Make delegation methods of std::net::IpAddr unstable const

Make the following methods of `std::net::IpAddr` unstable const under the `const_ip` feature:
- `is_unspecified`
- `is_loopback`
- `is_global`
- `is_multicast`

Also adds a test for these methods in a const context.

Possible because these methods delegate to the inner `Ipv4Addr` or `Ipv6Addr`, which were made const, and the recent stabilization of const control flow.

Part of #76205

library/std/src/lib.rs

@@ -238,6 +238,7 @@
 #![feature(const_cstr_unchecked)]
 #![feature(const_fn_transmute)]
 #![feature(const_fn)]
+#![feature(const_ip)]
 #![feature(const_ipv6)]
 #![feature(const_raw_ptr_deref)]
 #![feature(const_ipv4)]

library/std/src/net/ip.rs

@@ -148,8 +148,9 @@ impl IpAddr {
     /// assert_eq!(IpAddr::V4(Ipv4Addr::new(0, 0, 0, 0)).is_unspecified(), true);
     /// assert_eq!(IpAddr::V6(Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 0)).is_unspecified(), true);
     /// ```
+    #[rustc_const_unstable(feature = "const_ip", issue = "76205")]
     #[stable(feature = "ip_shared", since = "1.12.0")]
-    pub fn is_unspecified(&self) -> bool {
+    pub const fn is_unspecified(&self) -> bool {
         match self {
             IpAddr::V4(ip) => ip.is_unspecified(),
             IpAddr::V6(ip) => ip.is_unspecified(),
@@ -169,8 +170,9 @@ impl IpAddr {
     /// assert_eq!(IpAddr::V4(Ipv4Addr::new(127, 0, 0, 1)).is_loopback(), true);
     /// assert_eq!(IpAddr::V6(Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 0x1)).is_loopback(), true);
     /// ```
+    #[rustc_const_unstable(feature = "const_ip", issue = "76205")]
     #[stable(feature = "ip_shared", since = "1.12.0")]
-    pub fn is_loopback(&self) -> bool {
+    pub const fn is_loopback(&self) -> bool {
         match self {
             IpAddr::V4(ip) => ip.is_loopback(),
             IpAddr::V6(ip) => ip.is_loopback(),
@@ -192,7 +194,8 @@ impl IpAddr {
     /// assert_eq!(IpAddr::V4(Ipv4Addr::new(80, 9, 12, 3)).is_global(), true);
     /// assert_eq!(IpAddr::V6(Ipv6Addr::new(0, 0, 0x1c9, 0, 0, 0xafc8, 0, 0x1)).is_global(), true);
     /// ```
-    pub fn is_global(&self) -> bool {
+    #[rustc_const_unstable(feature = "const_ip", issue = "76205")]
+    pub const fn is_global(&self) -> bool {
         match self {
             IpAddr::V4(ip) => ip.is_global(),
             IpAddr::V6(ip) => ip.is_global(),
@@ -212,8 +215,9 @@ impl IpAddr {
     /// assert_eq!(IpAddr::V4(Ipv4Addr::new(224, 254, 0, 0)).is_multicast(), true);
     /// assert_eq!(IpAddr::V6(Ipv6Addr::new(0xff00, 0, 0, 0, 0, 0, 0, 0)).is_multicast(), true);
     /// ```
+    #[rustc_const_unstable(feature = "const_ip", issue = "76205")]
     #[stable(feature = "ip_shared", since = "1.12.0")]
-    pub fn is_multicast(&self) -> bool {
+    pub const fn is_multicast(&self) -> bool {
         match self {
             IpAddr::V4(ip) => ip.is_multicast(),
             IpAddr::V6(ip) => ip.is_multicast(),
@@ -238,7 +242,8 @@ impl IpAddr {
     ///     true
     /// );
     /// ```
-    pub fn is_documentation(&self) -> bool {
+    #[rustc_const_unstable(feature = "const_ip", issue = "76205")]
+    pub const fn is_documentation(&self) -> bool {
         match self {
             IpAddr::V4(ip) => ip.is_documentation(),
             IpAddr::V6(ip) => ip.is_documentation(),

library/std/src/net/ip/tests.rs

@@ -918,3 +918,22 @@ fn ipv6_const() {
     const IP_V4: Option<Ipv4Addr> = IP_ADDRESS.to_ipv4();
     assert_eq!(IP_V4.unwrap(), Ipv4Addr::new(0, 0, 0, 1));
 }
+
+#[test]
+fn ip_const() {
+    // test that the methods of `IpAddr` are usable in a const context
+
+    const IP_ADDRESS: IpAddr = IpAddr::V4(Ipv4Addr::LOCALHOST);
+
+    const IS_UNSPECIFIED: bool = IP_ADDRESS.is_unspecified();
+    assert!(!IS_UNSPECIFIED);
+
+    const IS_LOOPBACK: bool = IP_ADDRESS.is_loopback();
+    assert!(IS_LOOPBACK);
+
+    const IS_GLOBAL: bool = IP_ADDRESS.is_global();
+    assert!(!IS_GLOBAL);
+
+    const IS_MULTICAST: bool = IP_ADDRESS.is_multicast();
+    assert!(!IS_MULTICAST);
+}