[browser] Revert to full NativeName by interop with JS

src/libraries/Common/src/Interop/Browser/Interop.Locale.cs

@@ -13,5 +13,7 @@ internal static unsafe partial class JsGlobalization
         internal static extern unsafe int GetFirstDayOfWeek(in string culture, out int exceptionalResult, out object result);
         [MethodImplAttribute(MethodImplOptions.InternalCall)]
         internal static extern unsafe int GetFirstWeekOfYear(in string culture, out int exceptionalResult, out object result);
+        [MethodImplAttribute(MethodImplOptions.InternalCall)]
+        internal static extern unsafe int GetNativeName(in string locale, in string culture, char* buffer, int bufferLength, out int exceptionalResult, out object result);
     }
 }

src/libraries/System.Private.CoreLib/src/System/Globalization/CultureData.Browser.cs

@@ -11,6 +11,22 @@ internal sealed partial class CultureData
     {
         private const int CULTURE_INFO_BUFFER_LEN = 50;
 
+        private unsafe string JSGetNativeName(string localeName, string? uiCultureName = null)
+        {
+            if (string.IsNullOrEmpty(localeName))
+                return "Invariant Language (Invariant Country)";
+
+            string cultureName = uiCultureName ?? localeName;
+            // the longest possible NativeName is 50 characters
+            char* buffer = stackalloc char[CULTURE_INFO_BUFFER_LEN];
+            int exception;
+            object exResult;
+            int resultLength = Interop.JsGlobalization.GetNativeName(localeName, cultureName, buffer, CULTURE_INFO_BUFFER_LEN, out exception, out exResult);
+            if (exception != 0)
+                throw new Exception((string)exResult);
+            return new string(buffer, 0, resultLength);
+        }
+
         private static unsafe CultureData JSLoadCultureInfoFromBrowser(string localeName, CultureData culture)
         {
             char* buffer = stackalloc char[CULTURE_INFO_BUFFER_LEN];

src/libraries/System.Private.CoreLib/src/System/Globalization/CultureData.Icu.cs

@@ -203,6 +203,12 @@ private string IcuGetLocaleInfo(LocaleStringData type, string? uiCultureName = n
             Debug.Assert(!GlobalizationMode.Invariant);
             Debug.Assert(!GlobalizationMode.UseNls);
             Debug.Assert(_sWindowsName != null, "[CultureData.IcuGetLocaleInfo] Expected _sWindowsName to be populated already");
+#if TARGET_BROWSER
+            if (type == LocaleStringData.NativeDisplayName)
+            {
+                return JSGetNativeName(_sWindowsName, uiCultureName);
+            }
+#endif
             return IcuGetLocaleInfo(_sWindowsName, type, uiCultureName);
         }
 
@@ -302,7 +308,14 @@ private unsafe string IcuGetTimeFormatString(bool shortFormat)
         // no support to lookup by region name, other than the hard-coded list in CultureData
         private static CultureData? IcuGetCultureDataFromRegionName() => null;
 
-        private string IcuGetLanguageDisplayName(string cultureName) => IcuGetLocaleInfo(cultureName, LocaleStringData.LocalizedDisplayName, CultureInfo.CurrentUICulture.Name);
+        private string IcuGetLanguageDisplayName(string cultureName)
+        {
+#if TARGET_BROWSER
+            return JSGetNativeName(CultureInfo.CurrentUICulture.Name, cultureName);
+#else
+            return IcuGetLocaleInfo(cultureName, LocaleStringData.LocalizedDisplayName, CultureInfo.CurrentUICulture.Name);
+#endif
+        }
 
         // use the fallback which is to return NativeName
         private static string? IcuGetRegionDisplayName() => null;

src/libraries/System.Runtime/tests/System.Globalization.Tests/CultureInfo/CultureInfoNames.cs

