Back in the days of good old Delphi IDE I found some cool addon which had some very cool feature. It was using machine learning to detect some repetitive actions. Like when I get code:

  var poo = 
    [1,
     2,
     3,
     4];

and I start changing 1 to '1', 2 -> '2', then the addon all of sudden suggest me completion of other two cells.

It was amazing, too bad this feature did not come back in any of modern IDEs.

I love IntelliJ autocompletion while writing Java code, it increases my productivity so much that I can't imagine coding without it, however it could be better, always:)