Fixed ILVerify incorrectly flagging valid default interface implementations (#61185)

* Added logic for default interface method traversal to ILVerify method discovery

* Added Tests for DefaultImplFix

* Moved call to default interface impl resolution outside of ResolveInterfaceMethodTarget

3 files changed, 127 insertions, 51 deletions

diff --git a/src/tests/ilverify/ILTests/DefaultInterfaceMethod.il b/src/tests/ilverify/ILTests/DefaultInterfaceMethod.il
new file mode 100644
index 00000000000..a33f5cdddbe
--- /dev/null
+++ b/src/tests/ilverify/ILTests/DefaultInterfaceMethod.il
@@ -0,0 +1,124 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+.assembly DefaultInterfaceMethod
+{
+}
+
+.assembly extern System.Runtime
+{
+}
+
+.class interface private auto ansi abstract IInterface
+{
+	.method public hidebysig newslot abstract virtual
+		instance void Method () cil managed
+	{
+	}
+}
+
+.class public auto ansi beforefieldinit ChildClassDoesNotImplementDefaultInterfaceMethod_ValidType_Valid
+	extends [System.Runtime]System.Object
+	implements IDefaultImplInterface
+{
+	.method public hidebysig specialname rtspecialname
+		instance void .ctor () cil managed
+	{
+		.maxstack 8
+
+		IL_0000: ldarg.0
+		IL_0001: call instance void [System.Runtime]System.Object::.ctor()
+		IL_0006: nop
+		IL_0007: ret
+	}
+}
+
+.class public auto ansi beforefieldinit ChildClassDoesImplementDefaultInterfaceMethod_ValidType_Valid
+	extends [System.Runtime]System.Object
+	implements IDefaultImplInterface
+{
+	.method public final hidebysig newslot virtual
+		instance void DefaultImplementation () cil managed
+	{
+		.maxstack 8
+
+		IL_0000: ret
+	}
+
+	.method public hidebysig specialname rtspecialname
+		instance void .ctor () cil managed
+	{
+		.maxstack 8
+
+		IL_0000: ldarg.0
+		IL_0001: call instance void [System.Runtime]System.Object::.ctor()
+		IL_0006: nop
+		IL_0007: ret
+	}
+}
+
+.class interface public auto ansi abstract IDefaultImplInterface
+{
+    .method public hidebysig newslot virtual
+		instance void DefaultImplementation () cil managed
+	{
+		.maxstack 8
+
+		IL_0000: ret
+	}
+}
+
+.class interface public auto ansi abstract IInheritedDefaultImplInterface
+	implements IInterface
+{
+	.method private final hidebysig virtual
+		instance void IInterface.Method () cil managed
+	{
+		.override method instance void IInterface::Method()
+		.maxstack 8
+
+		IL_0001: ret
+	}
+}
+
+.class public auto ansi beforefieldinit ClassInheritsFromInterfaceWhereContractIsImplementedByDerivedInterface_ValidType_Valid
+	extends [System.Runtime]System.Object
+	implements IInheritedDefaultImplInterface, IInterface
+{
+	.method public hidebysig specialname rtspecialname
+		instance void .ctor () cil managed
+	{
+		.maxstack 8
+
+		IL_0000: ldarg.0
+		IL_0001: call instance void [System.Runtime]System.Object::.ctor()
+		IL_0006: nop
+		IL_0007: ret
+	}
+}
+
+.class interface public auto ansi abstract IReabstractDefaultImplementation
+	implements IInheritedDefaultImplInterface, IInterface
+{
+	.method private final hidebysig abstract virtual
+		instance void IInterface.Method () cil managed
+	{
+		.override method instance void IInterface::Method()
+	}
+}
+
+.class public auto ansi beforefieldinit ChildClassInheritsFromInterfaceWithDefaultImplementationWhereChildInterfaceReabstractsInterfaceMethod_InvalidType_InterfaceMethodNotImplemented
+	extends [System.Runtime]System.Object
+	implements IReabstractDefaultImplementation, IInheritedDefaultImplInterface, IInterface
+{
+	.method public hidebysig specialname rtspecialname
+		instance void .ctor () cil managed
+	{
+		.maxstack 8
+
+		IL_0000: ldarg.0
+		IL_0001: call instance void [System.Runtime]System.Object::.ctor()
+		IL_0006: nop
+		IL_0007: ret
+	}
+}
diff --git a/src/tests/ilverify/ILTests/DefaultInterfaceMethod.ilproj b/src/tests/ilverify/ILTests/DefaultInterfaceMethod.ilproj
new file mode 100644
index 00000000000..8e8765d14a5
--- /dev/null
+++ b/src/tests/ilverify/ILTests/DefaultInterfaceMethod.ilproj
@@ -0,0 +1,3 @@
+<Project ToolsVersion="15.0" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <Import Project="ILTests.targets" />
+</Project>
diff --git a/src/tests/ilverify/ILTests/InterfaceImplementation.il b/src/tests/ilverify/ILTests/InterfaceImplementation.il
index 29f5c49b503..5264e54bbbe 100644
--- a/src/tests/ilverify/ILTests/InterfaceImplementation.il
+++ b/src/tests/ilverify/ILTests/InterfaceImplementation.il
@@ -448,54 +448,3 @@
 	{
 	}
 }
-
-.class public auto ansi beforefieldinit ChildClassDoesNotImplementDefaultInterfaceMethod_ValidType_Valid
-	extends [System.Runtime]System.Object
-	implements IDefaultImplInterface
-{
-	.method public hidebysig specialname rtspecialname 
-		instance void .ctor () cil managed 
-	{
-		.maxstack 8
-
-		IL_0000: ldarg.0
-		IL_0001: call instance void [System.Runtime]System.Object::.ctor()
-		IL_0006: nop
-		IL_0007: ret
-	}
-}
-
-.class public auto ansi beforefieldinit ChildClassDoesImplementDefaultInterfaceMethod_ValidType_Valid
-	extends [System.Runtime]System.Object
-	implements IDefaultImplInterface
-{
-	.method public final hidebysig newslot virtual 
-		instance void DefaultImplementation () cil managed 
-	{
-		.maxstack 8
-
-		IL_0000: ret
-	}
-
-	.method public hidebysig specialname rtspecialname 
-		instance void .ctor () cil managed 
-	{
-		.maxstack 8
-
-		IL_0000: ldarg.0
-		IL_0001: call instance void [System.Runtime]System.Object::.ctor()
-		IL_0006: nop
-		IL_0007: ret
-	}
-}
-
-.class interface public auto ansi abstract IDefaultImplInterface
-{
-    .method public hidebysig newslot virtual 
-		instance void DefaultImplementation () cil managed 
-	{
-		.maxstack 8
-
-		IL_0000: ret
-	}
-}
\ No newline at end of file