Merge pull request #3686 from icsharpcode/custom-signature-decoder-comparer

Hide compiler-generated accessor methods

ICSharpCode.Decompiler.Tests/Helpers/Tester.cs

@@ -489,6 +489,17 @@ namespace System.Runtime.CompilerServices
 			{
 				sourceFileNames.Add(Path.GetFullPath(Path.Combine(Path.GetDirectoryName(sourceFileName), match.Groups[1].Value)));
 			}
+
+			List<string> dependencyAssemblies = new List<string>();
+			string sourceText = File.ReadAllText(sourceFileName);
+			foreach (Match match in Regex.Matches(sourceText, @"//\s*#dependency\s+([\w\d./\\]+)"))
+			{
+				string depSourcePath = Path.GetFullPath(Path.Combine(
+					Path.GetDirectoryName(sourceFileName), match.Groups[1].Value));
+				var depResults = await CompileCSharp(depSourcePath, flags | CompilerOptions.Library).ConfigureAwait(false);
+				dependencyAssemblies.Add(Path.GetFullPath(depResults.PathToAssembly));
+			}
+
 			bool targetNet40 = (flags & CompilerOptions.TargetNet40) != 0;
 			bool useRoslyn = (flags & CompilerOptions.UseRoslynMask) != 0;
 
@@ -556,6 +567,11 @@ namespace System.Runtime.CompilerServices
 
 				references = references.Select(r => "-r:\"" + Path.Combine(refAsmPath, r) + "\"");
 
+				foreach (var dependency in dependencyAssemblies)
+				{
+					references = references.Append($"-r:\"{dependency}\"");
+				}
+
 				string otherOptions = $"-nologo -noconfig " +
 					$"-langversion:{languageVersion} " +
 					$"-unsafe -o{(flags.HasFlag(CompilerOptions.Optimize) ? "+ " : "- ")}";

ICSharpCode.Decompiler.Tests/ICSharpCode.Decompiler.Tests.csproj

@@ -167,6 +167,9 @@
     <Compile Include="TestCases\Pretty\Issue3610.cs" />
     <Compile Include="TestCases\Pretty\Issue3611.cs" />
     <Compile Include="TestCases\Pretty\Issue3598.cs" />
+    <Compile Include="Metadata\SignatureBlobComparerTests.cs" />
+    <None Include="TestCases\Pretty\Issue3684.dep.cs" />
+    <None Include="TestCases\Pretty\Issue3684.cs" />
     <None Include="TestCases\Ugly\NoLocalFunctions.Expected.cs" />
     <None Include="TestCases\ILPretty\Issue3504.cs" />
     <Compile Include="TestCases\ILPretty\MonoFixed.cs" />

