Show trait method signature when impl differs

[estebank]

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

error[E0053]: method `fmt` has an incompatible type for trait
--> $DIR/trait_type.rs:17:4
|
17 | fn fmt(&self, x: &str) -> () { }
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ types differ in mutability
|
= note: expected type `fn(&MyType, &mut std::fmt::Formatter<'_>) -> std::result::Result<(), std::fmt::Error>`
found type `fn(&MyType, &str)`
error[E0050]: method `fmt` has 1 parameter but the declaration in trait `std::fmt::Display::fmt` has 2
--> $DIR/trait_type.rs:21:11
|
21 | fn fmt(&self) -> () { }
| ^^^^^ expected 2 parameters, found 1
|
= note: `fmt` from trait: `fn(&Self, &mut std::fmt::Formatter<'_>) -> std::result::Result<(), std::fmt::Error>`
error[E0186]: method `fmt` has a `&self` declaration in the trait, but not in the impl
--> $DIR/trait_type.rs:25:4
|
25 | fn fmt() -> () { }
| ^^^^^^^^^^^^^^^^^^ expected `&self` in impl
|
= note: `fmt` from trait: `fn(&Self, &mut std::fmt::Formatter<'_>) -> std::result::Result<(), std::fmt::Error>`
error[E0046]: not all trait items implemented, missing: `fmt`
--> $DIR/trait_type.rs:28:1
|
28 | impl std::fmt::Display for MyType4 {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ missing `fmt` in implementation
|
= note: `fmt` from trait: `fn(&Self, &mut std::fmt::Formatter<'_>) -> std::result::Result<(), std::fmt::Error>`

Fix#28011.

[rust-highfive]

r? @arielb1

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[shepmaster]

Thanks @estebank ! We'll get a wonderful reviewer like @arielb1 or someone equally awesome on the case.

[arielb1]

why the .0? It looks like a skip_binder that makes functions show as fn(&Self) rather than for<'a> fn(&'a Self). Could it be changed to skip_binder?

[arielb1]

Nice! r+ with skip_binder and comment instead of .0 (yes I know the .0 is in the original).

[Mark-Simulacrum]

@bors r=arielb1

[bors]

📌 Commit 98885c5 has been approved by arielb1

[arielb1]

@bors r-

with skip_binder and comment instead of .0

There should be comments for all skip_binder calls. For example, here we would want

pubfnsignature<'a,'tcx>(&self,tcx:&TyCtxt<'a,'tcx,'tcx>) -> String{matchself.kind{
ty::AssociatedKind::Method => {format!("{}",// We skip the binder here because the binder would deanonymize all// late-bound regions, and we don't want method signatures to show up// `as for<'r> fn(&'r MyType)`. Pretty-printing handles late-bound// regions just fine, showing `fn(&MyType)`.
tcx.type_of(self.def_id).fn_sig().skip_binder())}
ty::AssociatedKind::Type => format!("type {};",self.name.to_string()),
ty::AssociatedKind::Const => {format!("const {}: {:?};",self.name.to_string(), tcx.type_of(self.def_id))}}
+ }

[estebank]

@arielb1 forgot about the comment. Added the one proposed.

@bors r=arielb1

[bors]

📌 Commit e324919 has been approved by arielb1

[bors]

⌛ Testing commit e324919 with merge 0418fa9...

[bors]

☀️ Test successful - status-appveyor, status-travis
Approved by: arielb1
Pushing 0418fa9 to master...