Fix creating cultures with extensions in the name

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

@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using Microsoft.DotNet.RemoteExecutor;
 using System.Collections.Generic;
 using Xunit;
 
@@ -434,13 +435,65 @@ public void TestCreationWithTemporaryLCID(int lcid)
             Assert.NotEqual(lcid, new CultureInfo(lcid).LCID);
         }
 
-        [InlineData("zh-TW-u-co-zhuyin")]
-        [InlineData("de-DE-u-co-phoneb")]
-        [InlineData("de-u-co-phonebk")]
+        [InlineData("zh-TW-u-co-zhuyin", "zh-TW", "zh-TW_zhuyin")]
+        [InlineData("de-DE-u-co-phonebk", "de-DE", "de-DE_phoneboo")]
+        [InlineData("de-DE-u-co-phonebk-u-xx", "de-DE-u-xx", "de-DE-u-xx_phoneboo")]
+        [InlineData("de-DE-u-xx-u-co-phonebk", "de-DE-u-xx-u-co-phonebk", "de-DE-u-xx-u-co-phonebk")]
+        [InlineData("de-DE-t-xx-u-co-phonebk", "de-DE-t-xx-u-co-phonebk", "de-DE-t-xx-u-co-phonebk_phoneboo")]
+        [InlineData("de-DE-u-co-phonebk-t-xx", "de-DE-t-xx", "de-DE-t-xx_phoneboo")]
+        [InlineData("de-DE-u-co-phonebk-t-xx-u-yy", "de-DE-t-xx-u-yy", "de-DE-t-xx-u-yy_phoneboo")]
+        [InlineData("de-DE", "de-DE", "de-DE")]
         [ConditionalTheory(typeof(PlatformDetection), nameof(PlatformDetection.IsIcuGlobalization))]
-        public void TestCreationWithMangledSortName(string cultureName)
+        public void TestCreationWithMangledSortName(string cultureName, string expectedCultureName, string expectedSortName)
+        {
+            CultureInfo ci = CultureInfo.GetCultureInfo(cultureName);
+
+            Assert.Equal(expectedCultureName, ci.Name);
+            Assert.Equal(expectedSortName, ci.CompareInfo.Name);
+        }
+
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsIcuGlobalization))]
+        public void TestNeutralCultureWithCollationName()
         {
-            Assert.True(CultureInfo.GetCultureInfo(cultureName).CompareInfo.Name.Equals(cultureName, StringComparison.OrdinalIgnoreCase));
+            Assert.Throws<CultureNotFoundException>(() => CultureInfo.GetCultureInfo("zh-u-co-zhuyin"));
+            Assert.Throws<CultureNotFoundException>(() => CultureInfo.GetCultureInfo("de-u-co-phonebk"));
+        }
+
+        [InlineData("xx-u-XX", "xx-u-xx")]
+        [InlineData("xx-u-XX-u-yy", "xx-u-xx-u-yy")]
+        [InlineData("xx-t-ja-JP", "xx-t-ja-jp")]
+        [InlineData("qps-plocm", "qps-PLOCM")] // ICU normalize this name to "qps--plocm" which we normalize it back to "qps-plocm"
+        [ConditionalTheory(typeof(PlatformDetection), nameof(PlatformDetection.IsIcuGlobalization))]
+        public void TestCreationWithICUNormalizedNames(string cultureName, string expectedCultureName)
+        {
+            CultureInfo ci = CultureInfo.GetCultureInfo(cultureName);
+            Assert.Equal(expectedCultureName, ci.Name);
+        }
+
+        private static bool SupportRemoteExecutionWithIcu => RemoteExecutor.IsSupported && PlatformDetection.IsIcuGlobalization;
+
+        [InlineData("xx-u-XX")]
+        [InlineData("xx-u-XX-u-yy")]
+        [InlineData("xx-t-ja-JP")]
+        [InlineData("qps-plocm")]
+        [InlineData("zh-TW-u-co-zhuyin")]
+        [InlineData("de-DE-u-co-phonebk")]
+        [InlineData("de-DE-u-co-phonebk-u-xx")]
+        [InlineData("de-DE-u-xx-u-co-phonebk")]
+        [InlineData("de-DE-t-xx-u-co-phonebk")]
+        [InlineData("de-DE-u-co-phonebk-t-xx")]
+        [InlineData("de-DE-u-co-phonebk-t-xx-u-yy")]
+        [InlineData("de-DE")]
+        [ConditionalTheory(nameof(SupportRemoteExecutionWithIcu))]
+        public void TestWithResourceLookup(string cultureName)
+        {
+            RemoteExecutor.Invoke(name => {
+                CultureInfo.CurrentUICulture = CultureInfo.GetCultureInfo(name);
+                int Zero = 0;
+
+                // This should go through the resource manager to get the localized exception message using the current UI culture
+                Assert.Throws<DivideByZeroException>(() => 1 / Zero);
+            }, cultureName).Dispose();
         }
     }
 }

