Detect the default locale name during startup on Apple platforms

This change adds a function to lookup the current NSLocale and extract the language + country code to load into ICU by default.  Previously, we would defer to uloc_getDefault in ICU, which would return a value we would ignore (en_US_POSIX) and result in falling back to invariant mode.

Fixes #68321

src/libraries/System.Globalization/tests/CultureInfo/CultureInfoCurrentCulture.cs

@@ -33,6 +33,14 @@ public void CurrentCulture()
             }
         }
 
+        [Fact]
+        [PlatformSpecific(TestPlatforms.OSX | TestPlatforms.iOS | TestPlatforms.MacCatalyst | TestPlatforms.tvOS)]
+        public void CurrentCulture_Default_Not_Invariant()
+        {
+            Assert.NotEqual(CultureInfo.CurrentCulture, CultureInfo.InvariantCulture);
+            Assert.NotEqual(CultureInfo.CurrentUICulture, CultureInfo.InvariantCulture);
+        }
+
         [Fact]
         public void CurrentCulture_Set_Null_ThrowsArgumentNullException()
         {

src/mono/mono/mini/CMakeLists.txt

@@ -68,6 +68,13 @@ if(HAVE_SYS_ICU AND NOT HOST_WASI)
       pal_timeZoneInfo.c
       entrypoints.c
       ${pal_icushim_sources_base})
+
+  if (TARGET_DARWIN)
+    set(icu_shim_sources_base
+        ${icu_shim_sources_base}
+        pal_locale.m)
+  endif()
+
   addprefix(icu_shim_sources "${ICU_SHIM_PATH}" "${icu_shim_sources_base}")
   set_source_files_properties(${icu_shim_sources} PROPERTIES COMPILE_DEFINITIONS OSX_ICU_LIBRARY_PATH="${OSX_ICU_LIBRARY_PATH}")
   set_source_files_properties(${icu_shim_sources} PROPERTIES COMPILE_FLAGS "-I\"${ICU_INCLUDEDIR}\" -I\"${CLR_SRC_NATIVE_DIR}/libs/System.Globalization.Native/\" -I\"${CLR_SRC_NATIVE_DIR}/libs/Common/\" ${ICU_FLAGS}")

src/native/libs/System.Globalization.Native/CMakeLists.txt

@@ -60,6 +60,10 @@ set(NATIVEGLOBALIZATION_SOURCES
     pal_icushim.c
 )
 
+if (CLR_CMAKE_TARGET_OSX OR CLR_CMAKE_TARGET_MACCATALYST OR CLR_CMAKE_TARGET_IOS OR CLR_CMAKE_TARGET_TVOS)
+    set(NATIVEGLOBALIZATION_SOURCES ${NATIVEGLOBALIZATION_SOURCES} pal_locale.m)
+endif()
+
 # time zone names are filtered out of icu data for the browser and associated functionality is disabled
 if (NOT CLR_CMAKE_TARGET_BROWSER)
     set(NATIVEGLOBALIZATION_SOURCES ${NATIVEGLOBALIZATION_SOURCES} pal_timeZoneInfo.c)

src/native/libs/System.Globalization.Native/pal_locale.c

@@ -134,7 +134,11 @@ int32_t FixupLocaleName(UChar* value, int32_t valueLength)
 // is not desirable at all because it doesn't support case insensitive string comparisons.
 const char* DetectDefaultLocaleName()
 {
+#ifndef __APPLE__
     const char* icuLocale = uloc_getDefault();
+#else
+    const char* icuLocale = DetectDefaultAppleLocaleName();
+#endif
     if (strcmp(icuLocale, "en_US_POSIX") == 0)
     {
         return "";

src/native/libs/System.Globalization.Native/pal_locale.m

@@ -0,0 +1,27 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+#include "pal_locale_internal.h"
+#import <Foundation/Foundation.h>
+
+const char* DetectDefaultAppleLocaleName()
+{
+    NSLocale *currentLocale = [NSLocale currentLocale];
+    NSString *localeName = @"";
+
+    if (!currentLocale)
+    {
+        return strdup([localeName UTF8String]);
+    }
+
+    if ([currentLocale.languageCode length] > 0 && [currentLocale.countryCode length] > 0)
+    {
+        localeName = [NSString stringWithFormat:@"%@-%@", currentLocale.languageCode, currentLocale.countryCode];
+    }
+    else
+    {
+        localeName = [currentLocale.localeIdentifier stringByReplacingOccurrencesOfString:@"_" withString:@"-"];
+    }
+
+    return strdup([localeName UTF8String]);
+}

src/native/libs/System.Globalization.Native/pal_locale_internal.h

@@ -51,3 +51,13 @@ Detect the default locale for the machine, defaulting to Invaraint if
 we can't compute one (different from uloc_getDefault()) would do.
 */
 const char* DetectDefaultLocaleName(void);
+
+#ifdef __APPLE__
+/*
+Function:
+DetectDefaultSystemLocaleName
+
+Detects the default locale string for Apple platforms
+*/
+const char* DetectDefaultAppleLocaleName(void);
+#endif