From fa3de7bfa4b7b97b394e5ad304ea283b772fb996 Mon Sep 17 00:00:00 2001
From: Daniel Grunwald <daniel@danielgrunwald.de>
Date: Sun, 30 Aug 2026 12:09:40 +0200
Subject: [PATCH] MergeSimilarTypes: add support for more kinds of types

---
 .../Semantics/TypeInferenceTests.cs           | 25 ++++++++++
 .../CSharp/Resolver/TypeInference.cs          | 50 +++++++++++++++++++
 2 files changed, 75 insertions(+)

diff --git a/ICSharpCode.Decompiler.Tests/Semantics/TypeInferenceTests.cs b/ICSharpCode.Decompiler.Tests/Semantics/TypeInferenceTests.cs
index 8ff5c4dde..605d76e27 100644
--- a/ICSharpCode.Decompiler.Tests/Semantics/TypeInferenceTests.cs
+++ b/ICSharpCode.Decompiler.Tests/Semantics/TypeInferenceTests.cs
@@ -23,6 +23,7 @@ using System.Collections.Immutable;
 using System.Collections.ObjectModel;
 using System.IO;
 using System.Linq;
+using System.Reflection.Metadata;
 
 using ICSharpCode.Decompiler.CSharp.Resolver;
 using ICSharpCode.Decompiler.Metadata;
@@ -713,6 +714,15 @@ namespace ICSharpCode.Decompiler.Tests.Semantics
 				ImmutableArray.CreateRange(elementNames));
 		}
 
+		FunctionPointerType MakeFunctionPointerType(ICompilation comp, IType returnType)
+		{
+			return new FunctionPointerType(
+				(MetadataModule)comp.MainModule,
+				SignatureCallingConvention.Default, ImmutableArray<IType>.Empty,
+				returnType, returnIsRefReadOnly: false,
+				ImmutableArray<IType>.Empty, ImmutableArray<ReferenceKind>.Empty);
+		}
+
 		[Test]
 		public void BestCommonTypeMergesTupleElementNames()
 		{
@@ -730,6 +740,21 @@ namespace ICSharpCode.Decompiler.Tests.Semantics
 			Assert.That(success);
 		}
 
+		[Test]
+		public void BestCommonTypeMergesFunctionPointerTupleElementNames()
+		{
+			var comp = RefAssemblyCompilation.Instance;
+			var inference = new TypeInference(comp);
+
+			Assert.That(
+				inference.GetBestCommonType(new[] {
+					new ResolveResult(MakeFunctionPointerType(comp, MakeTupleType(comp, "a", "b"))),
+					new ResolveResult(MakeFunctionPointerType(comp, MakeTupleType(comp, "a", "c")))
+				}, out bool success),
+				Is.EqualTo(MakeFunctionPointerType(comp, MakeTupleType(comp, "a", null))));
+			Assert.That(success);
+		}
+
 		[Test]
 		public void FixingMergesTupleElementNamesOfExactAndLowerBounds()
 		{
diff --git a/ICSharpCode.Decompiler/CSharp/Resolver/TypeInference.cs b/ICSharpCode.Decompiler/CSharp/Resolver/TypeInference.cs
index 53816806c..f81bc7b50 100644
--- a/ICSharpCode.Decompiler/CSharp/Resolver/TypeInference.cs
+++ b/ICSharpCode.Decompiler/CSharp/Resolver/TypeInference.cs
@@ -1101,6 +1101,15 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 				var nullability = MergeNullability(arrA.Nullability, arrB.Nullability, variance);
 				return new ArrayType(arrA.Compilation, mergedElem, arrA.Dimensions, nullability);
 			}
+			if (a is ByReferenceType refA && b is ByReferenceType refB)
+			{
+				var mergedElem = MergeSimilarTypes(
+					refA.ElementType, refB.ElementType,
+					variance.Combine(VarianceModifier.Invariant));
+				if (mergedElem == null)
+					return null;
+				return new ByReferenceType(mergedElem);
+			}
 			if (a is PointerType ptrA && b is PointerType ptrB)
 			{
 				var mergedElem = MergeSimilarTypes(
@@ -1110,6 +1119,47 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 					return null;
 				return new PointerType(mergedElem);
 			}
+			if (a is FunctionPointerType fnPtrA && b is FunctionPointerType fnPtrB
+				&& fnPtrA.CallingConvention == fnPtrB.CallingConvention
+				&& fnPtrA.CustomCallingConventions.SequenceEqual(fnPtrB.CustomCallingConventions)
+				&& fnPtrA.ReturnIsRefReadOnly == fnPtrB.ReturnIsRefReadOnly
+				&& fnPtrA.ParameterTypes.Length == fnPtrB.ParameterTypes.Length
+				&& fnPtrA.ParameterReferenceKinds.SequenceEqual(fnPtrB.ParameterReferenceKinds))
+			{
+				var mergedReturn = MergeSimilarTypes(
+					fnPtrA.ReturnType, fnPtrB.ReturnType,
+					variance.Combine(VarianceModifier.Covariant));
+				if (mergedReturn == null)
+					return null;
+				var mergedParameters = ImmutableArray.CreateBuilder<IType>(fnPtrA.ParameterTypes.Length);
+				for (int i = 0; i < fnPtrA.ParameterTypes.Length; i++)
+				{
+					var mergedParameter = MergeSimilarTypes(
+						fnPtrA.ParameterTypes[i], fnPtrB.ParameterTypes[i],
+						variance.Combine(VarianceModifier.Contravariant));
+					if (mergedParameter == null)
+						return null;
+					mergedParameters.Add(mergedParameter);
+				}
+				return fnPtrA.WithSignature(mergedReturn, mergedParameters.MoveToImmutable());
+			}
+			if (a is ModifiedType modA && b is ModifiedType modB
+				&& modA.Kind == modB.Kind
+				&& modA.Modifier.Equals(modB.Modifier))
+			{
+				var mergedElem = MergeSimilarTypes(modA.ElementType, modB.ElementType, variance);
+				if (mergedElem == null)
+					return null;
+				return new ModifiedType(modA.Modifier, mergedElem, modA.Kind == TypeKind.ModReq);
+			}
+			if (a is UnknownType unknownTypeA && b is UnknownType unknownTypeB
+				&& unknownTypeA.FullTypeName == unknownTypeB.FullTypeName)
+			{
+				if (unknownTypeA.IsReferenceType == unknownTypeB.IsReferenceType)
+					return unknownTypeA;
+				else
+					return unknownTypeA.WithoutReferenceTypeKnowledge();
+			}
 			return null;
 		}