Why does field declaration with duplicated nested type in generic class results in huge source code increase?

Question

Scenario is very rare, but quite simple: you define a generic class, then create a nested class which inherits from outer class and define a associative field (of self type) wit

Answer 1

The core of your question is why Inner.Inner is a different type than Inner. Once you understand that, your observations about compile time and generated IL code size follow easily.

The first thing to note is that when you have this declaration

public class X
{
  public class Y { }
}

There are infinitely many types associated with the name Y. There is one for each generic type argument T, so X.Y is different than X