pal/unix: Implement SystemTime::{MIN, MAX}

Author: cvengler

library/std/src/sys/pal/unix/time.rs

@@ -29,6 +29,12 @@ pub(crate) struct Timespec {
 }
 
 impl SystemTime {
+    #[unstable(feature = "time_systemtime_limits", issue = "none")]
+    pub const MAX: SystemTime = SystemTime { t: Timespec::MAX };
+
+    #[unstable(feature = "time_systemtime_limits", issue = "none")]
+    pub const MIN: SystemTime = SystemTime { t: Timespec::MIN };
+
     #[cfg_attr(any(target_os = "horizon", target_os = "hurd"), allow(unused))]
     pub fn new(tv_sec: i64, tv_nsec: i64) -> Result<SystemTime, io::Error> {
         Ok(SystemTime { t: Timespec::new(tv_sec, tv_nsec)? })
@@ -61,6 +67,15 @@ impl fmt::Debug for SystemTime {
 }
 
 impl Timespec {
+    #[unstable(feature = "time_systemtime_limits", issue = "none")]
+    const MAX: Timespec = unsafe { Self::new_unchecked(i64::MAX, 1_000_000_000 - 1) };
+
+    // As described below, on AppleOS, dates before epoch are represented differently.
+    // This is not an issue here however, because we are using tv_sec = i64::MIN,
+    // which will cause the compatibility wrapper to not be executed at all.
+    #[unstable(feature = "time_systemtime_limits", issue = "none")]
+    const MIN: Timespec = unsafe { Self::new_unchecked(i64::MIN, 0) };
+
     const unsafe fn new_unchecked(tv_sec: i64, tv_nsec: i64) -> Timespec {
         Timespec { tv_sec, tv_nsec: unsafe { Nanoseconds::new_unchecked(tv_nsec as u32) } }
     }