Merge IDecompilerTypeSystem with ICompilation.

ICSharpCode.Decompiler.Tests/TypeSystem/TypeSystemLoaderTests.cs

@@ -1811,7 +1811,7 @@ namespace ICSharpCode.Decompiler.Tests.TypeSystem
 			var compilationWithSystemCore = new SimpleCompilation(SystemCore, Mscorlib);
 
 			var typeRef = ReflectionHelper.ParseReflectionName("System.Func`2, System.Core");
-			ITypeDefinition c = typeRef.Resolve(compilationWithSystemCore.TypeResolveContext).GetDefinition();
+			ITypeDefinition c = typeRef.Resolve(new SimpleTypeResolveContext(compilationWithSystemCore)).GetDefinition();
 			Assert.IsNotNull(c, "System.Func<,> not found");
 			Assert.AreEqual("mscorlib", c.ParentModule.AssemblyName);
 		}

ICSharpCode.Decompiler.Tests/Util/SequencePointTests.cs

@@ -24,8 +24,7 @@ namespace ICSharpCode.Decompiler.Tests.Util
 		{
 			var decompiler = Tester.GetDecompilerForSnippet(code);
 
-			var firstType = decompiler.TypeSystem.Compilation.GetTopLevelTypeDefinitions().First(t => code.Contains(t.Name));
-			var tree = decompiler.DecompileType(firstType.FullTypeName);
+			var tree = decompiler.DecompileType(new FullTypeName("C"));
 
 			var output = new StringWriter();
 			tree.AcceptVisitor(new InsertParenthesesVisitor { InsertParenthesesForReadability = true });

ICSharpCode.Decompiler/CSharp/CSharpDecompiler.cs

@@ -397,13 +397,13 @@ namespace ICSharpCode.Decompiler.CSharp
 
 		void DoDecompileModuleAndAssemblyAttributes(DecompileRun decompileRun, ITypeResolveContext decompilationContext, SyntaxTree syntaxTree)
 		{
-			foreach (var a in typeSystem.Compilation.MainModule.GetAssemblyAttributes()) {
+			foreach (var a in typeSystem.MainModule.GetAssemblyAttributes()) {
 				var astBuilder = CreateAstBuilder(decompilationContext);
 				var attrSection = new AttributeSection(astBuilder.ConvertAttribute(a));
 				attrSection.AttributeTarget = "assembly";
 				syntaxTree.AddChild(attrSection, SyntaxTree.MemberRole);
 			}
-			foreach (var a in typeSystem.Compilation.MainModule.GetModuleAttributes()) {
+			foreach (var a in typeSystem.MainModule.GetModuleAttributes()) {
 				var astBuilder = CreateAstBuilder(decompilationContext);
 				var attrSection = new AttributeSection(astBuilder.ConvertAttribute(a));
 				attrSection.AttributeTarget = "module";
@@ -603,7 +603,7 @@ namespace ICSharpCode.Decompiler.CSharp
 		/// </remarks>
 		public SyntaxTree DecompileType(FullTypeName fullTypeName)
 		{
-			var type = typeSystem.Compilation.FindType(fullTypeName.TopLevelTypeName).GetDefinition();
+			var type = typeSystem.FindType(fullTypeName.TopLevelTypeName).GetDefinition();
 			if (type == null)
 				throw new InvalidOperationException($"Could not find type definition {fullTypeName} in type system.");
 			var decompilationContext = new SimpleTypeResolveContext(typeSystem.MainModule);
@@ -933,12 +933,12 @@ namespace ICSharpCode.Decompiler.CSharp
 			MethodDeclaration method = new MethodDeclaration();
 			method.Name = name;
 			method.Modifiers = Modifiers.Private | Modifiers.Static;
-			method.Parameters.Add(new ParameterDeclaration(typeSystemAstBuilder.ConvertType(typeSystem.Compilation.FindType(source)), "input"));
-			method.ReturnType = typeSystemAstBuilder.ConvertType(typeSystem.Compilation.FindType(target));
+			method.Parameters.Add(new ParameterDeclaration(typeSystemAstBuilder.ConvertType(typeSystem.FindType(source)), "input"));
+			method.ReturnType = typeSystemAstBuilder.ConvertType(typeSystem.FindType(target));
 			method.Body = new BlockStatement {
 				new IfElseStatement {
 					Condition = new BinaryOperatorExpression {
-						Left = new MemberReferenceExpression(new TypeReferenceExpression(typeSystemAstBuilder.ConvertType(typeSystem.Compilation.FindType(KnownTypeCode.IntPtr))), "Size"),
+						Left = new MemberReferenceExpression(new TypeReferenceExpression(typeSystemAstBuilder.ConvertType(typeSystem.FindType(KnownTypeCode.IntPtr))), "Size"),
 						Operator = BinaryOperatorType.Equality,
 						Right = new PrimitiveExpression(4)
 					},