ICSharpCode.Decompiler.Tests/Metadata/SignatureBlobComparerTests.cs

@@ -0,0 +1,365 @@
+// Copyright (c) 2026 Siegfried Pammer
+// 
+// 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
+// without restriction, including without limitation the rights to use, copy, modify, merge,
+// publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons
+// to whom the Software is furnished to do so, subject to the following conditions:
+// 
+// The above copyright notice and this permission notice shall be included in all copies or
+// substantial portions of the Software.
+// 
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
+// INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
+// PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE
+// 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.
+
+using System.Collections.Generic;
+using System.Linq;
+using System.Reflection.Metadata;
+
+using ICSharpCode.Decompiler.Metadata;
+
+using NUnit.Framework;
+
+namespace ICSharpCode.Decompiler.Tests.Metadata
+{
+	[TestFixture]
+	public class SignatureBlobComparerTests
+	{
+		static MetadataReader Metadata => TypeSystem.TypeSystemLoaderTests.TestAssembly.Metadata;
+
+		#region Helper methods
+
+		/// <summary>
+		/// Finds all MethodDefinitionHandles for methods with the given name in the given type.
+		/// </summary>
+		static List<MethodDefinitionHandle> FindMethods(string typeName, string methodName)
+		{
+			var results = new List<MethodDefinitionHandle>();
+			foreach (var typeHandle in Metadata.TypeDefinitions)
+			{
+				var typeDef = Metadata.GetTypeDefinition(typeHandle);
+				if (!Metadata.StringComparer.Equals(typeDef.Name, typeName))
+					continue;
+
+				foreach (var methodHandle in typeDef.GetMethods())
+				{
+					var methodDef = Metadata.GetMethodDefinition(methodHandle);
+					if (Metadata.StringComparer.Equals(methodDef.Name, methodName))
+						results.Add(methodHandle);
+				}
+			}
+			return results;
+		}
+
+		/// <summary>
+		/// Finds a single MethodDefinitionHandle for a method with the given name in the given type.
+		/// </summary>
+		static MethodDefinitionHandle FindMethod(string typeName, string methodName)
+		{
+			var results = FindMethods(typeName, methodName);
+			Assert.That(results.Count, Is.EqualTo(1),
+				$"Expected exactly one method '{methodName}' in '{typeName}', found {results.Count}");
+			return results[0];
+		}
+
+		/// <summary>
+		/// Finds a MethodDefinitionHandle matching on name and parameter count.
+		/// </summary>
+		static MethodDefinitionHandle FindMethod(string typeName, string methodName, int parameterCount)
+		{
+			var results = FindMethods(typeName, methodName);
+			var filtered = results.Where(h => {
+				var m = Metadata.GetMethodDefinition(h);
+				return m.GetParameters().Count == parameterCount;
+			}).ToList();
+			Assert.That(filtered.Count, Is.EqualTo(1),
+				$"Expected exactly one method '{methodName}' with {parameterCount} params in '{typeName}', found {filtered.Count}");
+			return filtered[0];
+		}
+
+		static BlobReader GetSignatureBlob(MethodDefinitionHandle handle)
+		{
+			var method = Metadata.GetMethodDefinition(handle);
+			return Metadata.GetBlobReader(method.Signature);
+		}
+
+		static bool CompareSignatures(MethodDefinitionHandle a, MethodDefinitionHandle b)
+		{
+			return SignatureBlobComparer.EqualsMethodSignature(
+				GetSignatureBlob(a), GetSignatureBlob(b),
+				Metadata, Metadata);
+		}
+
+		#endregion
+
+		#region Identity / reflexive tests
+
+		[Test]
+		public void SameMethod_IsEqual()
+		{
+			// SimplePublicClass.Method() compared to itself
+			var method = FindMethod("SimplePublicClass", "Method");
+			Assert.That(CompareSignatures(method, method), Is.True);
+		}
+
+		[Test]
+		public void Constructor_ComparedToItself_IsEqual()
+		{
+			var ctor = FindMethod("SimplePublicClass", ".ctor");
+			Assert.That(CompareSignatures(ctor, ctor), Is.True);
+		}
+
+		[Test]
+		public void StaticMethod_ComparedToItself_IsEqual()
+		{
+			// StaticClass.Extension(this object) — it's static at the IL level
+			var method = FindMethod("StaticClass", "Extension");
+			Assert.That(CompareSignatures(method, method), Is.True);
+		}
+
+		#endregion
+
+		#region Same name, different signatures
+
+		[Test]
+		public void DifferentParameterTypes_NotEqual()
+		{
+			// MethodWithOptionalParameter(int) vs MethodWithParamsArray(object[])
+			var intParam = FindMethod("ParameterTests", "MethodWithOptionalParameter");
+			var arrayParam = FindMethod("ParameterTests", "MethodWithParamsArray");
+			Assert.That(CompareSignatures(intParam, arrayParam), Is.False);
+		}
+
+		[Test]
+		public void RefVsOut_SameAtSignatureLevel()
+		{
+			// ref and out are both ELEMENT_TYPE_BYREF at the blob level;
+			// the out modifier is only represented via attributes.
+			var methodRef = FindMethod("ParameterTests", "MethodWithRefParameter");
+			var methodOut = FindMethod("ParameterTests", "MethodWithOutParameter");
+			Assert.That(CompareSignatures(methodRef, methodOut), Is.True);
+		}
+
+		[Test]
+		public void RefVsIn_SameAtSignatureLevel()
+		{
+			// ref and in are both ELEMENT_TYPE_BYREF at the blob level;
+			// the in modifier is only represented via IsReadOnlyAttribute.
+			var methodRef = FindMethod("ParameterTests", "MethodWithRefParameter");
+			var methodIn = FindMethod("ParameterTests", "MethodWithInParameter");
+			Assert.That(CompareSignatures(methodRef, methodIn), Is.True);
+		}
+
+		[Test]
+		public void ByRefVsNonByRef_NotEqual()
+		{
+			// MethodWithRefParameter(ref int) vs MethodWithOptionalParameter(int)
+			// byref int vs plain int should differ at the blob level
+			var byRef = FindMethod("ParameterTests", "MethodWithRefParameter");
+			var plain = FindMethod("ParameterTests", "MethodWithOptionalParameter");
+			Assert.That(CompareSignatures(byRef, plain), Is.False);
+		}
+
+		[Test]
+		public void DifferentParameterCount_NotEqual()
+		{
+			// Compare a method with 0 params to one with 1 param
+			var method0 = FindMethod("SimplePublicClass", "Method"); // 0 params
+			var method1 = FindMethod("ParameterTests", "MethodWithOutParameter"); // 1 param
