1 files changed, 59 insertions, 0 deletions
diff --git a/js/src/tests/non262/Intl/DateTimeFormat/implied-script-has-consistent-output.js b/js/src/tests/non262/Intl/DateTimeFormat/implied-script-has-consistent-output.js
new file mode 100644
index 0000000000..6c0b4d2f59
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+++ b/js/src/tests/non262/Intl/DateTimeFormat/implied-script-has-consistent-output.js
@@ -0,0 +1,59 @@
+// |reftest| skip-if(!this.hasOwnProperty("Intl"))
+
+if (typeof getAvailableLocalesOf === "undefined") {
+  var getAvailableLocalesOf = SpecialPowers.Cu.getJSTestingFunctions().getAvailableLocalesOf;
+}
+
+// Retrieve all available locales of Intl.DateTimeFormat.
+const available = getAvailableLocalesOf("DateTimeFormat");
+
+const options = [
+  // Include "hour" to catch hour cycle differences.
+  //
+  // For example "ff-Latn-GH" (Fulah as spoken in Ghana) uses a 12-hour clock,
+  // whereas "ff" (Fulah) uses a 24-hour clock. When the user creates the
+  // formatter for "ff-GH", it should use the same formatter data as "ff-Latn-GH"
+  // and it shouldn't fallback to "ff".
+  {hour: "2-digit", minute: "2-digit", timeZone: "UTC"},
+
+  // Include "timeZoneName" to catch script differences, e.g traditional or
+  // simplified Chinese characters.
+  {timeZoneName: "long", timeZone: "America/Los_Angeles"},
+];
+
+// Pick a date after 12 pm to catch any hour cycle differences.
+const date = Date.UTC(2021, 6-1, 7, 15, 0);
+
+available.map(x => {
+  return new Intl.Locale(x);
+}).filter(loc => {
+  // Find all locales which have both a script and a region subtag.
+  return loc.script && loc.region;
+}).filter(loc => {
+  // Skip "sd-Deva-IN" and Fulah because of <https://unicode-org.atlassian.net/browse/ICU-21974>.
+  return !((loc.language === "sd" && loc.script === "Deva" && loc.region === "IN") ||
+           (loc.language === "ff" && (loc.script === "Adlm" || loc.script === "Latn") &&
+            (loc.region === "GH" || loc.region === "GM" || loc.region === "LR" || loc.region === "SL"))
+          );
+}).forEach(loc => {
+  // Remove the script subtag from the locale.
+  let noScript = new Intl.Locale(`${loc.language}-${loc.region}`);
+
+  // Add the likely script subtag.
+  let maximized = noScript.maximize();
+
+  for (let opt of options) {
+    // Formatter for the locale without a script subtag.
+    let df1 = new Intl.DateTimeFormat(noScript, opt);
+
+    // Formatter for the locale with the likely script subtag added.
+    let df2 = new Intl.DateTimeFormat(maximized, opt);
+
+    // The output for the locale without a script subtag should match the output
+    // with the likely script subtag added.
+    assertEq(df1.format(date), df2.format(date), `Mismatch for locale "${noScript}" (${maximized})`);
+  }
+});
+
+if (typeof reportCompare === "function")
+  reportCompare(0, 0, "ok");