rust: time: Check various time conversion errors

When debug assertions are enabled, ensure that the time conversions are
sensible.  If there is an overflow on time with the assertions disabled,
just use Default, which will be zero.

Signed-off-by: David Brown <[email protected]>

lib/rust/zephyr/src/time.rs

@@ -24,7 +24,9 @@
 //! by non-constant values).  Similarly, the `fugit` crate offers constructors that aim to result
 //! in constants when possible, avoiding costly division operations.
 
-use zephyr_sys::k_timeout_t;
+use zephyr_sys::{k_timeout_t, k_ticks_t};
+
+use core::fmt::Debug;
 
 // The system ticks, is mostly a constant, but there are some boards that use a dynamic tick
 // frequency, and thus need to read this at runtime.
@@ -70,14 +72,20 @@ pub struct Timeout(pub k_timeout_t);
 // From allows methods to take a time of various types and convert it into a Zephyr timeout.
 impl From<Duration> for Timeout {
     fn from(value: Duration) -> Timeout {
-        Timeout(k_timeout_t { ticks: value.ticks() as i64 })
+        let ticks: k_ticks_t = checked_cast(value.ticks());
+        debug_assert_ne!(ticks, crate::sys::K_FOREVER.ticks);
+        debug_assert_ne!(ticks, crate::sys::K_NO_WAIT.ticks);
+        Timeout(k_timeout_t { ticks })
     }
 }
 
 #[cfg(CONFIG_TIMEOUT_64BIT)]
 impl From<Instant> for Timeout {
     fn from(value: Instant) -> Timeout {
-        Timeout(k_timeout_t { ticks: -1 - 1 - (value.ticks() as i64) })
+        let ticks: k_ticks_t = checked_cast(value.ticks());
+        debug_assert_ne!(ticks, crate::sys::K_FOREVER.ticks);
+        debug_assert_ne!(ticks, crate::sys::K_NO_WAIT.ticks);
+        Timeout(k_timeout_t { ticks: -1 - 1 - ticks })
     }
 }
 
@@ -110,3 +118,18 @@ pub fn sleep<T>(timeout: T) -> Duration
     let rest = unsafe { crate::raw::k_sleep(timeout.0) };
     Duration::millis(rest as Tick)
 }
+
+/// Convert from the Tick time type, which is unsigned, to the `k_ticks_t` type. When debug
+/// assertions are enabled, it will panic on overflow.
+fn checked_cast<I, O>(tick: I) -> O
+where
+    I: TryInto<O>,
+    I::Error: Debug,
+    O: Default,
+{
+    if cfg!(debug_assertions) {
+        tick.try_into().expect("Overflow in time conversion")
+    } else {
+        tick.try_into().unwrap_or(O::default())
+    }
+}