ICSharpCode.Decompiler/CSharp/StatementBuilder.cs

@@ -290,7 +290,7 @@ namespace ICSharpCode.Decompiler.CSharp
 
 		protected internal override Statement VisitYieldReturn(YieldReturn inst)
 		{
-			var elementType = currentFunction.ReturnType.GetElementTypeFromIEnumerable(typeSystem.Compilation, true, out var isGeneric);
+			var elementType = currentFunction.ReturnType.GetElementTypeFromIEnumerable(typeSystem, true, out var isGeneric);
 			return new YieldReturnStatement {
 				Expression = exprBuilder.Translate(inst.Value, typeHint: elementType).ConvertTo(elementType, exprBuilder)
 			};

ICSharpCode.Decompiler/CSharp/Transforms/IntroduceExtensionMethods.cs

@@ -41,7 +41,7 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 		public void Run(AstNode rootNode, TransformContext context)
 		{
 			this.context = context;
-			this.conversions = CSharpConversions.Get(context.TypeSystem.Compilation);
+			this.conversions = CSharpConversions.Get(context.TypeSystem);
 			InitializeContext(rootNode.Annotation<UsingScope>());
 			rootNode.AcceptVisitor(this);
 		}
@@ -56,7 +56,7 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 					usingScope = new UsingScope(usingScope, ns);
 				}
 			}
-			var currentContext = new CSharpTypeResolveContext(context.TypeSystem.MainModule, usingScope.Resolve(context.TypeSystem.Compilation), context.DecompiledTypeDefinition);
+			var currentContext = new CSharpTypeResolveContext(context.TypeSystem.MainModule, usingScope.Resolve(context.TypeSystem), context.DecompiledTypeDefinition);
 			this.resolveContextStack.Push(currentContext);
 			this.resolver = new CSharpResolver(currentContext);
 		}

ICSharpCode.Decompiler/CSharp/Transforms/IntroduceUsingDeclarations.cs

@@ -130,7 +130,7 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 						usingScope = new UsingScope(usingScope, ns);
 					}
 				}
-				var currentContext = new CSharpTypeResolveContext(context.TypeSystem.MainModule, usingScope.Resolve(context.TypeSystem.Compilation), context.DecompiledTypeDefinition);
+				var currentContext = new CSharpTypeResolveContext(context.TypeSystem.MainModule, usingScope.Resolve(context.TypeSystem), context.DecompiledTypeDefinition);
 				this.context.Push(currentContext);
 				this.astBuilder = CreateAstBuilder(currentContext);
 			}

ICSharpCode.Decompiler/DebugInfo/PortablePdbWriter.cs

@@ -75,7 +75,7 @@ namespace ICSharpCode.Decompiler.DebugInfo
 						sequencePointBlobs.Add(method, (default, default));
 					else
 						sequencePointBlobs.Add(method, (document, EncodeSequencePoints(metadata, localSignatureRowId, points)));
-					importScopeBlobs.Add(method, (document, EncodeImportScope(metadata, reader, ast, decompiler.TypeSystem.Compilation)));
+					importScopeBlobs.Add(method, (document, EncodeImportScope(metadata, reader, ast, decompiler.TypeSystem)));
 				}
 
