Add FromSql/ToSql<Timestamp> to Pg backend for OffsetDateTime

diesel/src/pg/types/date_and_time/time.rs

@@ -17,6 +17,11 @@ use crate::sql_types::{Date, Time, Timestamp, Timestamptz};
 // Postgres timestamps start from January 1st 2000.
 const PG_EPOCH: PrimitiveDateTime = datetime!(2000-1-1 0:00:00);
 
+fn to_primitive_datetime(dt: OffsetDateTime) -> PrimitiveDateTime {
+    let dt = dt.to_offset(UtcOffset::UTC);
+    PrimitiveDateTime::new(dt.date(), dt.time())
+}
+
 #[cfg(all(feature = "time", feature = "postgres_backend"))]
 impl FromSql<Timestamp, Pg> for PrimitiveDateTime {
     fn from_sql(bytes: PgValue<'_>) -> deserialize::Result<Self> {
@@ -44,6 +49,23 @@ impl ToSql<Timestamp, Pg> for PrimitiveDateTime {
     }
 }
 
+// Delegate offset datetimes in terms of UTC primitive datetimes; this stores everything in the DB as UTC
+#[cfg(all(feature = "time", feature = "postgres_backend"))]
+impl ToSql<Timestamp, Pg> for OffsetDateTime {
+    fn to_sql<'b>(&'b self, out: &mut Output<'b, '_, Pg>) -> serialize::Result {
+        let prim = to_primitive_datetime(*self);
+        <PrimitiveDateTime as ToSql<Timestamp, Pg>>::to_sql(&prim, &mut out.reborrow())
+    }
+}
+
+#[cfg(all(feature = "time", feature = "postgres_backend"))]
+impl FromSql<Timestamp, Pg> for OffsetDateTime {
+    fn from_sql(bytes: PgValue<'_>) -> deserialize::Result<Self> {
+        let prim = <PrimitiveDateTime as FromSql<Timestamp, Pg>>::from_sql(bytes)?;
+        Ok(prim.assume_utc())
+    }
+}
+
 #[cfg(all(feature = "time", feature = "postgres_backend"))]
 impl FromSql<Timestamptz, Pg> for PrimitiveDateTime {
     fn from_sql(bytes: PgValue<'_>) -> deserialize::Result<Self> {

diesel/src/sql_types/mod.rs

@@ -331,14 +331,14 @@ pub struct Time;
 /// - [`std::time::SystemTime`][SystemTime] (PG only)
 /// - [`chrono::NaiveDateTime`][NaiveDateTime] with `feature = "chrono"`
 /// - [`time::PrimitiveDateTime`] with `feature = "time"`
-/// - [`time::OffsetDateTime`] with `feature = "time"` (MySQL only)
+/// - [`time::OffsetDateTime`] with `feature = "time"`
 ///
 /// ### [`FromSql`](crate::deserialize::FromSql) impls
 ///
 /// - [`std::time::SystemTime`][SystemTime] (PG only)
 /// - [`chrono::NaiveDateTime`][NaiveDateTime] with `feature = "chrono"`
 /// - [`time::PrimitiveDateTime`] with `feature = "time"`
-/// - [`time::OffsetDateTime`] with `feature = "time"` (MySQL only)
+/// - [`time::OffsetDateTime`] with `feature = "time"`
 ///
 /// [SystemTime]: std::time::SystemTime
 #[cfg_attr(