Incidentally, Darklang had this built into the language/editor combo from the start. You can see it in the examples on our youtube, maybe this one: https://www.youtube.com/watch?v=NQpBG9WkGus

To make a long story short, we added features for "incomplete" programs in the language and tools, so that your program was always valid and could not be invalid. It was a reasonable concept, and I think could have been a game changer if AI didn't first change the game.