 				foreach (var nestedTypeHandle in type.GetNestedTypes()) {

ICSharpCode.Decompiler/IL/ControlFlow/AsyncAwaitDecompiler.cs

@@ -197,12 +197,12 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 					return false;
 			} else if (taskType.IsKnownType(KnownTypeCode.Task)) {
 				methodType = AsyncMethodType.Task;
-				underlyingReturnType = context.TypeSystem.Compilation.FindType(KnownTypeCode.Void);
+				underlyingReturnType = context.TypeSystem.FindType(KnownTypeCode.Void);
 				if (builderType?.FullTypeName != new TopLevelTypeName(ns, "AsyncTaskMethodBuilder", 0))
 					return false;
 			} else if (taskType.IsKnownType(KnownTypeCode.TaskOfT)) {
 				methodType = AsyncMethodType.TaskOfT;
-				underlyingReturnType = TaskType.UnpackTask(context.TypeSystem.Compilation, taskType);
+				underlyingReturnType = TaskType.UnpackTask(context.TypeSystem, taskType);
 				if (builderType?.FullTypeName != new TopLevelTypeName(ns, "AsyncTaskMethodBuilder", 1))
 					return false;
 			} else {

ICSharpCode.Decompiler/IL/Transforms/CopyPropagation.cs

@@ -109,7 +109,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			ILVariable[] uninlinedArgs = new ILVariable[copiedExpr.Children.Count];
 			for (int j = 0; j < uninlinedArgs.Length; j++) {
 				var arg = copiedExpr.Children[j];
-				var type = context.TypeSystem.Compilation.FindType(arg.ResultType.ToKnownTypeCode());
+				var type = context.TypeSystem.FindType(arg.ResultType.ToKnownTypeCode());
 				uninlinedArgs[j] = new ILVariable(VariableKind.StackSlot, type, arg.ResultType, arg.ILRange.Start) {
 					Name = "C_" + arg.ILRange.Start
 				};

ICSharpCode.Decompiler/IL/Transforms/IILTransform.cs

@@ -50,7 +50,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		public Metadata.PEFile PEFile => TypeSystem.MainModule.PEFile;
 
 		internal DecompileRun DecompileRun { get; set; }
-		internal ResolvedUsingScope UsingScope => DecompileRun.UsingScope.Resolve(TypeSystem.Compilation);
+		internal ResolvedUsingScope UsingScope => DecompileRun.UsingScope.Resolve(TypeSystem);
 
 		public ILTransformContext(ILFunction function, IDecompilerTypeSystem typeSystem, IDebugInfoProvider debugInfo, DecompilerSettings settings = null)
 		{

ICSharpCode.Decompiler/IL/Transforms/NullPropagationTransform.cs

@@ -260,7 +260,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			{
 				return CSharp.Transforms.IntroduceExtensionMethods.CanTransformToExtensionMethodCall(
 					call.Method, new CSharp.TypeSystem.CSharpTypeResolveContext(
-						context.TypeSystem.Compilation.MainModule, context.UsingScope
+						context.TypeSystem.MainModule, context.UsingScope
 					)
 				);
 			}

ICSharpCode.Decompiler/IL/Transforms/NullableLiftingTransform.cs

@@ -542,7 +542,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			bool isNullCoalescingWithNonNullableFallback = false;
 			if (!MatchNullableCtor(trueInst, out var utype, out var exprToLift)) {
 				isNullCoalescingWithNonNullableFallback = true;
-				utype = context.TypeSystem.Compilation.FindType(trueInst.ResultType.ToKnownTypeCode());
+				utype = context.TypeSystem.FindType(trueInst.ResultType.ToKnownTypeCode());
 				exprToLift = trueInst;
 				if (nullableVars.Count == 1 && exprToLift.MatchLdLoc(nullableVars[0])) {
 					// v.HasValue ? ldloc v : fallback
@@ -779,7 +779,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		{
 			if (underlyingType == SpecialType.UnknownType)
 				return inst;
-			var nullable = context.TypeSystem.Compilation.FindType(KnownTypeCode.NullableOfT).GetDefinition();
+			var nullable = context.TypeSystem.FindType(KnownTypeCode.NullableOfT).GetDefinition();
 			var ctor = nullable?.Methods.FirstOrDefault(m => m.IsConstructor && m.Parameters.Count == 1);
 			if (ctor != null) {
 				ctor = ctor.Specialize(new TypeParameterSubstitution(new[] { underlyingType }, null));

