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")] }

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
+}

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

@@ -0,0 +1,234 @@
+error[E0277]: the trait bound `i8: From<&i16>` is not satisfied
+  --> $DIR/illegal.rs:5:17
+   |
+LL |     let _: i8 = From::from(&1_i16);
+   |                 ^^^^^^^^^^ the trait `From<&i16>` is not implemented for `i8`
+   |
+   = help: the following implementations were found:
+             <i8 as From<&bool>>
+             <i8 as From<&i8>>
+             <i8 as From<NonZeroI8>>
+             <i8 as From<bool>>
+note: required by `from`
+  --> $SRC_DIR/core/src/convert/mod.rs:LL:COL
+   |
+LL |     fn from(_: T) -> Self;
+   |     ^^^^^^^^^^^^^^^^^^^^^^
+
+error[E0277]: the trait bound `i16: From<&i32>` is not satisfied
+  --> $DIR/illegal.rs:6:18
+   |
+LL |     let _: i16 = From::from(&1_i32);
+   |                  ^^^^^^^^^^ the trait `From<&i32>` is not implemented for `i16`
+   |
+   = help: the following implementations were found:
+             <i16 as From<&bool>>
+             <i16 as From<&i16>>
+             <i16 as From<&i8>>
+             <i16 as From<&u8>>
+           and 4 others
+note: required by `from`
+  --> $SRC_DIR/core/src/convert/mod.rs:LL:COL
+   |
+LL |     fn from(_: T) -> Self;
+   |     ^^^^^^^^^^^^^^^^^^^^^^
+
+error[E0277]: the trait bound `i32: From<&i64>` is not satisfied
+  --> $DIR/illegal.rs:7:18
+   |
+LL |     let _: i32 = From::from(&1_i64);
+   |                  ^^^^^^^^^^ the trait `From<&i64>` is not implemented for `i32`
+   |
+   = help: the following implementations were found:
+             <i32 as From<&bool>>
+             <i32 as From<&i16>>
+             <i32 as From<&i32>>
+             <i32 as From<&i8>>
+           and 8 others
+note: required by `from`
+  --> $SRC_DIR/core/src/convert/mod.rs:LL:COL
+   |
+LL |     fn from(_: T) -> Self;
+   |     ^^^^^^^^^^^^^^^^^^^^^^
+
+error[E0277]: the trait bound `i64: From<&i128>` is not satisfied
+  --> $DIR/illegal.rs:8:18
+   |
+LL |     let _: i64 = From::from(&1_i128);
+   |                  ^^^^^^^^^^ the trait `From<&i128>` is not implemented for `i64`
+   |
+   = help: the following implementations were found:
+             <i64 as From<&bool>>
+             <i64 as From<&i16>>
+             <i64 as From<&i32>>
+             <i64 as From<&i64>>
+           and 12 others
+note: required by `from`
+  --> $SRC_DIR/core/src/convert/mod.rs:LL:COL
+   |
+LL |     fn from(_: T) -> Self;
+   |     ^^^^^^^^^^^^^^^^^^^^^^
+
+error[E0277]: the trait bound `u8: From<&u16>` is not satisfied
+  --> $DIR/illegal.rs:11:17
+   |
+LL |     let _: u8 = From::from(&1_u16);
+   |                 ^^^^^^^^^^ the trait `From<&u16>` is not implemented for `u8`
+   |
+   = help: the following implementations were found:
+             <u8 as From<&bool>>
+             <u8 as From<&u8>>
+             <u8 as From<NonZeroU8>>
+             <u8 as From<bool>>
+note: required by `from`
+  --> $SRC_DIR/core/src/convert/mod.rs:LL:COL
+   |
+LL |     fn from(_: T) -> Self;
+   |     ^^^^^^^^^^^^^^^^^^^^^^
+
+error[E0277]: the trait bound `u16: From<&u32>` is not satisfied
+  --> $DIR/illegal.rs:12:18
+   |
+LL |     let _: u16 = From::from(&1_u32);
+   |                  ^^^^^^^^^^ the trait `From<&u32>` is not implemented for `u16`
+   |
+   = help: the following implementations were found:
+             <u16 as From<&bool>>
+             <u16 as From<&u16>>
+             <u16 as From<&u8>>
+             <u16 as From<NonZeroU16>>
+           and 2 others
+note: required by `from`
+  --> $SRC_DIR/core/src/convert/mod.rs:LL:COL
+   |
+LL |     fn from(_: T) -> Self;
+   |     ^^^^^^^^^^^^^^^^^^^^^^
+
+error[E0277]: the trait bound `u32: From<&u64>` is not satisfied
+  --> $DIR/illegal.rs:13:18
+   |
+LL |     let _: u32 = From::from(&1_u64);
+   |                  ^^^^^^^^^^ the trait `From<&u64>` is not implemented for `u32`
+   |
+   = help: the following implementations were found:
+             <u32 as From<&bool>>
+             <u32 as From<&u16>>
+             <u32 as From<&u32>>
+             <u32 as From<&u8>>
+           and 6 others
+note: required by `from`
+  --> $SRC_DIR/core/src/convert/mod.rs:LL:COL
+   |
+LL |     fn from(_: T) -> Self;
+   |     ^^^^^^^^^^^^^^^^^^^^^^
+
+error[E0277]: the trait bound `u64: From<&u128>` is not satisfied
+  --> $DIR/illegal.rs:14:18
+   |
+LL |     let _: u64 = From::from(&1_u128);
