#nullable enable for most files in ICSharpCode.Decompiler/Util

ICSharpCode.Decompiler/Util/BitSet.cs

@@ -15,6 +15,7 @@
 // FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
 // OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 // DEALINGS IN THE SOFTWARE.
+#nullable enable
 
 using System;
 using System.Diagnostics;

ICSharpCode.Decompiler/Util/BusyManager.cs

@@ -15,6 +15,7 @@
 // FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
 // OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 // DEALINGS IN THE SOFTWARE.
+#nullable enable
 
 using System;
 using System.Collections.Generic;
@@ -36,9 +37,9 @@ namespace ICSharpCode.Decompiler.Util
 		{
 			public static readonly BusyLock Failed = new BusyLock(null);
 
-			readonly List<object> objectList;
+			readonly List<object?>? objectList;
 
-			internal BusyLock(List<object> objectList)
+			internal BusyLock(List<object?>? objectList)
 			{
 				this.objectList = objectList;
 			}
@@ -56,13 +57,13 @@ namespace ICSharpCode.Decompiler.Util
 			}
 		}
 
-		[ThreadStatic] static List<object> _activeObjects;
+		[ThreadStatic] static List<object?>? _activeObjects;
 
-		public static BusyLock Enter(object obj)
+		public static BusyLock Enter(object? obj)
 		{
-			List<object> activeObjects = _activeObjects;
+			List<object?>? activeObjects = _activeObjects;
 			if (activeObjects == null)
-				activeObjects = _activeObjects = new List<object>();
+				activeObjects = _activeObjects = new List<object?>();
 			for (int i = 0; i < activeObjects.Count; i++)
 			{
 				if (activeObjects[i] == obj)

ICSharpCode.Decompiler/Util/CSharpPrimitiveCast.cs

@@ -16,7 +16,10 @@
 // OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 // DEALINGS IN THE SOFTWARE.
 
+#nullable enable
+
 using System;
+using System.Diagnostics.CodeAnalysis;
 
 namespace ICSharpCode.Decompiler.Util
 {
@@ -34,7 +37,8 @@ namespace ICSharpCode.Decompiler.Util
 		/// </summary>
 		/// <exception cref="OverflowException">Overflow checking is enabled and an overflow occurred.</exception>
 		/// <exception cref="InvalidCastException">The cast is invalid, e.g. casting a boolean to an integer.</exception>
-		public static object Cast(TypeCode targetType, object input, bool checkForOverflow)
+		[return: NotNullIfNotNull("input")]
+		public static object? Cast(TypeCode targetType, object? input, bool checkForOverflow)
 		{
 			if (input == null)
 				return null;

ICSharpCode.Decompiler/Util/CacheManager.cs

@@ -16,6 +16,8 @@
 // OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 // DEALINGS IN THE SOFTWARE.
 
+#nullable enable
+
 using System;
 using System.Collections.Concurrent;
 

ICSharpCode.Decompiler/Util/CallbackOnDispose.cs

@@ -16,6 +16,8 @@
 // OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 // DEALINGS IN THE SOFTWARE.
 
+#nullable enable
+
 using System;
 using System.Threading;
 
@@ -30,7 +32,7 @@ namespace ICSharpCode.Decompiler.Util
 	/// </remarks>
 	public sealed class CallbackOnDispose : IDisposable
 	{
-		Action action;
+		Action? action;
 
 		public CallbackOnDispose(Action action)
 		{
@@ -41,7 +43,7 @@ namespace ICSharpCode.Decompiler.Util
 
 		public void Dispose()
 		{
-			Action a = Interlocked.Exchange(ref action, null);
+			Action? a = Interlocked.Exchange(ref action, null);
 			if (a != null)
 			{
 				a();

ICSharpCode.Decompiler/Util/CollectionExtensions.cs

@@ -1,4 +1,5 @@
-using System;
+#nullable enable
+using System;
 using System.Collections.Generic;
 using System.Collections.Immutable;
 using System.Linq;
@@ -14,13 +15,13 @@ namespace ICSharpCode.Decompiler.Util
 		}
 
 #if !NETCORE
-		public static IEnumerable<(A, B)> Zip<A, B>(this IEnumerable<A> input1, IEnumerable<B> input2)
+		public static IEnumerable<(A, B)> Zip<A, B>(this IEnumerable<A>? input1, IEnumerable<B>? input2)
 		{
 			return input1.Zip(input2, (a, b) => (a, b));
 		}
 #endif
 
-		public static IEnumerable<(A, B)> ZipLongest<A, B>(this IEnumerable<A> input1, IEnumerable<B> input2)
+		public static IEnumerable<(A?, B?)> ZipLongest<A, B>(this IEnumerable<A> input1, IEnumerable<B> input2)
 		{
 			using (var it1 = input1.GetEnumerator())
 			{
@@ -60,7 +61,7 @@ namespace ICSharpCode.Decompiler.Util
 		}
 
