Update E0446 label with improved wording

Author: Jonathan Turner

src/librustc_privacy/lib.rs

@@ -974,7 +974,7 @@ impl<'a, 'tcx: 'a, 'v> Visitor<'v> for SearchInterfaceForPrivateItemsVisitor<'a,
                                self.old_error_set.contains(&ty.id) {
                                 let mut err = struct_span_err!(self.tcx.sess, ty.span, E0446,
                                           "private type in public interface");
-                                err.span_label(ty.span, &format!("private type can't be public"));
+                                err.span_label(ty.span, &format!("can't leak private type"));
                                 err.emit();
                             } else {
                                 self.tcx.sess.add_lint(lint::builtin::PRIVATE_IN_PUBLIC,

src/test/compile-fail/E0446.rs

@@ -12,7 +12,7 @@ mod Foo {
     struct Bar(u32);
 
     pub fn bar() -> Bar { //~ ERROR E0446
-                          //~| NOTE private type can't be public
+                          //~| NOTE can't leak private type
         Bar(0)
     }
 }