Hey, I had the exact same WTF moment on a multithreaded C compiler for DOS * in the 90s
The compiler would bug out with an error along the lines "you shouldn't see this error message", add back exactly 1 comment line and it would compile fine.
IIRC the compiler was from a one man band company, and yes up to a point did somehow give you multithreading on DOS but eventually enough unexplained crashes occurred that I refactored my code to be single threaded and then all was good.
Biting the hand that feeds IT
