timerender: Use an explicit time zone for all rendering.

Signed-off-by: Anders Kaseorg <anders@zulip.com>

web/src/message_edit_history.js

@@ -1,4 +1,3 @@
-import {isSameDay} from "date-fns";
 import $ from "jquery";
 
 import render_message_edit_history from "../templates/message_edit_history.hbs";
@@ -14,6 +13,7 @@ import * as rendered_markdown from "./rendered_markdown";
 import * as rows from "./rows";
 import * as spectators from "./spectators";
 import * as sub_store from "./sub_store";
+import {is_same_day} from "./time_zone_util";
 import * as timerender from "./timerender";
 import * as ui_report from "./ui_report";
 import {user_settings} from "./user_settings";
@@ -38,7 +38,9 @@ export function fetch_and_render_message_history(message) {
                 const item = {
                     timestamp: timerender.stringify_time(time),
                     display_date: date_time_format.format(time),
-                    show_date_row: prev_time === null || !isSameDay(time, prev_time),
+                    show_date_row:
+                        prev_time === null ||
+                        !is_same_day(time, prev_time, timerender.display_time_zone),
                 };
 
                 if (!msg.user_id) {

web/src/message_list_view.js

@@ -1,4 +1,3 @@
-import {isSameDay} from "date-fns";
 import $ from "jquery";
 import _ from "lodash";
 
@@ -34,6 +33,7 @@ import * as stream_color from "./stream_color";
 import * as stream_data from "./stream_data";
 import * as sub_store from "./sub_store";
 import * as submessage from "./submessage";
+import {is_same_day} from "./time_zone_util";
 import * as timerender from "./timerender";
 import * as user_topics from "./user_topics";
 import * as util from "./util";
@@ -42,7 +42,11 @@ function same_day(earlier_msg, later_msg) {
     if (earlier_msg === undefined || later_msg === undefined) {
         return false;
     }
-    return isSameDay(earlier_msg.msg.timestamp * 1000, later_msg.msg.timestamp * 1000);
+    return is_same_day(
+        earlier_msg.msg.timestamp * 1000,
+        later_msg.msg.timestamp * 1000,
+        timerender.display_time_zone,
+    );
 }
 
 function same_sender(a, b) {

web/src/timerender.ts

@@ -1,12 +1,10 @@
 import {
-    differenceInCalendarDays,
     differenceInHours,
     differenceInMinutes,
     formatISO,
     isEqual,
     isValid,
     parseISO,
-    startOfToday,
 } from "date-fns";
 import $ from "jquery";
 import _ from "lodash";
@@ -14,15 +12,23 @@ import _ from "lodash";
 import render_markdown_time_tooltip from "../templates/markdown_time_tooltip.hbs";
 
 import {$t} from "./i18n";
+import {difference_in_calendar_days, start_of_day} from "./time_zone_util";
 import {parse_html} from "./ui_util";
 import {user_settings} from "./user_settings";
 
 let next_timerender_id = 0;
 
+export let display_time_zone = new Intl.DateTimeFormat().resolvedOptions().timeZone;
+
 export function clear_for_testing(): void {
     next_timerender_id = 0;
 }
 
+// Exported for testing only; we do not support live-updating the time zone.
+export function set_display_time_zone(time_zone: string): void {
+    display_time_zone = time_zone;
+}
+
 type DateFormat = "weekday" | "dayofyear" | "weekday_dayofyear_year" | "dayofyear_year";
 type DateWithTimeFormat =
     | "dayofyear_time"
@@ -107,15 +113,18 @@ export function get_localized_date_or_time_for_format(
     date: Date | number,
     format: DateOrTimeFormat,
 ): string {
-    return new Intl.DateTimeFormat(
+    return new Intl.DateTimeFormat(user_settings.default_language, {
-        user_settings.default_language,
+        timeZone: display_time_zone,
-        get_format_options_for_type(format),
+        ...get_format_options_for_type(format),
-    ).format(date);
+    }).format(date);
 }
 
 // Exported for tests only.
 export function get_tz_with_UTC_offset(time: number | Date): string {
-    let timezone = new Intl.DateTimeFormat(user_settings.default_language, {timeZoneName: "short"})
+    let timezone = new Intl.DateTimeFormat(user_settings.default_language, {
+        timeZone: display_time_zone,
+        timeZoneName: "short",
+    })
         .formatToParts(time)
         .find(({type}) => type === "timeZoneName")?.value;
 