+			Assert.That(CompareSignatures(method0, method1), Is.False);
+		}
+
+		[Test]
+		public void DifferentReturnType_NotEqual()
+		{
+			// SimplePublicClass.Method() returns void
+			// PropertyTest has a getter that returns string (get_Item)
+			var voidMethod = FindMethod("SimplePublicClass", "Method");
+			var stringGetter = FindMethod("PropertyTest", "get_Item");
+			Assert.That(CompareSignatures(voidMethod, stringGetter), Is.False);
+		}
+
+		#endregion
+
+		#region Generic methods
+
+		[Test]
+		public void GenericMethod_ComparedToItself_IsEqual()
+		{
+			// GenericClass<A,B>.TestMethod<K,V>(string)
+			var method = FindMethod("GenericClass`2", "TestMethod");
+			Assert.That(CompareSignatures(method, method), Is.True);
+		}
+
+		[Test]
+		public void GenericMethod_DifferentArity_NotEqual()
+		{
+			// TestMethod<K,V>(string) has 2 type params
+			// GetIndex<T>(T) has 1 type param
+			var testMethod = FindMethod("GenericClass`2", "TestMethod");
+			var getIndex = FindMethod("GenericClass`2", "GetIndex");
+			Assert.That(CompareSignatures(testMethod, getIndex), Is.False);
+		}
+
+		[Test]
+		public void GenericMethodWithOneTypeParam_ComparedToItself_IsEqual()
+		{
+			var method = FindMethod("GenericClass`2", "GetIndex");
+			Assert.That(CompareSignatures(method, method), Is.True);
+		}
+
+		[Test]
+		public void NonGenericVsGenericMethod_NotEqual()
+		{
+			// SimplePublicClass.Method() — non-generic
+			// GenericClass<A,B>.GetIndex<T>(T) — generic
+			var nonGeneric = FindMethod("SimplePublicClass", "Method");
+			var generic = FindMethod("GenericClass`2", "GetIndex");
+			Assert.That(CompareSignatures(nonGeneric, generic), Is.False);
+		}
+
+		#endregion
+
+		#region Instance vs static
+
+		[Test]
+		public void InstanceVsStatic_DifferentCallingConvention_NotEqual()
+		{
+			// An instance method vs a static method — calling convention differs in the signature header
+			// StaticClass.Extension is static; SimplePublicClass.Method is instance
+			var staticMethod = FindMethod("StaticClass", "Extension");
+			var instanceMethod = FindMethod("SimplePublicClass", "Method");
+			Assert.That(CompareSignatures(staticMethod, instanceMethod), Is.False);
+		}
+
+		#endregion
+
+		#region Methods with same signature across different types
+
+		[Test]
+		public void SameSignatureInDifferentTypes_IsEqual()
+		{
+			// Both SimplePublicClass and ParameterTests have parameterless instance constructors
+			var ctor1 = FindMethod("SimplePublicClass", ".ctor");
+			var ctor2 = FindMethod("ParameterTests", ".ctor");
+			Assert.That(CompareSignatures(ctor1, ctor2), Is.True);
+		}
+
+		#endregion
+
+		#region Methods involving complex types
+
+		[Test]
+		public void MethodWithArrayParam_ComparedToItself_IsEqual()
+		{
+			// ParameterTests.MethodWithParamsArray(params object[])
+			var method = FindMethod("ParameterTests", "MethodWithParamsArray");
+			Assert.That(CompareSignatures(method, method), Is.True);
+		}
+
+		[Test]
+		public void MethodWithOptionalParam_ComparedToNonOptional_IsEqual()
+		{
+			// At the signature blob level, optional vs required doesn't matter —
+			// the signatures are the same if the types match.
+			// MethodWithOptionalParameter(int) vs MethodWithEnumOptionalParameter(StringComparison)
+			// These have different parameter types, so they should NOT be equal.
+			var optionalInt = FindMethod("ParameterTests", "MethodWithOptionalParameter");
+			var optionalEnum = FindMethod("ParameterTests", "MethodWithEnumOptionalParameter");
+			Assert.That(CompareSignatures(optionalInt, optionalEnum), Is.False);
+		}
+
+		[Test]
+		public void VarArgsMethod_ComparedToItself_IsEqual()
+		{
+			var method = FindMethod("ParameterTests", "VarArgsMethod");
+			Assert.That(CompareSignatures(method, method), Is.True);
+		}
+
+		[Test]
+		public void VarArgsMethod_VsNormalMethod_NotEqual()
+		{
+			// VarArgsMethod uses __arglist calling convention
+			var varArgs = FindMethod("ParameterTests", "VarArgsMethod");
+			var normal = FindMethod("SimplePublicClass", "Method");
+			Assert.That(CompareSignatures(varArgs, normal), Is.False);
+		}
+
+		#endregion
+
+		#region Indexer accessors
+
+		[Test]
+		public void IndexerGetter_ComparedToItself_IsEqual()
+		{
+			var getter = FindMethod("PropertyTest", "get_Item");
+			Assert.That(CompareSignatures(getter, getter), Is.True);
+		}
+
+		[Test]
+		public void IndexerGetter_VsSetter_NotEqual()
+		{
+			var getter = FindMethod("PropertyTest", "get_Item");
+			var setter = FindMethod("PropertyTest", "set_Item");
+			Assert.That(CompareSignatures(getter, setter), Is.False);
+		}
+
+		#endregion
+
+		#region DllImport / extern methods
+
+		[Test]
+		public void DllImportMethod_ComparedToItself_IsEqual()
+		{
+			var method = FindMethod("NonCustomAttributes", "DllMethod");
+			Assert.That(CompareSignatures(method, method), Is.True);
+		}
+
+		#endregion
+
+		#region Explicit interface implementation
+
+		[Test]
+		public void ExplicitImpl_VsRegularMethod_SameSignature()
+		{
+			// ExplicitImplementationTests has both M(int) and IExplicitImplementationTests.M(int)
+			// Their signatures should be identical at the blob level
+			var methods = FindMethods("ExplicitImplementationTests", "M");
+			Assert.That(methods.Count, Is.EqualTo(1),
+				"Explicit impl has a mangled name, so only one 'M' should be found");
+		}
+
+		#endregion
+
+		#region Symmetric property
+
+		[Test]
+		public void Comparison_IsSymmetric()
+		{
+			var method1 = FindMethod("SimplePublicClass", "Method");
+			var method2 = FindMethod("ParameterTests", "MethodWithOutParameter");
+
+			bool forward = CompareSignatures(method1, method2);
+			bool backward = CompareSignatures(method2, method1);
+			Assert.That(forward, Is.EqualTo(backward), "Comparison should be symmetric");
+		}
+
+		[Test]
+		public void Comparison_IsSymmetric_WhenEqual()
+		{
+			var ctor1 = FindMethod("SimplePublicClass", ".ctor");
+			var ctor2 = FindMethod("ParameterTests", ".ctor");
+
+			bool forward = CompareSignatures(ctor1, ctor2);
+			bool backward = CompareSignatures(ctor2, ctor1);
+			Assert.That(forward, Is.True);
+			Assert.That(backward, Is.True);
+		}
+
+		#endregion
+	}
+}

