focus on CS8768 and CS8767

ICSharpCode.Decompiler/CSharp/Syntax/PatternMatching/INode.cs

@@ -26,8 +26,8 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax.PatternMatching
 	public interface INode
 	{
 		Role Role { get; }
-		INode FirstChild { get; }
+		INode? FirstChild { get; }
-		INode NextSibling { get; }
+		INode? NextSibling { get; }
 		bool IsNull { get; }
 
 		bool DoMatch(INode other, Match match);

ICSharpCode.Decompiler/Documentation/XmlDocumentationProvider.cs

@@ -437,7 +437,7 @@ namespace ICSharpCode.Decompiler.Documentation
 		}
 		#endregion
 
-		public virtual void OnDeserialization(object sender)
+		public virtual void OnDeserialization(object? sender)
 		{
 			cache = new XmlDocumentationCache();
 		}

ICSharpCode.Decompiler/Semantics/Conversion.cs

@@ -168,7 +168,7 @@ namespace ICSharpCode.Decompiler.Semantics
 					+ " conversion";
 			}
 
-			public override bool Equals(Conversion other)
+			public override bool Equals(Conversion? other)
 			{
 				NumericOrEnumerationConversion? o = other as NumericOrEnumerationConversion;
 				return o != null && isImplicit == o.isImplicit && isLifted == o.isLifted && isEnumeration == o.isEnumeration;
@@ -335,7 +335,7 @@ namespace ICSharpCode.Decompiler.Semantics
 				get { return method; }
 			}
 
-			public override bool Equals(Conversion other)
+			public override bool Equals(Conversion? other)
 			{
 				UserDefinedConv? o = other as UserDefinedConv;
 				return o != null && isLifted == o.isLifted && isImplicit == o.isImplicit && isValid == o.isValid && method.Equals(o.method);
@@ -394,7 +394,7 @@ namespace ICSharpCode.Decompiler.Semantics
 				get { return method; }
 			}
 
-			public override bool Equals(Conversion other)
+			public override bool Equals(Conversion? other)
 			{
 				MethodGroupConv? o = other as MethodGroupConv;
 				return o != null && method.Equals(o.method);
@@ -419,7 +419,7 @@ namespace ICSharpCode.Decompiler.Semantics
 				this.IsImplicit = elementConversions.All(c => c.IsImplicit);
 			}
 
-			public override bool Equals(Conversion other)
+			public override bool Equals(Conversion? other)
 			{
 				return other is TupleConv o
 					&& ElementConversions.SequenceEqual(o.ElementConversions);
@@ -534,14 +534,14 @@ namespace ICSharpCode.Decompiler.Semantics
 		/// <summary>
 		/// The conversion that is applied to the input before the user-defined conversion operator is invoked.
 		/// </summary>
-		public virtual Conversion ConversionBeforeUserDefinedOperator {
+		public virtual Conversion? ConversionBeforeUserDefinedOperator {
 			get { return null; }
 		}
 
 		/// <summary>
 		/// The conversion that is applied to the result of the user-defined conversion operator.
 		/// </summary>
-		public virtual Conversion ConversionAfterUserDefinedOperator {
+		public virtual Conversion? ConversionAfterUserDefinedOperator {
 			get { return null; }
 		}
 
@@ -602,7 +602,7 @@ namespace ICSharpCode.Decompiler.Semantics
 		/// For user-defined conversions, this is the method being called.
 		/// For method-group conversions, this is the method that was chosen from the group.
 		/// </summary>
-		public virtual IMethod Method {
+		public virtual IMethod? Method {
 			get { return null; }
 		}
 
@@ -621,7 +621,7 @@ namespace ICSharpCode.Decompiler.Semantics
 		/// </summary>
 		public virtual ImmutableArray<Conversion> ElementConversions => default(ImmutableArray<Conversion>);
 
-		public override sealed bool Equals(object obj)
+		public override sealed bool Equals(object? obj)
 		{
 			return Equals(obj as Conversion);
 		}
@@ -631,7 +631,7 @@ namespace ICSharpCode.Decompiler.Semantics
 			return base.GetHashCode();
 		}
 
-		public virtual bool Equals(Conversion other)
+		public virtual bool Equals(Conversion? other)
 		{
 			return this == other;
 		}

ICSharpCode.Decompiler/TypeSystem/Implementation/AbstractType.cs

@@ -83,16 +83,16 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 			get { return EmptyList<IType>.Instance; }
 		}
 
