Preserve all InternalsVisibleTo attributes in ILLink Trimmer

Removes previous special handling to only keep IVT attributes for
assemblies that were resolvable and marked at link time. This behaviour
could cause a noticeable difference in behaviour at runtime without emitting
any trim analysis warnings while providing no mechanism to retain the
attributes. The removal of these attributes provides only a neglible
size reduction.

Fixes #92582

Author: Xtansia

src/tools/illink/src/linker/Linker.Steps/MarkStep.cs

@@ -36,7 +36,6 @@
 using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using System.Reflection.Runtime.TypeParsing;
-using System.Runtime.CompilerServices;
 using System.Text.RegularExpressions;
 using ILLink.Shared;
 using ILLink.Shared.TrimAnalysis;
@@ -62,7 +61,6 @@ protected LinkContext Context {
 		protected Queue<(MethodDefinition, DependencyInfo, MessageOrigin)> _methods;
 		protected HashSet<(MethodDefinition, MarkScopeStack.Scope)> _virtual_methods;
 		protected Queue<AttributeProviderPair> _assemblyLevelAttributes;
-		readonly List<AttributeProviderPair> _ivt_attributes;
 		protected Queue<(AttributeProviderPair, DependencyInfo, MarkScopeStack.Scope)> _lateMarkedAttributes;
 		protected List<(TypeDefinition, MarkScopeStack.Scope)> _typesWithInterfaces;
 		protected HashSet<AssemblyDefinition> _dynamicInterfaceCastableImplementationTypesDiscovered;
@@ -222,7 +220,6 @@ public MarkStep ()
 			_methods = new Queue<(MethodDefinition, DependencyInfo, MessageOrigin)> ();
 			_virtual_methods = new HashSet<(MethodDefinition, MarkScopeStack.Scope)> ();
 			_assemblyLevelAttributes = new Queue<AttributeProviderPair> ();
-			_ivt_attributes = new List<AttributeProviderPair> ();
 			_lateMarkedAttributes = new Queue<(AttributeProviderPair, DependencyInfo, MarkScopeStack.Scope)> ();
 			_typesWithInterfaces = new List<(TypeDefinition, MarkScopeStack.Scope)> ();
 			_dynamicInterfaceCastableImplementationTypesDiscovered = new HashSet<AssemblyDefinition> ();
@@ -288,42 +285,6 @@ protected virtual void Complete ()
 			}
 		}
 
-		bool ProcessInternalsVisibleAttributes ()
-		{
-			bool marked_any = false;
-			foreach (var attr in _ivt_attributes) {
-
-				var provider = attr.Provider;
-				Debug.Assert (attr.Provider is ModuleDefinition or AssemblyDefinition);
-				var assembly = (provider is ModuleDefinition module) ? module.Assembly : provider as AssemblyDefinition;
-
-				using var assemblyScope = ScopeStack.PushLocalScope (new MessageOrigin (assembly));
-
-				if (!Annotations.IsMarked (attr.Attribute) && IsInternalsVisibleAttributeAssemblyMarked (attr.Attribute)) {
-					MarkCustomAttribute (attr.Attribute, new DependencyInfo (DependencyKind.AssemblyOrModuleAttribute, attr.Provider));
-					marked_any = true;
-				}
-			}
-
-			return marked_any;
-
-			bool IsInternalsVisibleAttributeAssemblyMarked (CustomAttribute ca)
-			{
-				System.Reflection.AssemblyName an;
-				try {
-					an = new System.Reflection.AssemblyName ((string) ca.ConstructorArguments[0].Value);
-				} catch {
-					return false;
-				}
-
-				var assembly = Context.GetLoadedAssembly (an.Name!);
-				if (assembly == null)
-					return false;
-
-				return Annotations.IsMarked (assembly.MainModule);
-			}
-		}
-
 		static bool TypeIsDynamicInterfaceCastableImplementation (TypeDefinition type)
 		{
 			if (!type.IsInterface || !type.HasInterfaces || !type.HasCustomAttributes)
@@ -416,8 +377,7 @@ void Process ()
 				ProcessMarkedPending () ||
 				ProcessLazyAttributes () ||
 				ProcessLateMarkedAttributes () ||
-				MarkFullyPreservedAssemblies () ||
-				ProcessInternalsVisibleAttributes ()) ;
+				MarkFullyPreservedAssemblies ()) ;
 
 			ProcessPendingTypeChecks ();
 		}
@@ -1170,6 +1130,9 @@ protected virtual bool ShouldMarkCustomAttribute (CustomAttribute ca, ICustomAtt
 				case "System.Runtime.InteropServices.InterfaceTypeAttribute":
 				case "System.Runtime.InteropServices.GuidAttribute":
 					return true;
+				// May be implicitly used by the runtime
+				case "System.Runtime.CompilerServices.InternalsVisibleToAttribute":
+					return true;
 				}
 
 				TypeDefinition? type = Context.Resolve (attr_type);
@@ -1547,10 +1510,7 @@ bool ProcessLazyAttributes ()
 				if (IsAttributeRemoved (customAttribute, resolved.DeclaringType) && Annotations.GetAction (CustomAttributeSource.GetAssemblyFromCustomAttributeProvider (assemblyLevelAttribute.Provider)) == AssemblyAction.Link)
 					continue;
 
-				if (customAttribute.AttributeType.IsTypeOf ("System.Runtime.CompilerServices", "InternalsVisibleToAttribute") && !Annotations.IsMarked (customAttribute)) {
-					_ivt_attributes.Add (assemblyLevelAttribute);
-					continue;
-				} else if (!ShouldMarkTopLevelCustomAttribute (assemblyLevelAttribute, resolved)) {
+				if (!ShouldMarkTopLevelCustomAttribute (assemblyLevelAttribute, resolved)) {
 					skippedItems.Add (assemblyLevelAttribute);
 					continue;
 				}

src/tools/illink/test/Mono.Linker.Tests.Cases/Attributes/IVTUnused.cs

@@ -1,15 +1,16 @@
-using System.Runtime.CompilerServices;
 using Mono.Linker.Tests.Cases.Expectations.Assertions;
 using Mono.Linker.Tests.Cases.Expectations.Metadata;
 
 #if IVT
-[assembly: InternalsVisibleTo ("missing")]
-[assembly: InternalsVisibleTo ("test-with-key, PublicKey=00240000")]
-
+[assembly: System.Runtime.CompilerServices.InternalsVisibleTo ("missing")]
+[assembly: System.Runtime.CompilerServices.InternalsVisibleTo ("test-with-key, PublicKey=00240000")]
 #endif
 
+[assembly: KeptAttributeAttribute ("System.Runtime.CompilerServices.InternalsVisibleToAttribute")]
+
 namespace Mono.Linker.Tests.Cases.Attributes
 {
+	[SetupLinkerArgument("--used-attrs-only", "true")]
 	[Define ("IVT")]
 	class IVTUnused
 	{