Auto merge of #32513 - japaric:try-test, r=alexcrichton

add regression test for try!

Our widespread internal use of `try` was like a regression test. Now that most of `try!`s have been converted to `?`, lets add a proper regression test.

cc @bstrie

src/test/run-pass/try-macro.rs

@@ -0,0 +1,57 @@
+// Copyright 2016 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.
+
+use std::num::{ParseFloatError, ParseIntError};
+
+fn main() {
+    assert_eq!(simple(), Ok(1));
+    assert_eq!(nested(), Ok(2));
+    assert_eq!(merge_ok(), Ok(3.0));
+    assert_eq!(merge_int_err(), Err(Error::Int));
+    assert_eq!(merge_float_err(), Err(Error::Float));
+}
+
+fn simple() -> Result<i32, ParseIntError> {
+    Ok(try!("1".parse()))
+}
+
+fn nested() -> Result<i32, ParseIntError> {
+    Ok(try!(try!("2".parse::<i32>()).to_string().parse::<i32>()))
+}
+
+fn merge_ok() -> Result<f32, Error> {
+    Ok(try!("1".parse::<i32>()) as f32 + try!("2.0".parse::<f32>()))
+}
+
+fn merge_int_err() -> Result<f32, Error> {
+    Ok(try!("a".parse::<i32>()) as f32 + try!("2.0".parse::<f32>()))
+}
+
+fn merge_float_err() -> Result<f32, Error> {
+    Ok(try!("1".parse::<i32>()) as f32 + try!("b".parse::<f32>()))
+}
+
+#[derive(Debug, PartialEq)]
+enum Error {
+    Int,
+    Float,
+}
+
+impl From<ParseIntError> for Error {
+    fn from(_: ParseIntError) -> Error {
+        Error::Int
+    }
+}
+
+impl From<ParseFloatError> for Error {
+    fn from(_: ParseFloatError) -> Error {
+        Error::Float
+    }
+}

src/test/run-pass/try-operator-hygiene.rs

@@ -12,7 +12,7 @@
 //
 // match expr {
 //     Ok(val) => val,
-//     Err(err) => return From::from(err),
+//     Err(err) => return Err(From::from(err)),
 // }
 //
 // This test verifies that the expansion is hygienic, i.e. it's not affected by other `val` and