Fix some nullable annotations from API Review

src/System.Private.CoreLib/System.Private.CoreLib.csproj

@@ -54,8 +54,7 @@
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
     <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
-    <!-- Remove CS8609 once https://github.com/dotnet/roslyn/issues/23268 is resolved -->
-    <NoWarn>$(NoWarn);649,1573,1591,0419,3021,CS8609</NoWarn>
+    <NoWarn>$(NoWarn);649,1573,1591,0419,3021</NoWarn>
     <Nullable>enable</Nullable>
 
     <!-- Ignore all previous constants since SPCL is sensitive to what is defined and the Sdk adds some by default -->

src/System.Private.CoreLib/shared/System/Activator.RuntimeType.cs

@@ -116,7 +116,7 @@ public static partial class Activator
                 if (assemblyName.ContentType == AssemblyContentType.WindowsRuntime)
                 {
                     // WinRT type - we have to use Type.GetType
-                    type = Type.GetType(typeName + ", " + assemblyString, true /*throwOnError*/, ignoreCase);
+                    type = Type.GetType(typeName + ", " + assemblyString, throwOnError: true, ignoreCase);
                 }
                 else
                 {
@@ -131,7 +131,7 @@ public static partial class Activator
                 type = assembly!.GetType(typeName, throwOnError: true, ignoreCase);
             }
 
-            object? o = CreateInstance(type, bindingAttr, binder, args, culture, activationAttributes);
+            object? o = CreateInstance(type!, bindingAttr, binder, args, culture, activationAttributes);
 
             return o != null ? new ObjectHandle(o) : null;          
         }

src/System.Private.CoreLib/shared/System/Activator.cs

@@ -45,7 +45,7 @@ public static partial class Activator
         public static ObjectHandle? CreateInstanceFrom(string assemblyFile, string typeName, bool ignoreCase, BindingFlags bindingAttr, Binder? binder, object?[]? args, CultureInfo? culture, object?[]? activationAttributes)
         {
             Assembly assembly = Assembly.LoadFrom(assemblyFile);
-            Type t = assembly.GetType(typeName, true, ignoreCase);
+            Type t = assembly.GetType(typeName, throwOnError: true, ignoreCase)!;
 
             object? o = CreateInstance(t, bindingAttr, binder, args, culture, activationAttributes);
 

src/System.Private.CoreLib/shared/System/AppContext.cs

@@ -17,14 +17,14 @@ public static partial class AppContext
         private static Dictionary<string, bool>? s_switches;
         private static string? s_defaultBaseDirectory;
 
-        public static string? BaseDirectory
+        public static string BaseDirectory
         {
             get
             {
                 // The value of APP_CONTEXT_BASE_DIRECTORY key has to be a string and it is not allowed to be any other type. 
                 // Otherwise the caller will get invalid cast exception
                 return (string?)GetData("APP_CONTEXT_BASE_DIRECTORY") ??
-                    (s_defaultBaseDirectory ?? (s_defaultBaseDirectory = GetBaseDirectoryCore()));
+                    (s_defaultBaseDirectory ?? (s_defaultBaseDirectory = GetBaseDirectoryCore())) ?? string.Empty;
             }
         }
 

src/System.Private.CoreLib/shared/System/ComponentModel/DefaultValueAttribute.cs

@@ -30,7 +30,7 @@ public class DefaultValueAttribute : Attribute
         /// class, converting the specified value to the specified type, and using the U.S. English
         /// culture as the translation context.
         /// </summary>
-        public DefaultValueAttribute(Type? type, string? value)
+        public DefaultValueAttribute(Type type, string? value)
         {
             // The null check and try/catch here are because attributes should never throw exceptions.
             // We would fail to load an otherwise normal class.

