Test First Day Overrides algorithm in Intl.Locale.p.getWeekInfo

test/intl402/Locale/prototype/getWeekInfo/firstDay-overrides.js

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+// Copyright 2026 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-intl.locale.prototype.getWeekInfo
+description: Compliance with First Day Overrides algorithm
+info: |
+  WeekInfoOfLocale ( _loc_ ):
+  9. Set _weekInfo_.[[FirstDay]] to FirstDayOverrides(_loc_).
+features: [Intl.Locale,Intl.Locale-info]
+locale: [en-AF, en-MV, en-CA, en-001, ps]
+---*/
+
+const regionAF = new Intl.Locale("en-AF").getWeekInfo().firstDay;
+const regionMV = new Intl.Locale("en-MV").getWeekInfo().firstDay;
+const regionCA = new Intl.Locale("en-CA").getWeekInfo().firstDay;
+const fallback = new Intl.Locale("en-001").getWeekInfo().firstDay;
+
+const localeIDTests = [
+  ["en-MV-u-ca-iso8601-fw-tue-rg-afzzzz-sd-cabc", 2, "always Tuesday due to fw tag"],
+  ["en-MV-u-ca-iso8601-rg-afzzzz-sd-cabc", regionAF, `AF (${regionAF}) due to rg tag`],
+  ["en-MV-u-ca-iso8601-sd-cabc", 1, "always Monday due to iso8601 calendar"],
+  ["en-MV-u-ca-iso8601-fw-blursday", 1, "invalid fw tag is ignored"],
+  ["en-MV-u-ca-iso8601-rg-qmzzzz", 1, "invalid rg tag is ignored (QM is private-use)"],
+  ["en-MV-u-sd-cabc", regionMV, `MV (${regionMV}) due to region subtag`],
+  ["en-MV-u-ca-gregory", regionMV, "gregory does not define a first-day-of-week"],
+  ["en-u-sd-cabc", regionCA, `CA (${regionCA}) due to sd tag`],
+  ["ps", regionAF, `AF (${regionAF}) due to Add Likely Subtags algorithm`],
+  ["ps-u-sd-qmqm", regionAF, "invalid sd tag is ignored (region QM is private-use)"],
+  ["zxx", fallback, `001 (${fallback}) because no other week info source`],
+];
+
+for (const [id, expected, message] of localeIDTests) {
+  const locale = new Intl.Locale(id);
+  assert.sameValue(locale.getWeekInfo().firstDay, expected, message);
+}
+
+const optionsTests = [
+  ["en-MV-u-ca-iso8601-fw-wed-rg-afzzzz-sd-cabc", { firstDayOfWeek: "tue" }, 2, "firstDayOfWeek option beats -u-fw-"],
+  ["en-MV-u-ca-iso8601-rg-cazzzz-sd-cabc", { region: "AF" }, regionCA, "region option does not beat -u-rg-"],
+  ["en-MV-u-sd-cabc", { region: "AF" }, regionAF, "region option beats region subtag"],
+  ["en-MV", { calendar: "gregory" }, regionMV, "gregory does not define a first-day-of-week"],
+  ["en-MV-u-ca-iso8601-sd-cabc", { calendar: "gregory" }, regionMV, "calendar option beats -u-ca-"],
+];
+
+for (const [id, options, expected, message] of optionsTests) {
+  const locale = new Intl.Locale(id, options);
+  assert.sameValue(locale.getWeekInfo().firstDay, expected, message);
+}