ICSharpCode.Decompiler.Tests/PrettyTestRunner.cs

@@ -852,6 +852,12 @@ namespace ICSharpCode.Decompiler.Tests
 			await RunForLibrary(cscOptions: cscOptions);
 		}
 
+		[Test]
+		public async Task Issue3684([ValueSource(nameof(roslyn4OrNewerOptions))] CompilerOptions cscOptions)
+		{
+			await RunForLibrary(cscOptions: cscOptions);
+		}
+
 		async Task RunForLibrary([CallerMemberName] string testName = null, AssemblerOptions asmOptions = AssemblerOptions.None, CompilerOptions cscOptions = CompilerOptions.None, Action<DecompilerSettings> configureDecompiler = null)
 		{
 			await Run(testName, asmOptions | AssemblerOptions.Library, cscOptions | CompilerOptions.Library, configureDecompiler);

ICSharpCode.Decompiler.Tests/TestCases/Pretty/Issue3684.cs

@@ -0,0 +1,22 @@
+// #dependency Issue3684.dep.cs
+using CrossAssemblyDep;
+
+namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
+{
+	public static class Issue3684
+	{
+		public interface IInterface
+		{
+			string Name { get; set; }
+			T Convert<T>(T input);
+		}
+
+		public class DerivedClass : BaseClass, IInterface
+		{
+			T IInterface.Convert<T>(T input)
+			{
+				return ((BaseClass)this).Convert<T>(input);
+			}
+		}
+	}
+}

ICSharpCode.Decompiler.Tests/TestCases/Pretty/Issue3684.dep.cs

@@ -0,0 +1,18 @@
+namespace CrossAssemblyDep
+{
+	public class BaseClass
+	{
+		private string name = "BaseClass";
+
+		public string Name {
+			get {
+				return name;
+			}
+			set {
+				name = value;
+			}
+		}
+
+		public T Convert<T>(T input) { return input; }
+	}
+}

