Rollup merge of #76388 - poliorcetics:system-time-document-panic, r=KodrAus

Add a note about the panic behavior of math operations on time objects

Fixes #71226.

Author: JohnTitor

library/std/src/time.rs

@@ -100,6 +100,11 @@ pub use core::time::Duration;
 /// [clock_time_get (Monotonic Clock)]: https://nuxi.nl/cloudabi/#clock_time_get
 ///
 /// **Disclaimer:** These system calls might change over time.
+///
+/// > Note: mathematical operations like [`add`] may panic if the underlying
+/// > structure cannot represent the new point in time.
+///
+/// [`add`]: Instant::add
 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
 #[stable(feature = "time2", since = "1.8.0")]
 pub struct Instant(time::Instant);
@@ -174,6 +179,11 @@ pub struct Instant(time::Instant);
 /// [GetSystemTimeAsFileTime]: https://docs.microsoft.com/en-us/windows/win32/api/sysinfoapi/nf-sysinfoapi-getsystemtimeasfiletime
 ///
 /// **Disclaimer:** These system calls might change over time.
+///
+/// > Note: mathematical operations like [`add`] may panic if the underlying
+/// > structure cannot represent the new point in time.
+///
+/// [`add`]: SystemTime::add
 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
 #[stable(feature = "time2", since = "1.8.0")]
 pub struct SystemTime(time::SystemTime);