From 4647156985404f07dc2e61eed6f2e24770b339a9 Mon Sep 17 00:00:00 2001
From: Andrew Cann <shum@canndrew.org>
Date: Thu, 15 Mar 2018 12:35:56 +0800
Subject: [PATCH 1/2] replace `convert::Infallible` with `!`

---
 src/libcore/convert.rs | 21 +--------------------
 src/libcore/num/mod.rs | 18 +++++-------------
 src/libstd/error.rs    |  9 ---------
 3 files changed, 6 insertions(+), 42 deletions(-)

diff --git a/src/libcore/convert.rs b/src/libcore/convert.rs
index d3a83dc795c85..a45f1ceab5ab2 100644
--- a/src/libcore/convert.rs
+++ b/src/libcore/convert.rs
@@ -48,25 +48,6 @@
 
 #![stable(feature = "rust1", since = "1.0.0")]
 
-use fmt;
-
-/// A type used as the error type for implementations of fallible conversion
-/// traits in cases where conversions cannot actually fail.
-///
-/// Because `Infallible` has no variants, a value of this type can never exist.
-/// It is used only to satisfy trait signatures that expect an error type, and
-/// signals to both the compiler and the user that the error case is impossible.
-#[unstable(feature = "try_from", issue = "33417")]
-#[derive(Clone, Copy, Debug, Eq, Hash, Ord, PartialEq, PartialOrd)]
-pub enum Infallible {}
-
-#[unstable(feature = "try_from", issue = "33417")]
-impl fmt::Display for Infallible {
-    fn fmt(&self, _: &mut fmt::Formatter) -> fmt::Result {
-        match *self {
-        }
-    }
-}
 /// A cheap reference-to-reference conversion. Used to convert a value to a
 /// reference value within generic code.
 ///
@@ -438,7 +419,7 @@ impl<T, U> TryInto<U> for T where U: TryFrom<T>
 // with an uninhabited error type.
 #[unstable(feature = "try_from", issue = "33417")]
 impl<T, U> TryFrom<U> for T where T: From<U> {
-    type Error = Infallible;
+    type Error = !;
 
     fn try_from(value: U) -> Result<Self, Self::Error> {
         Ok(T::from(value))
diff --git a/src/libcore/num/mod.rs b/src/libcore/num/mod.rs
index 09ab7060d37db..faeb87cf944c9 100644
--- a/src/libcore/num/mod.rs
+++ b/src/libcore/num/mod.rs
@@ -12,7 +12,7 @@
 
 #![stable(feature = "rust1", since = "1.0.0")]
 
-use convert::{Infallible, TryFrom};
+use convert::TryFrom;
 use fmt;
 use intrinsics;
 use ops;
@@ -3595,20 +3595,12 @@ impl fmt::Display for TryFromIntError {
     }
 }
 
-#[unstable(feature = "try_from", issue = "33417")]
-impl From<Infallible> for TryFromIntError {
-    fn from(infallible: Infallible) -> TryFromIntError {
-        match infallible {
-        }
-    }
-}
-
 // no possible bounds violation
 macro_rules! try_from_unbounded {
     ($source:ty, $($target:ty),*) => {$(
         #[unstable(feature = "try_from", issue = "33417")]
         impl TryFrom<$source> for $target {
-            type Error = Infallible;
+            type Error = !;
 
             #[inline]
             fn try_from(value: $source) -> Result<Self, Self::Error> {
@@ -3719,7 +3711,7 @@ try_from_lower_bounded!(isize, usize);
 #[cfg(target_pointer_width = "16")]
 mod ptr_try_from_impls {
     use super::TryFromIntError;
-    use convert::{Infallible, TryFrom};
+    use convert::TryFrom;
 
     try_from_upper_bounded!(usize, u8);
     try_from_unbounded!(usize, u16, u32, u64, u128);
@@ -3745,7 +3737,7 @@ mod ptr_try_from_impls {
 #[cfg(target_pointer_width = "32")]
 mod ptr_try_from_impls {
     use super::TryFromIntError;
-    use convert::{Infallible, TryFrom};
+    use convert::TryFrom;
 
     try_from_upper_bounded!(usize, u8, u16);
     try_from_unbounded!(usize, u32, u64, u128);
@@ -3771,7 +3763,7 @@ mod ptr_try_from_impls {
 #[cfg(target_pointer_width = "64")]
 mod ptr_try_from_impls {
     use super::TryFromIntError;
-    use convert::{Infallible, TryFrom};
+    use convert::TryFrom;
 
     try_from_upper_bounded!(usize, u8, u16, u32);
     try_from_unbounded!(usize, u64, u128);
diff --git a/src/libstd/error.rs b/src/libstd/error.rs
index f8dbe193fed27..79bb6af168fa0 100644
--- a/src/libstd/error.rs
+++ b/src/libstd/error.rs
@@ -56,7 +56,6 @@ use any::TypeId;
 use borrow::Cow;
 use cell;
 use char;
-use convert;
 use core::array;
 use fmt::{self, Debug, Display};
 use mem::transmute;
@@ -371,14 +370,6 @@ impl Error for char::ParseCharError {
     }
 }
 
-#[unstable(feature = "try_from", issue = "33417")]
-impl Error for convert::Infallible {
-    fn description(&self) -> &str {
-        match *self {
-        }
-    }
-}
-
 // copied from any.rs
 impl Error + 'static {
     /// Returns true if the boxed type is the same as `T`

From 15bab452f30ce6cb67a849f13e9de80586a8b180 Mon Sep 17 00:00:00 2001
From: Andrew Cann <shum@canndrew.org>
Date: Thu, 15 Mar 2018 14:14:48 +0800
Subject: [PATCH 2/2] Add From<!> for TryFromIntError

---
 src/libcore/num/mod.rs | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/src/libcore/num/mod.rs b/src/libcore/num/mod.rs
index faeb87cf944c9..4583e45bb12eb 100644
--- a/src/libcore/num/mod.rs
+++ b/src/libcore/num/mod.rs
@@ -3595,6 +3595,13 @@ impl fmt::Display for TryFromIntError {
     }
 }
 
+#[unstable(feature = "try_from", issue = "33417")]
+impl From<!> for TryFromIntError {
+    fn from(never: !) -> TryFromIntError {
+        never
+    }
+}
+
 // no possible bounds violation
 macro_rules! try_from_unbounded {
     ($source:ty, $($target:ty),*) => {$(