ILLink: give info message on duplicate members only when within a single descriptors file (dotnet#101574)

In the trimmer we rely on the order of marking to determine if a descriptors file has a duplicate member. As we transition to the dependency analysis framework, the marking order changes, and this exposed scenarios where a descriptors file is found after some items have already been marked. This caused unnecessary IL2025 warnings (Duplicate preserve in descriptor file) to be reported. Instead of using the global marking state, we will keep a per-descriptor-file set of which members are preserved and only report duplicates within that set.

Author: jtschuster

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

@@ -2,6 +2,7 @@
 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
 
 using System;
+using System.Collections.Generic;
 using System.Diagnostics;
 using System.IO;
 using System.Text;
@@ -23,14 +24,24 @@ public class DescriptorMarker : ProcessLinkerXmlBase
 		static readonly string[] _accessorsAll = new string[] { "all" };
 		static readonly char[] _accessorsSep = new char[] { ';' };
 
+		protected readonly HashSet<object> _preservedMembers;
+
 		public DescriptorMarker (LinkContext context, Stream documentStream, string xmlDocumentLocation)
 			: base (context, documentStream, xmlDocumentLocation)
 		{
+			_preservedMembers = new ();
 		}
 
 		public DescriptorMarker (LinkContext context, Stream documentStream, EmbeddedResource resource, AssemblyDefinition resourceAssembly, string xmlDocumentLocation = "<unspecified>")
 			: base (context, documentStream, resource, resourceAssembly, xmlDocumentLocation)
 		{
+			_preservedMembers = new ();
+		}
+
+		protected void LogDuplicatePreserve(string memberName, XPathNavigator duplicatePosition)
+		{
+			var origin = GetMessageOriginForPosition (duplicatePosition);
+			_context.LogMessage (MessageContainer.CreateInfoMessage (origin, $"Duplicate preserve of '{memberName}'"));
 		}
 
 		public void Mark ()
@@ -147,16 +158,16 @@ protected static TypePreserve GetTypePreserve (XPathNavigator nav)
 
 		protected override void ProcessField (TypeDefinition type, FieldDefinition field, XPathNavigator nav)
 		{
-			if (_context.Annotations.IsMarked (field))
-				LogWarning (nav, DiagnosticId.XmlDuplicatePreserveMember, field.FullName);
+			if (!_preservedMembers.Add (field))
+				LogDuplicatePreserve (field.FullName, nav);
 
 			_context.Annotations.Mark (field, new DependencyInfo (DependencyKind.XmlDescriptor, _xmlDocumentLocation), GetMessageOriginForPosition (nav));
 		}
 
 		protected override void ProcessMethod (TypeDefinition type, MethodDefinition method, XPathNavigator nav, object? customData)
 		{
-			if (_context.Annotations.IsMarked (method))
-				LogWarning (nav, DiagnosticId.XmlDuplicatePreserveMember, method.GetDisplayName ());
+			if (!_preservedMembers.Add (method))
+				LogDuplicatePreserve (method.GetDisplayName (), nav);
 
 			_context.Annotations.MarkIndirectlyCalledMethod (method);
 			_context.Annotations.SetAction (method, MethodAction.Parse);
@@ -212,8 +223,8 @@ public static string GetMethodSignature (MethodDefinition meth, bool includeGene
 
 		protected override void ProcessEvent (TypeDefinition type, EventDefinition @event, XPathNavigator nav, object? customData)
 		{
-			if (_context.Annotations.IsMarked (@event))
-				LogWarning (nav, DiagnosticId.XmlDuplicatePreserveMember, @event.FullName);
+			if (!_preservedMembers.Add (@event))
+				LogDuplicatePreserve(@event.FullName, nav);
 
 			ProcessMethod (type, @event.AddMethod, nav, customData);
 			ProcessMethod (type, @event.RemoveMethod, nav, customData);
@@ -224,8 +235,8 @@ protected override void ProcessProperty (TypeDefinition type, PropertyDefinition
 		{
 			string[] accessors = fromSignature ? GetAccessors (nav) : _accessorsAll;
 
-			if (_context.Annotations.IsMarked (property))
-				LogWarning (nav, DiagnosticId.XmlDuplicatePreserveMember, property.FullName);
+			if (!_preservedMembers.Add (property))
+				LogDuplicatePreserve(property.FullName, nav);
 
 			if (Array.IndexOf (accessors, "all") >= 0) {
 				ProcessMethodIfNotNull (type, property.GetMethod, nav, customData);

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

@@ -253,6 +253,11 @@ public static MessageContainer CreateInfoMessage (string text)
 			return new MessageContainer (MessageCategory.Info, text, null);
 		}
 