ICSharpCode.Decompiler/IL/Transforms/TransformCollectionAndObjectInitializers.cs

@@ -178,7 +178,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				possibleIndexVariables.Add(stloc.Variable, (stloc.ChildIndex, stloc.Value));
 				return true;
 			}
-			var resolveContext = new CSharpTypeResolveContext(context.TypeSystem.Compilation.MainModule, context.UsingScope);
+			var resolveContext = new CSharpTypeResolveContext(context.TypeSystem.MainModule, context.UsingScope);
 			(var kind, var newPath, var values, var targetVariable) = AccessPathElement.GetAccessPath(instructions[pos], rootType, context.Settings, resolveContext, possibleIndexVariables);
 			if (kind == AccessPathKind.Invalid || target != targetVariable)
 				return false;

ICSharpCode.Decompiler/IL/Transforms/TransformExpressionTrees.cs

@@ -98,8 +98,8 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		{
 			if (!context.Settings.ExpressionTrees) return;
 			this.context = context;
-			this.conversions = CSharpConversions.Get(context.TypeSystem.Compilation);
-			this.resolver = new CSharpResolver(context.TypeSystem.Compilation);
+			this.conversions = CSharpConversions.Get(context.TypeSystem);
+			this.resolver = new CSharpResolver(context.TypeSystem);
 			this.parameters = new Dictionary<ILVariable, (IType, string)>();
 			this.parameterMapping = new Dictionary<ILVariable, ILVariable>();
 			this.instructionsToRemove = new List<ILInstruction>();
@@ -377,7 +377,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			var (converted, arrayType) = ConvertInstruction(invocation.Arguments[0]);
 			if (converted == null)
 				return (null, SpecialType.UnknownType);
-			return (new LdLen(StackType.I4, converted), context.TypeSystem.Compilation.FindType(KnownTypeCode.Int32));
+			return (new LdLen(StackType.I4, converted), context.TypeSystem.FindType(KnownTypeCode.Int32));
 		}
 
 		(ILInstruction, IType) ConvertBinaryNumericOperator(CallInstruction invocation, BinaryNumericOperator op, bool? isChecked = null)
@@ -589,7 +589,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				}
 				return (new Call(operatorMethod) { Arguments = { left, right } }, operatorMethod.ReturnType);
 			}
-			var resultType = context.TypeSystem.Compilation.FindType(KnownTypeCode.Boolean);
+			var resultType = context.TypeSystem.FindType(KnownTypeCode.Boolean);
 			return (new Comp(kind, NullableType.IsNullable(leftType) ? ComparisonLiftingKind.CSharp : ComparisonLiftingKind.None, leftType.GetStackType(), leftType.GetSign(), left, right), resultType);
 		}
 
@@ -739,7 +739,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			IMember method;
 			switch (invocation.Arguments.Count) {
 				case 2:
-					var resultType = context.TypeSystem.Compilation.FindType(KnownTypeCode.Boolean);
+					var resultType = context.TypeSystem.FindType(KnownTypeCode.Boolean);
 					return (and ? IfInstruction.LogicAnd(left, right) : IfInstruction.LogicOr(left, right), resultType);
 				case 3:
 					if (!MatchGetMethodFromHandle(invocation.Arguments[2], out method))
@@ -810,7 +810,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 					return (null, SpecialType.UnknownType);
 				indices[i] = index;
 			}
-			return (new NewArr(type, indices), new ArrayType(context.TypeSystem.Compilation, type, arguments.Count));
+			return (new NewArr(type, indices), new ArrayType(context.TypeSystem, type, arguments.Count));
 		}
 
