Not true by the time I retired in 2007, but I've got a vague memory of talking to someone on the C++ front-end team some time after that and EDG for IntelliSense being mentioned. So no idea if that's really true or not, and if so, whether that's true today.

I was heavily involved in the first version of C++ IntelliSense, roughly 1997?, and it was all home-grown. It was also a miracle it worked at all. I've blocked out most of the ugly details from my memory, but parsing on the fly with a fast enough response time to be useful in the face of incomplete information about which #if branches to take and, especially, template definitions was a tower of heuristics and hacks that barely held together. Things are much better nowadays with more horsepower available to replace those heuristics.