ICSharpCode.Decompiler/CSharp/CSharpDecompiler.cs

@@ -292,6 +292,8 @@ namespace ICSharpCode.Decompiler.CSharp
 					name = metadata.GetString(method.Name);
 					if (name == ".ctor" && method.RelativeVirtualAddress == 0 && metadata.GetTypeDefinition(method.GetDeclaringType()).Attributes.HasFlag(System.Reflection.TypeAttributes.Import))
 						return true;
+					if (module is PEFile m && IsAccessorInterfaceImplementationRuntimeHelper(m, methodHandle))
+						return true;
 					if (settings.LocalFunctions && LocalFunctionDecompiler.IsLocalFunctionMethod(module, methodHandle))
 						return true;
 					if (settings.AnonymousMethods && methodHandle.HasGeneratedName(metadata) && methodHandle.IsCompilerGenerated(metadata))
@@ -386,6 +388,165 @@ namespace ICSharpCode.Decompiler.CSharp
 			return name.StartsWith("<", StringComparison.Ordinal) && name.EndsWith(">P", StringComparison.Ordinal);
 		}
 
+		static bool IsAccessorInterfaceImplementationRuntimeHelper(PEFile module, MethodDefinitionHandle handle)
+		{
+			var metadata = module.Metadata;
+			var method = metadata.GetMethodDefinition(handle);
+			if ((method.Attributes & System.Reflection.MethodAttributes.Static) != 0)
+				return false;
+			string rawName = metadata.GetString(method.Name);
+			int dot = rawName.LastIndexOf('.');
+			if (dot < 0)
+				return false;
+			string name = rawName.Substring(dot + 1);
+			if (handle.GetMethodImplementations(metadata).Length == 0)
+				return false;
+			if (method.RelativeVirtualAddress == 0)
+				return false;
+			if (!name.StartsWith("get_", StringComparison.Ordinal) &&
+				!name.StartsWith("set_", StringComparison.Ordinal) &&
+				!name.StartsWith("add_", StringComparison.Ordinal) &&
+				!name.StartsWith("remove_", StringComparison.Ordinal) &&
+				!name.StartsWith("raise_", StringComparison.Ordinal))
+			{
+				return false;
+			}
+
+			var signature = metadata.GetBlobReader(method.Signature);
+			(int genericParameterCount, int parameterCount) = SignatureBlobComparer.ReadParameterCount(ref signature);
+			if (genericParameterCount == -1 || parameterCount == -1)
+				return false;
+			signature.Reset();
+
+			int maximumMethodSize = 4 * (parameterCount + 1) + 5 + 1;
+
+			var body = module.Reader.GetMethodBody(method.RelativeVirtualAddress);
+			var reader = body.GetILReader();
+
+			if (reader.RemainingBytes > maximumMethodSize)
+				return false;
+
+			for (int i = 0; i < parameterCount + 1; i++)
+			{
+				int index;
+				switch (reader.DecodeOpCode())
+				{
+					case ILOpCode.Ldarg:
+						index = reader.ReadUInt16();
+						if (index != i)
+							return false;
+						break;
+					case ILOpCode.Ldarg_s:
+						index = reader.ReadByte();
+						if (index != i)
+							return false;
+						break;
+					case ILOpCode.Ldarg_0:
+						if (i != 0)
+							return false;
+						break;
+					case ILOpCode.Ldarg_1:
+						if (i != 1)
+							return false;
+						break;
+					case ILOpCode.Ldarg_2:
+						if (i != 2)
+							return false;
+						break;
+					case ILOpCode.Ldarg_3:
+						if (i != 3)
+							return false;
+						break;
+					default:
+						return false;
+				}
+			}
+
+			if (reader.DecodeOpCode() != ILOpCode.Call)
+				return false;
+
+			EntityHandle targetHandle = MetadataTokenHelpers.EntityHandleOrNil(reader.ReadInt32());
+			if (targetHandle.IsNil)
+				return false;
+
+			if (reader.DecodeOpCode() != ILOpCode.Ret)
+				return false;
+
+			if (reader.RemainingBytes != 0)
+				return false;
+
+			BlobReader signature2;
+			string otherName;
+
+			switch (targetHandle.Kind)
+			{
+				case HandleKind.MethodDefinition:
+					if (genericParameterCount != 0)
+						return false;
+					var methodDef = metadata.GetMethodDefinition((MethodDefinitionHandle)targetHandle);
+					signature2 = metadata.GetBlobReader(methodDef.Signature);
+					otherName = metadata.GetString(methodDef.Name);
+					break;
+				case HandleKind.MethodSpecification:
+					if (genericParameterCount == 0)
+						return false;
+					var methodSpec = metadata.GetMethodSpecification((MethodSpecificationHandle)targetHandle);
+					var instantiationBlob = metadata.GetBlobReader(methodSpec.Signature);
+					if (!IsIdentityInstantiation(ref instantiationBlob, genericParameterCount))
+						return false;
+					switch (methodSpec.Method.Kind)
+					{
+						case HandleKind.MethodDefinition:
+							var methodSpecDef = metadata.GetMethodDefinition((MethodDefinitionHandle)methodSpec.Method);
+							signature2 = metadata.GetBlobReader(methodSpecDef.Signature);
+							otherName = metadata.GetString(methodSpecDef.Name);
+							break;
+						case HandleKind.MemberReference:
+							var methodSpecRef = metadata.GetMemberReference((MemberReferenceHandle)methodSpec.Method);
+							if (methodSpecRef.GetKind() != MemberReferenceKind.Method)
+								return false;
+							signature2 = metadata.GetBlobReader(methodSpecRef.Signature);
+							otherName = metadata.GetString(methodSpecRef.Name);
+							break;
+						default:
+							return false;
+					}
+					break;
+				case HandleKind.MemberReference:
+					if (genericParameterCount != 0)
+						return false;
+					var methodRef = metadata.GetMemberReference((MemberReferenceHandle)targetHandle);
+					if (methodRef.GetKind() != MemberReferenceKind.Method)
+						return false;
+					signature2 = metadata.GetBlobReader(methodRef.Signature);
+					otherName = metadata.GetString(methodRef.Name);
+					break;
+				default:
+					return false;
+			}
+
+			if (otherName != name)
+				return false;
+			return SignatureBlobComparer.EqualsMethodSignature(signature, signature2, metadata, metadata, skipModifiers: true);
+
+			static bool IsIdentityInstantiation(ref BlobReader reader, int expectedCount)
+			{
+				// Format: GENRICINST count type1 type2 ...
+				if (reader.ReadByte() != 0x0A) // GENERICINST
+					return false;
+				if (!reader.TryReadCompressedInteger(out int count) || count != expectedCount)
+					return false;
+				for (int i = 0; i < count; i++)
+				{
+					if (reader.ReadByte() != 0x1E) // ELEMENT_TYPE_MVAR
+						return false;
+					if (!reader.TryReadCompressedInteger(out int index) || index != i)
+						return false;
+				}
+				return true;
+			}
+		}
+
 		static bool IsSwitchOnStringCache(SRM.FieldDefinition field, MetadataReader metadata)
 		{
 			return metadata.GetString(field.Name).StartsWith("<>f__switch", StringComparison.Ordinal);