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

@@ -3521,19 +3521,19 @@ private static void AddProviderEnumKind(ManifestBuilder manifest, FieldInfo stat
             if (!reflectionOnly && (staticFieldType == typeof(EventOpcode)) || AttributeTypeNamesMatch(staticFieldType, typeof(EventOpcode)))
             {
                 if (providerEnumKind != "Opcodes") goto Error;
-                int value = (int)staticField.GetRawConstantValue();
+                int value = (int)staticField.GetRawConstantValue()!;
                 manifest.AddOpcode(staticField.Name, value);
             }
             else if (!reflectionOnly && (staticFieldType == typeof(EventTask)) || AttributeTypeNamesMatch(staticFieldType, typeof(EventTask)))
             {
                 if (providerEnumKind != "Tasks") goto Error;
-                int value = (int)staticField.GetRawConstantValue();
+                int value = (int)staticField.GetRawConstantValue()!;
                 manifest.AddTask(staticField.Name, value);
             }
             else if (!reflectionOnly && (staticFieldType == typeof(EventKeywords)) || AttributeTypeNamesMatch(staticFieldType, typeof(EventKeywords)))
             {
                 if (providerEnumKind != "Keywords") goto Error;
-                ulong value = unchecked((ulong)(long)staticField.GetRawConstantValue());
+                ulong value = unchecked((ulong)(long)staticField.GetRawConstantValue()!);
                 manifest.AddKeyword(staticField.Name, value);
             }
 #if FEATURE_MANAGED_ETW_CHANNELS && FEATURE_ADVANCED_MANAGED_ETW_CHANNELS
@@ -3730,7 +3730,7 @@ private static int GetHelperCallFirstArg(MethodInfo method)
 #if ES_BUILD_STANDALONE
             (new ReflectionPermission(ReflectionPermissionFlag.MemberAccess)).Assert();
 #endif
-            byte[] instrs = method.GetMethodBody().GetILAsByteArray()!;
+            byte[] instrs = method.GetMethodBody()!.GetILAsByteArray()!;
             int retVal = -1;
             for (int idx = 0; idx < instrs.Length;)
             {
@@ -5828,7 +5828,7 @@ private string CreateManifestString()
                     bool anyValuesWritten = false;
                     foreach (FieldInfo staticField in staticFields)
                     {
-                        object constantValObj = staticField.GetRawConstantValue();
+                        object? constantValObj = staticField.GetRawConstantValue();
 
                         if (constantValObj != null)
                         {

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

@@ -655,15 +655,15 @@ internal static bool TryParseExact(ReadOnlySpan<char> input, ReadOnlySpan<char>
             return false;
         }
 
-        internal static TimeSpan ParseExactMultiple(ReadOnlySpan<char> input, string?[] formats, IFormatProvider? formatProvider, TimeSpanStyles styles)
+        internal static TimeSpan ParseExactMultiple(ReadOnlySpan<char> input, string[] formats, IFormatProvider? formatProvider, TimeSpanStyles styles)
         {
             var parseResult = new TimeSpanResult(throwOnFailure: true, originalTimeSpanString: input);
             bool success = TryParseExactMultipleTimeSpan(input, formats, formatProvider, styles, ref parseResult);
             Debug.Assert(success, "Should have thrown on failure");
             return parseResult.parsedTimeSpan;
         }
 
-        internal static bool TryParseExactMultiple(ReadOnlySpan<char> input, string?[]? formats, IFormatProvider? formatProvider, TimeSpanStyles styles, out TimeSpan result)
+        internal static bool TryParseExactMultiple(ReadOnlySpan<char> input, string[] formats, IFormatProvider? formatProvider, TimeSpanStyles styles, out TimeSpan result)
         {
             var parseResult = new TimeSpanResult(throwOnFailure: false, originalTimeSpanString: input);
 
@@ -1669,7 +1669,7 @@ internal void SkipBlanks()
         }
 
         /// <summary>Common private ParseExactMultiple method called by both ParseExactMultiple and TryParseExactMultiple.</summary>
-        private static bool TryParseExactMultipleTimeSpan(ReadOnlySpan<char> input, string?[]? formats, IFormatProvider? formatProvider, TimeSpanStyles styles, ref TimeSpanResult result)
+        private static bool TryParseExactMultipleTimeSpan(ReadOnlySpan<char> input, string[] formats, IFormatProvider? formatProvider, TimeSpanStyles styles, ref TimeSpanResult result)
         {
             if (formats == null)
             {
@@ -1690,8 +1690,7 @@ private static bool TryParseExactMultipleTimeSpan(ReadOnlySpan<char> input, stri
             // one of the formats.
             for (int i = 0; i < formats.Length; i++)
             {
-                // TODO-NULLABLE: Indexer nullability tracked (https://github.com/dotnet/roslyn/issues/34644)
-                if (formats[i] == null || formats[i]!.Length == 0)
+                if (formats[i] == null || formats[i].Length == 0)
                 {
                     return result.SetBadFormatSpecifierFailure();
                 }

src/System.Private.CoreLib/shared/System/Reflection/Assembly.cs

@@ -92,9 +92,9 @@ public virtual Type[] GetTypes()
         public virtual AssemblyName GetName() => GetName(copiedName: false);
         public virtual AssemblyName GetName(bool copiedName) { throw NotImplemented.ByDesign; }
 