-		public virtual IType DeclaringType {
+		public virtual IType? DeclaringType {
 			get { return null; }
 		}
 
-		public virtual ITypeDefinition GetDefinition()
+		public virtual ITypeDefinition? GetDefinition()
 		{
 			return null;
 		}
 
-		public virtual ITypeDefinitionOrUnknown GetDefinitionOrUnknown()
+		public virtual ITypeDefinitionOrUnknown? GetDefinitionOrUnknown()
 		{
 			return null;
 		}
@@ -165,7 +165,7 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 			return TypeParameterSubstitution.Identity;
 		}
 
-		public override sealed bool Equals(object obj)
+		public override sealed bool Equals(object? obj)
 		{
 			return Equals(obj as IType);
 		}
@@ -175,7 +175,7 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 			return base.GetHashCode();
 		}
 
-		public virtual bool Equals(IType other)
+		public virtual bool Equals(IType? other)
 		{
 			return this == other; // use reference equality by default
 		}

ICSharpCode.Decompiler/TypeSystem/Implementation/DecoratedType.cs

@@ -22,7 +22,7 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 		Nullability IType.Nullability => baseType.Nullability;
 		public abstract IType ChangeNullability(Nullability nullability);
 
-		IType IType.DeclaringType => baseType.DeclaringType;
+		IType? IType.DeclaringType => baseType.DeclaringType;
 
 		int IType.TypeParameterCount => baseType.TypeParameterCount;
 
@@ -42,7 +42,7 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 
 		public abstract IType AcceptVisitor(TypeVisitor visitor);
 
-		public abstract bool Equals(IType other);
+		public abstract bool Equals(IType? other);
 
 		IEnumerable<IMethod> IType.GetAccessors(Predicate<IMethod>? filter, GetMemberOptions options)
 		{
@@ -54,12 +54,12 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 			return baseType.GetConstructors(filter, options);
 		}
 
-		ITypeDefinition IType.GetDefinition()
+		ITypeDefinition? IType.GetDefinition()
 		{
 			return baseType.GetDefinition();
 		}
 
-		ITypeDefinitionOrUnknown IType.GetDefinitionOrUnknown()
+		ITypeDefinitionOrUnknown? IType.GetDefinitionOrUnknown()
 		{
 			return baseType.GetDefinitionOrUnknown();
 		}

ICSharpCode.Decompiler/TypeSystem/Implementation/GetMembersHelper.cs

@@ -98,12 +98,12 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 		#endregion
 
 		#region GetMethods
-		public static IEnumerable<IMethod> GetMethods(IType type, Predicate<IMethod> filter, GetMemberOptions options)
+		public static IEnumerable<IMethod> GetMethods(IType type, Predicate<IMethod>? filter, GetMemberOptions options)
 		{
 			return GetMethods(type, null, filter, options);
 		}
 
-		public static IEnumerable<IMethod> GetMethods(IType type, IReadOnlyList<IType> typeArguments, Predicate<IMethod> filter, GetMemberOptions options)
+		public static IEnumerable<IMethod> GetMethods(IType type, IReadOnlyList<IType>? typeArguments, Predicate<IMethod>? filter, GetMemberOptions options)
 		{
 			if (typeArguments != null && typeArguments.Count > 0)
 			{
@@ -127,7 +127,7 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 
 		const GetMemberOptions declaredMembers = GetMemberOptions.IgnoreInheritedMembers | GetMemberOptions.ReturnMemberDefinitions;
 
-		static IEnumerable<IMethod> GetMethodsImpl(IType baseType, IReadOnlyList<IType>? methodTypeArguments, Predicate<IMethod> filter, GetMemberOptions options)
+		static IEnumerable<IMethod> GetMethodsImpl(IType baseType, IReadOnlyList<IType>? methodTypeArguments, Predicate<IMethod>? filter, GetMemberOptions options)
 		{
 			IEnumerable<IMethod> declaredMethods = baseType.GetMethods(filter, options | declaredMembers);
 
@@ -164,7 +164,7 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 		#endregion
 
 		#region GetAccessors
-		public static IEnumerable<IMethod> GetAccessors(IType type, Predicate<IMethod> filter, GetMemberOptions options)
+		public static IEnumerable<IMethod> GetAccessors(IType type, Predicate<IMethod>? filter, GetMemberOptions options)
 		{
 			if ((options & GetMemberOptions.IgnoreInheritedMembers) == GetMemberOptions.IgnoreInheritedMembers)
 			{
@@ -323,7 +323,7 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 		#endregion
 
