Basic implementation of local functions.

ICSharpCode.Decompiler/CSharp/CSharpDecompiler.cs

@@ -156,6 +156,7 @@ namespace ICSharpCode.Decompiler.CSharp
 				},
 				new ProxyCallReplacer(),
 				new DelegateConstruction(),
+				new LocalFunctionDecompiler(),
 				new HighLevelLoopTransform(),
 				new ReduceNestingTransform(),
 				new IntroduceDynamicTypeOnLocals(),
@@ -395,7 +396,7 @@ namespace ICSharpCode.Decompiler.CSharp
 			return new DecompilerTypeSystem(file, resolver);
 		}
 
-		TypeSystemAstBuilder CreateAstBuilder(ITypeResolveContext decompilationContext)
+		internal static TypeSystemAstBuilder CreateAstBuilder(ITypeResolveContext decompilationContext)
 		{
 			var typeSystemAstBuilder = new TypeSystemAstBuilder();
 			typeSystemAstBuilder.ShowAttributes = true;

ICSharpCode.Decompiler/CSharp/OutputVisitor/CSharpOutputVisitor.cs

@@ -1883,6 +1883,25 @@ namespace ICSharpCode.Decompiler.CSharp.OutputVisitor
 			Semicolon();
 			EndNode(variableDeclarationStatement);
 		}
+
+		public virtual void VisitLocalFunctionDeclarationStatement(LocalFunctionDeclarationStatement localFunctionDeclarationStatement)
+		{
+			StartNode(localFunctionDeclarationStatement);
+
+			WriteModifiers(localFunctionDeclarationStatement.ModifierTokens);
+			localFunctionDeclarationStatement.ReturnType.AcceptVisitor(this);
+			Space();
+			WriteIdentifier(localFunctionDeclarationStatement.NameToken);
+			WriteTypeParameters(localFunctionDeclarationStatement.TypeParameters);
+			Space(policy.SpaceBeforeMethodDeclarationParentheses);
+			WriteCommaSeparatedListInParenthesis(localFunctionDeclarationStatement.Parameters, policy.SpaceWithinMethodDeclarationParentheses);
+			foreach (Constraint constraint in localFunctionDeclarationStatement.Constraints) {
+				constraint.AcceptVisitor(this);
+			}
+			WriteMethodBody(localFunctionDeclarationStatement.Body, policy.MethodBraceStyle);
+
+			EndNode(localFunctionDeclarationStatement);
+		}
 		
 		public virtual void VisitWhileStatement(WhileStatement whileStatement)
 		{

ICSharpCode.Decompiler/CSharp/StatementBuilder.cs

@@ -1015,5 +1015,16 @@ namespace ICSharpCode.Decompiler.CSharp
 			stmt.InsertChildAfter(null, new Comment(" IL cpblk instruction"), Roles.Comment);
 			return stmt;
 		}
+
+		protected internal override Statement VisitILFunction(ILFunction function)
+		{
+			var stmt = new LocalFunctionDeclarationStatement();
+			var tsab = CSharpDecompiler.CreateAstBuilder(null);
+			stmt.Name = function.Method.Name;
+			stmt.Parameters.AddRange(function.Method.Parameters.Select(tsab.ConvertParameter));
+			stmt.ReturnType = tsab.ConvertType(function.Method.ReturnType);
+			stmt.Body = ConvertAsBlock(function.Body);
+			return stmt;
+		}
 	}
 }

ICSharpCode.Decompiler/CSharp/Syntax/DepthFirstAstVisitor.cs

@@ -390,7 +390,12 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 		{
 			VisitChildren (variableDeclarationStatement);
 		}
-		
+
+		public virtual void VisitLocalFunctionDeclarationStatement(LocalFunctionDeclarationStatement localFunctionDeclarationStatement)
+		{
+			VisitChildren(localFunctionDeclarationStatement);
+		}
+
 		public virtual void VisitWhileStatement (WhileStatement whileStatement)
 		{
 			VisitChildren (whileStatement);
@@ -1037,7 +1042,12 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 		{
 			return VisitChildren (variableDeclarationStatement);
 		}
-		
+
+		public virtual T VisitLocalFunctionDeclarationStatement(LocalFunctionDeclarationStatement localFunctionDeclarationStatement)
+		{
+			return VisitChildren(localFunctionDeclarationStatement);
+		}
+
 		public virtual T VisitWhileStatement (WhileStatement whileStatement)
 		{
 			return VisitChildren (whileStatement);
@@ -1684,7 +1694,12 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 		{
 			return VisitChildren (variableDeclarationStatement, data);
 		}
-		
+
+		public virtual S VisitLocalFunctionDeclarationStatement(LocalFunctionDeclarationStatement localFunctionDeclarationStatement, T data)
+		{
+			return VisitChildren(localFunctionDeclarationStatement, data);
+		}
+
 		public virtual S VisitWhileStatement (WhileStatement whileStatement, T data)
 		{
 			return VisitChildren (whileStatement, data);

