuses to hold water.

I don’t want to automatically assume that this problem has existed for seven years (vs. being a more recent deterioration), and I don’t know exactly which native apps use SwiftUI, but either way, this reflects very poorly on Apple.

Software engineering typically has some categories of bugs and failures that result in immediate action – a night shift, a war room, “sevs,” and so on. Those are, in my experience, things like:

• the app crashes,
• the site doesn’t load,
• there is data loss.

Depending on what you work on, this list will also likely include security problems, regulatory considerations, privacy-leaking bugs, and so on. In a more mature organization, these are all well documented, but even in early startups there is some shared understanding that some bugs are bigger than life and they take immense priority over pretty much anything else.

At any company, a version of this list needs to exist for front-end and user-experience problems, and undo should be on top of that list. If you break undo, you drop what you’re doing to fix it.