Add UI tests

src/test/ui/suggestions/try-on-option.rs

@@ -0,0 +1,25 @@
+// Copyright 2017 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(try_trait)]
+
+fn main() {}
+
+fn foo() -> Result<u32, ()> {
+    let x: Option<u32> = None;
+    x?;
+    Ok(22)
+}
+
+fn bar() -> u32 {
+    let x: Option<u32> = None;
+    x?;
+    22
+}

src/test/ui/suggestions/try-on-option.stderr

@@ -0,0 +1,22 @@
+error[E0277]: the trait bound `(): std::convert::From<std::option::NoneError>` is not satisfied
+  --> $DIR/try-on-option.rs:17:5
+   |
+17 |     x?;
+   |     ^^ the trait `std::convert::From<std::option::NoneError>` is not implemented for `()`
+   |
+   = note: required by `std::convert::From::from`
+
+error[E0277]: the `?` operator can only be used in a function that returns `Result` (or another type that implements `std::ops::Try`)
+  --> $DIR/try-on-option.rs:23:5
+   |
+23 |     x?;
+   |     --
+   |     |
+   |     cannot use the `?` operator in a function that returns `u32`
+   |     in this macro invocation
+   |
+   = help: the trait `std::ops::Try` is not implemented for `u32`
+   = note: required by `std::ops::Try::from_error`
+
+error: aborting due to 2 previous errors
+