Add lossless integer conversion by reference

library/core/src/convert/num.rs

@@ -55,6 +55,8 @@ macro_rules! impl_from {
                 small as Self
             }
         }
+
+        impl_from_ref! { $Small, $Large }
     };
     ($Small: ty, $Large: ty, #[$attr:meta]) => {
         impl_from!($Small,
@@ -68,6 +70,21 @@ macro_rules! impl_from {
     }
 }
 
+macro_rules! impl_from_ref {
+    ($Small: ty, $Large: ty) => {
+        #[stable(feature = "num_from_num_ref", since = "1.60.0")]
+        #[rustc_const_unstable(feature = "const_num_from_num", issue = "87852")]
+        #[doc = concat!("Converts `&", stringify!($Small), "` to `", stringify!($Large), "` losslessly.")]
+        #[doc = concat!("See the documentation of the `", stringify!($Small), "` to `", stringify!($Large), "` conversion.")]
+        impl const From<&$Small> for $Large {
+            #[inline]
+            fn from(small: &$Small) -> Self {
+                From::from(*small)
+            }
+        }
+    }
+}
+
 macro_rules! impl_from_bool {
     ($target: ty, #[$attr:meta]) => {
         impl_from!(bool, $target, #[$attr], concat!("Converts a `bool` to a `",
@@ -98,30 +115,40 @@ impl_from_bool! { i128, #[stable(feature = "from_bool", since = "1.28.0")] }
 impl_from_bool! { isize, #[stable(feature = "from_bool", since = "1.28.0")] }
 
 // Unsigned -> Unsigned
+impl_from_ref! { u8, u8 }
 impl_from! { u8, u16, #[stable(feature = "lossless_int_conv", since = "1.5.0")] }
 impl_from! { u8, u32, #[stable(feature = "lossless_int_conv", since = "1.5.0")] }
 impl_from! { u8, u64, #[stable(feature = "lossless_int_conv", since = "1.5.0")] }
 impl_from! { u8, u128, #[stable(feature = "i128", since = "1.26.0")] }
 impl_from! { u8, usize, #[stable(feature = "lossless_int_conv", since = "1.5.0")] }
+impl_from_ref! { u16, u16 }
 impl_from! { u16, u32, #[stable(feature = "lossless_int_conv", since = "1.5.0")] }
 impl_from! { u16, u64, #[stable(feature = "lossless_int_conv", since = "1.5.0")] }
 impl_from! { u16, u128, #[stable(feature = "i128", since = "1.26.0")] }
+impl_from_ref! { u32, u32 }
 impl_from! { u32, u64, #[stable(feature = "lossless_int_conv", since = "1.5.0")] }
 impl_from! { u32, u128, #[stable(feature = "i128", since = "1.26.0")] }
+impl_from_ref! { u64, u64 }
 impl_from! { u64, u128, #[stable(feature = "i128", since = "1.26.0")] }
+impl_from_ref! { u128, u128 }
 
 // Signed -> Signed
+impl_from_ref! { i8, i8 }
 impl_from! { i8, i16, #[stable(feature = "lossless_int_conv", since = "1.5.0")] }
 impl_from! { i8, i32, #[stable(feature = "lossless_int_conv", since = "1.5.0")] }
 impl_from! { i8, i64, #[stable(feature = "lossless_int_conv", since = "1.5.0")] }
 impl_from! { i8, i128, #[stable(feature = "i128", since = "1.26.0")] }
 impl_from! { i8, isize, #[stable(feature = "lossless_int_conv", since = "1.5.0")] }
+impl_from_ref! { i16, i16 }
 impl_from! { i16, i32, #[stable(feature = "lossless_int_conv", since = "1.5.0")] }
 impl_from! { i16, i64, #[stable(feature = "lossless_int_conv", since = "1.5.0")] }
 impl_from! { i16, i128, #[stable(feature = "i128", since = "1.26.0")] }
+impl_from_ref! { i32, i32 }
 impl_from! { i32, i64, #[stable(feature = "lossless_int_conv", since = "1.5.0")] }
 impl_from! { i32, i128, #[stable(feature = "i128", since = "1.26.0")] }
+impl_from_ref! { i64, i64 }
 impl_from! { i64, i128, #[stable(feature = "i128", since = "1.26.0")] }
+impl_from_ref! { i128, i128 }
 
