docs

datafusion/substrait/src/logical_plan/consumer.rs

@@ -95,9 +95,11 @@ use substrait::proto::{
 };
 use substrait::proto::{FunctionArgument, SortField};
 
-// Substrait TimestampTz only says that the timestamp is relative to UTC, which
-// is the same as the expectation for any NON-empty timezone in DF. Any timezone would give
-// correct points on a timeline, but the timezone may get used for arithmetic and display.
+// Substrait PrecisionTimestampTz indicates that the timestamp is relative to UTC, which
+// is the same as the expectation for any non-empty timezone in DF, so any non-empty timezone
+// results in correct points on the timeline, and we pick UTC as a reasonable default.
+// However, DF uses the timezone also for some arithmetic and display purposes (see e.g.
+// https://github.com/apache/arrow-rs/blob/ee5694078c86c8201549654246900a4232d531a9/arrow-cast/src/cast/mod.rs#L1749).
 const DEFAULT_TIMEZONE: &str = "UTC";
 
 pub fn name_to_op(name: &str) -> Option<Operator> {