From 837dd14de31bd4adc92d962559047e7b449c20a6 Mon Sep 17 00:00:00 2001
From: Michael Sproul <micsproul@gmail.com>
Date: Mon, 10 Nov 2014 19:33:20 -0800
Subject: [PATCH] Add optional messages to the unreachable macro.

Closes #18842.
---
 src/libstd/macros.rs                               | 10 +++++++++-
 src/test/run-fail/unreachable-fmt-msg.rs           | 14 ++++++++++++++
 src/test/run-fail/unreachable-static-msg.rs        | 12 ++++++++++++
 .../{unreachable-macro-fail.rs => unreachable.rs}  |  0
 4 files changed, 35 insertions(+), 1 deletion(-)
 create mode 100644 src/test/run-fail/unreachable-fmt-msg.rs
 create mode 100644 src/test/run-fail/unreachable-static-msg.rs
 rename src/test/run-fail/{unreachable-macro-fail.rs => unreachable.rs} (100%)

diff --git a/src/libstd/macros.rs b/src/libstd/macros.rs
index d82147947de..0c91542e5eb 100644
--- a/src/libstd/macros.rs
+++ b/src/libstd/macros.rs
@@ -211,7 +211,15 @@ macro_rules! debug_assert_eq(
 /// ```
 #[macro_export]
 macro_rules! unreachable(
-    () => (panic!("internal error: entered unreachable code"))
+    () => ({
+        panic!("internal error: entered unreachable code")
+    });
+    ($msg:expr) => ({
+        unreachable!("{}", $msg)
+    });
+    ($fmt:expr, $($arg:tt)*) => ({
+        panic!(concat!("internal error: entered unreachable code: ", $fmt), $($arg)*)
+    });
 )
 
 /// A standardised placeholder for marking unfinished code. It panics with the
diff --git a/src/test/run-fail/unreachable-fmt-msg.rs b/src/test/run-fail/unreachable-fmt-msg.rs
new file mode 100644
index 00000000000..f005fa4476c
--- /dev/null
+++ b/src/test/run-fail/unreachable-fmt-msg.rs
@@ -0,0 +1,14 @@
+// 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.
+
+// error-pattern:internal error: entered unreachable code: 6 is not prime
+fn main() {
+    unreachable!("{} is not {}", 6u32, "prime");
+}
diff --git a/src/test/run-fail/unreachable-static-msg.rs b/src/test/run-fail/unreachable-static-msg.rs
new file mode 100644
index 00000000000..25894a88541
--- /dev/null
+++ b/src/test/run-fail/unreachable-static-msg.rs
@@ -0,0 +1,12 @@
+// 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.
+
+// error-pattern:internal error: entered unreachable code: uhoh
+fn main() { unreachable!("uhoh") }
diff --git a/src/test/run-fail/unreachable-macro-fail.rs b/src/test/run-fail/unreachable.rs
similarity index 100%
rename from src/test/run-fail/unreachable-macro-fail.rs
rename to src/test/run-fail/unreachable.rs