 		#region GetMembers
-		public static IEnumerable<IMember> GetMembers(IType type, Predicate<IMember> filter, GetMemberOptions options)
+		public static IEnumerable<IMember> GetMembers(IType type, Predicate<IMember>? filter, GetMemberOptions options)
 		{
 			if ((options & GetMemberOptions.IgnoreInheritedMembers) == GetMemberOptions.IgnoreInheritedMembers)
 			{
@@ -335,7 +335,7 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 			}
 		}
 
-		static IEnumerable<IMember> GetMembersImpl(IType baseType, Predicate<IMember> filter, GetMemberOptions options)
+		static IEnumerable<IMember> GetMembersImpl(IType baseType, Predicate<IMember>? filter, GetMemberOptions options)
 		{
 			foreach (var m in GetMethodsImpl(baseType, null, filter, options))
 				yield return m;

ICSharpCode.Decompiler/TypeSystem/Implementation/LocalFunctionMethod.cs

@@ -43,7 +43,7 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 			this.NumberOfCompilerGeneratedTypeParameters = numberOfCompilerGeneratedTypeParameters;
 		}
 
-		public bool Equals(IMember obj, TypeVisitor typeNormalization)
+		public bool Equals(IMember? obj, TypeVisitor typeNormalization)
 		{
 			if (!(obj is LocalFunctionMethod other))
 				return false;
@@ -53,7 +53,7 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 				&& IsStaticLocalFunction == other.IsStaticLocalFunction;
 		}
 
-		public override bool Equals(object obj)
+		public override bool Equals(object? obj)
 		{
 			if (!(obj is LocalFunctionMethod other))
 				return false;
@@ -108,7 +108,7 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 		public bool IsOperator => baseMethod.IsOperator;
 		public bool HasBody => baseMethod.HasBody;
 		public bool IsAccessor => baseMethod.IsAccessor;
-		public IMember AccessorOwner => baseMethod.AccessorOwner;
+		public IMember? AccessorOwner => baseMethod.AccessorOwner;
 		public MethodSemanticsAttributes AccessorKind => baseMethod.AccessorKind;
 		public IMethod ReducedFrom => baseMethod;
 
@@ -141,12 +141,12 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 
 		public System.Reflection.Metadata.EntityHandle MetadataToken => baseMethod.MetadataToken;
 		public SymbolKind SymbolKind => baseMethod.SymbolKind;
-		public ITypeDefinition DeclaringTypeDefinition => baseMethod.DeclaringTypeDefinition;
+		public ITypeDefinition? DeclaringTypeDefinition => baseMethod.DeclaringTypeDefinition;
 		public IType DeclaringType => baseMethod.DeclaringType;
-		public IModule ParentModule => baseMethod.ParentModule;
+		public IModule? ParentModule => baseMethod.ParentModule;
 		IEnumerable<IAttribute> IEntity.GetAttributes() => baseMethod.GetAttributes();
 		bool IEntity.HasAttribute(KnownAttribute attribute) => baseMethod.HasAttribute(attribute);
-		IAttribute IEntity.GetAttribute(KnownAttribute attribute) => baseMethod.GetAttribute(attribute);
+		IAttribute? IEntity.GetAttribute(KnownAttribute attribute) => baseMethod.GetAttribute(attribute);
 		IEnumerable<IAttribute> IMethod.GetReturnTypeAttributes() => baseMethod.GetReturnTypeAttributes();
 		bool IMethod.ReturnTypeIsRefReadOnly => baseMethod.ReturnTypeIsRefReadOnly;
 		bool IMethod.ThisIsRefReadOnly => baseMethod.ThisIsRefReadOnly;

ICSharpCode.Decompiler/TypeSystem/Implementation/MetadataMethod.cs

@@ -476,7 +476,7 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 			return b.HasAttribute(metadata, def.GetCustomAttributes(), attribute, symbolKind);
 		}
 
-		public IAttribute GetAttribute(KnownAttribute attribute)
+		public IAttribute? GetAttribute(KnownAttribute attribute)
 		{
 			if (!attribute.IsCustomAttribute())
 			{

ICSharpCode.Decompiler/TypeSystem/Implementation/SimpleCompilation.cs

@@ -140,7 +140,7 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 			get { return cacheManager; }
 		}
 
