Fix warning suppressions on types for type hierarchy

src/linker/Linker.Steps/MarkStep.cs

@@ -1756,14 +1756,16 @@ protected internal virtual TypeDefinition MarkType (TypeReference reference, Dep
 
 			MarkType (type.BaseType, new DependencyInfo (DependencyKind.BaseType, type));
 
+			MarkCustomAttributes (type, new DependencyInfo (DependencyKind.CustomAttribute, type));
+
 			// The DynamicallyAccessedMembers hiearchy processing must be done after the base type was marked
-			// (to avoid inconsistencies in the cache), but before anything else as work done below
+			// (to avoid inconsistencies in the cache), and after marking custom attributes (in case the attributes have
+			// warning suppressions for the type hierarchy marking) but before anything else as work done below
 			// might need the results of the processing here.
 			_dynamicallyAccessedMembersTypeHierarchy.ProcessMarkedTypeForDynamicallyAccessedMembersHierarchy (type);
 
 			if (type.DeclaringType != null)
 				MarkType (type.DeclaringType, new DependencyInfo (DependencyKind.DeclaringType, type));
-			MarkCustomAttributes (type, new DependencyInfo (DependencyKind.CustomAttribute, type));
 			MarkSecurityDeclarations (type, new DependencyInfo (DependencyKind.CustomAttribute, type));
 
 			if (type.IsMulticastDelegate ()) {

test/Mono.Linker.Tests.Cases/Reflection/TypeHierarchyLibraryModeSuppressions.cs

@@ -0,0 +1,51 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
+using System.Text;
+using Mono.Linker.Tests.Cases.Expectations.Assertions;
+using Mono.Linker.Tests.Cases.Expectations.Helpers;
+using Mono.Linker.Tests.Cases.Expectations.Metadata;
+
+namespace Mono.Linker.Tests.Cases.Reflection
+{
+	[SetupLinkerArgument ("-a", "test.exe", "library")]
+	[ExpectedNoWarnings]
+	[KeptMember (".ctor()")]
+	public class TypeHierarchyLibraryModeSuppressions
+	{
+		public static void Main ()
+		{
+			var t1 = typeof (Unsuppressed);
+			var t2 = typeof (Suppressed);
+		}
+
+		[Kept]
+		[KeptAttributeAttribute (typeof (DynamicallyAccessedMembersAttribute))]
+		[DynamicallyAccessedMembers (DynamicallyAccessedMemberTypes.PublicMethods)]
+		[ExpectedWarning ("IL2026", nameof (Unsuppressed))]
+		class Unsuppressed
+		{
+			[Kept]
+			[KeptAttributeAttribute (typeof (RequiresUnreferencedCodeAttribute))]
+			[RequiresUnreferencedCode ("--RUC on Unsuppressed--")]
+			public void RUCMethod () { }
+		}
+
+		[Kept]
+		[KeptAttributeAttribute (typeof (DynamicallyAccessedMembersAttribute))]
+		[KeptAttributeAttribute (typeof (UnconditionalSuppressMessageAttribute))]
+		[UnconditionalSuppressMessage ("TrimAnalysis", "IL2026")]
+		[DynamicallyAccessedMembers (DynamicallyAccessedMemberTypes.PublicMethods)]
+		class Suppressed
+		{
+			[Kept]
+			[KeptAttributeAttribute (typeof (RequiresUnreferencedCodeAttribute))]
+			[RequiresUnreferencedCode ("--RUC on Suppressed--")]
+			public void RUCMethod () { }
+		}
+	}
+}