-        public virtual Type GetType(string name) => GetType(name, throwOnError: false, ignoreCase: false);
-        public virtual Type GetType(string name, bool throwOnError) => GetType(name, throwOnError: throwOnError, ignoreCase: false);
-        public virtual Type GetType(string name, bool throwOnError, bool ignoreCase) { throw NotImplemented.ByDesign; }
+        public virtual Type? GetType(string name) => GetType(name, throwOnError: false, ignoreCase: false);
+        public virtual Type? GetType(string name, bool throwOnError) => GetType(name, throwOnError: throwOnError, ignoreCase: false);
+        public virtual Type? GetType(string name, bool throwOnError, bool ignoreCase) { throw NotImplemented.ByDesign; }
 
         public virtual bool IsDefined(Type attributeType, bool inherit) { throw NotImplemented.ByDesign; }
 
@@ -110,7 +110,7 @@ public virtual Type[] GetTypes()
         public object? CreateInstance(string typeName, bool ignoreCase) => CreateInstance(typeName, ignoreCase, BindingFlags.Public | BindingFlags.Instance, binder: null, args: null, culture: null, activationAttributes: null);
         public virtual object? CreateInstance(string typeName, bool ignoreCase, BindingFlags bindingAttr, Binder? binder, object[]? args, CultureInfo? culture, object[]? activationAttributes)
         {
-            Type t = GetType(typeName, throwOnError: false, ignoreCase: ignoreCase);
+            Type? t = GetType(typeName, throwOnError: false, ignoreCase: ignoreCase);
             if (t == null)
                 return null;
 
@@ -119,8 +119,8 @@ public virtual Type[] GetTypes()
 
         public virtual event ModuleResolveEventHandler ModuleResolve { add { throw NotImplemented.ByDesign; } remove { throw NotImplemented.ByDesign; } }
 
-        public virtual Module? ManifestModule { get { throw NotImplemented.ByDesign; } }
-        public virtual Module GetModule(string name) { throw NotImplemented.ByDesign; }
+        public virtual Module ManifestModule { get { throw NotImplemented.ByDesign; } }
+        public virtual Module? GetModule(string name) { throw NotImplemented.ByDesign; }
 
         public Module[] GetModules() => GetModules(getResourceModules: false);
         public virtual Module[] GetModules(bool getResourceModules) { throw NotImplemented.ByDesign; }
@@ -324,19 +324,19 @@ public static Assembly LoadFrom(string assemblyFile)
             return AssemblyLoadContext.Default.LoadFromAssemblyPath(fullPath);
         }
 
-        public static Assembly LoadFrom(string? assemblyFile, byte[]? hashValue, AssemblyHashAlgorithm hashAlgorithm)
+        public static Assembly LoadFrom(string assemblyFile, byte[]? hashValue, AssemblyHashAlgorithm hashAlgorithm)
         {
             throw new NotSupportedException(SR.NotSupported_AssemblyLoadFromHash);
         }
 
         public static Assembly UnsafeLoadFrom(string assemblyFile) => LoadFrom(assemblyFile);
 
-        public Module LoadModule(string? moduleName, byte[]? rawModule) => LoadModule(moduleName, rawModule, null);
-        public virtual Module LoadModule(string? moduleName, byte[]? rawModule, byte[]? rawSymbolStore) { throw NotImplemented.ByDesign; }
+        public Module LoadModule(string moduleName, byte[]? rawModule) => LoadModule(moduleName, rawModule, null);
+        public virtual Module LoadModule(string moduleName, byte[]? rawModule, byte[]? rawSymbolStore) { throw NotImplemented.ByDesign; }
 
