I did an experiment a few weeks back as a bit of a litmus test for a new data format my team and I have been working on. I fed the spec documentation into ChatGPT and asked it to write a file reader for it. It spat out a mostly-correct implementation almost immediately, and with some extra coaxing managed to fix the small bugs in it too.

To be fair, it's a very simple format, but it made me feel good about the quality of the documentation.