-		public virtual INamespace GetNamespaceForExternAlias(string alias)
+		public virtual INamespace? GetNamespaceForExternAlias(string? alias)
 		{
 			if (string.IsNullOrEmpty(alias))
 				return this.RootNamespace;

ICSharpCode.Decompiler/TypeSystem/Implementation/SpecializedField.cs

@@ -57,7 +57,7 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 			get { return fieldDefinition.IsConst; }
 		}
 
-		public object GetConstantValue(bool throwOnInvalidMetadata)
+		public object? GetConstantValue(bool throwOnInvalidMetadata)
 		{
 			return fieldDefinition.GetConstantValue(throwOnInvalidMetadata);
 		}

ICSharpCode.Decompiler/TypeSystem/Implementation/SpecializedMember.cs

@@ -157,7 +157,7 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 			get { return baseMember.SymbolKind; }
 		}
 
-		public ITypeDefinition DeclaringTypeDefinition {
+		public ITypeDefinition? DeclaringTypeDefinition {
 			get { return baseMember.DeclaringTypeDefinition; }
 		}
 
@@ -214,7 +214,7 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 			get { return baseMember.Compilation; }
 		}
 
-		public IModule ParentModule {
+		public IModule? ParentModule {
 			get { return baseMember.ParentModule; }
 		}
 
@@ -223,7 +223,7 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 			return baseMember.Specialize(TypeParameterSubstitution.Compose(newSubstitution, this.substitution));
 		}
 
-		public virtual bool Equals(IMember obj, TypeVisitor typeNormalization)
+		public virtual bool Equals(IMember? obj, TypeVisitor typeNormalization)
 		{
 			SpecializedMember? other = obj as SpecializedMember;
 			if (other == null)
@@ -232,7 +232,7 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 				&& this.substitution.Equals(other.substitution, typeNormalization);
 		}
 
-		public override bool Equals(object obj)
+		public override bool Equals(object? obj)
 		{
 			SpecializedMember? other = obj as SpecializedMember;
 			if (other == null)

ICSharpCode.Decompiler/TypeSystem/Implementation/SpecializedMethod.cs

@@ -146,13 +146,13 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 
 		public MethodSemanticsAttributes AccessorKind => methodDefinition.AccessorKind;
 
-		public IMethod ReducedFrom {
+		public IMethod? ReducedFrom {
 			get { return null; }
 		}
 
-		IMember accessorOwner;
+		IMember? accessorOwner;
 
-		public IMember AccessorOwner {
+		public IMember? AccessorOwner {
 			get {
 				var result = LazyInit.VolatileRead(ref accessorOwner);
 				if (result != null)
@@ -173,7 +173,7 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 			}
 		}
 
-		public override bool Equals(IMember obj, TypeVisitor typeNormalization)
+		public override bool Equals(IMember? obj, TypeVisitor typeNormalization)
 		{
 			SpecializedMethod? other = obj as SpecializedMethod;
 			if (other == null)
@@ -182,7 +182,7 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 				&& this.substitutionWithoutSpecializedTypeParameters.Equals(other.substitutionWithoutSpecializedTypeParameters, typeNormalization);
 		}
 
-		public override bool Equals(object obj)
+		public override bool Equals(object? obj)
 		{
 			SpecializedMethod? other = obj as SpecializedMethod;
 			if (other == null)
@@ -267,11 +267,11 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 				return baseTp.GetHashCode() ^ this.Owner.GetHashCode();
 			}
 
-			public override bool Equals(IType other)
+			public override bool Equals(IType? other)
 			{
 				// Compare the owner, not the substitution, because the substitution may contain this specialized type parameter recursively
 				SpecializedTypeParameter? o = other as SpecializedTypeParameter;
-				return o != null && baseTp.Equals(o.baseTp) && this.Owner.Equals(o.Owner);
+				return o != null && baseTp.Equals(o.baseTp) && this.Owner?.Equals(o.Owner) == true;
 			}
 
 			public override bool HasValueTypeConstraint => baseTp.HasValueTypeConstraint;

ICSharpCode.Decompiler/TypeSystem/Implementation/UnknownType.cs

@@ -122,7 +122,7 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 			return (namespaceKnown ? 812571 : 12651) ^ fullTypeName.GetHashCode();
 		}
 
-		public override bool Equals(IType other)
+		public override bool Equals(IType? other)
 		{
 			UnknownType? o = other as UnknownType;
 			if (o == null)