-        public static Assembly ReflectionOnlyLoad(byte[]? rawAssembly) { throw new PlatformNotSupportedException(SR.PlatformNotSupported_ReflectionOnly); }
-        public static Assembly ReflectionOnlyLoad(string? assemblyString) { throw new PlatformNotSupportedException(SR.PlatformNotSupported_ReflectionOnly); }
-        public static Assembly ReflectionOnlyLoadFrom(string? assemblyFile) { throw new PlatformNotSupportedException(SR.PlatformNotSupported_ReflectionOnly); }
+        public static Assembly ReflectionOnlyLoad(byte[] rawAssembly) { throw new PlatformNotSupportedException(SR.PlatformNotSupported_ReflectionOnly); }
+        public static Assembly ReflectionOnlyLoad(string assemblyString) { throw new PlatformNotSupportedException(SR.PlatformNotSupported_ReflectionOnly); }
+        public static Assembly ReflectionOnlyLoadFrom(string assemblyFile) { throw new PlatformNotSupportedException(SR.PlatformNotSupported_ReflectionOnly); }
 
         public virtual SecurityRuleSet SecurityRuleSet => SecurityRuleSet.None;
     }

src/System.Private.CoreLib/shared/System/Reflection/AssemblyName.cs

@@ -172,7 +172,7 @@ public void SetPublicKey(byte[]? publicKey)
 
         // The compressed version of the public key formed from a truncated hash.
         // Will throw a SecurityException if _publicKey is invalid
-        public byte[] GetPublicKeyToken()
+        public byte[]? GetPublicKeyToken()
         {
             if (_publicKeyToken == null)
                 _publicKeyToken = ComputePublicKeyToken();
@@ -226,7 +226,7 @@ public string FullName
                 if (this.Name == null)
                     return string.Empty;
                 // Do not call GetPublicKeyToken() here - that latches the result into AssemblyName which isn't a side effect we want.
-                byte[] pkt = _publicKeyToken ?? ComputePublicKeyToken();
+                byte[]? pkt = _publicKeyToken ?? ComputePublicKeyToken();
                 return AssemblyNameFormatter.ComputeDisplayName(Name, Version, CultureName, pkt, Flags, ContentType);
             }
         }

src/System.Private.CoreLib/shared/System/Reflection/CustomAttributeNamedArgument.cs

@@ -47,7 +47,7 @@ public CustomAttributeNamedArgument(MemberInfo memberInfo, CustomAttributeTypedA
         public override string ToString()
         {
             if (m_memberInfo == null)
-                return base.ToString();
+                return base.ToString()!;
 
             return string.Format("{0} = {1}", MemberInfo.Name, TypedValue.ToString(ArgumentType != typeof(object)));
         }

src/System.Private.CoreLib/shared/System/Reflection/CustomAttributeTypedArgument.cs

@@ -41,7 +41,7 @@ public CustomAttributeTypedArgument(object value)
         internal string ToString(bool typed)
         {
             if (m_argumentType == null)
-                return base.ToString();
+                return base.ToString()!;
 
             if (ArgumentType.IsEnum)
                 return string.Format(typed ? "{0}" : "({1}){0}", Value, ArgumentType.FullName);

src/System.Private.CoreLib/shared/System/Reflection/FieldInfo.cs

@@ -66,15 +66,15 @@ protected FieldInfo() { }
 
         [DebuggerHidden]
         [DebuggerStepThrough]
-        public void SetValue(object? obj, object value) => SetValue(obj, value, BindingFlags.Default, Type.DefaultBinder, null);
+        public void SetValue(object? obj, object? value) => SetValue(obj, value, BindingFlags.Default, Type.DefaultBinder, null);
         public abstract void SetValue(object? obj, object? value, BindingFlags invokeAttr, Binder? binder, CultureInfo? culture);
 
         [CLSCompliant(false)]
         public virtual void SetValueDirect(TypedReference obj, object value) { throw new NotSupportedException(SR.NotSupported_AbstractNonCLS); }
         [CLSCompliant(false)]
-        public virtual object GetValueDirect(TypedReference obj) { throw new NotSupportedException(SR.NotSupported_AbstractNonCLS); }
+        public virtual object? GetValueDirect(TypedReference obj) { throw new NotSupportedException(SR.NotSupported_AbstractNonCLS); }
 
