Rollup merge of #35355 - shri3k:E0046, r=jonathandturner

Updates compiler error E0046 with new format

Addresses #35209 as part of #35233.
r? @jonathandturner

I've repeated the following in my code. If this is something not desirable then let me know if there's any process to make this any cleaner. Thank you.
```rust
missing_items.iter()
    .map(|name| name.to_string())
     .collect::<Vec<_>>().join("`, `"))
```

src/librustc_typeck/check/mod.rs

@@ -1136,11 +1136,16 @@ fn check_impl_items_against_trait<'a, 'tcx>(ccx: &CrateCtxt<'a, 'tcx>,
     }
 
     if !missing_items.is_empty() {
-        span_err!(tcx.sess, impl_span, E0046,
+        struct_span_err!(tcx.sess, impl_span, E0046,
             "not all trait items implemented, missing: `{}`",
             missing_items.iter()
                   .map(|name| name.to_string())
                   .collect::<Vec<_>>().join("`, `"))
+            .span_label(impl_span, &format!("missing `{}` in implementation",
+                missing_items.iter()
+                    .map(|name| name.to_string())
+                    .collect::<Vec<_>>().join("`, `"))
+            ).emit();
     }
 
     if !invalidated_items.is_empty() {

src/test/compile-fail/E0046.rs

@@ -14,7 +14,9 @@ trait Foo {
 
 struct Bar;
 
-impl Foo for Bar {} //~ ERROR E0046
+impl Foo for Bar {}
+//~^ ERROR E0046
+//~| NOTE missing `foo` in implementation
 
 fn main() {
 }

src/test/compile-fail/impl-wrong-item-for-trait.rs

@@ -21,6 +21,7 @@ pub struct FooConstForMethod;
 
 impl Foo for FooConstForMethod {
     //~^ ERROR E0046
+    //~| NOTE missing `bar` in implementation
     const bar: u64 = 1;
     //~^ ERROR E0323
     //~| NOTE does not match trait
@@ -31,6 +32,7 @@ pub struct FooMethodForConst;
 
 impl Foo for FooMethodForConst {
     //~^ ERROR E0046
+    //~| NOTE missing `MY_CONST` in implementation
     fn bar(&self) {}
     fn MY_CONST() {}
     //~^ ERROR E0324
@@ -41,6 +43,7 @@ pub struct FooTypeForMethod;
 
 impl Foo for FooTypeForMethod {
     //~^ ERROR E0046
+    //~| NOTE missing `bar` in implementation
     type bar = u64;
     //~^ ERROR E0325
     //~| NOTE does not match trait

src/test/compile-fail/issue-23729.rs

@@ -18,7 +18,8 @@ fn main() {
         }
 
         impl Iterator for Recurrence {
-            //~^ ERROR not all trait items implemented, missing: `Item` [E0046]
+            //~^ ERROR E0046
+            //~| NOTE missing `Item` in implementation
             #[inline]
             fn next(&mut self) -> Option<u64> {
                 if self.pos < 2 {

src/test/compile-fail/issue-23827.rs

@@ -34,7 +34,8 @@ impl<C: Component> FnMut<(C,)> for Prototype {
 }
 
 impl<C: Component> FnOnce<(C,)> for Prototype {
-    //~^ ERROR not all trait items implemented, missing: `Output` [E0046]
+    //~^ ERROR E0046
+    //~| NOTE missing `Output` in implementation
     extern "rust-call" fn call_once(self, (comp,): (C,)) -> Prototype {
         Fn::call(&self, (comp,))
     }

src/test/compile-fail/issue-24356.rs

@@ -28,7 +28,8 @@ fn main() {
 
         // Causes ICE
         impl Deref for Thing {
-            //~^ ERROR not all trait items implemented, missing: `Target` [E0046]
+            //~^ ERROR E0046
+            //~| NOTE missing `Target` in implementation
             fn deref(&self) -> i8 { self.0 }
         }