ICSharpCode.Decompiler/CSharp/Syntax/IAstVisitor.cs

@@ -110,6 +110,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 		void VisitUnsafeStatement(UnsafeStatement unsafeStatement);
 		void VisitUsingStatement(UsingStatement usingStatement);
 		void VisitVariableDeclarationStatement(VariableDeclarationStatement variableDeclarationStatement);
+		void VisitLocalFunctionDeclarationStatement(LocalFunctionDeclarationStatement localFunctionDeclarationStatement);
 		void VisitWhileStatement(WhileStatement whileStatement);
 		void VisitYieldBreakStatement(YieldBreakStatement yieldBreakStatement);
 		void VisitYieldReturnStatement(YieldReturnStatement yieldReturnStatement);
@@ -251,6 +252,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 		S VisitUnsafeStatement(UnsafeStatement unsafeStatement);
 		S VisitUsingStatement(UsingStatement usingStatement);
 		S VisitVariableDeclarationStatement(VariableDeclarationStatement variableDeclarationStatement);
+		S VisitLocalFunctionDeclarationStatement(LocalFunctionDeclarationStatement localFunctionDeclarationStatement);
 		S VisitWhileStatement(WhileStatement whileStatement);
 		S VisitYieldBreakStatement(YieldBreakStatement yieldBreakStatement);
 		S VisitYieldReturnStatement(YieldReturnStatement yieldReturnStatement);
@@ -392,6 +394,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 		S VisitUnsafeStatement(UnsafeStatement unsafeStatement, T data);
 		S VisitUsingStatement(UsingStatement usingStatement, T data);
 		S VisitVariableDeclarationStatement(VariableDeclarationStatement variableDeclarationStatement, T data);
+		S VisitLocalFunctionDeclarationStatement(LocalFunctionDeclarationStatement localFunctionDeclarationStatement, T data);
 		S VisitWhileStatement(WhileStatement whileStatement, T data);
 		S VisitYieldBreakStatement(YieldBreakStatement yieldBreakStatement, T data);
 		S VisitYieldReturnStatement(YieldReturnStatement yieldReturnStatement, T data);

ICSharpCode.Decompiler/CSharp/Syntax/Statements/LocalFunctionDeclarationStatement.cs

