Update E0191 to the new error format

Author: munyari

src/librustc_typeck/astconv.rs

@@ -1194,10 +1194,13 @@ impl<'o, 'gcx: 'tcx, 'tcx> AstConv<'gcx, 'tcx>+'o {
         }
 
         for (trait_def_id, name) in associated_types {
-            span_err!(tcx.sess, span, E0191,
+            struct_span_err!(tcx.sess, span, E0191,
                 "the value of the associated type `{}` (from the trait `{}`) must be specified",
                         name,
-                        tcx.item_path_str(trait_def_id));
+                        tcx.item_path_str(trait_def_id))
+                        .span_label(span, &format!(
+                            "missing associated type `{}` value", name))
+                        .emit();
         }
 
         tcx.mk_trait(object.principal, object.bounds)

src/test/compile-fail/E0191.rs

@@ -13,6 +13,7 @@ trait Trait {
 }
 
 type Foo = Trait; //~ ERROR E0191
+                  //~| NOTE missing associated type `Bar` value
 
 fn main() {
 }

src/test/compile-fail/associated-type-projection-from-multiple-supertraits.rs

@@ -37,6 +37,7 @@ fn dent_object<COLOR>(c: BoxCar<Color=COLOR>) {
     //~| ERROR the value of the associated type `Color` (from the trait `Vehicle`) must be specified
     //~| NOTE could derive from `Vehicle`
     //~| NOTE could derive from `Box`
+    //~| NOTE missing associated type `Color` value
 }
 
 fn paint<C:BoxCar>(c: C, d: C::Color) {