1 files changed, 95 insertions, 4 deletions

diff --git a/src/System.Private.CoreLib/shared/System/Globalization/CalendarData.Unix.cs b/src/System.Private.CoreLib/shared/System/Globalization/CalendarData.Unix.cs
index 17d6ed7a0..c94ac0ae5 100644
--- a/src/System.Private.CoreLib/shared/System/Globalization/CalendarData.Unix.cs
+++ b/src/System.Private.CoreLib/shared/System/Globalization/CalendarData.Unix.cs
@@ -32,7 +32,7 @@ namespace System.Globalization
 
     internal partial class CalendarData
     {
-        private bool LoadCalendarDataFromSystem(String localeName, CalendarId calendarId)
+        private bool LoadCalendarDataFromSystem(string localeName, CalendarId calendarId)
         {
             bool result = true;
             result &= GetCalendarInfo(localeName, calendarId, CalendarDataType.NativeName, out this.sNativeName);
@@ -134,16 +134,107 @@ namespace System.Globalization
             {
                 List<string> datePatternsList = callbackContext.Results;
 
-                datePatterns = new string[datePatternsList.Count];
                 for (int i = 0; i < datePatternsList.Count; i++)
                 {
-                    datePatterns[i] = NormalizeDatePattern(datePatternsList[i]);
+                    datePatternsList[i] = NormalizeDatePattern(datePatternsList[i]);
                 }
+
+                if (dataType == CalendarDataType.ShortDates)
+                    FixDefaultShortDatePattern(datePatternsList);
+
+                datePatterns = datePatternsList.ToArray();
             }
 
             return result;
         }
 
+        // FixDefaultShortDatePattern will convert the default short date pattern from using 'yy' to using 'yyyy'
+        // And will ensure the original pattern still exist in the list.
+        // doing that will have the short date pattern format the year as 4-digit number and not just 2-digit number.
+        // Example: June 5, 2018 will be formatted to something like 6/5/2018 instead of 6/5/18 fro en-US culture.
+        private static void FixDefaultShortDatePattern(List<string> shortDatePatterns)
+        {
+            if (shortDatePatterns.Count == 0)
+                return;
+
+            string s = shortDatePatterns[0];
+
+            // We are not expecting any pattern have length more than 100.
+            // We have to do this check to prevent stack overflow as we allocate the buffer on the stack.
+            if (s.Length > 100)
+                return;
+
+            Span<char> modifiedPattern = stackalloc char[s.Length + 2];
+            int index = 0;
+
+            while (index < s.Length)
+            {
+                if (s[index] == '\'')
+                {
+                    do 
+                    {
+                        modifiedPattern[index] = s[index];
+                        index++;
+                    } while (index < s.Length && s[index] != '\'');
+
+                    if (index >= s.Length)
+                        return;                 
+                }
+                else if (s[index] == 'y')
+                {
+                    modifiedPattern[index] = 'y';
+                    break;
+                }
+
+                modifiedPattern[index] = s[index];
+                index++;
+            }
+
+            if (index >= s.Length - 1 || s[index + 1] != 'y')
+            {
+                // not a 'yy' pattern
+                return;
+            }
+
+            if (index + 2 < s.Length && s[index + 2] == 'y')
+            {
+                // we have 'yyy' then nothing to do
+                return;
+            }
+
+            // we are sure now we have 'yy' pattern
+
+            Debug.Assert(index + 3 < modifiedPattern.Length);
+
+            modifiedPattern[index + 1] = 'y'; // second y
+            modifiedPattern[index + 2] = 'y'; // third y
+            modifiedPattern[index + 3] = 'y'; // fourth y
+
+            index += 2;
+
+            // Now, copy the rest of the pattern to the destination buffer
+            while (index < s.Length)
+            {
+                modifiedPattern[index + 2] = s[index];
+                index++;
+            }
+
+            shortDatePatterns[0] = modifiedPattern.ToString();
+
+            for (int i = 1; i < shortDatePatterns.Count; i++)
+            {
+                if (shortDatePatterns[i] == shortDatePatterns[0])
+                {
+                    // Found match in the list to the new constructed pattern, then replace it with the original modified pattern
+                    shortDatePatterns[i] = s;
+                    return;
+                }
+            }
+
+            // if we come here means the newly constructed pattern not found on the list, then add the original pattern
+            shortDatePatterns.Add(s);
+        }
+
         /// <summary>
         /// The ICU date format characters are not exactly the same as the .NET date format characters.
         /// NormalizeDatePattern will take in an ICU date pattern and return the equivalent .NET date pattern.
@@ -220,7 +311,7 @@ namespace System.Globalization
                         break;
                     default:
                         const string unsupportedDateFieldSymbols = "YuUrQqwWDFg";
-                        Debug.Assert(unsupportedDateFieldSymbols.IndexOf(input[index]) == -1,
+                        Debug.Assert(!unsupportedDateFieldSymbols.Contains(input[index]),
                             string.Format(CultureInfo.InvariantCulture,
                                 "Encountered an unexpected date field symbol '{0}' from ICU which has no known corresponding .NET equivalent.", 
                                 input[index]));