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

@@ -12,6 +12,88 @@ internal sealed partial class CultureData
         // ICU constants
         private const int ICU_ULOC_KEYWORD_AND_VALUES_CAPACITY = 100; // max size of keyword or value
         private const int ICU_ULOC_FULLNAME_CAPACITY = 157;           // max size of locale name
+        private const int WINDOWS_MAX_COLLATION_NAME_LENGTH = 8;      // max collation name length in the culture name
+
+        /// <summary>
+        /// Process the locale name that ICU returns and convert it to the format that .NET expects.
+        /// </summary>
+        /// <param name="name">The locale name that ICU returns.</param>
+        /// <param name="extension">The extension part in the original culture name.</param>
+        /// <param name="collationStart">The index of the collation in the name.</param>
+        /// <remarks>
+        /// BCP 47 specifications allow for extensions in the locale name, following the format language-script-region-extensions-collation. However,
+        /// not all extensions supported by ICU are supported in .NET. In the locale name, extensions are separated from the rest of the name using '-u-' or '-t-'.
+        /// In .NET, only the collation extension is supported. If the name includes a collation extension, it will be prefixed with '-u-co-'.
+        /// For example, en-US-u-co-search would be converted to the ICU name en_US@collation=search, which would then be translated to the .NET name en-US_search.
+        /// All extensions in the ICU names start with @. When normalizing the name to the .NET format, we retain the extensions in the name to ensure differentiation
+        /// between names with extensions and those without. For example, we may have a name like en-US and en-US-u-xx. Although .NET doesn't support the extension xx,
+        /// we still include it in the name to distinguish it from the name without the extension.
+        /// </remarks>
+        private static string NormalizeCultureName(string name, ReadOnlySpan<char> extension, out int collationStart)
+        {
+            Debug.Assert(name is not null);
+            Debug.Assert(name.Length <= ICU_ULOC_FULLNAME_CAPACITY);
+
+            collationStart = -1;
+            bool changed = false;
+            Span<char> buffer = stackalloc char[ICU_ULOC_FULLNAME_CAPACITY];
+            int bufferIndex = 0;
+
+            for (int i = 0; i < name.Length && bufferIndex < ICU_ULOC_FULLNAME_CAPACITY; i++)
+            {
+                char c = name[i];
+                if (c == '-' && i < name.Length - 1 && name[i + 1] == '-')
+                {
+                    // ICU changes names like `qps_plocm` (one underscore) to `qps__plocm` (two underscores)
+                    // The reason this occurs is because, while ICU canonicalizing, ulocimp_getCountry returns an empty string since the country code value is > 3 (rightly so).
+                    // But append an extra '_' thinking that country code was in-fact appended (for the empty string value as well).
+                    // Before processing, the name qps__plocm will be converted to its .NET name equivalent, which is qps--plocm.
+                    changed = true;
+                    buffer[bufferIndex++] = '-';
+                    i++;
+                }
+                else if (c == '@')
+                {
+                    changed = true;
+
+                    if (!extension.IsEmpty && extension.TryCopyTo(buffer.Slice(bufferIndex)))
+                    {
+                        bufferIndex += extension.Length;
+                    }
+
+                    int collationIndex = name.IndexOf("collation=", i + 1, StringComparison.Ordinal);
+                    if (collationIndex > 0)
+                    {
+                        collationIndex += "collation=".Length;
+
+                        // format of the locale properties is @key=value;collation=collationName;key=value;key=value
+                        int endOfCollation = name.IndexOf(';', collationIndex);
+                        if (endOfCollation < 0)
+                        {
+                            endOfCollation = name.Length;
+                        }
+
+                        int length = Math.Min(WINDOWS_MAX_COLLATION_NAME_LENGTH, endOfCollation - collationIndex);  // Windows doesn't allow collation names longer than 8 characters
+                        if (buffer.Length - bufferIndex >= length + 1)
+                        {
+                            collationStart = bufferIndex;
+                            buffer[bufferIndex++] = '_';
+                            name.AsSpan(collationIndex, length).CopyTo(buffer.Slice(bufferIndex));
+                            bufferIndex += length;
+                        }
+                    }
+
+                    // done getting all parts can be supported in the .NET culture names.
+                    break;
+                }
+                else
+                {
+                    buffer[bufferIndex++] = name[i];
+                }
+            }
+
+            return changed ? new string(buffer.Slice(0, bufferIndex)) : name;
+        }
 
         /// <summary>
         /// This method uses the sRealName field (which is initialized by the constructor before this is called) to
@@ -26,16 +108,15 @@ private bool InitIcuCultureDataCore()
             string realNameBuffer = _sRealName;
 
             // Basic validation
-            if (!IsValidCultureName(realNameBuffer, out var index))
+            if (!IsValidCultureName(realNameBuffer, out var index, out int indexOfExtensions))
             {
                 return false;
             }
 
             // Replace _ (alternate sort) with @collation= for ICU
-            ReadOnlySpan<char> alternateSortName = default;
             if (index > 0)
             {
-                alternateSortName = realNameBuffer.AsSpan(index + 1);
+                ReadOnlySpan<char> alternateSortName = realNameBuffer.AsSpan(index + 1);
                 realNameBuffer = string.Concat(realNameBuffer.AsSpan(0, index), ICU_COLLATION_KEYWORD, alternateSortName);
             }
 
