#1563: Where possible, replace an explicit interface implementation call with a call to the interface member.

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

@@ -66,6 +66,7 @@
     <None Include="TestCases\ILPretty\FSharpLoops_Release.il" />
     <None Include="TestCases\ILPretty\FSharpUsing.fs" />
     <None Include="TestCases\ILPretty\FSharpUsing_Debug.il" />
+    <None Include="TestCases\ILPretty\DirectCallToExplicitInterfaceImpl.il" />
     <None Include="TestCases\ILPretty\FSharpUsing_Release.il" />
     <None Include="TestCases\Correctness\BitNot.il" />
     <None Include="TestCases\Correctness\Readme.txt" />
@@ -74,6 +75,7 @@
   <ItemGroup>
     <Compile Include="DisassemblerPrettyTestRunner.cs" />
     <Compile Include="TestCases\ILPretty\ConstantBlobs.cs" />
+    <None Include="TestCases\ILPretty\DirectCallToExplicitInterfaceImpl.cs" />
     <Compile Include="TestCases\ILPretty\Issue1389.cs" />
     <Compile Include="TestCases\ILPretty\Issue1454.cs" />
     <Compile Include="TestCases\Pretty\Discards.cs" />

ICSharpCode.Decompiler.Tests/ILPrettyTestRunner.cs

@@ -100,6 +100,12 @@ namespace ICSharpCode.Decompiler.Tests
 			Run(settings: new DecompilerSettings { RemoveDeadCode = true });
 		}
 
+		[Test]
+		public void DirectCallToExplicitInterfaceImpl()
+		{
+			Run();
+		}
+
 		[Test]
 		public void CS1xSwitch_Debug()
 		{

ICSharpCode.Decompiler.Tests/TestCases/ILPretty/DirectCallToExplicitInterfaceImpl.cs

@@ -0,0 +1,14 @@
+using System;
+
+public sealed class TestClass : IDisposable
+{
+	void IDisposable.Dispose()
+	{
+	}
+
+	public void Test(TestClass other)
+	{
+		((IDisposable)this).Dispose();
+		((IDisposable)other).Dispose();
+	}
+}

ICSharpCode.Decompiler.Tests/TestCases/ILPretty/DirectCallToExplicitInterfaceImpl.il

@@ -0,0 +1,36 @@
+.assembly extern mscorlib
+{
+  .publickeytoken = (B7 7A 5C 56 19 34 E0 89 )                         // .z\V.4..
+  .ver 4:0:0:0
+}
+.assembly DirectCallToExplicitInterfaceImpl
+{
+  .ver 1:0:0:0
+}
+.module DirectCallToExplicitInterfaceImpl.exe
+
+.class public auto ansi sealed TestClass
+	extends [mscorlib]System.Object
+  implements [mscorlib]System.IDisposable
+{
+	// Methods
+	
+  .method private final hidebysig newslot virtual 
+	instance void System.IDisposable.Dispose () cil managed 
+  {
+    .override method instance void [mscorlib]System.IDisposable::Dispose()
+    ret
+  }
+
+  .method public hidebysig void Test (class TestClass other) cil managed 
+  {
+    ldarg.0
+    call instance void TestClass::System.IDisposable.Dispose()
+
+    ldarg.1
+    call instance void TestClass::System.IDisposable.Dispose()
+
+    ret
+  }
+
+} // end of class DirectCallToExplicitInterfaceImpl

ICSharpCode.Decompiler/CSharp/CallBuilder.cs

@@ -172,6 +172,16 @@ namespace ICSharpCode.Decompiler.CSharp
 			IReadOnlyList<int> argumentToParameterMap = null,
 			IType constrainedTo = null)
 		{
+			if (method.IsExplicitInterfaceImplementation && callOpCode == OpCode.Call) {
+				// Direct non-virtual call to explicit interface implementation.
+				// This can't really be represented in C#, but at least in the case where
+				// the class is sealed, we can equivalently call the interface member instead:
+				var interfaceMembers = method.ExplicitlyImplementedInterfaceMembers.ToList();
+				if (method.DeclaringTypeDefinition?.Kind == TypeKind.Class && method.DeclaringTypeDefinition.IsSealed && interfaceMembers.Count == 1) {
+					method = (IMethod)interfaceMembers.Single();
+					callOpCode = OpCode.CallVirt;
+				}
+			}
 			// Used for Call, CallVirt and NewObj
 			var expectedTargetDetails = new ExpectedTargetDetails {
 				CallOpCode = callOpCode