Trait object coercions do not distribute over pattern bindings

[Kimundi]

This works:

trait Bar{} 
impl Bar for uint {}; 
let (a, b) = (~5u as ~Bar, ~9u as ~Bar); 

let c: &Bar = a; 
let d: &Bar = b; 

This doesn't:

trait Bar{} 
impl Bar for uint {}

fn main() {
    let (a, b) = (~5u as ~Bar, ~9u as ~Bar); 
    let (c, d): (&Bar, &Bar) = (a, b);
}


error: mismatched types: expected `(&main::Bar<no-bounds>,&main::Bar<no-bounds>)` but found `(~main::Bar:Send,~main::Bar:Send)` (trait storage differs: expected & but found ~)

[nikomatsakis]

This is not specific to trait coercions, but rather any coercion. We could make this work with mild effort. See also #8783, which is related in that it touches same parts of the compiler.

[flaper87]

Visiting for triage. Still valid.

[flaper87]

Triage bump:

This seems to be fixed now:

trait Bar{} 
impl Bar for usize {}
impl Bar for i32 {}

fn main() {
    let (a, b) = (&5u as &Bar, &9u as &Bar); 
    let (c, d): (&Bar, &Bar) = (a, b);


    let (a, b) = (Box::new(5u) as Box<Bar>, Box::new(9u) as Box<Bar>); 
    let (c, d): (&Bar, &Bar) = (&*a, &*b);


    let (c, d): (&Bar, &Bar) = (&5, &9);
}