Use convert::Infallible instead of never in the blanket TryFrom impl

Author: SimonSapin

src/libcore/convert.rs

@@ -467,7 +467,7 @@ 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 U: Into<T> {
-    type Error = !;
+    type Error = Infallible;
 
     fn try_from(value: U) -> Result<Self, Self::Error> {
         Ok(U::into(value))

src/libcore/num/mod.rs

@@ -2,7 +2,7 @@
 
 #![stable(feature = "rust1", since = "1.0.0")]
 
-use convert::TryFrom;
+use convert::{TryFrom, Infallible};
 use fmt;
 use intrinsics;
 use mem;
@@ -4531,9 +4531,19 @@ impl fmt::Display for TryFromIntError {
 }
 
 #[unstable(feature = "try_from", issue = "33417")]
+impl From<Infallible> for TryFromIntError {
+    fn from(x: Infallible) -> TryFromIntError {
+        match x {}
+    }
+}
+
+#[unstable(feature = "never_type", issue = "35121")]
 impl From<!> for TryFromIntError {
     fn from(never: !) -> TryFromIntError {
-        never
+        // Match rather than coerce to make sure that code like
+        // `From<Infallible> for TryFromIntError` above will keep working
+        // when `Infallible` becomes an alias to `!`.
+        match never {}
     }
 }
 

src/test/run-pass/try_from.rs

@@ -6,7 +6,7 @@
 
 #![feature(try_from, never_type)]
 
-use std::convert::TryInto;
+use std::convert::{TryInto, Infallible};
 
 struct Foo<T> {
     t: T,
@@ -32,6 +32,6 @@ impl<T> Into<Vec<T>> for Foo<T> {
 }
 
 pub fn main() {
-    let _: Result<Vec<i32>, !> = Foo { t: 10 }.try_into();
+    let _: Result<Vec<i32>, Infallible> = Foo { t: 10 }.try_into();
 }