Add DateTime{Offset}.TryFormat methods

The existing implementations just format to a StringBuilder and then get the string from that StringBuilder.  For now at least, these TryFormats share the same code, and just copy the StringBuilder to the span instead of using ToString.

3 files changed, 41 insertions, 8 deletions

diff --git a/src/mscorlib/shared/System/DateTime.cs b/src/mscorlib/shared/System/DateTime.cs
index 27c9fda805..ad4d3a0fd3 100644
--- a/src/mscorlib/shared/System/DateTime.cs
+++ b/src/mscorlib/shared/System/DateTime.cs
@@ -1290,6 +1290,9 @@ namespace System
             return DateTimeFormat.Format(this, format, DateTimeFormatInfo.GetInstance(provider));
         }
 
+        public bool TryFormat(Span<char> destination, out int charsWritten, string format = null, IFormatProvider provider = null) =>
+            DateTimeFormat.TryFormat(this, destination, out charsWritten, format, DateTimeFormatInfo.GetInstance(provider));
+
         public DateTime ToUniversalTime()
         {
             return TimeZoneInfo.ConvertTimeToUtc(this, TimeZoneInfoOptions.NoThrowOnInvalidTime);
diff --git a/src/mscorlib/shared/System/DateTimeOffset.cs b/src/mscorlib/shared/System/DateTimeOffset.cs
index 3855dc5ff3..9dc63e04ce 100644
--- a/src/mscorlib/shared/System/DateTimeOffset.cs
+++ b/src/mscorlib/shared/System/DateTimeOffset.cs
@@ -771,6 +771,9 @@ namespace System
             return DateTimeFormat.Format(ClockDateTime, format, DateTimeFormatInfo.GetInstance(formatProvider), Offset);
         }
 
+        public bool TryFormat(Span<char> destination, out int charsWritten, string format = null, IFormatProvider formatProvider = null) =>
+            DateTimeFormat.TryFormat(ClockDateTime, destination, out charsWritten, format, DateTimeFormatInfo.GetInstance(formatProvider), Offset);
+
         public DateTimeOffset ToUniversalTime()
         {
             return new DateTimeOffset(UtcDateTime);
diff --git a/src/mscorlib/shared/System/Globalization/DateTimeFormat.cs b/src/mscorlib/shared/System/Globalization/DateTimeFormat.cs
index f129f73136..ac5d8a04ba 100644
--- a/src/mscorlib/shared/System/Globalization/DateTimeFormat.cs
+++ b/src/mscorlib/shared/System/Globalization/DateTimeFormat.cs
@@ -446,7 +446,7 @@ namespace System
         //
         //  Actions: Format the DateTime instance using the specified format.
         // 
-        private static String FormatCustomized(DateTime dateTime, String format, DateTimeFormatInfo dtfi, TimeSpan offset)
+        private static StringBuilder FormatCustomized(DateTime dateTime, String format, DateTimeFormatInfo dtfi, TimeSpan offset)
         {
             Calendar cal = dtfi.Calendar;
             StringBuilder result = StringBuilderCache.Acquire();
@@ -532,6 +532,7 @@ namespace System
                         }
                         else
                         {
+                            StringBuilderCache.Release(result);
                             throw new FormatException(SR.Format_InvalidString);
                         }
                         break;
@@ -700,6 +701,7 @@ namespace System
                             // This means that '%' is at the end of the format string or
                             // "%%" appears in the format string.
                             //
+                            StringBuilderCache.Release(result);
                             throw new FormatException(SR.Format_InvalidString);
                         }
                         break;
@@ -723,6 +725,7 @@ namespace System
                             //
                             // This means that '\' is at the end of the formatting string.
                             //
+                            StringBuilderCache.Release(result);
                             throw new FormatException(SR.Format_InvalidString);
                         }
                         break;
@@ -737,7 +740,7 @@ namespace System
                 }
                 i += tokenLen;
             }
-            return StringBuilderCache.GetStringAndRelease(result);
+            return result;
         }
 
 
@@ -966,8 +969,32 @@ namespace System
             return Format(dateTime, format, dtfi, NullOffset);
         }
 
+        internal static string Format(DateTime dateTime, String format, DateTimeFormatInfo dtfi, TimeSpan offset) =>
+            StringBuilderCache.GetStringAndRelease(FormatStringBuilder(dateTime, format, dtfi, offset));
 
-        internal static String Format(DateTime dateTime, String format, DateTimeFormatInfo dtfi, TimeSpan offset)
+        internal static bool TryFormat(DateTime dateTime, Span<char> destination, out int charsWritten, string format, DateTimeFormatInfo dtfi) =>
+            TryFormat(dateTime, destination, out charsWritten, format, dtfi, NullOffset);
+
+        internal static bool TryFormat(DateTime dateTime, Span<char> destination, out int charsWritten, string format, DateTimeFormatInfo dtfi, TimeSpan offset)
+        {
+            StringBuilder sb = FormatStringBuilder(dateTime, format, dtfi, offset);
+
+            bool success = sb.Length <= destination.Length;
+            if (success)
+            {
+                sb.CopyTo(0, destination, sb.Length);
+                charsWritten = sb.Length;
+            }
+            else
+            {
+                charsWritten = 0;
+            }
+
+            StringBuilderCache.Release(sb);
+            return success;
+        }
+
+        internal static StringBuilder FormatStringBuilder(DateTime dateTime, String format, DateTimeFormatInfo dtfi, TimeSpan offset)
         {
             Debug.Assert(dtfi != null);
             if (format == null || format.Length == 0)
@@ -1043,10 +1070,10 @@ namespace System
                 format = ExpandPredefinedFormat(format, ref dateTime, ref dtfi, ref offset);
             }
 
-            return (FormatCustomized(dateTime, format, dtfi, offset));
+            return FormatCustomized(dateTime, format, dtfi, offset);
         }
 
-        internal static string FastFormatRfc1123(DateTime dateTime, TimeSpan offset, DateTimeFormatInfo dtfi)
+        internal static StringBuilder FastFormatRfc1123(DateTime dateTime, TimeSpan offset, DateTimeFormatInfo dtfi)
         {
             // ddd, dd MMM yyyy HH:mm:ss GMT
             const int Rfc1123FormatLength = 29;
@@ -1072,10 +1099,10 @@ namespace System
             result.Append(' ');
             result.Append(Gmt);
 
-            return StringBuilderCache.GetStringAndRelease(result);
+            return result;
         }
 
-        internal static string FastFormatRoundtrip(DateTime dateTime, TimeSpan offset)
+        internal static StringBuilder FastFormatRoundtrip(DateTime dateTime, TimeSpan offset)
         {
             // yyyy-MM-ddTHH:mm:ss.fffffffK
             const int roundTripFormatLength = 28;
@@ -1096,7 +1123,7 @@ namespace System
 
             FormatCustomizedRoundripTimeZone(dateTime, offset, result);
 
-            return StringBuilderCache.GetStringAndRelease(result);
+            return result;
         }
 
         private static void AppendHHmmssTimeOfDay(StringBuilder result, DateTime dateTime)