@@ -0,0 +1,94 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+using ICSharpCode.Decompiler.CSharp.Syntax.PatternMatching;
+
+namespace ICSharpCode.Decompiler.CSharp.Syntax
+{
+	public class LocalFunctionDeclarationStatement : Statement
+	{
+		public AstNodeCollection<TypeParameterDeclaration> TypeParameters {
+			get { return GetChildrenByRole(Roles.TypeParameter); }
+		}
+
+		public CSharpTokenNode LParToken {
+			get { return GetChildByRole(Roles.LPar); }
+		}
+
+		public AstNodeCollection<ParameterDeclaration> Parameters {
+			get { return GetChildrenByRole(Roles.Parameter); }
+		}
+
+		public CSharpTokenNode RParToken {
+			get { return GetChildByRole(Roles.RPar); }
+		}
+
+		public AstNodeCollection<Constraint> Constraints {
+			get { return GetChildrenByRole(Roles.Constraint); }
+		}
+
+		public BlockStatement Body {
+			get { return GetChildByRole(Roles.Body); }
+			set { SetChildByRole(Roles.Body, value); }
+		}
+
+		public Modifiers Modifiers {
+			get { return EntityDeclaration.GetModifiers(this); }
+			set { EntityDeclaration.SetModifiers(this, value); }
+		}
+
+		public bool HasModifier(Modifiers mod)
+		{
+			return (Modifiers & mod) == mod;
+		}
+
+		public IEnumerable<CSharpModifierToken> ModifierTokens {
+			get { return GetChildrenByRole(EntityDeclaration.ModifierRole); }
+		}
+
+		public virtual string Name {
+			get {
+				return GetChildByRole(Roles.Identifier).Name;
+			}
+			set {
+				SetChildByRole(Roles.Identifier, Identifier.Create(value, TextLocation.Empty));
+			}
+		}
+
+		public virtual Identifier NameToken {
+			get { return GetChildByRole(Roles.Identifier); }
+			set { SetChildByRole(Roles.Identifier, value); }
+		}
+
+		public virtual AstType ReturnType {
+			get { return GetChildByRole(Roles.Type); }
+			set { SetChildByRole(Roles.Type, value); }
+		}
+
+		public override void AcceptVisitor(IAstVisitor visitor)
+		{
+			visitor.VisitLocalFunctionDeclarationStatement(this);
+		}
+
+		public override T AcceptVisitor<T>(IAstVisitor<T> visitor)
+		{
+			return visitor.VisitLocalFunctionDeclarationStatement(this);
+		}
+
+		public override S AcceptVisitor<T, S>(IAstVisitor<T, S> visitor, T data)
+		{
+			return visitor.VisitLocalFunctionDeclarationStatement(this, data);
+		}
+
+		protected internal override bool DoMatch(AstNode other, Match match)
+		{
+			LocalFunctionDeclarationStatement o = other as LocalFunctionDeclarationStatement;
+			return o != null && MatchString(this.Name, o.Name)
+				&& (this.Modifiers == Modifiers.Any || this.Modifiers == o.Modifiers)
+				&& this.ReturnType.DoMatch(o.ReturnType, match)
+				&& this.TypeParameters.DoMatch(o.TypeParameters, match)
+				&& this.Parameters.DoMatch(o.Parameters, match) && this.Constraints.DoMatch(o.Constraints, match)
+				&& this.Body.DoMatch(o.Body, match);
+		}
+	}
+}

ICSharpCode.Decompiler/CSharp/Transforms/DeclareVariables.cs

@@ -260,7 +260,7 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 						} else {
 							newPoint = new InsertionPoint { level = nodeLevel, nextNode = identExpr };
 							if (variable.HasInitialValue) {
-								// Uninitialized variables are logically initialized at the beginning of the functin
+								// Uninitialized variables are logically initialized at the beginning of the function
 								// Because it's possible that the variable has a loop-carried dependency,
 								// declare it outside of any loops.
 								while (startIndex >= 0) {

ICSharpCode.Decompiler/DecompilerSettings.cs

@@ -942,7 +942,7 @@ namespace ICSharpCode.Decompiler
 			}
 		}
 
-		bool localFunctions = false;
+		bool localFunctions = true;
 
 		/// <summary>
 		/// Gets/Sets whether C# 7.0 local functions should be used.

ICSharpCode.Decompiler/ICSharpCode.Decompiler.csproj

@@ -161,6 +161,7 @@
     <Compile Include="CSharp\Syntax\Statements\GotoStatement.cs" />
     <Compile Include="CSharp\Syntax\Statements\IfElseStatement.cs" />
     <Compile Include="CSharp\Syntax\Statements\LabelStatement.cs" />
+    <Compile Include="CSharp\Syntax\Statements\LocalFunctionDeclarationStatement.cs" />
     <Compile Include="CSharp\Syntax\Statements\LockStatement.cs" />
     <Compile Include="CSharp\Syntax\Statements\ReturnStatement.cs" />
     <Compile Include="CSharp\Syntax\Statements\Statement.cs" />

ICSharpCode.Decompiler/IL/ControlFlow/YieldReturnDecompiler.cs

@@ -390,7 +390,7 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 				methodTypeParameters: null);
 			var body = context.TypeSystem.MainModule.PEFile.Reader.GetMethodBody(methodDef.RelativeVirtualAddress);
 			var il = context.CreateILReader()
-				.ReadIL(method, body, genericContext, context.CancellationToken);
+				.ReadIL(method, body, genericContext, context.Function.Kind, context.CancellationToken);
 			il.RunTransforms(CSharpDecompiler.EarlyILTransforms(true),
 				new ILTransformContext(il, context.TypeSystem, context.DebugInfo, context.Settings) {
 					CancellationToken = context.CancellationToken,