ICSharpCode.Decompiler/Metadata/SignatureBlobComparer.cs

@@ -16,18 +16,74 @@
 // OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 // DEALINGS IN THE SOFTWARE.
 
+using System.Diagnostics;
 using System.Reflection.Metadata;
 
 namespace ICSharpCode.Decompiler.Metadata
 {
 	public static class SignatureBlobComparer
 	{
-		public static bool EqualsMethodSignature(BlobReader a, BlobReader b, MetadataReader contextForA, MetadataReader contextForB)
+		internal static (int GenericParameterCount, int ParameterCount) ReadParameterCount(ref BlobReader reader)
 		{
-			return EqualsMethodSignature(ref a, ref b, contextForA, contextForB);
+			if (reader.RemainingBytes == 0)
+				return (-1, -1);
+
+			var header = reader.ReadSignatureHeader();
+			int gp;
+			if (header.IsGeneric)
+			{
+				if (!reader.TryReadCompressedInteger(out gp))
+					gp = -1;
+			}
+			else
+			{
+				gp = 0;
+			}
+
+			if (!reader.TryReadCompressedInteger(out int p))
+				p = -1;
+
+			return (gp, p);
+		}
+
+		public static bool EqualsMethodSignature(BlobReader a, BlobReader b, MetadataReader contextForA, MetadataReader contextForB, bool skipModifiers = false)
+		{
+			return EqualsMethodSignature(ref a, ref b, contextForA, contextForB, skipModifiers);
+		}
+
+		static int SkipCustomModifiers(ref BlobReader reader, int typeCode)
+		{
+			while (typeCode is 0x1F or 0x20) // ELEMENT_TYPE_CMOD_REQD or ELEMENT_TYPE_CMOD_OPT
+			{
+				reader.ReadTypeHandle(); // discard modifier
+				if (!reader.TryReadCompressedInteger(out typeCode))
+					return -1;
+			}
+			return typeCode;
+		}
+
+		static bool TypeSlotEquals(ref BlobReader a, ref BlobReader b, MetadataReader contextForA, MetadataReader contextForB, bool skipModifiers)
+		{
+			if (!skipModifiers)
+			{
+				if (!IsSameCompressedInteger(ref a, ref b, out int typeCode))
+					return false;
+				return TypesAreEqual(ref a, ref b, contextForA, contextForB, typeCode, false);
+			}
+
+			if (!a.TryReadCompressedInteger(out int typeCodeA) || !b.TryReadCompressedInteger(out int typeCodeB))
+				return false;
+			typeCodeA = SkipCustomModifiers(ref a, typeCodeA);
+			typeCodeB = SkipCustomModifiers(ref b, typeCodeB);
+			if (typeCodeA < 0 || typeCodeB < 0)
+				return false;
+			if (typeCodeA != typeCodeB)
+				return false;
+			return TypesAreEqual(ref a, ref b, contextForA, contextForB, typeCodeA, true);
 		}
 
