Auto merge of #42362 - estebank:type, r=arielb1

Show trait method signature when impl differs

When the trait's span is available, it is already being used, add a
`note` for the cases where the span isn't available:

<pre>
error[E0053]: <b>method `fmt` has an incompatible type for trait</b>
  --> $DIR/trait_type.rs:17:4
   |
17 |    fn fmt(&self, x: &str) -> () { }
   |    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ types differ in mutability
   |
   = note: expected type `<b>fn(&MyType, &mut std::fmt::Formatter<'_>) -> std::result::Result<(), std::fmt::Error></b>`
              found type `<b>fn(&MyType, &str)</b>`

error[E0050]: <b>method `fmt` has 1 parameter but the declaration in trait `std::fmt::Display::fmt` has 2</b>
  --> $DIR/trait_type.rs:21:11
   |
21 |    fn fmt(&self) -> () { }
   |           ^^^^^ expected 2 parameters, found 1
   |
   = note: `fmt` from trait: `<b>fn(&Self, &mut std::fmt::Formatter<'_>) -> std::result::Result<(), std::fmt::Error></b>`

error[E0186]: <b>method `fmt` has a `&self` declaration in the trait, but not in the impl</b>
  --> $DIR/trait_type.rs:25:4
   |
25 |    fn fmt() -> () { }
   |    ^^^^^^^^^^^^^^^^^^ expected `&self` in impl
   |
   = note: `fmt` from trait: `<b>fn(&Self, &mut std::fmt::Formatter<'_>) -> std::result::Result<(), std::fmt::Error></b>`

error[E0046]: <b>not all trait items implemented, missing: `fmt`</b>
  --> $DIR/trait_type.rs:28:1
   |
28 | impl std::fmt::Display for MyType4 {}
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ missing `fmt` in implementation
   |
   = note: `fmt` from trait: `<b>fn(&Self, &mut std::fmt::Formatter<'_>) -> std::result::Result<(), std::fmt::Error></b>`
</code></pre>

Fix #28011.

diff --cc src/librustc/ty/mod.rs
Simple merge

diff --cc src/librustc_typeck/check/compare_method.rs
Simple merge

diff --cc src/librustc_typeck/check/mod.rs
Simple merge