Early 2000s, compiler authors basically had to guess how types resolved and implement what made most sense. One week did not pass without filing a new kind of i

Early 2000s, compiler authors basically had to guess how types resolved and implement what made most sense. One week did not pass without filing a new kind of internal compiler error to gcc (well, I was lazy so I kept filing to debian). The specs improved immensely in the past 20 years. So much so that you can actually implement the entire grammar from the spec and the order of type resolution is well known. You could cut corners by ignoring every "compiler hint" and optional optimization that is left for the implementation to get things going, then go back and finish those.