Fix #1867: Captures of copies of this are not properly handled by the decompiler

ICSharpCode.Decompiler.Tests/TestCases/Pretty/DelegateConstruction.cs

@@ -429,4 +429,24 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 		}
 #endif
 	}
+
+	public class Issue1867
+	{
+		private int value;
+
+		public Func<bool> TestLambda(Issue1867 x)
+		{
+			Issue1867 m1;
+			Issue1867 m2;
+			if (x.value > value) {
+				m1 = this;
+				m2 = x;
+			} else {
+				m1 = x;
+				m2 = this;
+			}
+
+			return () => m1.value + 1 == 4 && m2.value > 5;
+		}
+	}
 }

ICSharpCode.Decompiler/IL/Transforms/LocalFunctionDecompiler.cs

@@ -97,7 +97,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 						if (target == null) {
 							target = info.UseSites[0].Arguments[0];
 							if (target.MatchLdFld(out var target1, out var field) && thisVar.Type.Equals(field.Type) && field.Type.Kind == TypeKind.Class && TransformDisplayClassUsage.IsPotentialClosure(context, field.Type.GetDefinition())) {
-								var variable = function.Descendants.OfType<ILFunction>().SelectMany(f => f.Variables).Where(v => !v.IsThis() && TransformDisplayClassUsage.IsClosure(context, v, null, out var varType, out _) && varType.Equals(field.Type)).OnlyOrDefault();
+								var variable = function.Descendants.OfType<ILFunction>().SelectMany(f => f.Variables).Where(v => !v.IsThis() && TransformDisplayClassUsage.IsClosure(context, v, out var varType, out _) && varType.Equals(field.Type)).OnlyOrDefault();
 								if (variable != null) {
 									target = new LdLoc(variable);
 									HandleArgument(localFunction, 1, 0, target);
@@ -399,7 +399,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				return false;
 			if (closureVar.Kind == VariableKind.NamedArgument)
 				return false;
-			if (!TransformDisplayClassUsage.IsClosure(context, closureVar, null, out _, out var initializer))
+			if (!TransformDisplayClassUsage.IsClosure(context, closureVar, out _, out var initializer))
 				return false;
 			if (i - firstArgumentIndex >= 0) {
 				Debug.Assert(i - firstArgumentIndex < function.Method.Parameters.Count && IsClosureParameter(function.Method.Parameters[i - firstArgumentIndex], resolveContext));

ICSharpCode.Decompiler/IL/Transforms/TransformDisplayClassUsage.cs

@@ -21,6 +21,7 @@ using System.Collections.Generic;
 using System.Diagnostics;
 using System.Linq;
 using ICSharpCode.Decompiler.TypeSystem;
+using ICSharpCode.Decompiler.Util;
 
 namespace ICSharpCode.Decompiler.IL.Transforms
 {
@@ -45,6 +46,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		ILTransformContext context;
 		readonly Dictionary<ILVariable, DisplayClass> displayClasses = new Dictionary<ILVariable, DisplayClass>();
 		readonly List<ILInstruction> instructionsToRemove = new List<ILInstruction>();
+		readonly MultiDictionary<IField, StObj> fieldAssignmentsWithVariableValue = new MultiDictionary<IField, StObj>();
 
 		public void Run(ILFunction function, ILTransformContext context)
 		{
@@ -61,10 +63,13 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 							continue;
 						if ((context.Settings.AnonymousMethods || context.Settings.ExpressionTrees) && IsClosure(context, v, instructionsToRemove, out ITypeDefinition closureType, out var inst)) {
 							AddOrUpdateDisplayClass(f, v, closureType, inst, localFunctionClosureParameter: false);
+							continue;
 						}
 						if (context.Settings.LocalFunctions && f.Kind == ILFunctionKind.LocalFunction && v.Kind == VariableKind.Parameter && v.Index > -1 && f.Method.Parameters[v.Index.Value] is IParameter p && LocalFunctionDecompiler.IsClosureParameter(p, decompilationContext)) {
 							AddOrUpdateDisplayClass(f, v, ((ByReferenceType)p.Type).ElementType.GetDefinition(), f.Body, localFunctionClosureParameter: true);
+							continue;
 						}
+						AnalyzeUseSites(v);
 					}
 				}
 				VisitILFunction(function);
@@ -79,10 +84,35 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			} finally {
 				instructionsToRemove.Clear();
 				displayClasses.Clear();
+				fieldAssignmentsWithVariableValue.Clear();
 				this.context = null;
 			}
 		}
 
