Stabilize const for integer {to,from}_{be,le,ne}_bytes methods

All of these functions can be implemented simply and naturally as
const functions, e.g. u32::from_le_bytes can be implemented as

    (bytes[0] as u32)
        | (bytes[1] as u32) << 8
        | (bytes[2] as u32) << 16
        | (bytes[3] as u32) << 24

So stabilizing the constness will not expose that internally they are
implemented using transmute which is not const in stable.

Author: tspiteri

src/libcore/lib.rs

@@ -131,7 +131,6 @@
 #![feature(rtm_target_feature)]
 #![feature(f16c_target_feature)]
 #![feature(hexagon_target_feature)]
-#![feature(const_int_conversion)]
 #![feature(const_transmute)]
 #![feature(structural_match)]
 #![feature(abi_unadjusted)]

src/libcore/num/mod.rs

@@ -2195,7 +2195,7 @@ let bytes = ", $swap_op, stringify!($SelfT), ".to_be_bytes();
 assert_eq!(bytes, ", $be_bytes, ");
 ```"),
             #[stable(feature = "int_to_from_bytes", since = "1.32.0")]
-            #[rustc_const_unstable(feature = "const_int_conversion", issue = "53718")]
+            #[rustc_const_stable(feature = "const_int_conversion", since = "1.43.0")]
             #[inline]
             pub const fn to_be_bytes(self) -> [u8; mem::size_of::<Self>()] {
                 self.to_be().to_ne_bytes()
@@ -2215,7 +2215,7 @@ let bytes = ", $swap_op, stringify!($SelfT), ".to_le_bytes();
 assert_eq!(bytes, ", $le_bytes, ");
 ```"),
             #[stable(feature = "int_to_from_bytes", since = "1.32.0")]
-            #[rustc_const_unstable(feature = "const_int_conversion", issue = "53718")]
+            #[rustc_const_stable(feature = "const_int_conversion", since = "1.43.0")]
             #[inline]
             pub const fn to_le_bytes(self) -> [u8; mem::size_of::<Self>()] {
                 self.to_le().to_ne_bytes()
@@ -2250,7 +2250,8 @@ assert_eq!(
 );
 ```"),
             #[stable(feature = "int_to_from_bytes", since = "1.32.0")]
-            #[rustc_const_unstable(feature = "const_int_conversion", issue = "53718")]
+            #[rustc_const_stable(feature = "const_int_conversion", since = "1.43.0")]
+            #[allow_internal_unstable(const_transmute)]
             #[inline]
             pub const fn to_ne_bytes(self) -> [u8; mem::size_of::<Self>()] {
                 // SAFETY: integers are plain old datatypes so we can always transmute them to
@@ -2284,7 +2285,7 @@ fn read_be_", stringify!($SelfT), "(input: &mut &[u8]) -> ", stringify!($SelfT),
 }
 ```"),
             #[stable(feature = "int_to_from_bytes", since = "1.32.0")]
-            #[rustc_const_unstable(feature = "const_int_conversion", issue = "53718")]
+            #[rustc_const_stable(feature = "const_int_conversion", since = "1.43.0")]
             #[inline]
             pub const fn from_be_bytes(bytes: [u8; mem::size_of::<Self>()]) -> Self {
                 Self::from_be(Self::from_ne_bytes(bytes))
@@ -2317,7 +2318,7 @@ fn read_le_", stringify!($SelfT), "(input: &mut &[u8]) -> ", stringify!($SelfT),
 }
 ```"),
             #[stable(feature = "int_to_from_bytes", since = "1.32.0")]
-            #[rustc_const_unstable(feature = "const_int_conversion", issue = "53718")]
+            #[rustc_const_stable(feature = "const_int_conversion", since = "1.43.0")]
             #[inline]
             pub const fn from_le_bytes(bytes: [u8; mem::size_of::<Self>()]) -> Self {
                 Self::from_le(Self::from_ne_bytes(bytes))
@@ -2360,7 +2361,8 @@ fn read_ne_", stringify!($SelfT), "(input: &mut &[u8]) -> ", stringify!($SelfT),
 }
 ```"),
             #[stable(feature = "int_to_from_bytes", since = "1.32.0")]
-            #[rustc_const_unstable(feature = "const_int_conversion", issue = "53718")]
+            #[rustc_const_stable(feature = "const_int_conversion", since = "1.43.0")]
+            #[allow_internal_unstable(const_transmute)]