ICSharpCode.Decompiler/IL/ILReader.cs

@@ -480,14 +480,14 @@ namespace ICSharpCode.Decompiler.IL
 		/// <summary>
 		/// Decodes the specified method body and returns an ILFunction.
 		/// </summary>
-		public ILFunction ReadIL(MethodDefinitionHandle method, MethodBodyBlock body, GenericContext genericContext = default, CancellationToken cancellationToken = default)
+		public ILFunction ReadIL(MethodDefinitionHandle method, MethodBodyBlock body, GenericContext genericContext = default, ILFunctionKind kind = ILFunctionKind.TopLevelFunction, CancellationToken cancellationToken = default)
 		{
 			cancellationToken.ThrowIfCancellationRequested();
 			Init(method, body, genericContext);
 			ReadInstructions(cancellationToken);
 			var blockBuilder = new BlockBuilder(body, variableByExceptionHandler);
 			blockBuilder.CreateBlocks(mainContainer, instructionBuilder, isBranchTarget, cancellationToken);
-			var function = new ILFunction(this.method, body.GetCodeSize(), this.genericContext, mainContainer);
+			var function = new ILFunction(this.method, body.GetCodeSize(), this.genericContext, mainContainer, kind);
 			CollectionExtensions.AddRange(function.Variables, parameterVariables);
 			CollectionExtensions.AddRange(function.Variables, localVariables);
 			CollectionExtensions.AddRange(function.Variables, stackVariables);

ICSharpCode.Decompiler/IL/Instructions/Block.cs

@@ -280,6 +280,21 @@ namespace ICSharpCode.Decompiler.IL
 			return inst;
 		}
 
+		/// <summary>
+		/// Gets the closest parent Block.
+		/// Returns null, if the instruction is not a descendant of a Block.
+		/// </summary>
+		public static Block FindClosestBlock(ILInstruction inst)
+		{
+			var curr = inst;
+			while (curr != null) {
+				if (curr is Block)
+					return (Block)curr;
+				curr = curr.Parent;
+			}
+			return null;
+		}
+
 		public bool MatchInlineAssignBlock(out CallInstruction call, out ILInstruction value)
 		{
 			call = null;

ICSharpCode.Decompiler/IL/Instructions/ILFunction.cs

@@ -99,13 +99,22 @@ namespace ICSharpCode.Decompiler.IL
 		/// </summary>
 		public IType DelegateType;
 
-		public bool IsExpressionTree => DelegateType != null && DelegateType.FullName == "System.Linq.Expressions.Expression" && DelegateType.TypeParameterCount == 1;
+		ILFunctionKind kind;
+
+		public ILFunctionKind Kind {
+			get => kind;
+			set {
+				if (kind == ILFunctionKind.TopLevelFunction || kind == ILFunctionKind.LocalFunction)
+					throw new InvalidOperationException("ILFunction.Kind of a top-level or local function may not be changed.");
+				kind = value;
+			}
+		}
 
 		public readonly IType ReturnType;
 
 		public readonly IReadOnlyList<IParameter> Parameters;
 
-		public ILFunction(IMethod method, int codeSize, GenericContext genericContext, ILInstruction body) : base(OpCode.ILFunction)
+		public ILFunction(IMethod method, int codeSize, GenericContext genericContext, ILInstruction body, ILFunctionKind kind = ILFunctionKind.TopLevelFunction) : base(OpCode.ILFunction)
 		{
 			this.Method = method;
 			this.CodeSize = codeSize;
@@ -114,6 +123,7 @@ namespace ICSharpCode.Decompiler.IL
 			this.ReturnType = Method?.ReturnType;
 			this.Parameters = Method?.Parameters;
 			this.Variables = new ILVariableCollection(this);
+			this.kind = kind;
 		}
 
 		public ILFunction(IType returnType, IReadOnlyList<IParameter> parameters, GenericContext genericContext, ILInstruction body) : base(OpCode.ILFunction)
@@ -123,10 +133,31 @@ namespace ICSharpCode.Decompiler.IL
 			this.ReturnType = returnType;
 			this.Parameters = parameters;
 			this.Variables = new ILVariableCollection(this);
+			this.kind = ILFunctionKind.ExpressionTree;
 		}
 