-		static bool EqualsMethodSignature(ref BlobReader a, ref BlobReader b, MetadataReader contextForA, MetadataReader contextForB)
+		static bool EqualsMethodSignature(ref BlobReader a, ref BlobReader b,
+			MetadataReader contextForA, MetadataReader contextForB, bool skipModifiers)
 		{
 			SignatureHeader header;
 			// compare signature headers
@@ -42,26 +98,37 @@ namespace ICSharpCode.Decompiler.Metadata
 			// read & compare parameter count
 			if (!IsSameCompressedInteger(ref a, ref b, out int totalParameterCount))
 				return false;
-			if (!IsSameCompressedInteger(ref a, ref b, out int typeCode))
-				return false;
-			if (!TypesAreEqual(ref a, ref b, contextForA, contextForB, typeCode))
+			// return type
+			if (!TypeSlotEquals(ref a, ref b, contextForA, contextForB, skipModifiers))
 				return false;
 			int i = 0;
 			for (; i < totalParameterCount; i++)
 			{
-				if (!IsSameCompressedInteger(ref a, ref b, out typeCode))
+				// peek at both sides for varargs sentinel or type code
+				if (!a.TryReadCompressedInteger(out int typeCodeA) || !b.TryReadCompressedInteger(out int typeCodeB))
 					return false;
 				// varargs sentinel
-				if (typeCode == 65)
+				if (typeCodeA == 65 || typeCodeB == 65)
+				{
+					if (typeCodeA != typeCodeB)
+						return false;
 					break;
-				if (!TypesAreEqual(ref a, ref b, contextForA, contextForB, typeCode))
+				}
+				if (skipModifiers)
+				{
+					typeCodeA = SkipCustomModifiers(ref a, typeCodeA);
+					typeCodeB = SkipCustomModifiers(ref b, typeCodeB);
+					if (typeCodeA < 0 || typeCodeB < 0)
+						return false;
+				}
+				if (typeCodeA != typeCodeB)
+					return false;
+				if (!TypesAreEqual(ref a, ref b, contextForA, contextForB, typeCodeA, skipModifiers))
 					return false;
 			}
 			for (; i < totalParameterCount; i++)
 			{
-				if (!IsSameCompressedInteger(ref a, ref b, out typeCode))
-					return false;
-				if (!TypesAreEqual(ref a, ref b, contextForA, contextForB, typeCode))
+				if (!TypeSlotEquals(ref a, ref b, contextForA, contextForB, skipModifiers))
 					return false;
 			}
 			return true;
@@ -76,7 +143,7 @@ namespace ICSharpCode.Decompiler.Metadata
 		{
 			if (!IsSameCompressedInteger(ref a, ref b, out int typeCode))
 				return false;
-			return TypesAreEqual(ref a, ref b, contextForA, contextForB, typeCode);
+			return TypesAreEqual(ref a, ref b, contextForA, contextForB, typeCode, false);
 		}
 
 		static bool IsSameCompressedInteger(ref BlobReader a, ref BlobReader b, out int value)
@@ -89,14 +156,15 @@ namespace ICSharpCode.Decompiler.Metadata
 			return a.TryReadCompressedSignedInteger(out value) && b.TryReadCompressedSignedInteger(out int otherValue) && value == otherValue;
 		}
 