+		internal static MessageContainer CreateInfoMessage (MessageOrigin origin, string text)
+		{
+			return new MessageContainer (MessageCategory.Info, text, null, "", origin);
+		}
+
 		/// <summary>
 		/// Create a diagnostics message.
 		/// </summary>

src/tools/illink/test/Mono.Linker.Tests.Cases/LinkXml/LinkXmlErrorCases.cs

@@ -6,6 +6,7 @@ namespace Mono.Linker.Tests.Cases.LinkXml
 {
 	[SetupLinkerDescriptorFile ("LinkXmlErrorCases.xml")]
 	[SetupLinkerArgument ("--skip-unresolved", "true")]
+	[SetupLinkerArgument ("--verbose")]
 
 	[ExpectedWarning ("IL2001", "TypeWithNoFields", FileName = "LinkXmlErrorCases.xml", SourceLine = 3, SourceColumn = 6)]
 	[ExpectedWarning ("IL2002", "TypeWithNoMethods", FileName = "LinkXmlErrorCases.xml", SourceLine = 4, SourceColumn = 6)]
@@ -17,10 +18,15 @@ namespace Mono.Linker.Tests.Cases.LinkXml
 	[ExpectedWarning ("IL2017", "NonExistentProperty", "TypeWithNoProperties", FileName = "LinkXmlErrorCases.xml", SourceLine = 21, SourceColumn = 8)]
 	[ExpectedWarning ("IL2018", "SetOnlyProperty", "TypeWithProperties", FileName = "LinkXmlErrorCases.xml", SourceLine = 25, SourceColumn = 8)]
 	[ExpectedWarning ("IL2019", "GetOnlyProperty", "TypeWithProperties", FileName = "LinkXmlErrorCases.xml", SourceLine = 26, SourceColumn = 8)]
-	[ExpectedWarning ("IL2025", "Method", Tool.Trimmer, "", FileName = "LinkXmlErrorCases.xml", SourceLine = 39, SourceColumn = 8)]
-	[ExpectedWarning ("IL2025", "Event", Tool.Trimmer, "", FileName = "LinkXmlErrorCases.xml", SourceLine = 40, SourceColumn = 8)]
-	[ExpectedWarning ("IL2025", "Field", Tool.Trimmer, "", FileName = "LinkXmlErrorCases.xml", SourceLine = 41, SourceColumn = 8)]
-	[ExpectedWarning ("IL2025", "Property", Tool.Trimmer, "", FileName = "LinkXmlErrorCases.xml", SourceLine = 42, SourceColumn = 8)]
+    [LogContains ("Duplicate preserve of 'System.Int32 Mono.Linker.Tests.Cases.LinkXml.LinkXmlErrorCases/TypeWithEverything::Field'", ProducedBy = Tool.Trimmer)]
+    [LogContains ("Duplicate preserve of 'Mono.Linker.Tests.Cases.LinkXml.LinkXmlErrorCases.TypeWithEverything.TypeWithEverything()'", ProducedBy = Tool.Trimmer)]
+    [LogContains ("Duplicate preserve of 'Mono.Linker.Tests.Cases.LinkXml.LinkXmlErrorCases.TypeWithEverything.Method()'", ProducedBy = Tool.Trimmer)]
+    [LogContains ("Duplicate preserve of 'System.EventHandler Mono.Linker.Tests.Cases.LinkXml.LinkXmlErrorCases/TypeWithEverything::Event'", ProducedBy = Tool.Trimmer)]
+    [LogContains ("Duplicate preserve of 'Mono.Linker.Tests.Cases.LinkXml.LinkXmlErrorCases.TypeWithEverything.Event.add'", ProducedBy = Tool.Trimmer)]
+    [LogContains ("Duplicate preserve of 'Mono.Linker.Tests.Cases.LinkXml.LinkXmlErrorCases.TypeWithEverything.Event.remove'", ProducedBy = Tool.Trimmer)]
+    [LogContains ("Duplicate preserve of 'System.Int32 Mono.Linker.Tests.Cases.LinkXml.LinkXmlErrorCases/TypeWithEverything::Property()'", ProducedBy = Tool.Trimmer)]
+    [LogContains ("Duplicate preserve of 'Mono.Linker.Tests.Cases.LinkXml.LinkXmlErrorCases.TypeWithEverything.Property.get'", ProducedBy = Tool.Trimmer)]
+    [LogContains ("Duplicate preserve of 'Mono.Linker.Tests.Cases.LinkXml.LinkXmlErrorCases.TypeWithEverything.Property.set'", ProducedBy = Tool.Trimmer)]
 	// NativeAOT doesn't support wildcard * and will skip usages of it, including if they would warn
 	// https://github.com/dotnet/runtime/issues/80466
 	[ExpectedWarning ("IL2100", Tool.Trimmer, "", FileName = "LinkXmlErrorCases.xml", SourceLine = 50, SourceColumn = 4)]