             #[inline]
             pub const fn from_ne_bytes(bytes: [u8; mem::size_of::<Self>()]) -> Self {
                 // SAFETY: integers are plain old datatypes so we can always transmute to them
@@ -4132,7 +4134,7 @@ let bytes = ", $swap_op, stringify!($SelfT), ".to_be_bytes();
 assert_eq!(bytes, ", $be_bytes, ");
 ```"),
             #[stable(feature = "int_to_from_bytes", since = "1.32.0")]
-            #[rustc_const_unstable(feature = "const_int_conversion", issue = "53718")]
+            #[rustc_const_stable(feature = "const_int_conversion", since = "1.43.0")]
             #[inline]
             pub const fn to_be_bytes(self) -> [u8; mem::size_of::<Self>()] {
                 self.to_be().to_ne_bytes()
@@ -4152,7 +4154,7 @@ let bytes = ", $swap_op, stringify!($SelfT), ".to_le_bytes();
 assert_eq!(bytes, ", $le_bytes, ");
 ```"),
             #[stable(feature = "int_to_from_bytes", since = "1.32.0")]
-            #[rustc_const_unstable(feature = "const_int_conversion", issue = "53718")]
+            #[rustc_const_stable(feature = "const_int_conversion", since = "1.43.0")]
             #[inline]
             pub const fn to_le_bytes(self) -> [u8; mem::size_of::<Self>()] {
                 self.to_le().to_ne_bytes()
@@ -4187,7 +4189,8 @@ assert_eq!(
 );
 ```"),
             #[stable(feature = "int_to_from_bytes", since = "1.32.0")]
-            #[rustc_const_unstable(feature = "const_int_conversion", issue = "53718")]
+            #[rustc_const_stable(feature = "const_int_conversion", since = "1.43.0")]
+            #[allow_internal_unstable(const_transmute)]
             #[inline]
             pub const fn to_ne_bytes(self) -> [u8; mem::size_of::<Self>()] {
                 // SAFETY: integers are plain old datatypes so we can always transmute them to
@@ -4221,7 +4224,7 @@ fn read_be_", stringify!($SelfT), "(input: &mut &[u8]) -> ", stringify!($SelfT),
 }
 ```"),
             #[stable(feature = "int_to_from_bytes", since = "1.32.0")]
-            #[rustc_const_unstable(feature = "const_int_conversion", issue = "53718")]
+            #[rustc_const_stable(feature = "const_int_conversion", since = "1.43.0")]
             #[inline]
             pub const fn from_be_bytes(bytes: [u8; mem::size_of::<Self>()]) -> Self {
                 Self::from_be(Self::from_ne_bytes(bytes))
@@ -4254,7 +4257,7 @@ fn read_le_", stringify!($SelfT), "(input: &mut &[u8]) -> ", stringify!($SelfT),
 }
 ```"),
             #[stable(feature = "int_to_from_bytes", since = "1.32.0")]
-            #[rustc_const_unstable(feature = "const_int_conversion", issue = "53718")]
+            #[rustc_const_stable(feature = "const_int_conversion", since = "1.43.0")]
             #[inline]
             pub const fn from_le_bytes(bytes: [u8; mem::size_of::<Self>()]) -> Self {
                 Self::from_le(Self::from_ne_bytes(bytes))
@@ -4297,7 +4300,8 @@ fn read_ne_", stringify!($SelfT), "(input: &mut &[u8]) -> ", stringify!($SelfT),
 }
 ```"),
             #[stable(feature = "int_to_from_bytes", since = "1.32.0")]
-            #[rustc_const_unstable(feature = "const_int_conversion", issue = "53718")]
+            #[rustc_const_stable(feature = "const_int_conversion", since = "1.43.0")]
+            #[allow_internal_unstable(const_transmute)]
             #[inline]
             pub const fn from_ne_bytes(bytes: [u8; mem::size_of::<Self>()]) -> Self {
                 // SAFETY: integers are plain old datatypes so we can always transmute to them

src/test/ui/consts/const-int-conversion-rpass.rs

@@ -1,7 +1,5 @@
 // run-pass
 
-#![feature(const_int_conversion)]
-
 const REVERSE: u32 = 0x12345678_u32.reverse_bits();
 const FROM_BE_BYTES: i32 = i32::from_be_bytes([0x12, 0x34, 0x56, 0x78]);
 const FROM_LE_BYTES: i32 = i32::from_le_bytes([0x12, 0x34, 0x56, 0x78]);