-		static bool TypesAreEqual(ref BlobReader a, ref BlobReader b, MetadataReader contextForA, MetadataReader contextForB, int typeCode)
+		static bool TypesAreEqual(ref BlobReader a, ref BlobReader b, MetadataReader contextForA, MetadataReader contextForB, int typeCode, bool skipModifiers)
 		{
+			Debug.Assert(typeCode != 0x1F && typeCode != 0x20, "Unexpected ELEMENT_TYPE_CMOD_REQD or ELEMENT_TYPE_CMOD_OPT");
 			switch (typeCode)
 			{
 				case 0x1: // ELEMENT_TYPE_VOID
-				case 0x2: // ELEMENT_TYPE_BOOLEAN 
-				case 0x3: // ELEMENT_TYPE_CHAR 
-				case 0x4: // ELEMENT_TYPE_I1 
+				case 0x2: // ELEMENT_TYPE_BOOLEAN
+				case 0x3: // ELEMENT_TYPE_CHAR
+				case 0x4: // ELEMENT_TYPE_I1
 				case 0x5: // ELEMENT_TYPE_U1
 				case 0x6: // ELEMENT_TYPE_I2
 				case 0x7: // ELEMENT_TYPE_U2
@@ -112,24 +180,24 @@ namespace ICSharpCode.Decompiler.Metadata
 				case 0x19: // ELEMENT_TYPE_U
 				case 0x1C: // ELEMENT_TYPE_OBJECT
 					return true;
-				case 0xF: // ELEMENT_TYPE_PTR 
-				case 0x10: // ELEMENT_TYPE_BYREF 
+				case 0xF: // ELEMENT_TYPE_PTR
+				case 0x10: // ELEMENT_TYPE_BYREF
 				case 0x45: // ELEMENT_TYPE_PINNED
 				case 0x1D: // ELEMENT_TYPE_SZARRAY
 					if (!IsSameCompressedInteger(ref a, ref b, out typeCode))
 						return false;
-					if (!TypesAreEqual(ref a, ref b, contextForA, contextForB, typeCode))
+					if (!TypesAreEqual(ref a, ref b, contextForA, contextForB, typeCode, skipModifiers))
 						return false;
 					return true;
-				case 0x1B: // ELEMENT_TYPE_FNPTR 
-					if (!EqualsMethodSignature(ref a, ref b, contextForA, contextForB))
+				case 0x1B: // ELEMENT_TYPE_FNPTR
+					if (!EqualsMethodSignature(ref a, ref b, contextForA, contextForB, skipModifiers))
 						return false;
 					return true;
-				case 0x14: // ELEMENT_TYPE_ARRAY 
+				case 0x14: // ELEMENT_TYPE_ARRAY
 						   // element type
 					if (!IsSameCompressedInteger(ref a, ref b, out typeCode))
 						return false;
-					if (!TypesAreEqual(ref a, ref b, contextForA, contextForB, typeCode))
+					if (!TypesAreEqual(ref a, ref b, contextForA, contextForB, typeCode, skipModifiers))
 						return false;
 					// rank
 					if (!IsSameCompressedInteger(ref a, ref b, out _))
@@ -151,22 +219,11 @@ namespace ICSharpCode.Decompiler.Metadata
 							return false;
 					}
 					return true;
-				case 0x1F: // ELEMENT_TYPE_CMOD_REQD 
-				case 0x20: // ELEMENT_TYPE_CMOD_OPT 
-						   // modifier
-					if (!TypeHandleEquals(ref a, ref b, contextForA, contextForB))
-						return false;
-					// unmodified type
-					if (!IsSameCompressedInteger(ref a, ref b, out typeCode))
-						return false;
-					if (!TypesAreEqual(ref a, ref b, contextForA, contextForB, typeCode))
-						return false;
-					return true;
-				case 0x15: // ELEMENT_TYPE_GENERICINST 
+				case 0x15: // ELEMENT_TYPE_GENERICINST
 						   // generic type
 					if (!IsSameCompressedInteger(ref a, ref b, out typeCode))
 						return false;
-					if (!TypesAreEqual(ref a, ref b, contextForA, contextForB, typeCode))
+					if (!TypesAreEqual(ref a, ref b, contextForA, contextForB, typeCode, skipModifiers))
 						return false;
 					if (!IsSameCompressedInteger(ref a, ref b, out int numOfArguments))
 						return false;
@@ -174,12 +231,12 @@ namespace ICSharpCode.Decompiler.Metadata
 					{
 						if (!IsSameCompressedInteger(ref a, ref b, out typeCode))
 							return false;
-						if (!TypesAreEqual(ref a, ref b, contextForA, contextForB, typeCode))
+						if (!TypesAreEqual(ref a, ref b, contextForA, contextForB, typeCode, skipModifiers))
 							return false;
 					}
 					return true;
 				case 0x13: // ELEMENT_TYPE_VAR
-				case 0x1E: // ELEMENT_TYPE_MVAR 
+				case 0x1E: // ELEMENT_TYPE_MVAR
 						   // index
 					if (!IsSameCompressedInteger(ref a, ref b, out _))
 						return false;
@@ -200,6 +257,8 @@ namespace ICSharpCode.Decompiler.Metadata
 			var typeB = b.ReadTypeHandle();
 			if (typeA.IsNil || typeB.IsNil)
 				return false;
+			if (contextForA == contextForB)
+				return typeA.Equals(typeB);
 			return typeA.GetFullTypeName(contextForA) == typeB.GetFullTypeName(contextForB);
 		}
 	}