Fix #3457: NRE when creating Mermaid diagram of assembly with (possibly) missing references.

ICSharpCode.Decompiler/TypeSystem/InheritanceHelper.cs

@@ -20,6 +20,8 @@ using System;
 using System.Collections.Generic;
 using System.Linq;
 
+#nullable enable
+
 namespace ICSharpCode.Decompiler.TypeSystem
 {
 	/// <summary>
@@ -34,7 +36,7 @@ namespace ICSharpCode.Decompiler.TypeSystem
 		/// <summary>
 		/// Gets the base member that has the same signature.
 		/// </summary>
-		public static IMember GetBaseMember(IMember member)
+		public static IMember? GetBaseMember(IMember member)
 		{
 			return GetBaseMembers(member, false).FirstOrDefault();
 		}
@@ -109,7 +111,7 @@ namespace ICSharpCode.Decompiler.TypeSystem
 		/// <summary>
 		/// Finds the member declared in 'derivedType' that has the same signature (could override) 'baseMember'.
 		/// </summary>
-		public static IMember GetDerivedMember(IMember baseMember, ITypeDefinition derivedType)
+		public static IMember? GetDerivedMember(IMember baseMember, ITypeDefinition derivedType)
 		{
 			if (baseMember == null)
 				throw new ArgumentNullException(nameof(baseMember));
@@ -120,9 +122,8 @@ namespace ICSharpCode.Decompiler.TypeSystem
 				throw new ArgumentException("baseMember and derivedType must be from the same compilation");
 
 			baseMember = baseMember.MemberDefinition;
-			bool includeInterfaces = baseMember.DeclaringTypeDefinition.Kind == TypeKind.Interface;
-			IMethod method = baseMember as IMethod;
-			if (method != null)
+			bool includeInterfaces = baseMember.DeclaringTypeDefinition?.Kind == TypeKind.Interface;
+			if (baseMember is IMethod method)
 			{
 				foreach (IMethod derivedMethod in derivedType.Methods)
 				{
@@ -137,8 +138,7 @@ namespace ICSharpCode.Decompiler.TypeSystem
 					}
 				}
 			}
-			IProperty property = baseMember as IProperty;
-			if (property != null)
+			if (baseMember is IProperty property)
 			{
 				foreach (IProperty derivedProperty in derivedType.Properties)
 				{
@@ -175,7 +175,7 @@ namespace ICSharpCode.Decompiler.TypeSystem
 		{
 			foreach (var baseType in typeDef.GetNonInterfaceBaseTypes().Reverse())
 			{
-				ITypeDefinition baseTypeDef = baseType.GetDefinition();
+				ITypeDefinition? baseTypeDef = baseType.GetDefinition();
 				if (baseTypeDef == null)
 					continue;
 				foreach (var attr in baseTypeDef.GetAttributes())
@@ -185,11 +185,11 @@ namespace ICSharpCode.Decompiler.TypeSystem
 			}
 		}
 
-		internal static IAttribute GetAttribute(ITypeDefinition typeDef, KnownAttribute attributeType)
+		internal static IAttribute? GetAttribute(ITypeDefinition typeDef, KnownAttribute attributeType)
 		{
 			foreach (var baseType in typeDef.GetNonInterfaceBaseTypes().Reverse())
 			{
-				ITypeDefinition baseTypeDef = baseType.GetDefinition();
+				ITypeDefinition? baseTypeDef = baseType.GetDefinition();
 				if (baseTypeDef == null)
 					continue;
 				var attr = baseTypeDef.GetAttribute(attributeType);
@@ -202,7 +202,7 @@ namespace ICSharpCode.Decompiler.TypeSystem
 		internal static IEnumerable<IAttribute> GetAttributes(IMember member)
 		{
 			HashSet<IMember> visitedMembers = new HashSet<IMember>();
-			do
+			while (true)
 			{
 				member = member.MemberDefinition; // it's sufficient to look at the definitions
 				if (!visitedMembers.Add(member))
@@ -214,13 +214,19 @@ namespace ICSharpCode.Decompiler.TypeSystem
 				{
 					yield return attr;
 				}
-			} while (member.IsOverride && (member = InheritanceHelper.GetBaseMember(member)) != null);
+				if (!member.IsOverride)
+					break;
+				var baseMember = GetBaseMember(member);
+				if (baseMember == null)
+					break;
+				member = baseMember;
+			}
 		}
 
-		internal static IAttribute GetAttribute(IMember member, KnownAttribute attributeType)
+		internal static IAttribute? GetAttribute(IMember member, KnownAttribute attributeType)
 		{
 			HashSet<IMember> visitedMembers = new HashSet<IMember>();
-			do
+			while (true)
 			{
 				member = member.MemberDefinition; // it's sufficient to look at the definitions
 				if (!visitedMembers.Add(member))
@@ -231,7 +237,13 @@ namespace ICSharpCode.Decompiler.TypeSystem
 				var attr = member.GetAttribute(attributeType);
 				if (attr != null)
 					return attr;
-			} while (member.IsOverride && (member = InheritanceHelper.GetBaseMember(member)) != null);
+				if (!member.IsOverride)
+					break;
+				var baseMember = GetBaseMember(member);
+				if (baseMember == null)
+					break;
+				member = baseMember;
+			}
 			return null;
 		}
 		#endregion

ICSharpCode.ILSpyX/MermaidDiagrammer/Factory.FlatMembers.cs

@@ -40,12 +40,34 @@ namespace ICSharpCode.ILSpyX.MermaidDiagrammer
 				&& !properties.Any(p => f.ReturnType.Equals(p.ReturnType)
 					&& Regex.IsMatch(f.Name, "_?" + p.Name, RegexOptions.IgnoreCase | RegexOptions.Singleline | RegexOptions.NonBacktracking))).ToArray();
 
-		private static IEnumerable<IMethod> GetMethods(ITypeDefinition type) => type.GetMethods(m =>
-			!m.IsOperator && !m.IsCompilerGenerated()
-			&& (m.DeclaringType == type // include methods if self-declared
-				/* but exclude methods declared by object and their overrides, if inherited */
-				|| (!m.DeclaringType.IsObject()
-					&& (!m.IsOverride || !InheritanceHelper.GetBaseMember(m).DeclaringType.IsObject()))));
+		private static IEnumerable<IMethod> GetMethods(ITypeDefinition type)
+		{
+			return type.GetMethods(IsDeclaredMethod);
+
+			bool IsDeclaredMethod(IMethod m)
+			{
+				if (m.IsOperator || m.IsCompilerGenerated())
+					return false;
+				if (m.DeclaringTypeDefinition == type)
+				{
+					// include methods if self-declared
+					return true;
+				}
+				else
+				{
+					//  but exclude methods declared by object and their overrides, if inherited
+					if (m.DeclaringType.IsObject())
+						return false;
+					IMember? baseMember;
+					if (m.IsOverride && (baseMember = InheritanceHelper.GetBaseMember(m)) != null)
+					{
+						if (baseMember.DeclaringType.IsObject())
+							return false;
+					}
+				}
+				return true;
+			}
+		}
 
 		private string FormatMethod(IMethod method)
 		{