[sillysaurus3]

One that fixes parentheses that I left off or automatically fixes typos in variable names or function calls.

Webstorm can do some of what you mention:

https://news.ycombinator.com/item?id=15514285

https://news.ycombinator.com/item?id=15638652

One that knows to keep things DRY and creates a function for me when it sees the same similar code written twice.

Unfortunately this is "sufficiently smart compiler" territory. I'd love to be wrong about that though.