+		private void AnalyzeUseSites(ILVariable v)
+		{
+			foreach (var use in v.LoadInstructions) {
+				if (!(use.Parent?.Parent is Block))
+					continue;
+				if (use.Parent.MatchStFld(out _, out var f, out var value) && value == use) {
+					fieldAssignmentsWithVariableValue.Add(f, (StObj)use.Parent);
+				}
+				if (use.Parent.MatchStsFld(out f, out value) && value == use) {
+					fieldAssignmentsWithVariableValue.Add(f, (StObj)use.Parent);
+				}
+			}
+			foreach (var use in v.AddressInstructions) {
+				if (!(use.Parent?.Parent is Block))
+					continue;
+				if (use.Parent.MatchStFld(out _, out var f, out var value) && value == use) {
+					fieldAssignmentsWithVariableValue.Add(f, (StObj)use.Parent);
+				}
+				if (use.Parent.MatchStsFld(out f, out value) && value == use) {
+					fieldAssignmentsWithVariableValue.Add(f, (StObj)use.Parent);
+				}
+			}
+		}
+
 		private void AddOrUpdateDisplayClass(ILFunction f, ILVariable v, ITypeDefinition closureType, ILInstruction inst, bool localFunctionClosureParameter)
 		{
 			var displayClass = displayClasses.Values.FirstOrDefault(c => c.Definition == closureType);
@@ -110,7 +140,12 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			}
 		}
 
-		internal static bool IsClosure(ILTransformContext context, ILVariable variable, List<ILInstruction> instructionsToRemove, out ITypeDefinition closureType, out ILInstruction initializer)
+		internal static bool IsClosure(ILTransformContext context, ILVariable variable, out ITypeDefinition closureType, out ILInstruction initializer)
+		{
+			return IsClosure(context, variable, instructionsToRemove: null, out closureType, out initializer);
+		}
+
+		static bool IsClosure(ILTransformContext context, ILVariable variable, List<ILInstruction> instructionsToRemove, out ITypeDefinition closureType, out ILInstruction initializer)
 		{
 			closureType = null;
 			initializer = null;
@@ -276,18 +311,22 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		protected internal override void VisitStObj(StObj inst)
 		{
 			inst.Value.AcceptVisitor(this);
-			if (IsParameterAssignment(inst, out var displayClass, out var field, out var parameter)) {
-				context.Step($"Detected parameter assignment {parameter.Name}", inst);
-				displayClass.Variables.Add((IField)field.MemberDefinition, parameter);
-				instructionsToRemove.Add(inst);
-			} else if (IsDisplayClassAssignment(inst, out displayClass, out field, out var variable)) {
-				context.Step($"Detected display-class assignment {variable.Name}", inst);
-				displayClass.Variables.Add((IField)field.MemberDefinition, variable);
-				instructionsToRemove.Add(inst);
-			} else {
-				inst.Target.AcceptVisitor(this);
-				EarlyExpressionTransforms.StObjToStLoc(inst, context);
+			if (inst.Parent is Block) {
+				if (IsParameterAssignment(inst, out var displayClass, out var field, out var parameter)) {
+					context.Step($"Detected parameter assignment {parameter.Name}", inst);
+					displayClass.Variables.Add((IField)field.MemberDefinition, parameter);
+					instructionsToRemove.Add(inst);
+					return;
+				}
+				if (IsDisplayClassAssignment(inst, out displayClass, out field, out var variable)) {
+					context.Step($"Detected display-class assignment {variable.Name}", inst);
+					displayClass.Variables.Add((IField)field.MemberDefinition, variable);
+					instructionsToRemove.Add(inst);
+					return;
+				}
 			}
+			inst.Target.AcceptVisitor(this);
+			EarlyExpressionTransforms.StObjToStLoc(inst, context);
 		}
 
 		protected internal override void VisitLdObj(LdObj inst)
@@ -322,6 +361,8 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			parameter = null;
 			if (!IsDisplayClassFieldAccess(inst.Target, out var displayClassVar, out displayClass, out field))
 				return false;
+			if (fieldAssignmentsWithVariableValue[field].Count != 1)
+				return false;
 			if (!(inst.Value.MatchLdLoc(out var v) && v.Kind == VariableKind.Parameter && v.Function == currentFunction && v.Type.Equals(field.Type)))
 				return false;
 			if (displayClass.Variables.ContainsKey((IField)field.MemberDefinition))