Added test case to make sure parsing of += is done correctly.

src/test/parse-fail/trait-plusequal-splitting.rs

@@ -0,0 +1,20 @@
+// Copyright 2018 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.
+
+// compile-flags: -Z parse-only
+// Fixes issue where `+` in generics weren't parsed if they were part of a `+=`.
+
+struct Whitespace<T: Clone + = ()> { t: T }
+struct TokenSplit<T: Clone +=  ()> { t: T }
+
+fn main() {
+}
+
+FAIL //~ ERROR