I just wanted to say I haven't been doing C# dev until as of late, and I forgot how flipping amazing the tooling is. One of the things the C# compiler (which is used for IDE tooling) can do out of the box is it can compile multiple versions of the file (syntax, and symbol resolution included), meaning you can still make sure the statically disabled codepaths are still valid, and all the symbols are consistently available in every feature flag combo.

When something does go wrong, the compiler degrades gracefully, and still can make sense of most of the code.

MS gets a lot of flak (sometimes deservedly so), but they can sometimes also show what a large organization of skilled individuals working under consistent direction is capable of.