 #if !NETCORE
-		public static HashSet<T> ToHashSet<T>(this IEnumerable<T> input)
+		public static HashSet<T> ToHashSet<T>(this IEnumerable<T>? input)
 		{
 			return new HashSet<T>(input);
 		}
@@ -76,14 +77,14 @@ namespace ICSharpCode.Decompiler.Util
 			return input.Skip(input.Count - count);
 		}
 
-		public static T PopOrDefault<T>(this Stack<T> stack)
+		public static T? PopOrDefault<T>(this Stack<T> stack)
 		{
 			if (stack.Count == 0)
 				return default(T);
 			return stack.Pop();
 		}
 
-		public static T PeekOrDefault<T>(this Stack<T> stack)
+		public static T? PeekOrDefault<T>(this Stack<T> stack)
 		{
 			if (stack.Count == 0)
 				return default(T);
@@ -277,7 +278,7 @@ namespace ICSharpCode.Decompiler.Util
 		/// Returns the minimum element.
 		/// </summary>
 		/// <exception cref="InvalidOperationException">The input sequence is empty</exception>
-		public static T MinBy<T, K>(this IEnumerable<T> source, Func<T, K> keySelector, IComparer<K> keyComparer)
+		public static T MinBy<T, K>(this IEnumerable<T> source, Func<T, K> keySelector, IComparer<K>? keyComparer)
 		{
 			if (source == null)
 				throw new ArgumentNullException(nameof(source));
@@ -318,7 +319,7 @@ namespace ICSharpCode.Decompiler.Util
 		/// Returns the maximum element.
 		/// </summary>
 		/// <exception cref="InvalidOperationException">The input sequence is empty</exception>
-		public static T MaxBy<T, K>(this IEnumerable<T> source, Func<T, K> keySelector, IComparer<K> keyComparer)
+		public static T MaxBy<T, K>(this IEnumerable<T> source, Func<T, K> keySelector, IComparer<K>? keyComparer)
 		{
 			if (source == null)
 				throw new ArgumentNullException(nameof(source));
@@ -353,12 +354,12 @@ namespace ICSharpCode.Decompiler.Util
 			list.RemoveAt(list.Count - 1);
 		}
 
-		public static T OnlyOrDefault<T>(this IEnumerable<T> source, Func<T, bool> predicate) => OnlyOrDefault(source.Where(predicate));
+		public static T? OnlyOrDefault<T>(this IEnumerable<T>? source, Func<T, bool>? predicate) => OnlyOrDefault(source.Where(predicate));
 
-		public static T OnlyOrDefault<T>(this IEnumerable<T> source)
+		public static T? OnlyOrDefault<T>(this IEnumerable<T> source)
 		{
 			bool any = false;
-			T first = default;
+			T? first = default;
 			foreach (var t in source)
 			{
 				if (any)
@@ -372,14 +373,14 @@ namespace ICSharpCode.Decompiler.Util
 
 		#region Aliases/shortcuts for Enumerable extension methods
 		public static bool Any<T>(this ICollection<T> list) => list.Count > 0;
-		public static bool Any<T>(this T[] array, Predicate<T> match) => Array.Exists(array, match);
-		public static bool Any<T>(this List<T> list, Predicate<T> match) => list.Exists(match);
+		public static bool Any<T>(this T[]? array, Predicate<T>? match) => Array.Exists(array, match);
+		public static bool Any<T>(this List<T> list, Predicate<T>? match) => list.Exists(match);
 
-		public static bool All<T>(this T[] array, Predicate<T> match) => Array.TrueForAll(array, match);
-		public static bool All<T>(this List<T> list, Predicate<T> match) => list.TrueForAll(match);
+		public static bool All<T>(this T[]? array, Predicate<T>? match) => Array.TrueForAll(array, match);
+		public static bool All<T>(this List<T> list, Predicate<T>? match) => list.TrueForAll(match);
 
-		public static T FirstOrDefault<T>(this T[] array, Predicate<T> predicate) => Array.Find(array, predicate);
-		public static T FirstOrDefault<T>(this List<T> list, Predicate<T> predicate) => list.Find(predicate);
+		public static T FirstOrDefault<T>(this T[]? array, Predicate<T>? predicate) => Array.Find(array, predicate);
+		public static T FirstOrDefault<T>(this List<T> list, Predicate<T>? predicate) => list.Find(predicate);
 
 		public static T Last<T>(this IList<T> list) => list[list.Count - 1];
 		#endregion

ICSharpCode.Decompiler/Util/EmptyList.cs

@@ -15,6 +15,7 @@
 // FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
 // OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 // DEALINGS IN THE SOFTWARE.
+#nullable enable
 
 using System;
 using System.Collections;
@@ -91,11 +92,11 @@ namespace ICSharpCode.Decompiler.Util
 		}
 
