I had some code for the Servant type-level HTTP API library in Haskell that does type-correct property testing on arbitrary web apis without user input, then Servant changed their type structure from a basic list-based format to a record-based one. This was a good change for lots of reasons, but adding the type-level code to make my library (roboservant) compile was absurdly hard, i burned days on it.
GPT 5.something got it in two prompts.