Rollup merge of rust-lang#35366 - medzin:E0282, r=jonathandturner

Updated error message E0282

Fixes rust-lang#35312 as part of rust-lang#35233.

r? @GuillaumeGomez

Author: Jonathan Turner

src/librustc/traits/error_reporting.rs

@@ -870,10 +870,12 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
 
 
     fn need_type_info(&self, span: Span, ty: Ty<'tcx>) {
-        span_err!(self.tcx.sess, span, E0282,
-                  "unable to infer enough type information about `{}`; \
-                   type annotations or generic parameter binding required",
-                  ty);
+        let mut err = struct_span_err!(self.tcx.sess, span, E0282,
+                                       "unable to infer enough type information about `{}`",
+                                       ty);
+        err.note("type annotations or generic parameter binding required");
+        err.span_label(span, &format!("cannot infer type for `{}`", ty));
+        err.emit()
     }
 
     fn note_obligation_cause<T>(&self,

src/test/compile-fail/issue-23041.rs

@@ -14,4 +14,6 @@ fn main()
     fn bar(x:i32) ->i32 { 3*x };
     let b:Box<Any> = Box::new(bar as fn(_)->_);
     b.downcast_ref::<fn(_)->_>(); //~ ERROR E0282
+                                  //~| NOTE cannot infer type for `_`
+                                  //~| NOTE type annotations or generic parameter binding required
 }