@@ -10,19 +10,31 @@ namespace System.Globalization.Tests
 {
     public class CultureInfoNames
     {
-        private static bool SupportFullIcuResources => (PlatformDetection.IsNotMobile && PlatformDetection.IsIcuGlobalization) || PlatformDetection.IsHybridGlobalizationOnApplePlatform;
+        private static bool SupportFullIcuResources =>
+            (PlatformDetection.IsNotMobile && PlatformDetection.IsIcuGlobalization) ||
+            PlatformDetection.IsHybridGlobalizationOnApplePlatform ||
+            PlatformDetection.IsBrowser;
+
+        public static IEnumerable<object[]> SupportedCultures_TestData()
+        {
+            // Browser does not support all ICU locales but it uses JS to get the correct native name
+            if (!PlatformDetection.IsBrowser)
+            {
+                yield return new object[] { "aa", "aa", "Afar", "Afar" };
+                yield return new object[] { "aa-ER", "aa-ER", "Afar (Eritrea)", "Afar (Eritrea)" };
+            }
+            yield return new object[] { "en", "en", "English", "English" };
+            yield return new object[] { "en", "fr", "English", "anglais" };
+            yield return new object[] { "en-US", "en-US", "English (United States)", "English (United States)" };
+            yield return new object[] { "en-US", "fr-FR", "English (United States)", "anglais (\u00C9tats-Unis)" };
+            yield return new object[] { "en-US", "de-DE", "English (United States)", "Englisch (Vereinigte Staaten)" };
+            yield return new object[] { "", "en-US", "Invariant Language (Invariant Country)", "Invariant Language (Invariant Country)" };
+            yield return new object[] { "", "fr-FR", "Invariant Language (Invariant Country)", "Invariant Language (Invariant Country)" };
+            yield return new object[] { "", "", "Invariant Language (Invariant Country)", "Invariant Language (Invariant Country)" };
+        }
 
         [ConditionalTheory(nameof(SupportFullIcuResources))]
-        [InlineData("en", "en", "English", "English")]
-        [InlineData("en", "fr", "English", "anglais")]
-        [InlineData("aa", "aa", "Afar", "Afar")]
-        [InlineData("en-US", "en-US", "English (United States)", "English (United States)")]
-        [InlineData("en-US", "fr-FR", "English (United States)", "anglais (\u00C9tats-Unis)")]
-        [InlineData("en-US", "de-DE", "English (United States)", "Englisch (Vereinigte Staaten)")]
-        [InlineData("aa-ER", "aa-ER", "Afar (Eritrea)", "Afar (Eritrea)")]
-        [InlineData("", "en-US", "Invariant Language (Invariant Country)", "Invariant Language (Invariant Country)")]
-        [InlineData("", "fr-FR", "Invariant Language (Invariant Country)", "Invariant Language (Invariant Country)")]
-        [InlineData("", "", "Invariant Language (Invariant Country)", "Invariant Language (Invariant Country)")]
+        [MemberData(nameof(SupportedCultures_TestData))]
         public void TestDisplayName(string cultureName, string uiCultureName, string nativeName, string displayName)
         {
             using (new ThreadCultureChange(null, CultureInfo.GetCultureInfo(uiCultureName)))

src/mono/browser/runtime/corebindings.c

@@ -64,6 +64,7 @@ extern mono_bool mono_wasm_starts_with (MonoString **culture, const uint16_t* st
 extern mono_bool mono_wasm_ends_with (MonoString **culture, const uint16_t* str1, int32_t str1Length, const uint16_t* str2, int32_t str2Length, int32_t options, int *is_exception, MonoObject** ex_result);
 extern int mono_wasm_index_of (MonoString **culture, const uint16_t* str1, int32_t str1Length, const uint16_t* str2, int32_t str2Length, int32_t options, mono_bool fromBeginning, int *is_exception, MonoObject** ex_result);
 extern int mono_wasm_get_calendar_info (MonoString **culture, int32_t calendarId, const uint16_t* result, int32_t resultLength, int *is_exception, MonoObject** ex_result);
+extern int mono_wasm_get_native_display_name (MonoString **locale, MonoString **culture, const uint16_t* result, int32_t resultLength, int *is_exception, MonoObject** ex_result);
 extern int mono_wasm_get_culture_info (MonoString **culture, const uint16_t* result, int32_t resultLength, int *is_exception, MonoObject** ex_result);
 extern int mono_wasm_get_first_day_of_week (MonoString **culture, int *is_exception, MonoObject** ex_result);
 extern int mono_wasm_get_first_week_of_year (MonoString **culture, int *is_exception, MonoObject** ex_result);
@@ -105,6 +106,7 @@ void bindings_initialize_internals (void)
 	mono_add_internal_call ("Interop/JsGlobalization::EndsWith", mono_wasm_ends_with);
 	mono_add_internal_call ("Interop/JsGlobalization::IndexOf", mono_wasm_index_of);
 	mono_add_internal_call ("Interop/JsGlobalization::GetCalendarInfo", mono_wasm_get_calendar_info);
+	mono_add_internal_call ("Interop/JsGlobalization::GetNativeName", mono_wasm_get_native_display_name);
 	mono_add_internal_call ("Interop/JsGlobalization::GetCultureInfo", mono_wasm_get_culture_info);
 	mono_add_internal_call ("Interop/JsGlobalization::GetFirstDayOfWeek", mono_wasm_get_first_day_of_week);
 	mono_add_internal_call ("Interop/JsGlobalization::GetFirstWeekOfYear", mono_wasm_get_first_week_of_year);

