Update E0392 to new error format

Author: canova

src/librustc_typeck/check/wfcheck.rs

@@ -653,8 +653,10 @@ fn error_380(ccx: &CrateCtxt, span: Span) {
 
 fn error_392<'a, 'tcx>(ccx: &CrateCtxt<'a, 'tcx>, span: Span, param_name: ast::Name)
                        -> DiagnosticBuilder<'tcx> {
-    struct_span_err!(ccx.tcx.sess, span, E0392,
-                     "parameter `{}` is never used", param_name)
+    let mut err = struct_span_err!(ccx.tcx.sess, span, E0392,
+                  "parameter `{}` is never used", param_name);
+    err.span_label(span, &format!("unused type parameter"));
+    err
 }
 
 fn error_194(tcx: TyCtxt, span: Span, name: ast::Name) {

src/test/compile-fail/E0392.rs

@@ -9,6 +9,7 @@
 // except according to those terms.
 
 enum Foo<T> { Bar } //~ ERROR E0392
+                    //~| NOTE unused type parameter
 
 fn main() {
 }