 // Unsigned -> Signed
 impl_from! { u8, i16, #[stable(feature = "lossless_int_conv", since = "1.5.0")] }
@@ -403,6 +430,8 @@ macro_rules! nzint_impl_from {
                 }
             }
         }
+
+        impl_from_ref! { $Small, $Large }
     };
     ($Small: ty, $Large: ty, #[$attr:meta]) => {
         nzint_impl_from!($Small,
@@ -417,31 +446,39 @@ macro_rules! nzint_impl_from {
 }
 
 // Non-zero Unsigned -> Non-zero Unsigned
+impl_from_ref! { NonZeroU8, NonZeroU8 }
 nzint_impl_from! { NonZeroU8, NonZeroU16, #[stable(feature = "nz_int_conv", since = "1.41.0")] }
 nzint_impl_from! { NonZeroU8, NonZeroU32, #[stable(feature = "nz_int_conv", since = "1.41.0")] }
 nzint_impl_from! { NonZeroU8, NonZeroU64, #[stable(feature = "nz_int_conv", since = "1.41.0")] }
 nzint_impl_from! { NonZeroU8, NonZeroU128, #[stable(feature = "nz_int_conv", since = "1.41.0")] }
 nzint_impl_from! { NonZeroU8, NonZeroUsize, #[stable(feature = "nz_int_conv", since = "1.41.0")] }
+impl_from_ref! { NonZeroU16, NonZeroU16 }
 nzint_impl_from! { NonZeroU16, NonZeroU32, #[stable(feature = "nz_int_conv", since = "1.41.0")] }
 nzint_impl_from! { NonZeroU16, NonZeroU64, #[stable(feature = "nz_int_conv", since = "1.41.0")] }
 nzint_impl_from! { NonZeroU16, NonZeroU128, #[stable(feature = "nz_int_conv", since = "1.41.0")] }
 nzint_impl_from! { NonZeroU16, NonZeroUsize, #[stable(feature = "nz_int_conv", since = "1.41.0")] }
+impl_from_ref! { NonZeroU32, NonZeroU32 }
 nzint_impl_from! { NonZeroU32, NonZeroU64, #[stable(feature = "nz_int_conv", since = "1.41.0")] }
 nzint_impl_from! { NonZeroU32, NonZeroU128, #[stable(feature = "nz_int_conv", since = "1.41.0")] }
+impl_from_ref! { NonZeroU64, NonZeroU64 }
 nzint_impl_from! { NonZeroU64, NonZeroU128, #[stable(feature = "nz_int_conv", since = "1.41.0")] }
 
 // Non-zero Signed -> Non-zero Signed
+impl_from_ref! { NonZeroI8, NonZeroI8 }
 nzint_impl_from! { NonZeroI8, NonZeroI16, #[stable(feature = "nz_int_conv", since = "1.41.0")] }
 nzint_impl_from! { NonZeroI8, NonZeroI32, #[stable(feature = "nz_int_conv", since = "1.41.0")] }
 nzint_impl_from! { NonZeroI8, NonZeroI64, #[stable(feature = "nz_int_conv", since = "1.41.0")] }
 nzint_impl_from! { NonZeroI8, NonZeroI128, #[stable(feature = "nz_int_conv", since = "1.41.0")] }
 nzint_impl_from! { NonZeroI8, NonZeroIsize, #[stable(feature = "nz_int_conv", since = "1.41.0")] }
+impl_from_ref! { NonZeroI16, NonZeroI16 }
 nzint_impl_from! { NonZeroI16, NonZeroI32, #[stable(feature = "nz_int_conv", since = "1.41.0")] }
 nzint_impl_from! { NonZeroI16, NonZeroI64, #[stable(feature = "nz_int_conv", since = "1.41.0")] }
 nzint_impl_from! { NonZeroI16, NonZeroI128, #[stable(feature = "nz_int_conv", since = "1.41.0")] }
 nzint_impl_from! { NonZeroI16, NonZeroIsize, #[stable(feature = "nz_int_conv", since = "1.41.0")] }
+impl_from_ref! { NonZeroI32, NonZeroI32 }
 nzint_impl_from! { NonZeroI32, NonZeroI64, #[stable(feature = "nz_int_conv", since = "1.41.0")] }
 nzint_impl_from! { NonZeroI32, NonZeroI128, #[stable(feature = "nz_int_conv", since = "1.41.0")] }
+impl_from_ref! { NonZeroI64, NonZeroI64 }
 nzint_impl_from! { NonZeroI64, NonZeroI128, #[stable(feature = "nz_int_conv", since = "1.41.0")] }
 
