branch start, add const fn from_duration for Timestamp

Author: ParkMyCar

src/adapter/src/coord.rs

@@ -151,21 +151,14 @@ mod read_policy;
 mod sequencer;
 mod sql;
 
-// TODO: We can have only two consts here, instead of three,
-// once there exists a `const` way to convert between a `Timestamp`
-// and a `Duration`
-
-/// `DEFAULT_LOGICAL_COMPACTION_WINDOW`, in milliseconds.
-/// The default is set to a second to track the default timestamp frequency for sources.
-const DEFAULT_LOGICAL_COMPACTION_WINDOW_MILLIS: u64 = 1000;
-
 /// The default logical compaction window for new objects
-pub const DEFAULT_LOGICAL_COMPACTION_WINDOW: Duration =
-    Duration::from_millis(DEFAULT_LOGICAL_COMPACTION_WINDOW_MILLIS);
+/// 
+/// The default is set to a second to track the default timestamp frequency for sources.
+pub const DEFAULT_LOGICAL_COMPACTION_WINDOW: Duration = Duration::from_secs(1);
 
 /// `DEFAULT_LOGICAL_COMPACTION_WINDOW` as an `EpochMillis` timestamp
 pub const DEFAULT_LOGICAL_COMPACTION_WINDOW_TS: mz_repr::Timestamp =
-    Timestamp::new(DEFAULT_LOGICAL_COMPACTION_WINDOW_MILLIS);
+    Timestamp::from_duration(DEFAULT_LOGICAL_COMPACTION_WINDOW);
 
 /// A dummy availability zone to use when no availability zones are explicitly
 /// specified.

src/repr/src/timestamp.rs

@@ -85,6 +85,30 @@ impl Timestamp {
         }
     }
 
+    /// Creates a [`Timestamp`] from a [`Duration`]
+    /// 
+    /// # Panics
+    /// * If the provided [`Duration`], when represented in milliseconds, overflows a `u64`
+    /// 
+    /// ```should_panic
+    /// use mz_repr::Timestamp;
+    /// use std::time::Duration;
+    /// 
+    /// let d = Duration::from_secs(u64::MAX);
+    /// let t = Timestamp::from_duration(d);
+    /// ```
+    pub const fn from_duration(duration: Duration) -> Self {
+        let millis = duration.as_millis();
+        assert!(
+            millis <= u64::MAX as u128,
+            "overflow when creating Timestamp from Duration!"
+        );
+
+        Self {
+            internal: millis as u64,
+        }
+    }
+
     pub fn to_bytes(&self) -> [u8; 8] {
         self.internal.to_le_bytes()
     }