Bug 1697729: Re-add alias and parent links in ICU filters. r=tcampbell

The `-/*` filter also removes the alias (`%%ALIAS`) and parent locale (`%%Parent`)
links, so we have to manually add them back when we're using `-/*`.

The ICU docs warn about this issue, but unfortunately that warning wasn't
present when we originally created our filter file, so this bug went unnoticed
for a long time.

Differential Revision: https://phabricator.services.mozilla.com/D116981

intl/icu/data_filter.json

@@ -53,6 +53,8 @@
             ],
             "rules": [
                 "-/*",
+                "+/%%ALIAS",
+                "+/%%Parent",
 
                 "+/*/area/acre",
                 "+/*/digital/bit",
@@ -194,6 +196,8 @@
             ],
             "rules": [
                 "-/*",
+                "+/%%ALIAS",
+                "+/%%Parent",
 
                 "+/Languages",
                 "+/Languages%short",
@@ -212,6 +216,8 @@
             ],
             "rules": [
                 "-/*",
+                "+/%%ALIAS",
+                "+/%%Parent",
 
                 "+/Countries",
                 "+/Countries%short"

js/src/tests/non262/Intl/DisplayNames/alias-and-parent-locales.js

@@ -0,0 +1,33 @@
+// |reftest| skip-if(!this.hasOwnProperty('Intl'))
+
+// Ensure alias and parent locales are correctly picked up when calling into ICU.
+
+// "zh-HK" is an alias to "zh-Hant-HK", so display names should default to
+// traditional instead of simplified characters.
+{
+  const zh_Hant = new Intl.DisplayNames("zh-Hant", {type: "region"});
+  const zh_Hans = new Intl.DisplayNames("zh-Hans", {type: "region"});
+  const zh_HK = new Intl.DisplayNames("zh-HK", {type: "region"});
+
+  // We assume traditional and simplified have different outputs.
+  assertEq(zh_Hant.of("US") === zh_Hans.of("US"), false);
+
+  // "zh-HK" should use traditional characters.
+  assertEq(zh_HK.of("US"), zh_Hant.of("US"));
+}
+
+// The parent locale of "en-AU" is "en-001" and not "en" (because "en" actually means "en-US").
+{
+  const en = new Intl.DisplayNames("en", {type: "language"});
+  const en_001 = new Intl.DisplayNames("en-001", {type: "language"});
+  const en_AU = new Intl.DisplayNames("en-AU", {type: "language"});
+
+  // We assume "en" and "en-001" have different outputs.
+  assertEq(en.of("nds-NL") === en_001.of("nds-NL"), false);
+
+  // "en-AU" should have the same output as "en-001".
+  assertEq(en_AU.of("nds-NL"), en_001.of("nds-NL"));
+}
+
+if (typeof reportCompare === "function")
+  reportCompare(true, true);