I had a bunch of deeply-nested map/flatmap code and it rewrote it into a short pretty for-comprehension, error free. For those that haven't learned those desugaring rules cold, it's a massive help.
The cool thing about GPT is that it understands code contextually and flexibly. I can literally throw it syntax that was developed specifically for a single project, that it's almost certainly never seen before, and as long as it's similar to something it's seen elsewhere, GPT can figure it out. There's no way you're getting that from an IDE feature.
I got GPT 3.5 to transform a (simple) function into return-early style a few days ago. It didn't quite get it right, but it got the correct idea. I did this by typing "Transform this code into return-early style." With an IDE feature, I'd have to hope the developers had heard of and cared about return-early style in the first place, and then that their tool was powerful enough to realize when and how to apply it. (Highly unlikely, IMO.)
edit: In other words,
> Aren't there a relatively small, finite number of these cases that would cover a large percent of typical transformations, and do so with 100% reliability?
I believe the opposite is the case.
It's like a barely-got-a-passing-grade coding bootcamp grad with above-average-for-that-cohort Googling skills and a problem with dishonesty. Sometimes that's helpful, a little, but mostly it's a time-wasting distraction.
What it can revolutionize in its current form is mainly limited to high-automation bullshit industries. Spammers, scammers, certain kinds of marketing content that's currently farmed out to the lowest bidder, astruturfed media campaigns, targeted mass propaganda. That part, I think will be big, but will be entirely bad for society. Unless it makes another leap forward at least as big as the last one, programming's nowhere near being threatened yet, nor, even, is most writing that's not already bullshit-heavy (though it'll help make normal writing somewhat more efficient, probably)