Readd suggestion in enum variants with incorrect args

Author: estebank

src/librustc_resolve/lib.rs

@@ -2730,6 +2730,18 @@ impl<'a> Resolver<'a> {
                         }
                         return (err, candidates);
                     }
+                    (Def::VariantCtor(_, ctor_kind), _) if ns == ValueNS && is_struct_like(def) => {
+                        let block = match ctor_kind {
+                            CtorKind::Fn => "(/* fields */)",
+                            CtorKind::Fictive => " { /* fields */ }",
+                            def => bug!("found def `{:?}` when looking for a ctor",
+                                        def),
+                        };
+                        err.span_label(span, format!("did you mean `{}{}`?",
+                                                     path_str,
+                                                     block));
+                        return (err, candidates);
+                    }
                     _ => {}
                 }
             }

src/test/ui/resolve/issue-18252.stderr

@@ -2,7 +2,7 @@ error[E0423]: expected function, found struct variant `Foo::Variant`
   --> $DIR/issue-18252.rs:16:13
    |
 16 |     let f = Foo::Variant(42);
-   |             ^^^^^^^^^^^^ not a function
+   |             ^^^^^^^^^^^^ did you mean `Foo::Variant { /* fields */ }`?
 
 error: aborting due to previous error
 

src/test/ui/resolve/issue-19452.stderr

@@ -2,13 +2,13 @@ error[E0423]: expected value, found struct variant `Homura::Madoka`
   --> $DIR/issue-19452.rs:19:18
    |
 19 |     let homura = Homura::Madoka;
-   |                  ^^^^^^^^^^^^^^ not a value
+   |                  ^^^^^^^^^^^^^^ did you mean `Homura::Madoka { /* fields */ }`?
 
 error[E0423]: expected value, found struct variant `issue_19452_aux::Homura::Madoka`
   --> $DIR/issue-19452.rs:22:18
    |
 22 |     let homura = issue_19452_aux::Homura::Madoka;
-   |                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not a value
+   |                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ did you mean `issue_19452_aux::Homura::Madoka { /* fields */ }`?
 
 error: aborting due to 2 previous errors