Use field to replace a few more explicit ThreadStatic fields

src/libraries/Common/src/System/Net/LazyAsyncResult.cs

@@ -15,23 +15,8 @@ internal class LazyAsyncResult : IAsyncResult
         private const int ForceAsyncCount = 50;
 
         // This is to avoid user mistakes when they queue another async op from a callback the completes sync.
-        [ThreadStatic]
-        private static ThreadContext? t_threadContext;
-
-        private static ThreadContext CurrentThreadContext
-        {
-            get
-            {
-                ThreadContext? threadContext = t_threadContext;
-                if (threadContext == null)
-                {
-                    threadContext = new ThreadContext();
-                    t_threadContext = threadContext;
-                }
-
-                return threadContext;
-            }
-        }
+        [field: ThreadStatic]
+        private static ThreadContext CurrentThreadContext => field ??= new();
 
         private sealed class ThreadContext
         {

src/libraries/System.ComponentModel.Composition/src/System/ComponentModel/Composition/ContractNameServices.cs

@@ -25,16 +25,8 @@ internal static class ContractNameServices
         private const char GenericFormatOpeningBracket = '{';
         private const char GenericFormatClosingBracket = '}';
 
-        [ThreadStatic]
-        private static Dictionary<Type, string>? typeIdentityCache;
-
-        private static Dictionary<Type, string> TypeIdentityCache
-        {
-            get
-            {
-                return typeIdentityCache ??= new Dictionary<Type, string>();
-            }
-        }
+        [field: ThreadStatic]
+        private static Dictionary<Type, string> TypeIdentityCache => field ??= new();
 
         internal static string GetTypeIdentity(Type type)
         {

src/libraries/System.ComponentModel.Composition/src/System/ComponentModel/Composition/ReflectionModel/ImportType.cs

@@ -21,16 +21,8 @@ internal sealed class ImportType
         private Func<Export, object>? _castSingleValue;
         private readonly bool _isOpenGeneric;
 
-        [ThreadStatic]
-        internal static Dictionary<Type, Func<Export, object>?>? _castSingleValueCache;
-
-        private static Dictionary<Type, Func<Export, object>?> CastSingleValueCache
-        {
-            get
-            {
-                return _castSingleValueCache ??= new Dictionary<Type, Func<Export, object>?>();
-            }
-        }
+        [field: ThreadStatic]
+        private static Dictionary<Type, Func<Export, object>?> CastSingleValueCache => field ??= new();
 
         public ImportType(Type type, ImportCardinality cardinality)
         {

src/libraries/System.Diagnostics.DiagnosticSource/src/System/Diagnostics/RandomNumberGenerator.cs

@@ -8,11 +8,10 @@ namespace System.Diagnostics
     /// </summary>
     internal sealed class RandomNumberGenerator
     {
-        [ThreadStatic] private static RandomNumberGenerator? t_random;
-
         private ulong _s0, _s1, _s2, _s3;
 
-        public static RandomNumberGenerator Current => t_random ??= new RandomNumberGenerator();
+        [field: ThreadStatic]
+        public static RandomNumberGenerator Current => field ??= new();
 
         public unsafe RandomNumberGenerator()
         {

src/libraries/System.Private.CoreLib/src/System/Diagnostics/Debug.cs

@@ -32,15 +32,14 @@ public static bool AutoFlush
             set { }
         }
 
-        [ThreadStatic]
-        private static int t_indentLevel;
+        [field: ThreadStatic]
         public static int IndentLevel
         {
-            get => t_indentLevel;
+            get => field;
             set
             {
-                t_indentLevel = value < 0 ? 0 : value;
-                s_provider.OnIndentLevelChanged(t_indentLevel);
+                field = value < 0 ? 0 : value;
+                s_provider.OnIndentLevelChanged(field);
             }
         }
 

src/libraries/System.Security.Cryptography.Cose/tests/CoseTestHelpers.cs

@@ -464,9 +464,8 @@ private static void AssertHeaders(CborReader reader, List<(CoseHeaderLabel, Read
             }
         }
 
-        [ThreadStatic]
-        private static TestKeyRing? t_threadKeys;
-        private static TestKeyRing ThreadKeys => (t_threadKeys ??= new TestKeyRing());
+        [field: ThreadStatic]
+        private static TestKeyRing ThreadKeys => field ??= new();
 
         internal static ECDsa ES256 => ThreadKeys.ES256;
         internal static ECDsa ES384 => ThreadKeys.ES384;

src/libraries/System.Transactions.Local/src/System/Transactions/Transaction.cs

@@ -1126,31 +1126,29 @@ internal sealed class ContextData
 
         internal bool _asyncFlow;
 
-        [ThreadStatic]
-        private static ContextData? t_staticData;
-
         internal ContextData(bool asyncFlow)
         {
             _asyncFlow = asyncFlow;
         }
 
         [AllowNull]
+        [field: ThreadStatic]
         internal static ContextData TLSCurrentData
         {
-            get => t_staticData ??= new ContextData(false);
+            get => field ??= new(false);
             set
             {
-                if (value == null && t_staticData != null)
+                if (value == null && field != null)
                 {
                     // set each property to null to retain one TLS ContextData copy.
-                    t_staticData.CurrentScope = null;
-                    t_staticData.CurrentTransaction = null;
-                    t_staticData.DefaultComContextState = DefaultComContextState.Unknown;
-                    t_staticData.WeakDefaultComContext = null;
+                    field.CurrentScope = null;
+                    field.CurrentTransaction = null;
+                    field.DefaultComContextState = DefaultComContextState.Unknown;
+                    field.WeakDefaultComContext = null;
                 }
                 else
                 {
-                    t_staticData = value;
+                    field = value;
                 }
             }
         }