Specialization does not find the default impl

#![feature(specialization)]

struct JsonSerializer;
struct CborSerializer;

fn main() {
    0i32.serialize(&mut CborSerializer);
}

trait Serialize<S: Serializer> {
    fn serialize(&self, &mut S);
}

trait Serializer {}
impl Serializer for JsonSerializer {}
impl Serializer for CborSerializer {}

impl<S: Serializer> Serialize<S> for i32 {
    default fn serialize(&self, _: &mut S) {
        println!("default");
    }
}

impl Serialize<JsonSerializer> for i32 {
    fn serialize(&self, _: &mut JsonSerializer) {
        println!("specialized");
    }
}

Expected:

Compiles and prints out "default". This is the behavior if you comment out the impl Serialize<JsonSerializer> for i32.

Actual:

rustc 1.15.0-nightly (71c06a56a 2016-12-18)
error[E0308]: mismatched types
 --> <anon>:7:20
  |
7 |     0i32.serialize(&mut CborSerializer);
  |                    ^^^^^^^^^^^^^^^^^^^ expected struct `JsonSerializer`, found struct `CborSerializer`
  |
  = note: expected type `&mut JsonSerializer`
  = note:    found type `&mut CborSerializer`

1. #![feature(specialization)]
   
   struct JsonSerializer;
   struct CborSerializer;
   
   fn main() {
       0i32.serialize(&mut CborSerializer);
   }
   
   trait Serialize<S: Serializer> {
       fn serialize(&self, _: &mut S);
   }
   
   trait Serializer {}
   impl Serializer for JsonSerializer {}
   impl Serializer for CborSerializer {}
   
   impl<S: Serializer> Serialize<S> for i32 {
       default fn serialize(&self, _: &mut S) {
           println!("default");
       }
   }
   
   impl Serialize<JsonSerializer> for i32 {
       fn serialize(&self, _: &mut JsonSerializer) {
           println!("specialized");
       }
   }
   

   Expected:

   Compiles and prints out "default". This is the behavior if you comment out the impl Serialize<JsonSerializer> for i32.

   Actual:

   rustc 1.15.0-nightly (71c06a56a 2016-12-18)
   error[E0308]: mismatched types
    --> <anon>:7:20
     |
   7 |     0i32.serialize(&mut CborSerializer);
     |                    ^^^^^^^^^^^^^^^^^^^ expected struct `JsonSerializer`, found struct `CborSerializer`
     |
     = note: expected type `&mut JsonSerializer`
     = note:    found type `&mut CborSerializer`
   

   David Tolnay at 2019-10-28 15:28:20

2. triage: no change

   Maayan Hanin at 2022-10-17 18:55:54