ILLink: Add test for dataflow in local method group passed as argument to delegate

Adds a test for issue #95258 which passes without any source code fix.

Author: jtschuster

src/tools/illink/test/ILLink.RoslynAnalyzer.Tests/DataFlowTests.cs

@@ -118,6 +118,12 @@ public Task ConstructorDataFlow ()
 			return RunTest ();
 		}
 
+		[Fact]
+		public Task DataflowInLocalMethodGroupArgument ()
+		{
+			return RunTest ();
+		}
+
 		[Fact]
 		public Task DynamicDependencyDataflow ()
 		{

src/tools/illink/test/Mono.Linker.Tests.Cases/DataFlow/DataflowInLocalMethodGroupArgument.cs

@@ -0,0 +1,66 @@
+// Copyright (c) .NET Foundation and contributors. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using System;
+using System.Collections.Concurrent;
+using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using Mono.Linker.Tests.Cases.Expectations.Assertions;
+using Mono.Linker.Tests.Cases.Expectations.Helpers;
+
+namespace Mono.Linker.Tests.Cases.DataFlow
+{
+	[ExpectedNoWarnings]
+	[SkipKeptItemsValidation]
+	public class DataflowInLocalMethodGroupArgument
+	{
+		public static void Main ()
+		{
+			new GenericWithNonPublicConstructors<int> ().Test ();
+			GenericWithNonPublicConstructors<int>.TestInstanceLocalMethod ();
+		}
+
+		public class GenericWithNonPublicConstructors<[DynamicallyAccessedMembers (DynamicallyAccessedMemberTypes.NonPublicConstructors)] T>
+		{
+			public void Test ()
+			{
+				[ExpectedWarning ("IL2087", "PublicFields", "RequiresPublicFields", "T", "GenericWithNonPublicConstructors")]
+				static int GetIntWithBadDataflow (int x)
+				{
+					typeof (T).RequiresPublicFields();
+					return 0;
+				}
+
+				new Dictionary<int, int> ().GetOrAdd (0, GetIntWithBadDataflow);
+			}
+
+			public static void TestInstanceLocalMethod ()
+			{
+				[ExpectedWarning ("IL2087", "PublicFields", "RequiresPublicFields", "T", "GenericWithNonPublicConstructors")]
+				int GetIntWithBadDataflow (int x)
+				{
+					typeof (T).RequiresPublicFields();
+					return 0;
+				}
+
+				new Dictionary<int, int> ().GetOrAdd (0, GetIntWithBadDataflow);
+			}
+		}
+	}
+
+	public static class DictionaryExtensions
+	{
+		public static TValue GetOrAdd<TKey, TValue> (this Dictionary<TKey, TValue> dictionary, TKey key, Func<TKey, TValue> valueFactory)
+		{
+			if (dictionary.TryGetValue (key, out var value))
+				return value;
+
+			value = valueFactory (key);
+			dictionary.TryAdd (key, value);
+			return value;
+		}
+	}
+}