From 3c044c995644f668515c0a648ab568c5bf525e8c Mon Sep 17 00:00:00 2001
From: Jackson Schuster <36744439+jtschuster@users.noreply.github.com>
Date: Mon, 14 Sep 2026 13:27:12 -0700
Subject: [PATCH] ILTrim: Preserve implemented interfaces on constructed types

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Copilot-Session: 5f633264-d8a6-4199-a816-4c0da8e63873
---
 .../TokenBased/TypeDefinitionNode.cs                |  5 ++++-
 .../tools/ILTrim.Tests/ILTrimExpectedFailures.txt   | 13 -------------
 2 files changed, 4 insertions(+), 14 deletions(-)

diff --git a/src/coreclr/tools/ILTrim.Core/DependencyAnalysis/TokenBased/TypeDefinitionNode.cs b/src/coreclr/tools/ILTrim.Core/DependencyAnalysis/TokenBased/TypeDefinitionNode.cs
index 081d10ba87bd76..66c97b15b9355d 100644
--- a/src/coreclr/tools/ILTrim.Core/DependencyAnalysis/TokenBased/TypeDefinitionNode.cs
+++ b/src/coreclr/tools/ILTrim.Core/DependencyAnalysis/TokenBased/TypeDefinitionNode.cs
@@ -162,7 +162,10 @@ protected override EntityHandle WriteInternal(ModuleWritingContext writeContext)
             {
                 InterfaceImplementation intfImpl = reader.GetInterfaceImplementation(intfImplHandle);
                 EcmaType interfaceType = _module.TryGetType(intfImpl.Interface)?.GetTypeDefinition() as EcmaType;
-                if (interfaceType != null && writeContext.Factory.InterfaceUse(interfaceType).Marked)
+                if (interfaceType != null &&
+                    (writeContext.Factory.InterfaceUse(interfaceType).Marked ||
+                     (writeContext.Factory.ConstructedType((EcmaType)_module.GetObject(Handle)).Marked &&
+                      writeContext.Factory.TypeDefinition(interfaceType.Module, interfaceType.Handle).Marked)))
                 {
                     builder.AddInterfaceImplementation(outputHandle,
                         writeContext.TokenMap.MapToken(intfImpl.Interface));
diff --git a/src/coreclr/tools/ILTrim.Tests/ILTrimExpectedFailures.txt b/src/coreclr/tools/ILTrim.Tests/ILTrimExpectedFailures.txt
index a872f2dffdec3f..48ab85175bdcd8 100644
--- a/src/coreclr/tools/ILTrim.Tests/ILTrimExpectedFailures.txt
+++ b/src/coreclr/tools/ILTrim.Tests/ILTrimExpectedFailures.txt
@@ -51,9 +51,7 @@ Attributes.StructLayout.ExplicitClass
 Attributes.StructLayout.SequentialClass
 Attributes.TypeWithDynamicInterfaceCastableImplementationAttributeIsKept
 Basic.InstantiatedTypeWithOverridesFromObject
-Basic.UninvokedInterfaceMemberGetsRemoved
 Basic.UsedGenericInterfaceIsKept
-Basic.UsedInterfaceIsKept
 BCLFeatures.ETW.CustomEventSource
 BCLFeatures.ETW.CustomLibraryEventSource
 CommandLine.AddCustomStep
@@ -186,15 +184,11 @@ Inheritance.Interfaces.OnReferenceType.BaseProvidesInterfaceMember.GenericInterf
 Inheritance.Interfaces.OnReferenceType.BaseProvidesInterfaceMember.GenericInterfaceWithMethodOnNoInstanceCtor2
 Inheritance.Interfaces.OnReferenceType.BaseProvidesInterfaceMember.SimpleMethodOnNoInstanceCtor
 Inheritance.Interfaces.OnReferenceType.BaseProvidesInterfaceMember.SimpleMethodOnNoInstanceCtor2
-Inheritance.Interfaces.OnReferenceType.ClassImplementingInterfaceMethodsNested2
-Inheritance.Interfaces.OnReferenceType.ClassUsedFromConcreteTypeHasInterfaceMethodRemoved2
 Inheritance.Interfaces.OnReferenceType.InterfaceMarkOrderingDoesNotMatter
