Add note when trying to use Self as a ctor

Author: estebank

src/librustc_resolve/lib.rs

@@ -898,7 +898,7 @@ impl<'a> LexicalScopeBinding<'a> {
     }
 }
 
-#[derive(Clone)]
+#[derive(Clone, Debug)]
 enum PathResult<'a> {
     Module(Module<'a>),
     NonModule(PathResolution),
@@ -2742,6 +2742,10 @@ impl<'a> Resolver<'a> {
                                                      block));
                         return (err, candidates);
                     }
+                    (Def::SelfTy(_, _), _) if ns == ValueNS && is_struct_like(def) => {
+                        err.note("can't instantiate `Self`, you must use the implemented struct \
+                                  directly");
+                    }
                     _ => {}
                 }
             }

src/test/ui/resolve/tuple-struct-alias.stderr

@@ -3,12 +3,16 @@ error[E0423]: expected function, found self type `Self`
    |
 16 |         let s = Self(0, 1); //~ ERROR expected function
    |                 ^^^^ not a function
+   |
+   = note: can't instantiate `Self`, you must use the implemented struct directly
 
 error[E0532]: expected tuple struct/variant, found self type `Self`
   --> $DIR/tuple-struct-alias.rs:18:13
    |
 18 |             Self(..) => {} //~ ERROR expected tuple struct/variant
    |             ^^^^ not a tuple struct/variant
+   |
+   = note: can't instantiate `Self`, you must use the implemented struct directly
 
 error[E0423]: expected function, found type alias `A`
   --> $DIR/tuple-struct-alias.rs:24:13