 		T IEnumerator<T>.Current {
-			get { return default(T); }
+			get { throw new NotSupportedException(); }
 		}
 
 		object IEnumerator.Current {
-			get { return default(T); }
+			get { throw new NotSupportedException(); }
 		}
 
 		void IDisposable.Dispose()

ICSharpCode.Decompiler/Util/ExtensionMethods.cs

@@ -1,4 +1,5 @@
-// Copyright (c) 2010-2013 AlphaSierraPapa for the SharpDevelop Team
+#nullable enable
+// Copyright (c) 2010-2013 AlphaSierraPapa for the SharpDevelop Team
 // 
 // Permission is hereby granted, free of charge, to any person obtaining a copy of this
 // software and associated documentation files (the "Software"), to deal in the Software
@@ -26,7 +27,7 @@ namespace ICSharpCode.Decompiler.Util
 	/// </summary>
 	static class ExtensionMethods
 	{
-		public static Predicate<T> And<T>(this Predicate<T> filter1, Predicate<T> filter2)
+		public static Predicate<T>? And<T>(this Predicate<T>? filter1, Predicate<T>? filter2)
 		{
 			if (filter1 == null)
 				return filter2;

ICSharpCode.Decompiler/Util/FileUtility.cs

@@ -16,7 +16,10 @@
 // OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 // DEALINGS IN THE SOFTWARE.
 
+#nullable enable
+
 using System;
+using System.Diagnostics.CodeAnalysis;
 using System.IO;
 using System.Text;
 
@@ -28,9 +31,10 @@ namespace ICSharpCode.Decompiler.Util
 		/// Gets the normalized version of fileName.
 		/// Slashes are replaced with backslashes, backreferences "." and ".." are 'evaluated'.
 		/// </summary>
-		public static string NormalizePath(string fileName)
+		[return: NotNullIfNotNull("fileName")]
+		public static string? NormalizePath(string? fileName)
 		{
-			if (string.IsNullOrEmpty(fileName))
+			if (fileName == null || fileName.Length == 0)
 				return fileName;
 
 			int i;
@@ -169,14 +173,14 @@ namespace ICSharpCode.Decompiler.Util
 				&& (fileName[1] == '\\' || fileName[1] == '/');
 		}
 
-		public static bool IsEqualFileName(string fileName1, string fileName2)
+		public static bool IsEqualFileName(string? fileName1, string? fileName2)
 		{
 			return string.Equals(NormalizePath(fileName1),
 								 NormalizePath(fileName2),
 								 StringComparison.OrdinalIgnoreCase);
 		}
 
-		public static bool IsBaseDirectory(string baseDirectory, string testDirectory)
+		public static bool IsBaseDirectory(string? baseDirectory, string? testDirectory)
 		{
 			if (baseDirectory == null || testDirectory == null)
 				return false;
@@ -189,9 +193,10 @@ namespace ICSharpCode.Decompiler.Util
 			return testDirectory.StartsWith(baseDirectory, StringComparison.OrdinalIgnoreCase);
 		}
 
-		static string AddTrailingSeparator(string input)
+		[return: NotNullIfNotNull("input")]
+		static string? AddTrailingSeparator(string? input)
 		{
-			if (string.IsNullOrEmpty(input))
+			if (input == null || input.Length == 0)
 				return input;
 			if (input[input.Length - 1] == Path.DirectorySeparatorChar || input[input.Length - 1] == Path.AltDirectorySeparatorChar)
 				return input;
@@ -212,9 +217,9 @@ namespace ICSharpCode.Decompiler.Util
 		/// Converts a given absolute path and a given base path to a path that leads
 		/// from the base path to the absoulte path. (as a relative path)
 		/// </summary>
-		public static string GetRelativePath(string baseDirectoryPath, string absPath)
+		public static string GetRelativePath(string? baseDirectoryPath, string absPath)
 		{
-			if (string.IsNullOrEmpty(baseDirectoryPath))
+			if (baseDirectoryPath == null || baseDirectoryPath.Length == 0)
 			{
 				return absPath;
 			}
@@ -252,7 +257,8 @@ namespace ICSharpCode.Decompiler.Util
 			return erg.ToString();
 		}
 
-		public static string TrimPath(string path, int max_chars)
+		[return: NotNullIfNotNull("path")]
+		public static string? TrimPath(string? path, int max_chars)
 		{
 			const char ellipsis = '\u2026'; // HORIZONTAL ELLIPSIS
 			const int ellipsisLength = 2;

ICSharpCode.Decompiler/Util/GraphVizGraph.cs

@@ -16,6 +16,8 @@
 // OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 // DEALINGS IN THE SOFTWARE.
 