@@ -45,22 +126,9 @@ private bool InitIcuCultureDataCore()
                 return false; // fail
             }
 
-            // Replace the ICU collation keyword with an _
             Debug.Assert(_sWindowsName != null);
-            index = _sWindowsName.IndexOf(ICU_COLLATION_KEYWORD, StringComparison.Ordinal);
-            if (index >= 0)
-            {
-                // Use original culture name if alternateSortName is not set, which is possible even if the normalized
-                // culture name has "@collation=".
-                // "zh-TW-u-co-zhuyin" is a good example. The term "u-co-" means the following part will be the sort name
-                // and it will be treated in ICU as "zh-TW@collation=zhuyin".
-                _sName = alternateSortName.Length == 0 ? realNameBuffer : string.Concat(_sWindowsName.AsSpan(0, index), "_", alternateSortName);
-            }
-            else
-            {
-                _sName = _sWindowsName;
-            }
-            _sRealName = _sName;
+
+            _sRealName = NormalizeCultureName(_sWindowsName, indexOfExtensions > 0 ? _sRealName.AsSpan(indexOfExtensions) : ReadOnlySpan<char>.Empty, out int collationStart);
 
             _iLanguage = LCID;
             if (_iLanguage == 0)
@@ -69,11 +137,15 @@ private bool InitIcuCultureDataCore()
             }
             _bNeutral = TwoLetterISOCountryName.Length == 0;
             _sSpecificCulture = _bNeutral ? IcuLocaleData.GetSpecificCultureName(_sRealName) : _sRealName;
-            // Remove the sort from sName unless custom culture
-            if (index > 0 && !_bNeutral && !IsCustomCultureId(_iLanguage))
+
+            if (_bNeutral && collationStart > 0)
             {
-                _sName = _sWindowsName.Substring(0, index);
+                return false; // neutral cultures cannot have collation
             }
+
+            // Remove the sort from sName unless custom culture
+            _sName = collationStart < 0 ? _sRealName : _sRealName.Substring(0, collationStart);
+
             return true;
         }
 
@@ -367,7 +439,7 @@ private static CultureInfo[] IcuEnumCultures(CultureTypes types)
             }
 
             bool enumNeutrals   = (types & CultureTypes.NeutralCultures) != 0;
-            bool enumSpecificss = (types & CultureTypes.SpecificCultures) != 0;
+            bool enumSpecifics = (types & CultureTypes.SpecificCultures) != 0;
 
             List<CultureInfo> list = new List<CultureInfo>();
             if (enumNeutrals)
@@ -382,7 +454,7 @@ private static CultureInfo[] IcuEnumCultures(CultureTypes types)
                 if (index + length <= bufferLength)
                 {
                     CultureInfo ci = CultureInfo.GetCultureInfo(new string(chars, index, length));
-                    if ((enumNeutrals && ci.IsNeutralCulture) || (enumSpecificss && !ci.IsNeutralCulture))
+                    if ((enumNeutrals && ci.IsNeutralCulture) || (enumSpecifics && !ci.IsNeutralCulture))
                     {
                         list.Add(ci);
                     }
@@ -416,10 +488,14 @@ private static string IcuGetConsoleFallbackName(string cultureName)
         /// * Disallow input that starts or ends with '-' or '_'.
         /// * Disallow input that has any combination of consecutive '-' or '_'.
         /// * Disallow input that has multiple '_'.
+        ///
+        /// The IsValidCultureName method also identifies the presence of any extensions in the name (such as -u- or -t-) and returns the index of the extension.
+        /// This is necessary because we need to append the extensions to the name when normalizing it to the .NET format.
         /// </remarks>
-        private static bool IsValidCultureName(string subject, out int indexOfUnderscore)
+        private static bool IsValidCultureName(string subject, out int indexOfUnderscore, out int indexOfExtensions)
         {
             indexOfUnderscore = -1;
+            indexOfExtensions = -1;
 
             if (subject.Length == 0) return true; // Invariant Culture
             if (subject.Length == 1 || subject.Length > LocaleNameMaxLength) return false;
@@ -444,6 +520,16 @@ private static bool IsValidCultureName(string subject, out int indexOfUnderscore
                         seenUnderscore = true;
                         indexOfUnderscore = i;
                     }
+                    else
+                    {
+                        if (indexOfExtensions < 0 && i < subject.Length - 2 && (subject[i + 1] is 'u' or 't') && subject[i + 2] == '-') // we have -u- or -t- which is an extension
+                        {
+                            if (subject[i + 1] == 't' || i >= subject.Length - 6 || subject[i + 3] != 'c' || subject[i + 4] != 'o' || subject[i + 5] != '-' ) // not -u-co- collation extension
+                            {
+                                indexOfExtensions = i;
+                            }
+                        }
+                    }
                 }
                 else
                 {