Earlier quoted context omitted.
There are, despite the often very aggressive IntelliJ proponents, many areas where Eclipse beats IntelliJ, and incremental compilation is indeed one of the most important. It is also possibly the most important feature in a Java IDE. Ctrl+s and you know the whole codebase is compiled. Go to another file and any code change is available in the code completion (like new or changed methods signatures). Any errors from t…
When's the last time you checked out IntelliJ? It does incremental compilation these days, plus auto-save-and-compile whenever you switch tabs (not just when you save the current tab, which bit me many times in Eclipse; though I haven't used Eclipse in at least four years now), so code completion is immediately updated. I'm pretty sure this has been the case for a few years now.
Given that performance is a recurring topic in the Intellij release notes I conclude that they know they still have issues there and they are slowly looking for ways to make things faster. This is not a solved problem.
Part of this is the Kotlin compiler; part of this is indexing; part of this is simply caching logic.
I recently worked on the Elasticsearch code base in intellij. Fast is not a word I would use to describe that. It's a big code base and it clearly was struggling with it. I know some Elastic developers that still use Eclipse basically for this reason.