From 83df0ab9b9dfd74dd3440d5d27d544c88a7bc205 Mon Sep 17 00:00:00 2001
From: ds5678 <49847914+ds5678@users.noreply.github.com>
Date: Fri, 21 Nov 2025 19:08:09 -0800
Subject: [PATCH] Handle multiple calling conventions at once

---
 .../TestCases/Pretty/FunctionPointers.cs      | 26 +++++++++++++
 .../CSharp/ExpressionBuilder.cs               |  2 +-
 .../TypeSystem/FunctionPointerType.cs         | 39 +++++++++++--------
 3 files changed, 50 insertions(+), 17 deletions(-)

diff --git a/ICSharpCode.Decompiler.Tests/TestCases/Pretty/FunctionPointers.cs b/ICSharpCode.Decompiler.Tests/TestCases/Pretty/FunctionPointers.cs
index 9ebcc0524..5379e4948 100644
--- a/ICSharpCode.Decompiler.Tests/TestCases/Pretty/FunctionPointers.cs
+++ b/ICSharpCode.Decompiler.Tests/TestCases/Pretty/FunctionPointers.cs
@@ -129,6 +129,32 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 			}
 		}
 
+		public unsafe delegate* unmanaged[Cdecl, Fastcall]<void> AddressOfLocalFunction_CDeclAndFastcall()
+		{
+			return &LocalFunction;
+
+			[UnmanagedCallersOnly(CallConvs = new Type[] {
+				typeof(CallConvCdecl),
+				typeof(CallConvFastcall)
+			})]
+			static void LocalFunction()
+			{
+			}
+		}
+
+		public unsafe delegate* unmanaged[Fastcall, Cdecl]<void> AddressOfLocalFunction_FastcallAndCDecl()
+		{
+			return &LocalFunction;
+
+			[UnmanagedCallersOnly(CallConvs = new Type[] {
+				typeof(CallConvFastcall),
+				typeof(CallConvCdecl)
+			})]
+			static void LocalFunction()
+			{
+			}
+		}
+
 #if NET60
 		public unsafe delegate* unmanaged[Cdecl, SuppressGCTransition]<void> AddressOfLocalFunction_CDeclAndSuppressGCTransition()
 		{
diff --git a/ICSharpCode.Decompiler/CSharp/ExpressionBuilder.cs b/ICSharpCode.Decompiler/CSharp/ExpressionBuilder.cs
index d4990a944..0e79d9b5d 100644
--- a/ICSharpCode.Decompiler/CSharp/ExpressionBuilder.cs
+++ b/ICSharpCode.Decompiler/CSharp/ExpressionBuilder.cs
@@ -4611,7 +4611,7 @@ namespace ICSharpCode.Decompiler.CSharp
 					var builder = ImmutableArray.CreateBuilder<IType>(array.Length);
 					foreach (var type in array.Select(a => a.Value).OfType<IType>())
 					{
-						SignatureCallingConvention? foundCallingConvention = type.Namespace is not "System.Runtime.CompilerServices" ? null : type.Name switch {
+						SignatureCallingConvention? foundCallingConvention = type.Namespace is not "System.Runtime.CompilerServices" || callingConvention != SignatureCallingConvention.Unmanaged ? null : type.Name switch {
 							"CallConvCdecl" => SignatureCallingConvention.CDecl,
 							"CallConvFastcall" => SignatureCallingConvention.FastCall,
 							"CallConvStdcall" => SignatureCallingConvention.StdCall,
diff --git a/ICSharpCode.Decompiler/TypeSystem/FunctionPointerType.cs b/ICSharpCode.Decompiler/TypeSystem/FunctionPointerType.cs
index 79abcd92c..75fe0fd75 100644
--- a/ICSharpCode.Decompiler/TypeSystem/FunctionPointerType.cs
+++ b/ICSharpCode.Decompiler/TypeSystem/FunctionPointerType.cs
@@ -46,23 +46,30 @@ namespace ICSharpCode.Decompiler.TypeSystem
 					&& modReturn.Modifier.Namespace == "System.Runtime.CompilerServices")
 				{
 					returnType = modReturn.ElementType;
-					switch (modReturn.Modifier.Name)
+					if (callingConvention == SignatureCallingConvention.Unmanaged)
 					{
-						case "CallConvCdecl":
-							callingConvention = SignatureCallingConvention.CDecl;
-							break;
-						case "CallConvFastcall":
-							callingConvention = SignatureCallingConvention.FastCall;
-							break;
-						case "CallConvStdcall":
-							callingConvention = SignatureCallingConvention.StdCall;
-							break;
-						case "CallConvThiscall":
-							callingConvention = SignatureCallingConvention.ThisCall;
-							break;
-						default:
-							customCallConvs.Add(modReturn.Modifier);
-							break;
+						switch (modReturn.Modifier.Name)
+						{
+							case "CallConvCdecl":
+								callingConvention = SignatureCallingConvention.CDecl;
+								break;
+							case "CallConvFastcall":
+								callingConvention = SignatureCallingConvention.FastCall;
+								break;
+							case "CallConvStdcall":
+								callingConvention = SignatureCallingConvention.StdCall;
+								break;
+							case "CallConvThiscall":
+								callingConvention = SignatureCallingConvention.ThisCall;
+								break;
+							default:
+								customCallConvs.Add(modReturn.Modifier);
+								break;
+						}
+					}
+					else
+					{
+						customCallConvs.Add(modReturn.Modifier);
 					}
 				}
 				else