+#nullable enable
+
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
@@ -34,8 +36,8 @@ namespace ICSharpCode.Decompiler.Util
 		List<GraphVizNode> nodes = new List<GraphVizNode>();
 		List<GraphVizEdge> edges = new List<GraphVizEdge>();
 
-		public string rankdir;
-		public string Title;
+		public string? rankdir;
+		public string? Title;
 
 		public void AddEdge(GraphVizEdge edge)
 		{
@@ -58,7 +60,7 @@ namespace ICSharpCode.Decompiler.Util
 			Show(null);
 		}
 
-		public void Show(string name)
+		public void Show(string? name)
 		{
 			if (name == null)
 				name = Title;
@@ -83,7 +85,7 @@ namespace ICSharpCode.Decompiler.Util
 			}
 		}
 
-		static void WriteGraphAttribute(TextWriter writer, string name, string value)
+		static void WriteGraphAttribute(TextWriter writer, string name, string? value)
 		{
 			if (value != null)
 				writer.WriteLine("{0}={1};", name, Escape(value));
@@ -105,7 +107,7 @@ namespace ICSharpCode.Decompiler.Util
 			}
 		}
 
-		internal static void WriteAttribute(TextWriter writer, string name, string value, ref bool isFirst)
+		internal static void WriteAttribute(TextWriter writer, string name, string? value, ref bool isFirst)
 		{
 			if (value != null)
 			{
@@ -141,13 +143,13 @@ namespace ICSharpCode.Decompiler.Util
 		public readonly string Source, Target;
 
 		/// <summary>edge stroke color</summary>
-		public string color;
+		public string? color;
 		/// <summary>use edge to affect node ranking</summary>
 		public bool? constraint;
 
-		public string label;
+		public string? label;
 
-		public string style;
+		public string? style;
 
 		/// <summary>point size of label</summary>
 		public int? fontsize;
@@ -184,9 +186,9 @@ namespace ICSharpCode.Decompiler.Util
 	sealed class GraphVizNode
 	{
 		public readonly string ID;
-		public string label;
+		public string? label;
 
-		public string labelloc;
+		public string? labelloc;
 
 		/// <summary>point size of label</summary>
 		public int? fontsize;
@@ -195,10 +197,10 @@ namespace ICSharpCode.Decompiler.Util
 		public double? height;
 
 		/// <summary>space around label</summary>
-		public string margin;
+		public string? margin;
 
 		/// <summary>node shape</summary>
-		public string shape;
+		public string? shape;
 
 		public GraphVizNode(string id)
 		{

ICSharpCode.Decompiler/Util/Interval.cs

@@ -1,4 +1,5 @@
-// Copyright (c) 2016 Daniel Grunwald
+#nullable enable
+// Copyright (c) 2016 Daniel Grunwald
 // 
 // Permission is hereby granted, free of charge, to any person obtaining a copy of this
 // software and associated documentation files (the "Software"), to deal in the Software
@@ -111,7 +112,7 @@ namespace ICSharpCode.Decompiler.Util
 		}
 
 		#region Equals and GetHashCode implementation
-		public override bool Equals(object obj)
+		public override bool Equals(object? obj)
 		{
 			return (obj is Interval) && Equals((Interval)obj);
 		}
@@ -281,7 +282,7 @@ namespace ICSharpCode.Decompiler.Util
 		}
 
 		#region Equals and GetHashCode implementation
-		public override bool Equals(object obj)
+		public override bool Equals(object? obj)
 		{
 			return (obj is LongInterval) && Equals((LongInterval)obj);
 		}

ICSharpCode.Decompiler/Util/KeyComparer.cs

@@ -1,4 +1,5 @@
-// Copyright (c) 2010-2013 AlphaSierraPapa for the SharpDevelop Team
+#nullable enable
+// Copyright (c) 2010-2013 AlphaSierraPapa for the SharpDevelop Team
 // 
 // Permission is hereby granted, free of charge, to any person obtaining a copy of this
 // software and associated documentation files (the "Software"), to deal in the Software

ICSharpCode.Decompiler/Util/LongSet.cs

@@ -1,4 +1,5 @@
-// Copyright (c) 2016 Daniel Grunwald
+#nullable enable
+// Copyright (c) 2016 Daniel Grunwald
 // 
 // Permission is hereby granted, free of charge, to any person obtaining a copy of this
 // software and associated documentation files (the "Software"), to deal in the Software
@@ -82,7 +83,7 @@ namespace ICSharpCode.Decompiler.Util
 		/// <summary>
 		/// Creates a new LongSet the contains the values from the specified intervals.
 		/// </summary>
-		public LongSet(IEnumerable<LongInterval> intervals)
+		public LongSet(IEnumerable<LongInterval>? intervals)
 			: this(MergeOverlapping(intervals.Where(i => !i.IsEmpty).OrderBy(i => i.Start)).ToImmutableArray())
 		{
 		}
@@ -350,7 +351,7 @@ namespace ICSharpCode.Decompiler.Util
 		}
 
 		#region Equals and GetHashCode implementation
-		public override bool Equals(object obj)
+		public override bool Equals(object? obj)
 		{
 			return obj is LongSet && SetEquals((LongSet)obj);
 		}

