From 3bcdf9eb8cb9b58df2cb860e18db958da6658392 Mon Sep 17 00:00:00 2001
From: Simon Sapin <simon.sapin@exyr.org>
Date: Tue, 29 Sep 2015 05:15:59 +0200
Subject: [PATCH] =?UTF-8?q?Convert=20errors=20in=20libcore=E2=80=99s=20try?=
 =?UTF-8?q?!=20macro=20too.?=
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It is still a separate definition from libstd’s
so that `$crate` expands to `std::` in the latter, not `core::`.

See discussion at https://github.com/rust-lang/rust/issues/27701 .
There is an expectation that `core::foo` is the same as `std::foo`.
We should not have two things with the same name
but subtly different behavior.
---
 src/libcore/macros.rs | 5 ++---
 src/libcore/result.rs | 2 ++
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/src/libcore/macros.rs b/src/libcore/macros.rs
index 25ca33a3d5011..c8f5399a6f7af 100644
--- a/src/libcore/macros.rs
+++ b/src/libcore/macros.rs
@@ -154,16 +154,15 @@ macro_rules! debug_assert_eq {
 }
 
 /// Short circuiting evaluation on Err
-///
-/// `libstd` contains a more general `try!` macro that uses `From<E>`.
 #[macro_export]
 macro_rules! try {
     ($e:expr) => ({
         use $crate::result::Result::{Ok, Err};
+        use $crate::convert::From;
 
         match $e {
             Ok(e) => e,
-            Err(e) => return Err(e),
+            Err(e) => return Err(From::from(e)),
         }
     })
 }
diff --git a/src/libcore/result.rs b/src/libcore/result.rs
index fe0fdb5baa5f3..8b9571e7461d1 100644
--- a/src/libcore/result.rs
+++ b/src/libcore/result.rs
@@ -223,6 +223,8 @@
 //! }
 //! ```
 //!
+//! (The real `try!` macro uses `From<E>` to convert between error types automatically.)
+//!
 //! `try!` is imported by the prelude and is available everywhere, but it can only
 //! be used in functions that return `Result` because of the early return of
 //! `Err` that it provides.