 // NonZero UnSigned -> Non-zero Signed

library/core/src/lib.rs

@@ -104,6 +104,7 @@
 #![feature(const_bigint_helper_methods)]
 #![feature(const_caller_location)]
 #![feature(const_cell_into_inner)]
+#![feature(const_convert)]
 #![feature(const_discriminant)]
 #![cfg_attr(not(bootstrap), feature(const_eval_select))]
 #![feature(const_float_bits_conv)]

src/test/ui/num-from-num-ref/allowed.rs

@@ -0,0 +1,35 @@
+// check-pass
+
+fn main () {
+    // same size, signed
+    let _: i8 = From::from(&1_i8);
+    let _: i16 = From::from(&1_i16);
+    let _: i32 = From::from(&1_i32);
+    let _: i64 = From::from(&1_i64);
+    let _: i128 = From::from(&1_i128);
+
+    // same size, unsigned
+    let _: u8 = From::from(&1_u8);
+    let _: u16 = From::from(&1_u16);
+    let _: u32 = From::from(&1_u32);
+    let _: u64 = From::from(&1_u64);
+    let _: u128 = From::from(&1_u128);
+
+    // smaller, signed
+    let _: i16 = From::from(&1_i8);
+    let _: i32 = From::from(&1_i16);
+    let _: i64 = From::from(&1_i32);
+    let _: i128 = From::from(&1_i64);
+
+    // smaller, unsigned
+    let _: u16 = From::from(&1_u8);
+    let _: u32 = From::from(&1_u16);
+    let _: u64 = From::from(&1_u32);
+    let _: u128 = From::from(&1_u64);
+
+    // mixed signs
+    let _: i16 = From::from(&1_u8);
+    let _: i32 = From::from(&1_u16);
+    let _: i64 = From::from(&1_u32);
+    let _: i128 = From::from(&1_u64);
+}

src/test/ui/num-from-num-ref/illegal.rs

@@ -0,0 +1,22 @@
+// Check that conversions by reference which are not lossless are not implemented.
+
+fn main () {
+    // larger, signed
+    let _: i8 = From::from(&1_i16); //~ ERROR
+    let _: i16 = From::from(&1_i32); //~ ERROR
+    let _: i32 = From::from(&1_i64); //~ ERROR
+    let _: i64 = From::from(&1_i128); //~ ERROR
+
+    // larger, unsigned
+    let _: u8 = From::from(&1_u16); //~ ERROR
+    let _: u16 = From::from(&1_u32); //~ ERROR
+    let _: u32 = From::from(&1_u64); //~ ERROR
+    let _: u64 = From::from(&1_u128); //~ ERROR
+
+    // mixed signs
+    let _: i8 = From::from(&1_u8); //~ ERROR
+    let _: u16 = From::from(&1_i8); //~ ERROR
+    let _: i32 = From::from(&1_u32); //~ ERROR
+    let _: u64 = From::from(&1_i32); //~ ERROR
+    let _: i128 = From::from(&1_u128); //~ ERROR
+}