ILLink: Allow TypePreserve info to be applied multiple times (#103140)

Allows TypePreserve info to be applied multiple times. Pending preserve items may not be processed when the preserve info is applied, and the preserve info may be applied twice (in ProcessMarkedPending and ProcessType). If the preserve has already been applied in these cases, we will just return early rather than throwing an exception.

Adds a test that applies a preserve on an otherwise unreferenced type.

Author: jtschuster

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

@@ -477,7 +477,6 @@ bool ProcessMarkedPending ()
 
 			foreach (var type in Annotations.GetPendingPreserve ()) {
 				marked = true;
-				Debug.Assert (Annotations.IsProcessed (type));
 				ApplyPreserveInfo (type);
 			}
 
@@ -2785,7 +2784,7 @@ void ApplyPreserveInfo (TypeDefinition type)
 
 			if (Annotations.TryGetPreserve (type, out TypePreserve preserve)) {
 				if (!Annotations.SetAppliedPreserve (type, preserve))
-					throw new InternalErrorException ($"Type {type} already has applied {preserve}.");
+					return;
 
 				var di = new DependencyInfo (DependencyKind.TypePreserve, type);
 

src/tools/illink/src/linker/Linker/Annotations.cs

@@ -34,7 +34,6 @@
 using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
 using System.Linq;
-using System.Reflection.Metadata.Ecma335;
 using ILLink.Shared.TrimAnalysis;
 using Mono.Cecil;
 using Mono.Cecil.Cil;
@@ -303,25 +302,12 @@ public bool SetAppliedPreserve (TypeDefinition type, TypePreserve preserve)
 			return true;
 		}
 
-		public bool HasAppliedPreserve (TypeDefinition type, TypePreserve preserve)
-		{
-			if (!preserved_types.TryGetValue (type, out (TypePreserve preserve, bool applied) existing))
-				throw new InternalErrorException ($"Type {type} must have a TypePreserve before it can be applied.");
-
-			if (preserve != existing.preserve)
-				throw new InternalErrorException ($"Type {type} does not have {preserve}. The TypePreserve may have changed before the call to {nameof (HasAppliedPreserve)}.");
-
-			return existing.applied;
-		}
-
 		public void SetPreserve (TypeDefinition type, TypePreserve preserve)
 		{
 			Debug.Assert (preserve != TypePreserve.Nothing);
 			if (!preserved_types.TryGetValue (type, out (TypePreserve preserve, bool applied) existing)) {
 				preserved_types.Add (type, (preserve, false));
 				if (IsProcessed (type)) {
-					// Required to track preserve for marked types where the existing preserve
-					// was Nothing (since these aren't explicitly tracked.)
 					var addedPending = pending_preserve.Add (type);
 					Debug.Assert (addedPending);
 				}

src/tools/illink/test/Mono.Linker.Tests.Cases/CommandLine/CustomStepApplyPreserve.cs

@@ -0,0 +1,35 @@
+using System;
+using Mono.Linker.Tests.Cases.Expectations.Assertions;
+using Mono.Linker.Tests.Cases.Expectations.Metadata;
+
+namespace Mono.Linker.Tests.Cases.CommandLine
+{
+	[SetupCompileBefore ("CustomApplyPreserveStep.dll", new[] { "Dependencies/CustomApplyPreserveStep.cs" }, new[] { "illink.dll", "Mono.Cecil.dll" }, addAsReference: false)]
+	[SetupLinkerArgument ("--custom-step", "-MarkStep:CustomStep.CustomApplyPreserveStep,CustomApplyPreserveStep.dll")]
+	[SetupLinkerArgument ("--verbose")]
+	public class CustomStepApplyPreserve
+	{
+		[Kept]
+		public class HasPreserveApplied
+		{
+			[Kept]
+			public int Field;
+
+			[Kept]
+			public HasPreserveApplied () { }
+
+			[Kept]
+			public void Method ()
+			{
+			}
+
+			public class Nested { }
+		}
+
+		[Kept]
+		public static void Main ()
+		{
+			Console.WriteLine (typeof (HasPreserveApplied).FullName);
+		}
+	}
+}

src/tools/illink/test/Mono.Linker.Tests.Cases/CommandLine/Dependencies/CustomApplyPreserveStep.cs

@@ -0,0 +1,13 @@
+namespace CustomStep
+{
+    public class CustomApplyPreserveStep : Mono.Linker.Steps.IStep
+    {
+        public void Process(Mono.Linker.LinkContext context)
+        {
+            var myType = context.GetType("Mono.Linker.Tests.Cases.CommandLine.CustomStepApplyPreserve/HasPreserveApplied");
+            context.Annotations.SetPreserve(myType, Mono.Linker.TypePreserve.Methods);
+            // Make sure we can set preserve multiple times
+            context.Annotations.SetPreserve(myType, Mono.Linker.TypePreserve.All);
+        }
+    }
+}

src/tools/illink/test/Mono.Linker.Tests.Cases/Mono.Linker.Tests.Cases.csproj

@@ -22,6 +22,7 @@
     <Compile Remove="TypeForwarding\Dependencies\TypeForwardersRewriteForwarders.cs" />
     <Compile Remove="CommandLine\Dependencies\CustomStepDummy.cs" />
     <Compile Remove="CommandLine\Dependencies\CustomStepUser.cs" />
+    <Compile Remove="CommandLine\Dependencies\CustomApplyPreserveStep.cs" />
     <Compile Remove="Logging\Dependencies\LogStep.cs" />
     <Compile Remove="Extensibility\Dependencies\*.cs" />
     <Compile Remove="DynamicDependencies\Dependencies\FacadeAssembly.cs" />