ICSharpCode.Decompiler/TypeSystem/ModifiedType.cs

@@ -132,7 +132,7 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 				return visitor.VisitModOpt(this);
 		}
 
-		public override bool Equals(IType other)
+		public override bool Equals(IType? other)
 		{
 			return other is ModifiedType o && kind == o.kind && modifier.Equals(o.modifier) && elementType.Equals(o.elementType);
 		}

ICSharpCode.Decompiler/TypeSystem/ParameterListComparer.cs

@@ -52,7 +52,7 @@ namespace ICSharpCode.Decompiler.TypeSystem
 			};
 		}
 
-		public bool Equals(IReadOnlyList<IParameter> x, IReadOnlyList<IParameter> y)
+		public bool Equals(IReadOnlyList<IParameter>? x, IReadOnlyList<IParameter>? y)
 		{
 			if (x == y)
 				return true;
@@ -125,7 +125,7 @@ namespace ICSharpCode.Decompiler.TypeSystem
 		/// </summary>
 		public static readonly SignatureComparer Ordinal = new SignatureComparer(StringComparer.Ordinal);
 
-		public bool Equals(IMember x, IMember y)
+		public bool Equals(IMember? x, IMember? y)
 		{
 			if (x == y)
 				return true;

ICSharpCode.Decompiler/TypeSystem/ParameterizedType.cs

@@ -291,12 +291,12 @@ namespace ICSharpCode.Decompiler.TypeSystem
 				return GetMembersHelper.GetAccessors(this, filter, options);
 		}
 
-		public override bool Equals(object obj)
+		public override bool Equals(object? obj)
 		{
 			return Equals(obj as IType);
 		}
 
-		public bool Equals(IType other)
+		public bool Equals(IType? other)
 		{
 			if (this == other)
 				return true;

ICSharpCode.Decompiler/TypeSystem/SimpleTypeResolveContext.cs

@@ -79,12 +79,12 @@ namespace ICSharpCode.Decompiler.TypeSystem
 			get { return currentMember; }
 		}
 
-		public ITypeResolveContext WithCurrentTypeDefinition(ITypeDefinition typeDefinition)
+		public ITypeResolveContext WithCurrentTypeDefinition(ITypeDefinition? typeDefinition)
 		{
 			return new SimpleTypeResolveContext(compilation, currentModule, typeDefinition, currentMember);
 		}
 
-		public ITypeResolveContext WithCurrentMember(IMember member)
+		public ITypeResolveContext WithCurrentMember(IMember? member)
 		{
 			return new SimpleTypeResolveContext(compilation, currentModule, currentTypeDefinition, member);
 		}

ICSharpCode.Decompiler/TypeSystem/VarArgInstanceMethod.cs

@@ -58,7 +58,7 @@ namespace ICSharpCode.Decompiler.TypeSystem
 			get { return parameters; }
 		}
 
-		public override bool Equals(object obj)
+		public override bool Equals(object? obj)
 		{
 			VarArgInstanceMethod? other = obj as VarArgInstanceMethod;
 			return other != null && baseMethod.Equals(other.baseMethod);
@@ -69,7 +69,7 @@ namespace ICSharpCode.Decompiler.TypeSystem
 			return baseMethod.GetHashCode();
 		}
 
-		public bool Equals(IMember obj, TypeVisitor typeNormalization)
+		public bool Equals(IMember? obj, TypeVisitor typeNormalization)
 		{
 			VarArgInstanceMethod? other = obj as VarArgInstanceMethod;
 			return other != null && baseMethod.Equals(other.baseMethod, typeNormalization);
@@ -119,7 +119,7 @@ namespace ICSharpCode.Decompiler.TypeSystem
 
 		IEnumerable<IAttribute> IEntity.GetAttributes() => baseMethod.GetAttributes();
 		bool IEntity.HasAttribute(KnownAttribute attribute) => baseMethod.HasAttribute(attribute);
-		IAttribute IEntity.GetAttribute(KnownAttribute attribute) => baseMethod.GetAttribute(attribute);
+		IAttribute? IEntity.GetAttribute(KnownAttribute attribute) => baseMethod.GetAttribute(attribute);
 
 		IEnumerable<IAttribute> IMethod.GetReturnTypeAttributes() => baseMethod.GetReturnTypeAttributes();
 		bool IMethod.ReturnTypeIsRefReadOnly => baseMethod.ReturnTypeIsRefReadOnly;