hare

commit 19e380ccb7dfe2bcab5f94e6bd03004e3e2c6005
parent 4d909ad613a6d2c8552ab14ed0c8639439c348cd
Author: Byron Torres <b@torresjrjr.com>
Date:   Tue, 24 May 2022 04:00:29 +0100

time::chrono: make in() handle multiple timescales

The following now works properly:

	const earth = datetime::now();
	const mars = datetime::in(chrono::MTC, earth);

Fixes: https://todo.sr.ht/~sircmpwn/hare/618
Signed-off-by: Byron Torres <b@torresjrjr.com>

Diffstat:
M
time/chrono/timezone.ha
 | 
23
+++++++++++++++++++++++

1 file changed, 23 insertions(+), 0 deletions(-)
diff --git a/time/chrono/timezone.ha b/time/chrono/timezone.ha
@@ -71,7 +71,30 @@ type tzname = struct {
 };
 
 // Creates an equivalent [[moment]] with a different [[locality]].
+//
+// If the old and new localities have different timescales, a direct conversion
+// between them will be tried, and will abort if unsuccessful. To avoid this,
+// consider manually converting moments to instants, and those instants between
+// timescales.
 export fn in(loc: locality, m: moment) moment = {
+	if (m.loc.timescale != loc.timescale) {
+		const i = to_instant(m);
+		const i = match (m.loc.timescale.to_tai(i)) {
+		case let i: time::instant =>
+			yield i;
+		case time::error =>
+			abort("time::chrono::in(): direct timescale conversion failed");
+		};
+		const i = match (loc.timescale.from_tai(i)) {
+		case let i: time::instant =>
+			yield i;
+		case time::error =>
+			abort("time::chrono::in(): direct timescale conversion failed");
+		};
+		const m = from_instant(i, loc);
+		return m;
+	};
+
 	assert(m.time < loc.daylength, "Internal error: time excedes daylength");
 	return new(loc, m.date, m.time)!; // resets .zone
 };