impl From<Infallible> for TryFromIntError.

src/libcore/num/mod.rs

@@ -12,7 +12,7 @@
 
 #![stable(feature = "rust1", since = "1.0.0")]
 
-use convert::TryFrom;
+use convert::{Infallible, TryFrom};
 use fmt;
 use intrinsics;
 use str::FromStr;
@@ -2503,6 +2503,13 @@ impl fmt::Display for TryFromIntError {
     }
 }
 
+#[unstable(feature = "try_from", issue = "33417")]
+impl From<Infallible> for TryFromIntError {
+    fn from(_: Infallible) -> TryFromIntError {
+        TryFromIntError(())
+    }
+}
+
 // no possible bounds violation
 macro_rules! try_from_unbounded {
     ($source:ty, $($target:ty),*) => {$(

src/libcore/tests/num/mod.rs

@@ -8,10 +8,11 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-use core::convert::TryFrom;
+use core::convert::{TryFrom, TryInto};
 use core::cmp::PartialEq;
 use core::fmt::Debug;
 use core::marker::Copy;
+use core::num::TryFromIntError;
 use core::ops::{Add, Sub, Mul, Div, Rem};
 use core::option::Option;
 use core::option::Option::{Some, None};
@@ -134,6 +135,13 @@ fn test_empty() {
     assert_eq!("".parse::<u8>().ok(), None);
 }
 
+#[test]
+fn test_infallible_try_from_int_error() {
+    let func = |x: i8| -> Result<i32, TryFromIntError> { Ok(x.try_into()?) };
+
+    assert!(func(0).is_ok());
+}
+
 macro_rules! test_impl_from {
     ($fn_name: ident, $Small: ty, $Large: ty) => {
         #[test]