 		internal override void CheckInvariant(ILPhase phase)
 		{
+			switch (kind) {
+				case ILFunctionKind.TopLevelFunction:
+					Debug.Assert(Parent == null);
+					Debug.Assert(DelegateType == null);
+					break;
+				case ILFunctionKind.Delegate:
+					Debug.Assert(Parent != null && !(Parent is Block));
+					Debug.Assert(DelegateType != null);
+					Debug.Assert(!(DelegateType?.FullName == "System.Linq.Expressions.Expression" && DelegateType.TypeParameterCount == 1));
+					break;
+				case ILFunctionKind.ExpressionTree:
+					Debug.Assert(Parent != null && !(Parent is Block));
+					Debug.Assert(DelegateType != null);
+					Debug.Assert(DelegateType?.FullName == "System.Linq.Expressions.Expression" && DelegateType.TypeParameterCount == 1);
+					break;
+				case ILFunctionKind.LocalFunction:
+					Debug.Assert(Parent is Block);
+					Debug.Assert(DelegateType == null);
+					break;
+			}
 			for (int i = 0; i < Variables.Count; i++) {
 				Debug.Assert(Variables[i].Function == this);
 				Debug.Assert(Variables[i].IndexInFunction == i);
@@ -148,8 +179,13 @@ namespace ICSharpCode.Decompiler.IL
 				output.Write(' ');
 				Method.WriteTo(output);
 			}
-			if (IsExpressionTree) {
+			switch (kind) {
-				output.Write(".ET");
+				case ILFunctionKind.ExpressionTree:
+					output.Write(".ET");
+					break;
+				case ILFunctionKind.LocalFunction:
+					output.Write(".local");
+					break;
 			}
 			if (DelegateType != null) {
 				output.Write("[");
@@ -290,4 +326,24 @@ namespace ICSharpCode.Decompiler.IL
 			Debug.Assert(ok);
 		}
 	}
+
+	public enum ILFunctionKind
+	{
+		/// <summary>
+		/// ILFunction is a "top-level" function, i.e., method, accessor, constructor, destructor or operator.
+		/// </summary>
+		TopLevelFunction,
+		/// <summary>
+		/// ILFunction is a delegate or lambda expression.
+		/// </summary>
+		Delegate,
+		/// <summary>
+		/// ILFunction is an expression tree lambda.
+		/// </summary>
+		ExpressionTree,
+		/// <summary>
+		/// ILFunction is a C# 7.0 local function.
+		/// </summary>
+		LocalFunction
+	}
 }

ICSharpCode.Decompiler/IL/Transforms/DelegateConstruction.cs

@@ -175,11 +175,11 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			var targetMethod = ((IInstructionWithMethodOperand)value.Arguments[1]).Method;
 			if (!IsAnonymousMethod(decompilationContext.CurrentTypeDefinition, targetMethod))
 				return null;
-			if (LocalFunctionDecompiler.IsLocalFunctionMethod(targetMethod.ParentModule.PEFile, (MethodDefinitionHandle)targetMethod.MetadataToken))
-				return null;
-			target = value.Arguments[0];
 			if (targetMethod.MetadataToken.IsNil)
 				return null;
+			if (LocalFunctionDecompiler.IsLocalFunctionMethod(targetMethod))
+				return null;
+			target = value.Arguments[0];
 			var methodDefinition = context.PEFile.Metadata.GetMethodDefinition((MethodDefinitionHandle)targetMethod.MetadataToken);
 			if (!methodDefinition.HasBody())
 				return null;
@@ -188,7 +188,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				return null;
 			var ilReader = context.CreateILReader();
 			var body = context.PEFile.Reader.GetMethodBody(methodDefinition.RelativeVirtualAddress);
-			var function = ilReader.ReadIL((MethodDefinitionHandle)targetMethod.MetadataToken, body, genericContext.Value, context.CancellationToken);
+			var function = ilReader.ReadIL((MethodDefinitionHandle)targetMethod.MetadataToken, body, genericContext.Value, ILFunctionKind.Delegate, context.CancellationToken);
 			function.DelegateType = value.Method.DeclaringType;
 			function.CheckInvariant(ILPhase.Normal);
 			// Embed the lambda into the parent function's ILAst, so that "Show steps" can show

