libsyntax: don't allow enum structs with no fields

Unit-like structs are written as `struct Foo;`, but we erroneously
accepted `struct Foo();` and took it to mean the same thing. Now we
don't, so use the `struct Foo;` form!

[breaking-change]

1 files changed, 13 insertions, 0 deletions

diff --git a/src/test/compile-fail/struct-no-fields-enumlike.rs b/src/test/compile-fail/struct-no-fields-enumlike.rs
new file mode 100644
index 00000000000..379d310a60b
--- /dev/null
+++ b/src/test/compile-fail/struct-no-fields-enumlike.rs
@@ -0,0 +1,13 @@
+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+struct Foo(); //~ ERROR unit-like struct definition should be written as `struct Foo;`
+
+fn main() {}