Add tests for the parsing of + and the error messages if people get it wrong.

Fixes #18772.

src/test/compile-fail/hrtb-precedence-of-plus-error-message.rs

@@ -0,0 +1,35 @@
+// 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.
+
+#![feature(unboxed_closures)]
+
+// Test that we suggest the correct parentheses
+
+trait Bar {
+    fn dummy(&self) { }
+}
+
+struct Foo<'a> {
+    a: &'a Bar+'a,
+        //~^ ERROR E0171
+        //~^^ NOTE perhaps you meant `&'a (Bar + 'a)`?
+
+    b: &'a mut Bar+'a,
+        //~^ ERROR E0171
+        //~^^ NOTE perhaps you meant `&'a mut (Bar + 'a)`?
+
+    c: Box<Bar+'a>, // OK, no paren needed in this context
+
+    d: fn() -> Bar+'a,
+        //~^ ERROR E0171
+        //~^^ NOTE perhaps you forgot parentheses
+}
+
+fn main() { }

src/test/run-pass/hrtb-precedence-of-plus-where-clause.rs

@@ -0,0 +1,27 @@
+// 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.
+
+#![feature(unboxed_closures)]
+
+// Test that `F : Fn(int) -> int + Send` is interpreted as two
+// distinct bounds on `F`.
+
+fn foo<F>(f: F)
+    where F : FnOnce(int) -> int + Send
+{
+    bar(f);
+    baz(f);
+}
+
+fn bar<F:Send>(f: F) { }
+
+fn baz<F:FnOnce(int) -> int>(f: F) { }
+
+fn main() {}

src/test/run-pass/hrtb-precedence-of-plus.rs

@@ -0,0 +1,21 @@
+// 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.
+
+#![feature(unboxed_closures)]
+
+// Test that `Fn(int) -> int + 'static` parses as `(Fn(int) -> int) +
+// 'static` and not `Fn(int) -> (int + 'static)`. The latter would
+// cause a compilation error. Issue #18772.
+
+fn adder(y: int) -> Box<Fn(int) -> int + 'static> {
+    box move |&: x| y + x
+}
+
+fn main() {}