ICSharpCode.Decompiler/IL/Transforms/LocalFunctionDecompiler.cs

@@ -1,20 +1,121 @@
 using System;
 using System.Collections.Generic;
 using System.Collections.Immutable;
+using System.Linq;
 using System.Reflection;
 using System.Reflection.Metadata;
 using System.Text;
 using System.Text.RegularExpressions;
+using ICSharpCode.Decompiler.CSharp;
 using ICSharpCode.Decompiler.Metadata;
+using ICSharpCode.Decompiler.TypeSystem;
 using ICSharpCode.Decompiler.Util;
 
 namespace ICSharpCode.Decompiler.IL.Transforms
 {
 	class LocalFunctionDecompiler : IILTransform
 	{
+		ILTransformContext context;
+		ITypeResolveContext decompilationContext;
+
 		public void Run(ILFunction function, ILTransformContext context)
 		{
-			throw new NotImplementedException();
+			if (!context.Settings.LocalFunctions)
+				return;
+			this.context = context;
+			this.decompilationContext = new SimpleTypeResolveContext(function.Method);
+			var localFunctions = new Dictionary<IMethod, List<Call>>();
+			var cancellationToken = context.CancellationToken;
+			// Find use-sites
+			foreach (var inst in function.Descendants) {
+				cancellationToken.ThrowIfCancellationRequested();
+				if (inst is Call call && IsLocalFunctionMethod(call.Method)) {
+					context.StepStartGroup($"LocalFunctionDecompiler {call.StartILOffset}", call);
+					if (!localFunctions.TryGetValue(call.Method, out var info)) {
+						info = new List<Call>() { call };
+						localFunctions.Add(call.Method, info);
+					} else {
+						info.Add(call);
+					}
+					context.StepEndGroup();
+				}
+			}
+
+			foreach (var (method, useSites) in localFunctions) {
+				var insertionPoint = FindInsertionPoint(useSites);
+				if (TransformLocalFunction(method, (Block)insertionPoint.Parent, insertionPoint.ChildIndex + 1) == null)
+					continue;
+			}
+		}
+
+		static ILInstruction FindInsertionPoint(List<Call> useSites)
+		{
+			ILInstruction insertionPoint = null;
+			foreach (var call in useSites) {
+				if (insertionPoint == null) {
+					insertionPoint = GetStatement(call);
+					continue;
+				}
+
+				var ancestor = FindCommonAncestorInstruction(insertionPoint, GetStatement(call));
+
+				if (ancestor == null)
+					return null;
+
+				insertionPoint = ancestor;
+			}
+
+			switch (insertionPoint) {
+				case BlockContainer bc:
+					return insertionPoint;
+				case Block b:
+					return insertionPoint;
+				default:
+					return insertionPoint;
+			}
+		}
+
+		static ILInstruction FindCommonAncestorInstruction(ILInstruction a, ILInstruction b)
+		{
+			var ancestorsOfB = new HashSet<ILInstruction>(b.Ancestors);
+			return a.Ancestors.FirstOrDefault(ancestorsOfB.Contains);
+		}
+
+		static ILInstruction GetStatement(ILInstruction inst)
+		{
+			while (inst.Parent != null) {
+				if (inst.Parent is Block)
+					return inst;
+				inst = inst.Parent;
+			}
+			return inst;
+		}
+
+		private ILFunction TransformLocalFunction(IMethod targetMethod, Block parent, int insertionPoint)
+		{
+			var methodDefinition = context.PEFile.Metadata.GetMethodDefinition((MethodDefinitionHandle)targetMethod.MetadataToken);
+			if (!methodDefinition.HasBody())
+				return null;
+			var genericContext = DelegateConstruction.GenericContextFromTypeArguments(targetMethod.Substitution);
+			if (genericContext == null)
+				return null;
+			var ilReader = context.CreateILReader();
+			var body = context.PEFile.Reader.GetMethodBody(methodDefinition.RelativeVirtualAddress);
+			var function = ilReader.ReadIL((MethodDefinitionHandle)targetMethod.MetadataToken, body, genericContext.Value, ILFunctionKind.LocalFunction, context.CancellationToken);
+			// Embed the local function into the parent function's ILAst, so that "Show steps" can show
+			// how the local function body is being transformed.
+			parent.Instructions.Insert(insertionPoint, function);
+			function.CheckInvariant(ILPhase.Normal);
+
+			var nestedContext = new ILTransformContext(context, function);
+			function.RunTransforms(CSharpDecompiler.GetILTransforms().TakeWhile(t => !(t is LocalFunctionDecompiler)), nestedContext);
+
+			return function;
+		}
+
+		public static bool IsLocalFunctionMethod(IMethod method)
+		{
+			return IsLocalFunctionMethod(method.ParentModule.PEFile, (MethodDefinitionHandle)method.MetadataToken);
 		}
 
 		public static bool IsLocalFunctionMethod(PEFile module, MethodDefinitionHandle methodHandle)

