Type checker depends on generic type bounds too aggressively

[eefriedman]

fn f<T>(t:T) -> Box<T> { t.into() } // accepted
fn f2<T: Into<u32>>(t:T) -> Box<T> { t.into() } // error
fn f3<T: Into<u32>>(t:T) -> Box<T> { <T as Into<Box<T>>>::into(t) } // accepted

This seems counterintuitive: adding the Into<u32> suppresses the other implementations of Into<...>.

[hanna-kruppe]

Seems related or perhaps even identical to #24066

[Mark-Simulacrum]

All three forms now compile, so I'm going to close.

[Mark-Simulacrum]

Not again, I tested in the wrong directory. Re-opening....

[Mark-Simulacrum]

I'm going to close this in favor of #24066. That contains the same problem (masking other impls with a where clause).