Rollup merge of rust-lang#49038 - canndrew:replace-infallible-with-never, r=SimonSapin

replace `convert::Infallible` with `!`

Author: kennytm

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))

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;
@@ -3596,10 +3596,9 @@ impl fmt::Display for TryFromIntError {
 }
 
 #[unstable(feature = "try_from", issue = "33417")]
-impl From<Infallible> for TryFromIntError {
-    fn from(infallible: Infallible) -> TryFromIntError {
-        match infallible {
-        }
+impl From<!> for TryFromIntError {
+    fn from(never: !) -> TryFromIntError {
+        never
     }
 }
 
@@ -3608,7 +3607,7 @@ 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 +3718,7 @@ 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 +3744,7 @@ 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 +3770,7 @@ 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);

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`