@@ -129,6 +138,7 @@ export function get_tz_with_UTC_offset(time: number | Date): string {
     timezone = /GMT[+-][\d:]*/.test(timezone ?? "") ? "" : timezone;
 
     const tz_offset = new Intl.DateTimeFormat(user_settings.default_language, {
+        timeZone: display_time_zone,
         timeZoneName: "longOffset",
     })
         .formatToParts(time)
@@ -166,7 +176,7 @@ export function render_now(time: Date, today = new Date()): TimeRender {
     // Presumably the result of diffDays will be an integer in this
     // case, but round it to be sure before comparing to integer
     // constants.
-    const days_old = differenceInCalendarDays(today, time);
+    const days_old = difference_in_calendar_days(today, time, display_time_zone);
 
     if (days_old === 0) {
         time_str = $t({defaultMessage: "Today"});
@@ -210,7 +220,7 @@ export function relative_time_string_from_date({
         return $t({defaultMessage: "{minutes} minutes ago"}, {minutes});
     }
 
-    const days_old = differenceInCalendarDays(current_date, date);
+    const days_old = difference_in_calendar_days(current_date, date, display_time_zone);
     const hours = Math.floor(minutes / 60);
 
     if (hours < 24) {
@@ -252,7 +262,7 @@ export function last_seen_status_from_date(
         return $t({defaultMessage: "Active {minutes} minutes ago"}, {minutes});
     }
 
-    const days_old = differenceInCalendarDays(current_date, last_active_date);
+    const days_old = difference_in_calendar_days(current_date, last_active_date, display_time_zone);
     const hours = Math.floor(minutes / 60);
 
     if (hours < 24) {
@@ -310,7 +320,7 @@ let update_list: UpdateEntry[] = [];
 let last_update: Date;
 
 export function initialize(): void {
-    last_update = startOfToday();
+    last_update = start_of_day(new Date(), display_time_zone);
 }
 
 function maybe_add_update_list_entry(entry: UpdateEntry): void {
@@ -363,7 +373,7 @@ export function get_markdown_time_tooltip(reference: HTMLElement): DocumentFragm
 // This isn't expected to be called externally except manually for
 // testing purposes.
 export function update_timestamps(): void {
-    const today = startOfToday();
+    const today = start_of_day(new Date(), display_time_zone);
     if (!isEqual(today, last_update)) {
         const to_process = update_list;
         update_list = [];
@@ -422,7 +432,7 @@ export function stringify_time(time: number | Date): string {
 
 export function format_time_modern(time: number | Date, today = new Date()): string {
     const hours = differenceInHours(today, time);
-    const days_old = differenceInCalendarDays(today, time);
+    const days_old = difference_in_calendar_days(today, time, display_time_zone);
 
     if (time > today) {
         /* For timestamps in the future, we always show the year*/
@@ -466,7 +476,9 @@ export function get_full_datetime_clarification(
     time: Date,
     time_format: TimeFormat = "time_sec",
 ): string {
-    const date_string = time.toLocaleDateString(user_settings.default_language);
+    const date_string = time.toLocaleDateString(user_settings.default_language, {
+        timeZone: display_time_zone,
+    });
     let time_string = get_localized_date_or_time_for_format(time, time_format);
 
     const tz_offset_str = get_tz_with_UTC_offset(time);
@@ -501,7 +513,7 @@ export function get_time_limit_setting_in_appropriate_unit(
 export function should_display_profile_incomplete_alert(timestamp: number): boolean {
     const today = new Date(Date.now());
     const time = new Date(timestamp);
-    const days_old = differenceInCalendarDays(today, time);
+    const days_old = difference_in_calendar_days(today, time, display_time_zone);
 
     if (days_old >= 15) {
         return true;

web/tests/dispatch.test.js

@@ -419,6 +419,7 @@ run_test("scheduled_messages", ({override}) => {
 
 run_test("realm settings", ({override}) => {
     page_params.is_admin = true;
+    page_params.realm_date_created = new Date("2023-01-01Z");
 
     override(settings_org, "sync_realm_settings", noop);
     override(settings_bots, "update_bot_permissions_ui", noop);

web/tests/timerender.test.js

@@ -174,20 +174,19 @@ run_test("get_tz_with_UTC_offset", () => {
     let time = date_2019;
 
     assert.equal(timerender.get_tz_with_UTC_offset(time), "UTC");
-    const previous_env_tz = process.env.TZ;
 