ICSharpCode.Decompiler/IL/Transforms/ProxyCallReplacer.cs

@@ -36,7 +36,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			// partially copied from CSharpDecompiler
 			var ilReader = context.CreateILReader();
 			var body = context.PEFile.Reader.GetMethodBody(methodDef.RelativeVirtualAddress);
-			var proxyFunction = ilReader.ReadIL(handle, body, genericContext.Value, context.CancellationToken);
+			var proxyFunction = ilReader.ReadIL(handle, body, genericContext.Value, ILFunctionKind.TopLevelFunction, context.CancellationToken);
 			var transformContext = new ILTransformContext(context, proxyFunction);
 			proxyFunction.RunTransforms(CSharp.CSharpDecompiler.EarlyILTransforms(), transformContext);
 			if (!(proxyFunction.Body is BlockContainer blockContainer))

ICSharpCode.Decompiler/IL/Transforms/TransformExpressionTrees.cs

@@ -197,6 +197,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 
 		void SetExpressionTreeFlag(ILFunction lambda, CallInstruction call)
 		{
+			lambda.Kind = IsExpressionTree(call.Method.ReturnType) ? ILFunctionKind.ExpressionTree : ILFunctionKind.Delegate;
 			lambda.DelegateType = call.Method.ReturnType;
 		}
 
@@ -341,7 +342,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 						}
 						return (null, SpecialType.UnknownType);
 					case ILFunction function:
-						if (function.IsExpressionTree) {
+						if (function.Kind == ILFunctionKind.ExpressionTree) {
 							function.DelegateType = UnwrapExpressionTree(function.DelegateType);
 						}
 						return (function, function.DelegateType);
@@ -372,6 +373,10 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			}
 		}
 
+		bool IsExpressionTree(IType delegateType) => delegateType is ParameterizedType pt
+			&& pt.FullName == "System.Linq.Expressions.Expression"
+			&& pt.TypeArguments.Count == 1;
+
 		IType UnwrapExpressionTree(IType delegateType)
 		{
 			if (delegateType is ParameterizedType pt && pt.FullName == "System.Linq.Expressions.Expression" && pt.TypeArguments.Count == 1) {

ILSpy.BamlDecompiler/Rewrite/ConnectionIdRewritePass.cs

@@ -94,7 +94,7 @@ namespace ILSpy.BamlDecompiler.Rewrite
 
 			// decompile method and optimize the switch
 			var ilReader = new ILReader(ctx.TypeSystem.MainModule);
-			var function = ilReader.ReadIL((MethodDefinitionHandle)method.MetadataToken, body, genericContext, ctx.CancellationToken);
+			var function = ilReader.ReadIL((MethodDefinitionHandle)method.MetadataToken, body, genericContext, ILFunctionKind.TopLevelFunction, ctx.CancellationToken);
 
 			var context = new ILTransformContext(function, ctx.TypeSystem, null) {
 				CancellationToken = ctx.CancellationToken

ILSpy/Languages/ILAstLanguage.cs

@@ -119,7 +119,7 @@ namespace ICSharpCode.ILSpy
 				var reader = new ILReader(typeSystem.MainModule);
 				reader.UseDebugSymbols = options.DecompilerSettings.UseDebugSymbols;
 				var methodBody = module.Reader.GetMethodBody(methodDef.RelativeVirtualAddress);
-				ILFunction il = reader.ReadIL((SRM.MethodDefinitionHandle)method.MetadataToken, methodBody, cancellationToken: options.CancellationToken);
+				ILFunction il = reader.ReadIL((SRM.MethodDefinitionHandle)method.MetadataToken, methodBody, kind: ILFunctionKind.TopLevelFunction, cancellationToken: options.CancellationToken);
 				var namespaces = new HashSet<string>();
 				var decompiler = new CSharpDecompiler(typeSystem, options.DecompilerSettings) { CancellationToken = options.CancellationToken };
 				ILTransformContext context = decompiler.CreateILTransformContext(il);