+   |                  ^^^^^^^^^^ the trait `From<&u128>` is not implemented for `u64`
+   |
+   = help: the following implementations were found:
+             <u64 as From<&bool>>
+             <u64 as From<&u16>>
+             <u64 as From<&u32>>
+             <u64 as From<&u64>>
+           and 7 others
+note: required by `from`
+  --> $SRC_DIR/core/src/convert/mod.rs:LL:COL
+   |
+LL |     fn from(_: T) -> Self;
+   |     ^^^^^^^^^^^^^^^^^^^^^^
+
+error[E0277]: the trait bound `i8: From<&u8>` is not satisfied
+  --> $DIR/illegal.rs:17:17
+   |
+LL |     let _: i8 = From::from(&1_u8);
+   |                 ^^^^^^^^^^ the trait `From<&u8>` is not implemented for `i8`
+   |
+   = help: the following implementations were found:
+             <i8 as From<&bool>>
+             <i8 as From<&i8>>
+             <i8 as From<NonZeroI8>>
+             <i8 as From<bool>>
+note: required by `from`
+  --> $SRC_DIR/core/src/convert/mod.rs:LL:COL
+   |
+LL |     fn from(_: T) -> Self;
+   |     ^^^^^^^^^^^^^^^^^^^^^^
+
+error[E0277]: the trait bound `u16: From<&i8>` is not satisfied
+  --> $DIR/illegal.rs:18:18
+   |
+LL |     let _: u16 = From::from(&1_i8);
+   |                  ^^^^^^^^^^ the trait `From<&i8>` is not implemented for `u16`
+   |
+   = help: the following implementations were found:
+             <u16 as From<&bool>>
+             <u16 as From<&u16>>
+             <u16 as From<&u8>>
+             <u16 as From<NonZeroU16>>
+           and 2 others
+note: required by `from`
+  --> $SRC_DIR/core/src/convert/mod.rs:LL:COL
+   |
+LL |     fn from(_: T) -> Self;
+   |     ^^^^^^^^^^^^^^^^^^^^^^
+
+error[E0277]: the trait bound `i32: From<&u32>` is not satisfied
+  --> $DIR/illegal.rs:19:18
+   |
+LL |     let _: i32 = From::from(&1_u32);
+   |                  ^^^^^^^^^^ the trait `From<&u32>` is not implemented for `i32`
+   |
+   = help: the following implementations were found:
+             <i32 as From<&bool>>
+             <i32 as From<&i16>>
+             <i32 as From<&i32>>
+             <i32 as From<&i8>>
+           and 8 others
+note: required by `from`
+  --> $SRC_DIR/core/src/convert/mod.rs:LL:COL
+   |
+LL |     fn from(_: T) -> Self;
+   |     ^^^^^^^^^^^^^^^^^^^^^^
+
+error[E0277]: the trait bound `u64: From<&i32>` is not satisfied
+  --> $DIR/illegal.rs:20:18
+   |
+LL |     let _: u64 = From::from(&1_i32);
+   |                  ^^^^^^^^^^ the trait `From<&i32>` is not implemented for `u64`
+   |
+   = help: the following implementations were found:
+             <u64 as From<&bool>>
+             <u64 as From<&u16>>
+             <u64 as From<&u32>>
+             <u64 as From<&u64>>
+           and 7 others
+note: required by `from`
+  --> $SRC_DIR/core/src/convert/mod.rs:LL:COL
+   |
+LL |     fn from(_: T) -> Self;
+   |     ^^^^^^^^^^^^^^^^^^^^^^
+
+error[E0277]: the trait bound `i128: From<&u128>` is not satisfied
+  --> $DIR/illegal.rs:21:19
+   |
+LL |     let _: i128 = From::from(&1_u128);
+   |                   ^^^^^^^^^^ the trait `From<&u128>` is not implemented for `i128`
+   |
+   = help: the following implementations were found:
+             <i128 as From<&bool>>
+             <i128 as From<&i128>>
+             <i128 as From<&i16>>
+             <i128 as From<&i32>>
+           and 16 others
+note: required by `from`
+  --> $SRC_DIR/core/src/convert/mod.rs:LL:COL
+   |
+LL |     fn from(_: T) -> Self;
+   |     ^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 13 previous errors
+
+For more information about this error, try `rustc --explain E0277`.

src/test/ui/traits/issue-77982.stderr

@@ -49,7 +49,7 @@ LL |     let ips: Vec<_> = (0..100_000).map(|_| u32::from(0u32.into())).collect(
            - impl From<NonZeroU32> for u32;
            - impl From<bool> for u32;
            - impl From<char> for u32;
-           and 3 more
+           and 7 more
 note: required by `from`
   --> $SRC_DIR/core/src/convert/mod.rs:LL:COL
    |

src/test/ui/try-trait/bad-interconversion.stderr

@@ -8,6 +8,8 @@ LL |     Ok(Err(123_i32)?)
    |
    = note: the question mark operation (`?`) implicitly performs a conversion on the error value using the `From` trait
    = help: the following implementations were found:
+             <u8 as From<&bool>>
+             <u8 as From<&u8>>
              <u8 as From<NonZeroU8>>
              <u8 as From<bool>>
    = note: required because of the requirements on the impl of `FromResidual<Result<Infallible, i32>>` for `Result<u64, u8>`