ICSharpCode.Decompiler/Util/MultiDictionary.cs

@@ -1,4 +1,5 @@
-// Copyright (c) 2010-2013 AlphaSierraPapa for the SharpDevelop Team
+#nullable enable
+// Copyright (c) 2010-2013 AlphaSierraPapa for the SharpDevelop Team
 // 
 // Permission is hereby granted, free of charge, to any person obtaining a copy of this
 // software and associated documentation files (the "Software"), to deal in the Software
@@ -33,7 +34,7 @@ namespace ICSharpCode.Decompiler.Util
 			dict = new Dictionary<TKey, List<TValue>>();
 		}
 
-		public MultiDictionary(IEqualityComparer<TKey> comparer)
+		public MultiDictionary(IEqualityComparer<TKey>? comparer)
 		{
 			dict = new Dictionary<TKey, List<TValue>>(comparer);
 		}

ICSharpCode.Decompiler/Util/Platform.cs

@@ -1,4 +1,5 @@
-// Copyright (c) 2010-2013 AlphaSierraPapa for the SharpDevelop Team
+#nullable enable
+// Copyright (c) 2010-2013 AlphaSierraPapa for the SharpDevelop Team
 // 
 // Permission is hereby granted, free of charge, to any person obtaining a copy of this
 // software and associated documentation files (the "Software"), to deal in the Software

ICSharpCode.Decompiler/Util/ProjectedList.cs

@@ -1,4 +1,5 @@
-// Copyright (c) 2010-2013 AlphaSierraPapa for the SharpDevelop Team
+#nullable enable
+// Copyright (c) 2010-2013 AlphaSierraPapa for the SharpDevelop Team
 // 
 // Permission is hereby granted, free of charge, to any person obtaining a copy of this
 // software and associated documentation files (the "Software"), to deal in the Software
@@ -25,7 +26,7 @@ namespace ICSharpCode.Decompiler.Util
 	{
 		readonly IList<TInput> input;
 		readonly Func<TInput, TOutput> projection;
-		readonly TOutput[] items;
+		readonly TOutput?[] items;
 
 		public ProjectedList(IList<TInput> input, Func<TInput, TOutput> projection)
 		{
@@ -35,12 +36,12 @@ namespace ICSharpCode.Decompiler.Util
 				throw new ArgumentNullException(nameof(projection));
 			this.input = input;
 			this.projection = projection;
-			this.items = new TOutput[input.Count];
+			this.items = new TOutput?[input.Count];
 		}
 
 		public TOutput this[int index] {
 			get {
-				TOutput output = LazyInit.VolatileRead(ref items[index]);
+				TOutput? output = LazyInit.VolatileRead(ref items[index]);
 				if (output != null)
 				{
 					return output;
@@ -72,7 +73,7 @@ namespace ICSharpCode.Decompiler.Util
 		readonly IList<TInput> input;
 		readonly TContext context;
 		readonly Func<TContext, TInput, TOutput> projection;
-		readonly TOutput[] items;
+		readonly TOutput?[] items;
 
 		public ProjectedList(TContext context, IList<TInput> input, Func<TContext, TInput, TOutput> projection)
 		{
@@ -83,12 +84,12 @@ namespace ICSharpCode.Decompiler.Util
 			this.input = input;
 			this.context = context;
 			this.projection = projection;
-			this.items = new TOutput[input.Count];
+			this.items = new TOutput?[input.Count];
 		}
 
 		public TOutput this[int index] {
 			get {
-				TOutput output = LazyInit.VolatileRead(ref items[index]);
+				TOutput? output = LazyInit.VolatileRead(ref items[index]);
 				if (output != null)
 				{
 					return output;

ICSharpCode.Decompiler/Util/ReferenceComparer.cs

@@ -15,22 +15,23 @@
 // FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
 // OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 // DEALINGS IN THE SOFTWARE.
+#nullable enable
 
 using System.Collections.Generic;
 using System.Runtime.CompilerServices;
 
 namespace ICSharpCode.Decompiler.Util
 {
-	public sealed class ReferenceComparer : IEqualityComparer<object>
+	public sealed class ReferenceComparer : IEqualityComparer<object?>
 	{
 		public readonly static ReferenceComparer Instance = new ReferenceComparer();
 
-		public new bool Equals(object x, object y)
+		public new bool Equals(object? x, object? y)
 		{
 			return x == y;
 		}
 
-		public int GetHashCode(object obj)
+		public int GetHashCode(object? obj)
 		{
 			return RuntimeHelpers.GetHashCode(obj);
 		}

