rustc: Error messages feel like they're backwards

[rusty-objects]

This code snippet illustrates a problem I've always had with the Rust compiler's error messages:

use std::ops::Deref;

fn foo<Inner: Deref<Target=[u8]>, Outer: Deref<Target=[Inner]>>(buf: Outer) {}

pub fn main() {
    let data = [0_u8];
    foo(&&[&data]);
}

The compiler error is:

error[E0271]: type mismatch resolving `<&&[&[u8; 1]; 1] as std::ops::Deref>::Target == [_]`
 --> src/main.rs:7:5
  |
7 |     foo(&&[&data]);
  |     ^^^ expected reference, found slice
  |
  = note: expected type `&[&[u8; 1]; 1]`
             found type `[_]`
note: required by `foo`
 --> src/main.rs:3:1
  |
3 | fn foo<Inner: Deref<Target=[u8]>, Outer: Deref<Target=[Inner]>>(buf: Outer) {}
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Intuitively, for me, found and expected are swapped. I expect the function to be the point of reference, and therefore the expected value and I expect the call site to be the candidate, and therefore the found value. However it seems reverse. Above you can see the expected type is the call site's &[&[u8; 1]; 1] and the found type is the function's [_]. I this often slows me down when chasing compile errors as I have to stop and mentally reverse my perception about expected and found.

I hesitate to call this a bug, as I think it's a matter of opinion. But it does feel the opposite of intuitive for me.

$ rustc --version
rustc 1.28.0 (9634041f0 2018-07-30)

[Centril]

Not a bug; but I agree that it should be swapped.

[atorstling]

I agree. Came here to report the same type of confusing error message for this code:

#![feature(trait_alias)]

trait F8 = FnOnce() -> u8;

fn higher<T: F8>(t: T) -> u8 {
    t()
}

fn main() {
    higher(|| 3u16);
}

This yields:

higher(|| 3u16);
   |     ^^^^^^ expected u16, found u8

[Centril]

cc @estebank

[estebank]

Current output:

error[E0271]: type mismatch resolving `<&&[&[u8; 1]; 1] as std::ops::Deref>::Target == [_]`
 --> src/main.rs:7:5
  |
3 | fn foo<Inner: Deref<Target=[u8]>, Outer: Deref<Target=[Inner]>>(buf: Outer) {}
  |    ---                                         -------------- required by this bound in `foo`
...
7 |     foo(&&[&data]);
  |     ^^^ expected slice, found `&[&[u8; 1]; 1]`
  |
  = note: expected slice `[_]`
              found type `&[&[u8; 1]; 1]`

error[E0271]: type mismatch resolving `<[closure@src/main.rs:10:12: 10:19] as std::ops::FnOnce<()>>::Output == u8`
  --> src/main.rs:10:5
   |
5  | fn higher<T: F8>(t: T) -> u8 {
   |    ------    -- required by this bound in `higher`
...
10 |     higher(|| 3u16);
   |     ^^^^^^ expected `u8`, found `u16`