From d8389ad0f224d1ffc3711fd58eba40f889a89609 Mon Sep 17 00:00:00 2001
From: Oleg Rakhmatulin <oleg.rakhmatulin@gmail.com>
Date: Mon, 1 May 2023 13:19:46 +0200
Subject: [PATCH] Issue #172 - Never add method implementation if the
 declaration handle equals to body handle (default interface method case).

---
 src/AssemblyGenerator.Types.cs      | 18 +++++++++++++++---
 src/Lokad.ILPack.csproj             |  4 ++--
 test/TestSubject/IMyItf.cs          |  4 ++++
 test/TestSubject/TestSubject.csproj |  2 +-
 4 files changed, 22 insertions(+), 6 deletions(-)

diff --git a/src/AssemblyGenerator.Types.cs b/src/AssemblyGenerator.Types.cs
index 798cf6c..714912e 100644
--- a/src/AssemblyGenerator.Types.cs
+++ b/src/AssemblyGenerator.Types.cs
@@ -209,16 +209,28 @@ HashSet<Type> interfaces
                     var targetMethod = interfaceMapping.TargetMethods[i];
                     var ifcMethod = interfaceMapping.InterfaceMethods[i];
 
+                    if (targetMethod == null || ifcMethod == null)
+                    {
+                        continue;
+                    }
+
+                    var bodyHandle =_metadata.GetMethodHandle(targetMethod);
+                    var declarationHandle = _metadata.GetMethodHandle(ifcMethod);
+
+                    if (bodyHandle == declarationHandle)
+                    {
+                        continue;
+                    }
+
                     // Declare a method override either when the interface implementation or
                     // the interface method implementation is declared by the type.
-                    if (targetMethod != null && (implementedByType || targetMethod.DeclaringType == type))
+                    if (implementedByType || targetMethod.DeclaringType == type)
                     {
                         // Mark the target method as implementing the interface method.
                         // (This is the equivalent of .Override in msil)
                         _metadata.Builder.AddMethodImplementation(
                            (TypeDefinitionHandle)_metadata.GetTypeHandle(targetMethod.DeclaringType),
-                           _metadata.GetMethodHandle(targetMethod),
-                           _metadata.GetMethodHandle(ifcMethod));
+                           bodyHandle, declarationHandle);
                     }
                 }
             }
diff --git a/src/Lokad.ILPack.csproj b/src/Lokad.ILPack.csproj
index aa72a9a..b0aaed2 100644
--- a/src/Lokad.ILPack.csproj
+++ b/src/Lokad.ILPack.csproj
@@ -2,7 +2,7 @@
 
   <PropertyGroup>
     <TargetFramework>netstandard2.0</TargetFramework>
-	<AllowUnsafeBlocks>true</AllowUnsafeBlocks>
+    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <OutputType>Library</OutputType>
     <LangVersion>8.0</LangVersion>
 
@@ -13,7 +13,7 @@
     <Copyright>Copyright © Lokad 2020 - 2022</Copyright>
 
     <PackageId>Lokad.ILPack</PackageId>
-	  
+
     <AssemblyVersion>0.2.0.0</AssemblyVersion>
     <FileVersion>0.2.0.0</FileVersion>
     <PackageVersion>0.2.0.0</PackageVersion>
diff --git a/test/TestSubject/IMyItf.cs b/test/TestSubject/IMyItf.cs
index 9066de0..15da9c5 100644
--- a/test/TestSubject/IMyItf.cs
+++ b/test/TestSubject/IMyItf.cs
@@ -15,5 +15,9 @@ public interface IMyItf
         int InterfaceMethod2();
 
         TResult InterfaceMethod3<TResult>(Func<TResult> f);
+
+#if NETCOREAPP3_0_OR_GREATER
+        void DefaultInterfaceMethod() { }
+#endif
     }
 }
diff --git a/test/TestSubject/TestSubject.csproj b/test/TestSubject/TestSubject.csproj
index 20f1a23..cfedc9f 100644
--- a/test/TestSubject/TestSubject.csproj
+++ b/test/TestSubject/TestSubject.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>netcoreapp3.1;netstandard2.0</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;net6.0</TargetFrameworks>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <SignAssembly>True</SignAssembly>
     <AssemblyOriginatorKeyFile>..\..\Lokad.ILPack.snk</AssemblyOriginatorKeyFile>