ICSharpCode.Decompiler/Util/ResourcesFile.cs

@@ -1,4 +1,5 @@
-// Copyright (c) 2018 Daniel Grunwald
+#nullable enable
+// Copyright (c) 2018 Daniel Grunwald
 // Based on the .NET Core ResourceReader; make available under the MIT license
 // by the .NET Foundation.
 // 
@@ -30,7 +31,7 @@ namespace ICSharpCode.Decompiler.Util
 	/// <summary>
 	/// .resources file.
 	/// </summary>
-	public class ResourcesFile : IEnumerable<KeyValuePair<string, object>>, IDisposable
+	public class ResourcesFile : IEnumerable<KeyValuePair<string, object?>>, IDisposable
 	{
 		sealed class MyBinaryReader : BinaryReader
 		{
@@ -87,7 +88,7 @@ namespace ICSharpCode.Decompiler.Util
 		readonly long fileStartPosition;
 		readonly long nameSectionPosition;
 		readonly long dataSectionPosition;
-		long[] startPositions;
+		long[]? startPositions;
 
 		/// <summary>
 		/// Creates a new ResourcesFile.
@@ -285,7 +286,7 @@ namespace ICSharpCode.Decompiler.Util
 			return true;
 		}
 
-		object LoadObject(int dataOffset)
+		object? LoadObject(int dataOffset)
 		{
 			try
 			{
@@ -318,7 +319,7 @@ namespace ICSharpCode.Decompiler.Util
 		// from that location.
 		// Anyone who calls LoadObject should make sure they take a lock so 
 		// no one can cause us to do a seek in here.
-		private object LoadObjectV1(int dataOffset)
+		private object? LoadObjectV1(int dataOffset)
 		{
 			Debug.Assert(System.Threading.Monitor.IsEntered(reader));
 			reader.Seek(dataSectionPosition + dataOffset, SeekOrigin.Begin);
@@ -372,7 +373,7 @@ namespace ICSharpCode.Decompiler.Util
 			}
 		}
 
-		private object LoadObjectV2(int dataOffset)
+		private object? LoadObjectV2(int dataOffset)
 		{
 			Debug.Assert(System.Threading.Monitor.IsEntered(reader));
 			reader.Seek(dataSectionPosition + dataOffset, SeekOrigin.Begin);
@@ -464,19 +465,19 @@ namespace ICSharpCode.Decompiler.Util
 			}
 		}
 
-		public object GetResourceValue(int index)
+		public object? GetResourceValue(int index)
 		{
 			GetResourceName(index, out int dataOffset);
 			return LoadObject(dataOffset);
 		}
 
-		public IEnumerator<KeyValuePair<string, object>> GetEnumerator()
+		public IEnumerator<KeyValuePair<string, object?>> GetEnumerator()
 		{
 			for (int i = 0; i < numResources; i++)
 			{
 				string name = GetResourceName(i, out int dataOffset);
-				object val = LoadObject(dataOffset);
-				yield return new KeyValuePair<string, object>(name, val);
+				object? val = LoadObject(dataOffset);
+				yield return new KeyValuePair<string, object?>(name, val);
 			}
 		}
 
@@ -487,7 +488,7 @@ namespace ICSharpCode.Decompiler.Util
 
 		long[] GetStartPositions()
 		{
-			long[] positions = LazyInit.VolatileRead(ref startPositions);
+			long[]? positions = LazyInit.VolatileRead(ref startPositions);
 			if (positions != null)
 				return positions;
 			lock (reader)
@@ -541,11 +542,11 @@ namespace ICSharpCode.Decompiler.Util
 
 	public class ResourceSerializedObject
 	{
-		public string TypeName { get; }
+		public string? TypeName { get; }
 		readonly ResourcesFile file;
 		readonly long position;
 
-		internal ResourceSerializedObject(string typeName, ResourcesFile file, long position)
+		internal ResourceSerializedObject(string? typeName, ResourcesFile file, long position)
 		{
 			this.TypeName = typeName;
 			this.file = file;