src/mono/browser/runtime/exports-binding.ts

@@ -22,7 +22,7 @@ import { mono_wasm_compare_string, mono_wasm_ends_with, mono_wasm_starts_with, m
 import { mono_wasm_get_calendar_info } from "./hybrid-globalization/calendar";
 
 import { mono_wasm_get_culture_info } from "./hybrid-globalization/culture-info";
-import { mono_wasm_get_first_day_of_week, mono_wasm_get_first_week_of_year } from "./hybrid-globalization/locales";
+import { mono_wasm_get_native_display_name, mono_wasm_get_first_day_of_week, mono_wasm_get_first_week_of_year } from "./hybrid-globalization/locales";
 import { mono_wasm_browser_entropy } from "./crypto";
 import { mono_wasm_cancel_promise } from "./cancelable-promise";
 
@@ -107,6 +107,7 @@ export const mono_wasm_imports = [
     mono_wasm_index_of,
     mono_wasm_get_calendar_info,
     mono_wasm_get_culture_info,
+    mono_wasm_get_native_display_name,
     mono_wasm_get_first_day_of_week,
     mono_wasm_get_first_week_of_year,
 ];

src/mono/browser/runtime/hybrid-globalization/locales.ts

@@ -3,11 +3,47 @@
 
 import { wrap_error_root, wrap_no_error_root } from "../invoke-js";
 import { mono_wasm_new_external_root } from "../roots";
-import { monoStringToString } from "../strings";
+import { monoStringToString, stringToUTF16 } from "../strings";
 import { Int32Ptr } from "../types/emscripten";
 import { MonoObject, MonoObjectRef, MonoString, MonoStringRef } from "../types/internal";
 import { normalizeLocale } from "./helpers";
 
+export function mono_wasm_get_native_display_name(locale: MonoStringRef, culture: MonoStringRef, dst: number, dstLength: number, isException: Int32Ptr, exAddress: MonoObjectRef) : number
+{
+    const localeRoot = mono_wasm_new_external_root<MonoString>(locale),
+        cultureRoot = mono_wasm_new_external_root<MonoString>(culture),
+        exceptionRoot = mono_wasm_new_external_root<MonoObject>(exAddress);
+    try {
+        const localeName = monoStringToString(localeRoot);
+        const cultureName = monoStringToString(cultureRoot);
+        if (!localeName || !cultureName)
+            throw new Error("Locale or culture name is null or empty.");
+
+        const [language, region] = cultureName.split("-");
+        const languageName = new Intl.DisplayNames([localeName], {type: "language"}).of(language);
+        const regionName = region ? new Intl.DisplayNames([localeName], {type: "region"}).of(region) : undefined;
+        const result = region ? `${languageName} (${regionName})` : languageName;
+
+        if (!result)
+            throw new Error(`Native display name for culture=${cultureName} is null or empty.`);    
+
+        if (result.length > dstLength)
+            throw new Error(`Native display name for culture=${cultureName} exceeds length of ${dstLength}.`);
+
+        stringToUTF16(dst, dst + 2 * result.length, result);
+        wrap_no_error_root(isException, exceptionRoot);
+        return result.length;
+    }
+    catch (ex: any) {
+        wrap_error_root(isException, ex, exceptionRoot);
+        return -1;
+    }
+    finally {
+        cultureRoot.release();
+        exceptionRoot.release();
+    }
+}
+
 export function mono_wasm_get_first_day_of_week(culture: MonoStringRef, isException: Int32Ptr, exAddress: MonoObjectRef): number{
 
     const cultureRoot = mono_wasm_new_external_root<MonoString>(culture),