Auto merge of #44174 - jimmycuadra:try-from-infallible, r=sfackler

Add blanket TryFrom impl when From is implemented.

Adds `impl<T, U> TryFrom<T> for U where U: From<T>`.

Removes `impl<'a, T> TryFrom<&'a str> for T where T: FromStr` (originally added in #40281) due to overlapping impls caused by the new blanket impl. This removal is to be discussed further on the tracking issue for TryFrom.

Refs #33417.

/cc @sfackler, @scottmcm (thank you for the help!), and @aturon

1 files changed, 21 insertions, 29 deletions

diff --git a/src/libcore/num/mod.rs b/src/libcore/num/mod.rs
index bf31deae7a6..85be8a08728 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::TryFrom;
+use convert::{Infallible, TryFrom};
 use fmt;
 use intrinsics;
 use str::FromStr;
@@ -2507,16 +2507,24 @@ 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 = TryFromIntError;
+            type Error = Infallible;
 
             #[inline]
-            fn try_from(u: $source) -> Result<$target, TryFromIntError> {
-                Ok(u as $target)
+            fn try_from(value: $source) -> Result<Self, Self::Error> {
+                Ok(value as $target)
             }
         }
     )*}
@@ -2588,31 +2596,17 @@ macro_rules! rev {
 }
 
 /// intra-sign conversions
-try_from_unbounded!(u8, u8, u16, u32, u64, u128);
-try_from_unbounded!(u16, u16, u32, u64, u128);
-try_from_unbounded!(u32, u32, u64, u128);
-try_from_unbounded!(u64, u64, u128);
-try_from_unbounded!(u128, u128);
 try_from_upper_bounded!(u16, u8);
 try_from_upper_bounded!(u32, u16, u8);
 try_from_upper_bounded!(u64, u32, u16, u8);
 try_from_upper_bounded!(u128, u64, u32, u16, u8);
 
-try_from_unbounded!(i8, i8, i16, i32, i64, i128);
-try_from_unbounded!(i16, i16, i32, i64, i128);
-try_from_unbounded!(i32, i32, i64, i128);
-try_from_unbounded!(i64, i64, i128);
-try_from_unbounded!(i128, i128);
 try_from_both_bounded!(i16, i8);
 try_from_both_bounded!(i32, i16, i8);
 try_from_both_bounded!(i64, i32, i16, i8);
 try_from_both_bounded!(i128, i64, i32, i16, i8);
 
 // unsigned-to-signed
-try_from_unbounded!(u8, i16, i32, i64, i128);
-try_from_unbounded!(u16, i32, i64, i128);
-try_from_unbounded!(u32, i64, i128);
-try_from_unbounded!(u64, i128);
 try_from_upper_bounded!(u8, i8);
 try_from_upper_bounded!(u16, i8, i16);
 try_from_upper_bounded!(u32, i8, i16, i32);
@@ -2631,15 +2625,13 @@ try_from_both_bounded!(i64, u32, u16, u8);
 try_from_both_bounded!(i128, u64, u32, u16, u8);
 
 // usize/isize
-try_from_unbounded!(usize, usize);
 try_from_upper_bounded!(usize, isize);
 try_from_lower_bounded!(isize, usize);
-try_from_unbounded!(isize, isize);
 
 #[cfg(target_pointer_width = "16")]
 mod ptr_try_from_impls {
     use super::TryFromIntError;
-    use convert::TryFrom;
+    use convert::{Infallible, TryFrom};
 
     try_from_upper_bounded!(usize, u8);
     try_from_unbounded!(usize, u16, u32, u64, u128);
@@ -2651,21 +2643,21 @@ mod ptr_try_from_impls {
     try_from_both_bounded!(isize, i8);
     try_from_unbounded!(isize, i16, i32, i64, i128);
 
-    rev!(try_from_unbounded, usize, u8, u16);
+    rev!(try_from_unbounded, usize, u16);
     rev!(try_from_upper_bounded, usize, u32, u64, u128);
     rev!(try_from_lower_bounded, usize, i8, i16);
     rev!(try_from_both_bounded, usize, i32, i64, i128);
 
     rev!(try_from_unbounded, isize, u8);
     rev!(try_from_upper_bounded, isize, u16, u32, u64, u128);
-    rev!(try_from_unbounded, isize, i8, i16);
+    rev!(try_from_unbounded, isize, i16);
     rev!(try_from_both_bounded, isize, i32, i64, i128);
 }
 
 #[cfg(target_pointer_width = "32")]
 mod ptr_try_from_impls {
     use super::TryFromIntError;
-    use convert::TryFrom;
+    use convert::{Infallible, TryFrom};
 
     try_from_upper_bounded!(usize, u8, u16);
     try_from_unbounded!(usize, u32, u64, u128);
@@ -2677,21 +2669,21 @@ mod ptr_try_from_impls {
     try_from_both_bounded!(isize, i8, i16);
     try_from_unbounded!(isize, i32, i64, i128);
 
-    rev!(try_from_unbounded, usize, u8, u16, u32);
+    rev!(try_from_unbounded, usize, u16, u32);
     rev!(try_from_upper_bounded, usize, u64, u128);
     rev!(try_from_lower_bounded, usize, i8, i16, i32);
     rev!(try_from_both_bounded, usize, i64, i128);
 
     rev!(try_from_unbounded, isize, u8, u16);
     rev!(try_from_upper_bounded, isize, u32, u64, u128);
-    rev!(try_from_unbounded, isize, i8, i16, i32);
+    rev!(try_from_unbounded, isize, i16, i32);
     rev!(try_from_both_bounded, isize, i64, i128);
 }
 
 #[cfg(target_pointer_width = "64")]
 mod ptr_try_from_impls {
     use super::TryFromIntError;
-    use convert::TryFrom;
+    use convert::{Infallible, TryFrom};
 
     try_from_upper_bounded!(usize, u8, u16, u32);
     try_from_unbounded!(usize, u64, u128);
@@ -2703,14 +2695,14 @@ mod ptr_try_from_impls {
     try_from_both_bounded!(isize, i8, i16, i32);
     try_from_unbounded!(isize, i64, i128);
 
-    rev!(try_from_unbounded, usize, u8, u16, u32, u64);
+    rev!(try_from_unbounded, usize, u16, u32, u64);
     rev!(try_from_upper_bounded, usize, u128);
     rev!(try_from_lower_bounded, usize, i8, i16, i32, i64);
     rev!(try_from_both_bounded, usize, i128);
 
     rev!(try_from_unbounded, isize, u8, u16, u32);
     rev!(try_from_upper_bounded, isize, u64, u128);
-    rev!(try_from_unbounded, isize, i8, i16, i32, i64);
+    rev!(try_from_unbounded, isize, i16, i32, i64);
     rev!(try_from_both_bounded, isize, i128);
 }