Yeah I won’t defend it too much, Xcode/SourceKit/etc are clearly written in a way that assumes devs are writing perfectly idiomatic, smell-free code which isn’t very aligned with reality. I’ve more or less got a feel for what makes it grumpy so I don’t trip it up too often any more but it’s annoying on the odd occasion I do.
Xcode also trips on simple type errors and sometimes fails to even provide a line number where the error lies. As someone who just wrote a Swift app after no prior exposure, it's oddly immature in some basic ways after nearly a decade from launch.