ICSharpCode.Decompiler/Util/TreeTraversal.cs

@@ -1,4 +1,5 @@
-// Copyright (c) 2010-2013 AlphaSierraPapa for the SharpDevelop Team
+#nullable enable
+// Copyright (c) 2010-2013 AlphaSierraPapa for the SharpDevelop Team
 // 
 // Permission is hereby granted, free of charge, to any person obtaining a copy of this
 // software and associated documentation files (the "Software"), to deal in the Software
@@ -32,7 +33,7 @@ namespace ICSharpCode.Decompiler.Util
 		/// <param name="root">The root element of the tree.</param>
 		/// <param name="recursion">The function that gets the children of an element.</param>
 		/// <returns>Iterator that enumerates the tree structure in pre-order.</returns>
-		public static IEnumerable<T> PreOrder<T>(T root, Func<T, IEnumerable<T>> recursion)
+		public static IEnumerable<T> PreOrder<T>(T root, Func<T, IEnumerable<T>?> recursion)
 		{
 			return PreOrder(new T[] { root }, recursion);
 		}
@@ -43,7 +44,7 @@ namespace ICSharpCode.Decompiler.Util
 		/// <param name="input">The root elements of the forest.</param>
 		/// <param name="recursion">The function that gets the children of an element.</param>
 		/// <returns>Iterator that enumerates the tree structure in pre-order.</returns>
-		public static IEnumerable<T> PreOrder<T>(IEnumerable<T> input, Func<T, IEnumerable<T>> recursion)
+		public static IEnumerable<T> PreOrder<T>(IEnumerable<T> input, Func<T, IEnumerable<T>?> recursion)
 		{
 			Stack<IEnumerator<T>> stack = new Stack<IEnumerator<T>>();
 			try
@@ -55,7 +56,7 @@ namespace ICSharpCode.Decompiler.Util
 					{
 						T element = stack.Peek().Current;
 						yield return element;
-						IEnumerable<T> children = recursion(element);
+						IEnumerable<T>? children = recursion(element);
 						if (children != null)
 						{
 							stack.Push(children.GetEnumerator());
@@ -79,7 +80,7 @@ namespace ICSharpCode.Decompiler.Util
 		/// <param name="root">The root element of the tree.</param>
 		/// <param name="recursion">The function that gets the children of an element.</param>
 		/// <returns>Iterator that enumerates the tree structure in post-order.</returns>
-		public static IEnumerable<T> PostOrder<T>(T root, Func<T, IEnumerable<T>> recursion)
+		public static IEnumerable<T> PostOrder<T>(T root, Func<T, IEnumerable<T>?> recursion)
 		{
 			return PostOrder(new T[] { root }, recursion);
 		}
@@ -90,7 +91,7 @@ namespace ICSharpCode.Decompiler.Util
 		/// <param name="input">The root elements of the forest.</param>
 		/// <param name="recursion">The function that gets the children of an element.</param>
 		/// <returns>Iterator that enumerates the tree structure in post-order.</returns>
-		public static IEnumerable<T> PostOrder<T>(IEnumerable<T> input, Func<T, IEnumerable<T>> recursion)
+		public static IEnumerable<T> PostOrder<T>(IEnumerable<T> input, Func<T, IEnumerable<T>?> recursion)
 		{
 			Stack<IEnumerator<T>> stack = new Stack<IEnumerator<T>>();
 			try
@@ -101,7 +102,7 @@ namespace ICSharpCode.Decompiler.Util
 					while (stack.Peek().MoveNext())
 					{
 						T element = stack.Peek().Current;
-						IEnumerable<T> children = recursion(element);
+						IEnumerable<T>? children = recursion(element);
 						if (children != null)
 						{
 							stack.Push(children.GetEnumerator());

ICSharpCode.Decompiler/Util/UnicodeNewline.cs

@@ -1,3 +1,4 @@
+#nullable enable
 //
 // UnicodeNewline.cs
 //
@@ -118,7 +119,7 @@ namespace ICSharpCode.Decompiler.Util
 		/// <returns>0 == no new line, otherwise it returns either 1 or 2 depending of the length of the delimiter.</returns>
 		/// <param name="curChar">The current character.</param>
 		/// <param name="nextChar">A callback getting the next character (may be null).</param>
-		public static int GetDelimiterLength(char curChar, Func<char> nextChar = null)
+		public static int GetDelimiterLength(char curChar, Func<char>? nextChar = null)
 		{
 			if (curChar == CR)
 			{
@@ -161,7 +162,7 @@ namespace ICSharpCode.Decompiler.Util
 		/// <param name = "length">The length of the delimiter</param>
 		/// <param name = "type">The type of the delimiter</param>
 		/// <param name="nextChar">A callback getting the next character (may be null).</param>
-		public static bool TryGetDelimiterLengthAndType(char curChar, out int length, out UnicodeNewline type, Func<char> nextChar = null)
+		public static bool TryGetDelimiterLengthAndType(char curChar, out int length, out UnicodeNewline type, Func<char>? nextChar = null)
 		{
 			if (curChar == CR)
 			{
@@ -275,7 +276,7 @@ namespace ICSharpCode.Decompiler.Util
 		/// <returns>0 == no new line, otherwise it returns either 1 or 2 depending of the length of the delimiter.</returns>
 		/// <param name="curChar">The current character.</param>
 		/// <param name="nextChar">A callback getting the next character (may be null).</param>
-		public static UnicodeNewline GetDelimiterType(char curChar, Func<char> nextChar = null)
+		public static UnicodeNewline GetDelimiterType(char curChar, Func<char>? nextChar = null)
 		{
 			switch (curChar)
 			{

ICSharpCode.Decompiler/Util/UnionFind.cs

@@ -15,6 +15,7 @@
 // FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
 // OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 // DEALINGS IN THE SOFTWARE.
+#nullable enable
 
 using System.Collections.Generic;
 