 		(ILInstruction, IType) ConvertNewArrayInit(CallInstruction invocation)
@@ -821,7 +821,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				return (null, SpecialType.UnknownType);
 			if (!MatchArgumentList(invocation.Arguments[1], out var arguments))
 				return (null, SpecialType.UnknownType);
-			ArrayType arrayType = new ArrayType(context.BlockContext.TypeSystem.Compilation, type);
+			ArrayType arrayType = new ArrayType(context.BlockContext.TypeSystem, type);
 			if (arguments.Count == 0)
 				return (new NewArr(type, new LdcI4(0)), arrayType);
 			var block = (Block)invocation.Arguments[1];
@@ -959,7 +959,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			var converted = ConvertInstruction(invocation.Arguments[0]).Item1;
 			if (!MatchGetTypeFromHandle(invocation.Arguments[1], out var type))
 				return (null, SpecialType.UnknownType);
-			var resultType = context.TypeSystem.Compilation.FindType(KnownTypeCode.Boolean);
+			var resultType = context.TypeSystem.FindType(KnownTypeCode.Boolean);
 			if (converted != null)
 				return (new Comp(ComparisonKind.Inequality, Sign.None, new IsInst(converted, type), new LdNull()), resultType);
 			return (null, SpecialType.UnknownType);
@@ -1061,7 +1061,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			//castclass System.Reflection.MethodInfo(call GetMethodFromHandle(ldmembertoken op_Addition))
 			if (!inst.MatchCastClass(out var arg, out var type))
 				return false;
-			if (!type.Equals(context.TypeSystem.Compilation.FindType(new FullTypeName("System.Reflection.MethodInfo"))))
+			if (!type.Equals(context.TypeSystem.FindType(new FullTypeName("System.Reflection.MethodInfo"))))
 				return false;
 			if (!(arg is CallInstruction call && call.Method.FullName == "System.Reflection.MethodBase.GetMethodFromHandle"))
 				return false;
@@ -1086,7 +1086,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			//castclass System.Reflection.ConstructorInfo(call GetMethodFromHandle(ldmembertoken op_Addition))
 			if (!inst.MatchCastClass(out var arg, out var type))
 				return false;
-			if (!type.Equals(context.TypeSystem.Compilation.FindType(new FullTypeName("System.Reflection.ConstructorInfo"))))
+			if (!type.Equals(context.TypeSystem.FindType(new FullTypeName("System.Reflection.ConstructorInfo"))))
 				return false;
 			if (!(arg is CallInstruction call && call.Method.FullName == "System.Reflection.MethodBase.GetMethodFromHandle"))
 				return false;

ICSharpCode.Decompiler/TypeSystem/DecompilerTypeSystem.cs

@@ -74,51 +74,54 @@ namespace ICSharpCode.Decompiler.TypeSystem
 	/// <remarks>
 	/// This class is thread-safe.
 	/// </remarks>
-	public class DecompilerTypeSystem : IDecompilerTypeSystem
+	public class DecompilerTypeSystem : SimpleCompilation, IDecompilerTypeSystem
 	{
-		readonly Metadata.PEFile moduleDefinition;
-		readonly ICompilation compilation;
-		readonly IAssemblyResolver assemblyResolver;
-		readonly TypeSystemOptions typeSystemOptions;
-		readonly MetadataModule mainModule;
-
-		public DecompilerTypeSystem(Metadata.PEFile moduleDefinition, IAssemblyResolver assemblyResolver)
-			: this(moduleDefinition, assemblyResolver, new DecompilerSettings())
+		public DecompilerTypeSystem(PEFile mainModule, IAssemblyResolver assemblyResolver)
+			: this(mainModule, assemblyResolver, TypeSystemOptions.Default)
 		{
 		}
 