 Inheritance.Interfaces.OnReferenceType.InterfaceMarkOrderingDoesNotMatter2
-Inheritance.Interfaces.OnReferenceType.InterfaceMarkOrderingDoesNotMatter3
 Inheritance.Interfaces.OnReferenceType.InterfaceNeededOnUnrelatedInterfaceList
 Inheritance.Interfaces.OnReferenceType.InterfaceTypeInOtherUsedOnlyByCopiedAssembly
 Inheritance.Interfaces.OnReferenceType.InterfaceTypeInOtherUsedOnlyByCopiedAssemblyExplicit
-Inheritance.Interfaces.OnReferenceType.InterfaceUsedOnlyAsConstraintIsKept
 Inheritance.Interfaces.OnReferenceType.NoInstanceCtor.NoInstanceCtorAndAssemblyPreserveAll
 Inheritance.Interfaces.OnReferenceType.NoInstanceCtor.NoInstanceCtorAndTypePreserveAll
 Inheritance.Interfaces.OnReferenceType.NoInstanceCtor.NoInstanceCtorAndTypePreserveMethodsWithInterfacesMarked
@@ -208,7 +202,6 @@ Inheritance.Interfaces.OnReferenceType.NoKeptCtor.LocalDowncastDoesNotCuaseOther
 Inheritance.Interfaces.OnReferenceType.NoKeptCtor.PreserveDependencyPreservesInterfaceMethod
 Inheritance.Interfaces.OnReferenceType.NoKeptCtor.UnusedTypeHasExplicitInterfaceMethodPreservedViaXml
 Inheritance.Interfaces.OnReferenceType.NoKeptCtor.UnusedTypeHasExplicitInterfacePropertyPreservedViaXml
-Inheritance.Interfaces.OnReferenceType.NoKeptCtor.UnusedTypeWithPreserveMethodsAndInterfaceTypeMarked
 Inheritance.Interfaces.OnReferenceType.NoKeptCtorButInterfaceNeeded.ArrayWithIndexAssignedToReturnValue
 Inheritance.Interfaces.OnReferenceType.NoKeptCtorButInterfaceNeeded.FieldDowncastedToInterface
 Inheritance.Interfaces.OnReferenceType.NoKeptCtorButInterfaceNeeded.GenericType
@@ -232,13 +225,8 @@ Inheritance.Interfaces.OnReferenceType.NoKeptCtorButInterfaceNeeded.ParameterAnd
 Inheritance.Interfaces.OnReferenceType.NoKeptCtorButInterfaceNeeded.ParameterOutAndLocal
 Inheritance.Interfaces.OnReferenceType.NoKeptCtorButInterfaceNeeded.ParameterRefAndLocal
 Inheritance.Interfaces.OnReferenceType.NoKeptCtorButInterfaceNeeded.ReturnValueDowncastedToInterface
-Inheritance.Interfaces.OnReferenceType.ObjectCastedToSecondInterfaceHasMemberRemovedButInterfaceKept
 Inheritance.Interfaces.OnReferenceType.UnusedComInterfaceIsKept
 Inheritance.Interfaces.OnReferenceType.UnusedExplicitInterfaceHasMethodPreservedViaXml
-Inheritance.Interfaces.OnValueType.NoKeptCtor.InterfaceTypeRemovedWhenOnlyUsedByClassWithOnlyStaticMethod
-Inheritance.Interfaces.OnValueType.NoKeptCtor.InterfaceTypeRemovedWhenOnlyUsedByClassWithOnlyStaticMethodMultiple
-Inheritance.Interfaces.OnValueType.StructImplementingInterfaceMethodsNested2
-Inheritance.Interfaces.OnValueType.StructUsedFromConcreteTypeHasInterfaceMethodRemoved2
 Inheritance.Interfaces.OnValueType.StructWithNestedStructImplementingInterface
 Inheritance.Interfaces.OnValueType.UnusedExplicitInterfaceHasMethodPreservedViaXml
 Inheritance.Interfaces.RecursiveInterfaces.GenericInterfaceImplementedRecursively
@@ -304,7 +292,6 @@ LinkXml.EmbeddedLinkXmlPreservesAdditionalAssemblyWithOverriddenMethod
 LinkXml.LinkXmlErrorCases
 LinkXml.TypeWithPreserveFieldsHasBackingFieldsOfPropertiesRemoved
 LinkXml.UnusedFieldPreservedByLinkXmlIsKept
-LinkXml.UnusedInterfaceTypeOnTypeWithPreserveAllIsKept
 LinkXml.UnusedNonRequiredTypeIsRemoved
 LinkXml.UsedNonRequiredExportedTypeIsKept
 LinkXml.UsedNonRequiredExportedTypeIsKeptWhenRooted