@@ -32,6 +33,12 @@ namespace ICSharpCode.Decompiler.Util
 			public int rank;
 			public Node parent;
 			public T value;
+
+			internal Node(T value)
+			{
+				this.value = value;
+				this.parent = this;
+			}
 		}
 
 		public UnionFind()
@@ -44,10 +51,7 @@ namespace ICSharpCode.Decompiler.Util
 			Node node;
 			if (!mapping.TryGetValue(element, out node))
 			{
-				node = new Node {
-					value = element,
-					rank = 0
-				};
+				node = new Node(element);
 				node.parent = node;
 				mapping.Add(element, node);
 			}
@@ -84,5 +88,3 @@ namespace ICSharpCode.Decompiler.Util
 		}
 	}
 }
-
-

ICSharpCode.Decompiler/Util/Win32Resources.cs

@@ -1,4 +1,5 @@
-using System;
+#nullable enable
+using System;
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.Reflection.PortableExecutable;
@@ -15,21 +16,21 @@ namespace ICSharpCode.Decompiler.Util
 		/// </summary>
 		/// <param name="pe"></param>
 		/// <returns></returns>
-		public static unsafe Win32ResourceDirectory ReadWin32Resources(this PEReader pe)
+		public static unsafe Win32ResourceDirectory? ReadWin32Resources(this PEReader pe)
 		{
 			if (pe == null)
 			{
 				throw new ArgumentNullException(nameof(pe));
 			}
 
-			int rva = pe.PEHeaders.PEHeader.ResourceTableDirectory.RelativeVirtualAddress;
+			int rva = pe.PEHeaders.PEHeader?.ResourceTableDirectory.RelativeVirtualAddress ?? 0;
 			if (rva == 0)
 				return null;
 			byte* pRoot = pe.GetSectionData(rva).Pointer;
 			return new Win32ResourceDirectory(pe, pRoot, 0, new Win32ResourceName("Root"));
 		}
 
-		public static Win32ResourceDirectory Find(this Win32ResourceDirectory root, Win32ResourceName type)
+		public static Win32ResourceDirectory? Find(this Win32ResourceDirectory root, Win32ResourceName type)
 		{
 			if (root is null)
 				throw new ArgumentNullException(nameof(root));
@@ -41,7 +42,7 @@ namespace ICSharpCode.Decompiler.Util
 			return root.FindDirectory(type);
 		}
 
-		public static Win32ResourceDirectory Find(this Win32ResourceDirectory root, Win32ResourceName type, Win32ResourceName name)
+		public static Win32ResourceDirectory? Find(this Win32ResourceDirectory root, Win32ResourceName type, Win32ResourceName name)
 		{
 			if (root is null)
 				throw new ArgumentNullException(nameof(root));
@@ -55,7 +56,7 @@ namespace ICSharpCode.Decompiler.Util
 			return root.FindDirectory(type)?.FindDirectory(name);
 		}
 
-		public static Win32ResourceData Find(this Win32ResourceDirectory root, Win32ResourceName type, Win32ResourceName name, Win32ResourceName langId)
+		public static Win32ResourceData? Find(this Win32ResourceDirectory root, Win32ResourceName type, Win32ResourceName name, Win32ResourceName langId)
 		{
 			if (root is null)
 				throw new ArgumentNullException(nameof(root));
@@ -122,7 +123,7 @@ namespace ICSharpCode.Decompiler.Util
 			return new string(pString->NameString, 0, pString->Length);
 		}
 
-		public Win32ResourceDirectory FindDirectory(Win32ResourceName name)
+		public Win32ResourceDirectory? FindDirectory(Win32ResourceName name)
 		{
 			foreach (var directory in Directories)
 			{
@@ -132,7 +133,7 @@ namespace ICSharpCode.Decompiler.Util
 			return null;
 		}
 
-		public Win32ResourceData FindData(Win32ResourceName name)
+		public Win32ResourceData? FindData(Win32ResourceName name)
 		{
 			foreach (var data in Datas)
 			{
@@ -142,12 +143,12 @@ namespace ICSharpCode.Decompiler.Util
 			return null;
 		}
 
-		public Win32ResourceDirectory FirstDirectory()
+		public Win32ResourceDirectory? FirstDirectory()
 		{
 			return Directories.Count != 0 ? Directories[0] : null;
 		}
 
-		public Win32ResourceData FirstData()
+		public Win32ResourceData? FirstData()
 		{
 			return Datas.Count != 0 ? Datas[0] : null;
 		}
@@ -248,7 +249,7 @@ namespace ICSharpCode.Decompiler.Util
 			return _name.GetHashCode();
 		}
 
-		public override bool Equals(object obj)
+		public override bool Equals(object? obj)
 		{
 			if (!(obj is Win32ResourceName name))
 				return false;

ILSpy.BamlDecompiler.Tests/ILSpy.BamlDecompiler.Tests.csproj

@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="utf-8"?>
-<Project Sdk="Microsoft.NET.Sdk">
+<Project Sdk="Microsoft.NET.Sdk.WindowsDesktop">
 
   <PropertyGroup>
     <TargetFramework>net472</TargetFramework>
@@ -112,4 +112,4 @@
     <Page Include="Cases\Issue445.xaml" />
   </ItemGroup>
 
-</Project>
+</Project>