     // Test the GMT[+-]x:y logic.
-    process.env.TZ = "Asia/Kolkata";
+    timerender.set_display_time_zone("Asia/Kolkata");
     assert.equal(timerender.get_tz_with_UTC_offset(time), "(UTC+05:30)");
 
-    process.env.TZ = "America/Los_Angeles";
+    timerender.set_display_time_zone("America/Los_Angeles");
     assert.equal(timerender.get_tz_with_UTC_offset(time), "PDT (UTC-07:00)");
 
     time = date_2025;
 
     assert.equal(timerender.get_tz_with_UTC_offset(time), "PST (UTC-08:00)");
 
-    process.env.TZ = previous_env_tz;
+    timerender.set_display_time_zone("UTC");
 });
 
 run_test("render_now_returns_today", () => {
@@ -285,40 +284,38 @@ run_test("format_time_modern", () => {
 });
 
 run_test("format_time_modern_different_timezones", () => {
-    const utc_tz = process.env.TZ;
-
     // Day is yesterday in UTC+0 but is 2 days ago in local timezone hence DOW is returned.
     let today = date_2017_PM;
     let yesterday = add(date_2017, {days: -1});
     assert.equal(timerender.format_time_modern(yesterday, today), "translated: Yesterday");
 
-    process.env.TZ = "America/Juneau";
+    timerender.set_display_time_zone("America/Juneau");
     let expected = "translated: 5/16/2017 at 11:12:53 PM AKDT (UTC-08:00)";
     assert.equal(timerender.get_full_datetime_clarification(yesterday), expected);
     assert.equal(timerender.format_time_modern(yesterday, today), "Tuesday");
-    process.env.TZ = utc_tz;
+    timerender.set_display_time_zone("UTC");
 
     // Day is 2 days ago in UTC+0 but is yesterday in local timezone.
     today = date_2017;
     yesterday = add(date_2017_PM, {days: -2});
     assert.equal(timerender.format_time_modern(yesterday, today), "Tuesday");
 
-    process.env.TZ = "Asia/Brunei";
+    timerender.set_display_time_zone("Asia/Brunei");
     expected = "translated: 5/17/2017 at 5:12:53 AM (UTC+08:00)";
     assert.equal(timerender.get_full_datetime_clarification(yesterday), expected);
     assert.equal(timerender.format_time_modern(yesterday, today), "translated: Yesterday");
-    process.env.TZ = utc_tz;
+    timerender.set_display_time_zone("UTC");
 
     // Day is 6 days ago in UTC+0 but a week ago in local timezone hence difference in returned strings.
     today = date_2017_PM;
     yesterday = add(date_2017, {days: -6});
     assert.equal(timerender.format_time_modern(yesterday, today), "Friday");
 
-    process.env.TZ = "America/Juneau";
+    timerender.set_display_time_zone("America/Juneau");
     expected = "translated: 5/11/2017 at 11:12:53 PM AKDT (UTC-08:00)";
     assert.equal(timerender.get_full_datetime_clarification(yesterday), expected);
     assert.equal(timerender.format_time_modern(yesterday, today), "May 11");
-    process.env.TZ = utc_tz;
+    timerender.set_display_time_zone("UTC");
 });
 
 run_test("render_now_returns_year_with_year_boundary", () => {
@@ -471,13 +468,12 @@ run_test("get_full_datetime", () => {
     user_settings.twenty_four_hour_time = false;
 
     // Test the GMT[+-]x:y logic.
-    const previous_env_tz = process.env.TZ;
+    timerender.set_display_time_zone("Asia/Kolkata");
-    process.env.TZ = "Asia/Kolkata";
     expected = "translated: 5/19/2017 at 2:42:53 AM (UTC+05:30)";
     assert.equal(timerender.get_full_datetime_clarification(time), expected);
     expected = "translated: May 19, 2017 at 2:42:53 AM";
     assert.equal(timerender.get_full_datetime(time), expected);
-    process.env.TZ = previous_env_tz;
+    timerender.set_display_time_zone("UTC");
 });
 
 run_test("last_seen_status_from_date", () => {