Fix nullability annotations for static (#25914)

The compiler is now analyzing statics.  Get compliant.

Author: stephentoub

src/System.Private.CoreLib/shared/System/Diagnostics/Tracing/EventSource.cs

@@ -3956,7 +3956,7 @@ private bool SelfDescribingEvents
         // Rather than depending on initialized statics, use lazy initialization to ensure that the statics are initialized exactly when they are needed.
 
         // used for generating GUID from eventsource name
-        private static byte[] namespaceBytes;
+        private static byte[]? namespaceBytes;
 
 #endregion
     }

src/System.Private.CoreLib/shared/System/Environment.Win32.cs

@@ -404,7 +404,7 @@ private static string GetKnownFolderPath(string folderGuid, SpecialFolderOption
 #if FEATURE_APPX
         private static class WinRTFolderPaths
         {
-            private static Func<SpecialFolder, SpecialFolderOption, string> s_winRTFolderPathsGetFolderPath;
+            private static Func<SpecialFolder, SpecialFolderOption, string>? s_winRTFolderPathsGetFolderPath;
 
             public static string GetFolderPath(SpecialFolder folder, SpecialFolderOption option)
             {

src/System.Private.CoreLib/shared/System/Globalization/CultureInfo.Windows.cs

@@ -13,7 +13,7 @@ public partial class CultureInfo : IFormatProvider
     {
 #if FEATURE_APPX
         // When running under AppX, we use this to get some information about the language list
-        private static volatile WindowsRuntimeResourceManagerBase s_WindowsRuntimeResourceManager;
+        private static volatile WindowsRuntimeResourceManagerBase? s_WindowsRuntimeResourceManager;
 
         [ThreadStatic]
         private static bool ts_IsDoingAppXCultureInfoLookup;

src/System.Private.CoreLib/shared/System/Globalization/DateTimeFormatInfo.cs

@@ -51,7 +51,7 @@ public sealed class DateTimeFormatInfo : IFormatProvider, ICloneable
     {
         // cache for the invariant culture.
         // invariantInfo is constant irrespective of your current culture.
-        private static volatile DateTimeFormatInfo s_invariantInfo;
+        private static volatile DateTimeFormatInfo? s_invariantInfo;
 
         // an index which points to a record in Culture Data Table.
         private CultureData _cultureData;
@@ -2135,8 +2135,8 @@ internal bool YearMonthAdjustment(ref int year, ref int month, bool parsedMonthN
         internal const string JapaneseLangName = "ja";
         internal const string EnglishLangName = "en";
 
-        private static volatile DateTimeFormatInfo s_jajpDTFI;
-        private static volatile DateTimeFormatInfo s_zhtwDTFI;
+        private static volatile DateTimeFormatInfo? s_jajpDTFI;
+        private static volatile DateTimeFormatInfo? s_zhtwDTFI;
 
         /// <summary>
         /// Create a Japanese DTFI which uses JapaneseCalendar.  This is used to parse
@@ -2146,7 +2146,7 @@ internal bool YearMonthAdjustment(ref int year, ref int month, bool parsedMonthN
         /// </summary>
         internal static DateTimeFormatInfo GetJapaneseCalendarDTFI()
         {
-            DateTimeFormatInfo temp = s_jajpDTFI;
+            DateTimeFormatInfo? temp = s_jajpDTFI;
             if (temp == null)
             {
                 temp = new CultureInfo("ja-JP", false).DateTimeFormat;
@@ -2164,7 +2164,7 @@ internal static DateTimeFormatInfo GetJapaneseCalendarDTFI()
         /// </summary>
         internal static DateTimeFormatInfo GetTaiwanCalendarDTFI()
         {
-            DateTimeFormatInfo temp = s_zhtwDTFI;
+            DateTimeFormatInfo? temp = s_zhtwDTFI;
             if (temp == null)
             {
                 temp = new CultureInfo("zh-TW", false).DateTimeFormat;

src/System.Private.CoreLib/shared/System/Globalization/DateTimeFormatInfoScanner.cs

@@ -115,7 +115,7 @@ internal class DateTimeFormatInfoScanner
         // The collection fo date words & postfix.
         internal List<string> m_dateWords = new List<string>();
         // Hashtable for the known words.
-        private static volatile Dictionary<string, string> s_knownWords;
+        private static volatile Dictionary<string, string>? s_knownWords;
 
         static Dictionary<string, string> KnownWords
         {
@@ -147,7 +147,7 @@ static Dictionary<string, string> KnownWords
 
                     s_knownWords = temp;
                 }
-                return (s_knownWords);
+                return s_knownWords;
             }
         }
 

src/System.Private.CoreLib/shared/System/Globalization/GregorianCalendar.cs

@@ -27,7 +27,7 @@ public class GregorianCalendar : Calendar
 
         private static readonly int[] DaysToMonth366 = { 0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335, 366 };
 
-        private static volatile Calendar s_defaultInstance;
+        private static volatile Calendar? s_defaultInstance;
 
         public override DateTime MinSupportedDateTime => DateTime.MinValue;
 

src/System.Private.CoreLib/shared/System/Globalization/JapaneseCalendar.cs

@@ -81,7 +81,7 @@ internal static EraInfo[] GetEraInfo()
                 });
         }
 
-        internal static volatile Calendar s_defaultInstance;
+        internal static volatile Calendar? s_defaultInstance;
         internal GregorianCalendarHelper _helper;
 
         internal static Calendar GetDefaultInstance()

src/System.Private.CoreLib/shared/System/Globalization/NumberFormatInfo.cs

@@ -35,7 +35,7 @@ namespace System.Globalization
     /// </remarks>
     public sealed class NumberFormatInfo : IFormatProvider, ICloneable
     {
-        private static volatile NumberFormatInfo s_invariantInfo;
+        private static volatile NumberFormatInfo? s_invariantInfo;
 
         internal int[] _numberGroupSizes = new int[] { 3 };
         internal int[] _currencyGroupSizes = new int[] { 3 };

src/System.Private.CoreLib/shared/System/Globalization/TaiwanCalendar.cs

@@ -30,7 +30,7 @@ public class TaiwanCalendar : Calendar
             new EraInfo( 1, 1912, 1, 1, 1911, 1, GregorianCalendar.MaxYear - 1911)    // era #, start year/month/day, yearOffset, minEraYear
         };
 
-        private static volatile Calendar s_defaultInstance;
+        private static volatile Calendar? s_defaultInstance;
 
         private readonly GregorianCalendarHelper _helper;
 

src/System.Private.CoreLib/shared/System/IO/FileStreamCompletionSource.Win32.cs

@@ -24,7 +24,7 @@ private unsafe class FileStreamCompletionSource : TaskCompletionSource<int>
             private const long CompletedCallback = (long)8 << 32;
             private const ulong ResultMask = ((ulong)uint.MaxValue) << 32;
 
-            private static Action<object?> s_cancelCallback;
+            private static Action<object?>? s_cancelCallback;
 
             private readonly FileStream _stream;
             private readonly int _numBufferedBytes;