-		public DecompilerTypeSystem(PEFile moduleDefinition, IAssemblyResolver assemblyResolver, DecompilerSettings settings)
+		static TypeSystemOptions GetOptions(DecompilerSettings settings)
 		{
-			if (settings == null)
-				throw new ArgumentNullException(nameof(settings));
-			this.moduleDefinition = moduleDefinition ?? throw new ArgumentNullException(nameof(moduleDefinition));
-			this.assemblyResolver = assemblyResolver ?? throw new ArgumentNullException(nameof(assemblyResolver));
-			typeSystemOptions = TypeSystemOptions.None;
+			var typeSystemOptions = TypeSystemOptions.None;
 			if (settings.Dynamic)
 				typeSystemOptions |= TypeSystemOptions.Dynamic;
 			if (settings.TupleTypes)
 				typeSystemOptions |= TypeSystemOptions.Tuple;
 			if (settings.ExtensionMethods)
 				typeSystemOptions |= TypeSystemOptions.ExtensionMethods;
-			var mainAssembly = moduleDefinition.WithOptions(typeSystemOptions);
+			return typeSystemOptions;
+		}
+
+		public DecompilerTypeSystem(PEFile mainModule, IAssemblyResolver assemblyResolver, DecompilerSettings settings)
+			: this(mainModule, assemblyResolver, GetOptions(settings ?? throw new ArgumentNullException(nameof(settings))))
+		{
+		}
+
+		public DecompilerTypeSystem(PEFile mainModule, IAssemblyResolver assemblyResolver, TypeSystemOptions typeSystemOptions)
+		{
+			if (mainModule == null)
+				throw new ArgumentNullException(nameof(mainModule));
+			if (assemblyResolver == null)
+				throw new ArgumentNullException(nameof(assemblyResolver));
 			// Load referenced assemblies and type-forwarder references.
 			// This is necessary to make .NET Core/PCL binaries work better.
-			var referencedAssemblies = new List<IModuleReference>();
+			var referencedAssemblies = new List<PEFile>();
 			var assemblyReferenceQueue = new Queue<(bool IsAssembly, PEFile MainModule, object Reference)>();
-			var mainMetadata = moduleDefinition.Metadata;
+			var mainMetadata = mainModule.Metadata;
 			foreach (var h in mainMetadata.GetModuleReferences()) {
 				var moduleRef = mainMetadata.GetModuleReference(h);
 				var moduleName = mainMetadata.GetString(moduleRef.Name);
 				foreach (var fileHandle in mainMetadata.AssemblyFiles) {
 					var file = mainMetadata.GetAssemblyFile(fileHandle);
 					if (mainMetadata.StringComparer.Equals(file.Name, moduleName) && file.ContainsMetadata) {
-						assemblyReferenceQueue.Enqueue((false, moduleDefinition, moduleName));
+						assemblyReferenceQueue.Enqueue((false, mainModule, moduleName));
 						break;
 					}
 				}
 			}
-			foreach (var refs in moduleDefinition.AssemblyReferences) {
-				assemblyReferenceQueue.Enqueue((true, moduleDefinition, refs));
+			foreach (var refs in mainModule.AssemblyReferences) {
+				assemblyReferenceQueue.Enqueue((true, mainModule, refs));
 			}
 			var comparer = KeyComparer.Create(((bool IsAssembly, PEFile MainModule, object Reference) reference) =>
 				reference.IsAssembly ? "A:" + ((AssemblyReference)reference.Reference).FullName :
@@ -135,7 +138,7 @@ namespace ICSharpCode.Decompiler.TypeSystem
 					asm = assemblyResolver.ResolveModule(asmRef.MainModule, (string)asmRef.Reference);
 				}
 				if (asm != null) {
-					referencedAssemblies.Add(asm.WithOptions(typeSystemOptions));
+					referencedAssemblies.Add(asm);
 					var metadata = asm.Metadata;
 					foreach (var h in metadata.ExportedTypes) {
 						var exportedType = metadata.GetExportedType(h);
@@ -151,27 +154,30 @@ namespace ICSharpCode.Decompiler.TypeSystem
 					}
 				}
 			}
-			compilation = new SimpleCompilation(mainAssembly, referencedAssemblies);
+			var mainModuleWithOptions = mainModule.WithOptions(typeSystemOptions);
+			var referencedAssembliesWithOptions = referencedAssemblies.Select(file => file.WithOptions(typeSystemOptions));
 			// Primitive types are necessary to avoid assertions in ILReader.
 			// Fallback to MinimalCorlib to provide the primitive types.
-			if (compilation.FindType(KnownTypeCode.Void).Kind == TypeKind.Unknown || compilation.FindType(KnownTypeCode.Int32).Kind == TypeKind.Unknown) {
-				referencedAssemblies.Add(MinimalCorlib.Instance);
-				compilation = new SimpleCompilation(mainAssembly, referencedAssemblies);
-			}
-			this.mainModule = (MetadataModule)compilation.MainModule;
+			if (!HasType(KnownTypeCode.Void) || !HasType(KnownTypeCode.Int32)) {
+				Init(mainModule.WithOptions(typeSystemOptions), referencedAssembliesWithOptions.Concat(new[] { MinimalCorlib.Instance }));
+			} else {
+				Init(mainModuleWithOptions, referencedAssembliesWithOptions);
 			}
+			this.MainModule = (MetadataModule)base.MainModule;
 