-        public virtual object GetRawConstantValue() { throw new NotSupportedException(SR.NotSupported_AbstractNonCLS); }
+        public virtual object? GetRawConstantValue() { throw new NotSupportedException(SR.NotSupported_AbstractNonCLS); }
 
         public virtual Type[] GetOptionalCustomModifiers() { throw NotImplemented.ByDesign; }
         public virtual Type[] GetRequiredCustomModifiers() { throw NotImplemented.ByDesign; }

src/System.Private.CoreLib/shared/System/Reflection/IReflect.cs

@@ -67,7 +67,7 @@ public interface IReflect
         // For the default binder, the most specific method will be selected.
         // 
         // This will invoke a specific member...
-        object? InvokeMember(string name, BindingFlags invokeAttr, Binder? binder, object? target, object[]? args, ParameterModifier[]? modifiers, CultureInfo? culture, string[]? namedParameters);
+        object? InvokeMember(string name, BindingFlags invokeAttr, Binder? binder, object? target, object?[]? args, ParameterModifier[]? modifiers, CultureInfo? culture, string[]? namedParameters);
 
         // Return the underlying Type that represents the IReflect Object.  For expando object,
         // this is the (Object) IReflectInstance.GetType().  For Type object it is this.

src/System.Private.CoreLib/shared/System/Reflection/MemberFilter.cs

@@ -4,5 +4,5 @@
 
 namespace System.Reflection
 {
-    public delegate bool MemberFilter(MemberInfo m, object filterCriteria);
+    public delegate bool MemberFilter(MemberInfo m, object? filterCriteria);
 }

src/System.Private.CoreLib/shared/System/Reflection/MethodBase.cs

@@ -16,7 +16,7 @@ protected MethodBase() { }
         public abstract MethodAttributes Attributes { get; }
         public virtual MethodImplAttributes MethodImplementationFlags => GetMethodImplementationFlags();
         public abstract MethodImplAttributes GetMethodImplementationFlags();
-        public virtual MethodBody GetMethodBody() { throw new InvalidOperationException(); }
+        public virtual MethodBody? GetMethodBody() { throw new InvalidOperationException(); }
         public virtual CallingConventions CallingConvention => CallingConventions.Standard;
 
         public bool IsAbstract => (Attributes & MethodAttributes.Abstract) != 0;

src/System.Private.CoreLib/shared/System/Reflection/MethodInfo.cs

@@ -13,15 +13,15 @@ protected MethodInfo() { }
         public override MemberTypes MemberType => MemberTypes.Method;
 
         public virtual ParameterInfo? ReturnParameter { get { throw NotImplemented.ByDesign; } }
-        public virtual Type? ReturnType { get { throw NotImplemented.ByDesign; } }
+        public virtual Type ReturnType { get { throw NotImplemented.ByDesign; } }
 
         public override Type[] GetGenericArguments() { throw new NotSupportedException(SR.NotSupported_SubclassOverride); }
-        public virtual MethodInfo? GetGenericMethodDefinition() { throw new NotSupportedException(SR.NotSupported_SubclassOverride); }
-        public virtual MethodInfo? MakeGenericMethod(params Type[] typeArguments) { throw new NotSupportedException(SR.NotSupported_SubclassOverride); }
+        public virtual MethodInfo GetGenericMethodDefinition() { throw new NotSupportedException(SR.NotSupported_SubclassOverride); }
+        public virtual MethodInfo MakeGenericMethod(params Type[] typeArguments) { throw new NotSupportedException(SR.NotSupported_SubclassOverride); }
 
-        public abstract MethodInfo? GetBaseDefinition();
+        public abstract MethodInfo GetBaseDefinition();
 
-        public abstract ICustomAttributeProvider? ReturnTypeCustomAttributes { get; }
+        public abstract ICustomAttributeProvider ReturnTypeCustomAttributes { get; }
 
         public virtual Delegate CreateDelegate(Type delegateType) { throw new NotSupportedException(SR.NotSupported_SubclassOverride); }
         public virtual Delegate CreateDelegate(Type delegateType, object? target) { throw new NotSupportedException(SR.NotSupported_SubclassOverride); }