CFE: Improperly failed inference with promoted type parameters

[MichaelRFairhurst]

Here, the call to f should be valid and inferrable as Cloneable<T>.

class Clonable<T> {}                                                                             
class SubClonable<T> extends Clonable<T> {
  T m(T t) => t;  
} 

void f<T extends Clonable<T>>(T object) {
  if (object is SubClonable<T>) {
    f(object);
  }     
}

However it fails in analyzer and CFE. This is the CFE ticket for this issue. (analyzer is #35799)

I can't speak to the CFE's architecture, but in the analyzer codebase object is promoted to type T' extends SubCloneable<T>. So if the analyzer attempts to infer SubClonable<T> for T in f(object), then that will fail. However, it should be possible to infer Clonable, which in fact works when typed explicitly.

May be related to #35100

[bwilkerson]

analyzer's technique of replacing the bounds came up in a discussion yesterday with @leafpetersen.