-		public ICompilation Compilation {
-			get { return compilation; }
+			bool HasType(KnownTypeCode code)
+			{
+				TopLevelTypeName name = KnownTypeReference.Get(code).TypeName;
+				if (mainModule.GetTypeDefinition(name) != null)
+					return true;
+				foreach (var file in referencedAssemblies) {
+					if (file.GetTypeDefinition(name) != null)
+						return true;
 				}
-		
-		public MetadataModule MainModule {
-			get { return mainModule; }
+				return false;
 			}
-
-		public Metadata.PEFile ModuleDefinition {
-			get { return moduleDefinition; }
 		}
 		
+		public new MetadataModule MainModule { get; }
 	}
 }

ICSharpCode.Decompiler/TypeSystem/ICompilation.cs

@@ -31,24 +31,19 @@ namespace ICSharpCode.Decompiler.TypeSystem
 		/// </summary>
 		IModule MainModule { get; }
 		
-		/// <summary>
-		/// Gets the type resolve context that specifies this compilation and no current assembly or entity.
-		/// </summary>
-		ITypeResolveContext TypeResolveContext { get; }
-
 		/// <summary>
 		/// Gets the list of all modules in the compilation.
 		/// </summary>
 		/// <remarks>
 		/// This main module is the first entry in the list.
 		/// </remarks>
-		IList<IModule> Modules { get; }
+		IReadOnlyList<IModule> Modules { get; }
 
 		/// <summary>
 		/// Gets the referenced modules.
 		/// This list does not include the main module.
 		/// </summary>
-		IList<IModule> ReferencedModules { get; }
+		IReadOnlyList<IModule> ReferencedModules { get; }
 		
 		/// <summary>
 		/// Gets the root namespace of this compilation.

ICSharpCode.Decompiler/TypeSystem/IDecompilerTypeSystem.cs

@@ -23,11 +23,12 @@ using ICSharpCode.Decompiler.Metadata;
 namespace ICSharpCode.Decompiler.TypeSystem
 {
 	/// <summary>
-	/// Allows resolving cecil types into the NRefactory type system.
+	/// Main interface for the decompiler type system.
+	/// 
+	/// The MetadataModule class allows decoding/resolving metadata tokens into type system entities.
 	/// </summary>
-	public interface IDecompilerTypeSystem
+	public interface IDecompilerTypeSystem : ICompilation
 	{
-		ICompilation Compilation { get; }
-		MetadataModule MainModule { get; }
+		new MetadataModule MainModule { get; }
 	}
 }

ICSharpCode.Decompiler/TypeSystem/Implementation/SimpleCompilation.cs

@@ -27,26 +27,35 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 	/// </summary>
 	public class SimpleCompilation : ICompilation
 	{
-		readonly ITypeResolveContext context;
 		readonly CacheManager cacheManager = new CacheManager();
-		readonly KnownTypeCache knownTypeCache;
-		readonly IModule mainModule;
-		readonly IList<IModule> assemblies;
-		readonly IList<IModule> referencedAssemblies;
+		IModule mainModule;
+		KnownTypeCache knownTypeCache;
+		IReadOnlyList<IModule> assemblies;
+		IReadOnlyList<IModule> referencedAssemblies;
+		bool initialized;
 		INamespace rootNamespace;
 		
 		public SimpleCompilation(IModuleReference mainAssembly, params IModuleReference[] assemblyReferences)
-			: this(mainAssembly, (IEnumerable<IModuleReference>)assemblyReferences)
 		{
+			Init(mainAssembly, assemblyReferences);
 		}
 
 		public SimpleCompilation(IModuleReference mainAssembly, IEnumerable<IModuleReference> assemblyReferences)
+		{
+			Init(mainAssembly, assemblyReferences);
+		}
+
+		protected SimpleCompilation()
+		{
+		}
+
+		protected void Init(IModuleReference mainAssembly, IEnumerable<IModuleReference> assemblyReferences)
 		{
 			if (mainAssembly == null)
 				throw new ArgumentNullException("mainAssembly");
 			if (assemblyReferences == null)
 				throw new ArgumentNullException("assemblyReferences");
-			this.context = new SimpleTypeResolveContext(this);
+			var context = new SimpleTypeResolveContext(this);
 			this.mainModule = mainAssembly.Resolve(context);
 			List<IModule> assemblies = new List<IModule>();
 			assemblies.Add(this.mainModule);
@@ -66,43 +75,40 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 			this.assemblies = assemblies.AsReadOnly();
 			this.referencedAssemblies = referencedAssemblies.AsReadOnly();
 			this.knownTypeCache = new KnownTypeCache(this);
+			this.initialized = true;
 		}
 
 		public IModule MainModule {
 			get {
-				if (mainModule == null)
+				if (!initialized)
 					throw new InvalidOperationException("Compilation isn't initialized yet");
 				return mainModule;
 			}
 		}
 		
-		public IList<IModule> Modules {
+		public IReadOnlyList<IModule> Modules {
 			get {
-				if (assemblies == null)
+				if (!initialized)
 					throw new InvalidOperationException("Compilation isn't initialized yet");
 				return assemblies;
 			}
 		}
 		
-		public IList<IModule> ReferencedModules {
+		public IReadOnlyList<IModule> ReferencedModules {
 			get {
-				if (referencedAssemblies == null)
+				if (!initialized)
 					throw new InvalidOperationException("Compilation isn't initialized yet");
 				return referencedAssemblies;
 			}
 		}
 		
-		public ITypeResolveContext TypeResolveContext {
-			get { return context; }
-		}
-		
 		public INamespace RootNamespace {
 			get {
 				INamespace ns = LazyInit.VolatileRead(ref this.rootNamespace);
 				if (ns != null) {
 					return ns;
 				} else {
-					if (referencedAssemblies == null)
+					if (!initialized)
 						throw new InvalidOperationException("Compilation isn't initialized yet");
 					return LazyInit.GetOrSet(ref this.rootNamespace, CreateRootNamespace());
 				}
@@ -144,7 +150,7 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 		
 		public override string ToString()
 		{
-			return "[SimpleCompilation " + mainModule.AssemblyName + "]";
+			return "[" + GetType().Name + " " + mainModule.AssemblyName + "]";
 		}
 	}
 }

ICSharpCode.Decompiler/TypeSystem/ReflectionHelper.cs

@@ -53,7 +53,7 @@ namespace ICSharpCode.Decompiler.TypeSystem
 		/// </remarks>
 		public static IType FindType(this ICompilation compilation, Type type)
 		{
-			return type.ToTypeReference().Resolve(compilation.TypeResolveContext);
+			return type.ToTypeReference().Resolve(new SimpleTypeResolveContext(compilation));
 		}
 		#endregion
 		

ILSpy.BamlDecompiler/CecilTypeResolver.cs

@@ -16,18 +16,16 @@ namespace ILSpy.BamlDecompiler
 	{
 		readonly PEFile module;
 		readonly DecompilerTypeSystem typeSystem;
-		readonly ICompilation compilation;
 	
 		public NRTypeResolver(PEFile module, IAssemblyResolver resolver)
 		{
 			this.module = module ?? throw new ArgumentNullException(nameof(module));
 			this.typeSystem = new DecompilerTypeSystem(module, resolver);
-			this.compilation = typeSystem.Compilation;
 		}
 		
 		public bool IsLocalAssembly(string name)
 		{
-			return MakeShort(name) == compilation.MainModule.AssemblyName;
+			return MakeShort(name) == typeSystem.MainModule.AssemblyName;
 		}
 		
 		string MakeShort(string name)
@@ -50,7 +48,7 @@ namespace ILSpy.BamlDecompiler
 			string fullName = bracket > -1 ? name.Substring(0, name.IndexOf('[')) : name.Substring(0, comma);
 			string assemblyName = name.Substring(comma + 1).Trim();
 
-			var type = compilation.FindType(new FullTypeName(fullName)).GetDefinition();
+			var type = typeSystem.FindType(new FullTypeName(fullName)).GetDefinition();
 			
 			if (type == null)
 				return new UnresolvableType(name);

ILSpy.BamlDecompiler/ConnectMethodDecompiler.cs

@@ -37,7 +37,7 @@ namespace ILSpy.BamlDecompiler
 			var result = new List<(LongSet, EventRegistration[])>();
 			var typeSystem = new DecompilerTypeSystem(module, assemblyResolver);
 
-			var typeDefinition = typeSystem.Compilation.FindType(new FullTypeName(fullTypeName)).GetDefinition();
+			var typeDefinition = typeSystem.FindType(new FullTypeName(fullTypeName)).GetDefinition();
 			if (typeDefinition == null)
 				return result;