ILLink: Keep parameter names unless DebuggerSupport is disabled

src/libraries/System.Runtime/tests/System.Runtime.Tests/TrimmingTests/DebuggerSupportFalse.cs

@@ -0,0 +1,34 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+#nullable enable
+
+using System;
+using System.Diagnostics.CodeAnalysis;
+using System.Runtime.CompilerServices;
+using System.Reflection;
+
+/// <summary>
+/// Ensures setting DebuggerSupport = false causes parameter names to be removed
+/// </summary>
+class Program
+{
+    static int Main(string[] args)
+    {
+        // Ensure the method is kept
+        MethodWithParameter ("");
+
+        // Get parameter name via trim-incompatible reflection
+        var parameterName = reflectedType.GetMethod("MethodWithParameter")!.GetParameters()[0].Name;
+
+        // Parameter name should be removed
+        if (!string.IsNullOrEmpty(parameterName))
+            return -1;
+
+        return 100;
+    }
+
+    static Type reflectedType = typeof(Program);
+
+    public static void MethodWithParameter(string parameter) {}
+}

src/libraries/System.Runtime/tests/System.Runtime.Tests/TrimmingTests/DebuggerSupportTrue.cs

@@ -0,0 +1,34 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+#nullable enable
+
+using System;
+using System.Diagnostics.CodeAnalysis;
+using System.Runtime.CompilerServices;
+using System.Reflection;
+
+/// <summary>
+/// Ensures setting DebuggerSupport = true causes parameter names to be kept
+/// </summary>
+class Program
+{
+    static int Main(string[] args)
+    {
+        // Ensure the method is kept
+        MethodWithParameter ("");
+
+        // Get parameter name via trim-incompatible reflection
+        var parameterName = reflectedType.GetMethod("MethodWithParameter")!.GetParameters()[0].Name;
+
+        // Parameter name should be kept
+        if (parameterName != "parameter")
+            return -1;
+
+        return 100;
+    }
+
+    static Type reflectedType = typeof(Program);
+
+    public static void MethodWithParameter(string parameter) {}
+}

src/libraries/System.Runtime/tests/System.Runtime.Tests/TrimmingTests/System.Runtime.TrimmingTests.proj

@@ -10,6 +10,14 @@
     <TestConsoleAppSourceFiles Include="AppDomainGetThreadWindowsPrincipalTest.cs">
       <SkipOnTestRuntimes>osx-x64;linux-x64;browser-wasm</SkipOnTestRuntimes>
     </TestConsoleAppSourceFiles>
+    <TestConsoleAppSourceFiles Include="DebuggerSupportTrue.cs">
+      <EnabledProperties>DebuggerSupport</EnabledProperties>
+      <NativeAotIncompatible>true</NativeAotIncompatible>
+    </TestConsoleAppSourceFiles>
+    <TestConsoleAppSourceFiles Include="DebuggerSupportFalse.cs">
+      <DisabledProperties>DebuggerSupport</DisabledProperties>
+      <NativeAotIncompatible>true</NativeAotIncompatible>
+    </TestConsoleAppSourceFiles>
     <TestConsoleAppSourceFiles Include="DebuggerTypeProxyAttributeTests.cs" >
       <EnabledProperties>DebuggerSupport</EnabledProperties>
     </TestConsoleAppSourceFiles>

src/tools/illink/src/ILLink.Tasks/build/Microsoft.NET.ILLink.targets

@@ -156,6 +156,7 @@ Copyright (c) .NET Foundation. All rights reserved.
             UnusedInterfaces="$(_TrimmerUnusedInterfaces)"
             IPConstProp="$(_TrimmerIPConstProp)"
             Sealer="$(_TrimmerSealer)"
+            KeepMetadata="@(_TrimmerKeepMetadata)"
 
             Warn="$(ILLinkWarningLevel)"
             NoWarn="$(NoWarn)"
@@ -240,6 +241,11 @@ Copyright (c) .NET Foundation. All rights reserved.
       <TrimmerRemoveSymbols Condition=" '$(DebuggerSupport)' != 'false' ">false</TrimmerRemoveSymbols>
     </PropertyGroup>
 
+    <ItemGroup>
+      <!-- Keep parameter name and other metadata unless debugger support is disabled. -->
+      <_TrimmerKeepMetadata Include="all" Condition=" '$(DebuggerSupport)' != 'false' " />
+    </ItemGroup>
+
     <PropertyGroup>
       <_TrimmerPreserveSymbolPaths Condition=" '$(_TrimmerPreserveSymbolPaths)' == '' and '$(DeterministicSourcePaths)' == 'true' ">true</_TrimmerPreserveSymbolPaths>
       <_TrimmerPreserveSymbolPaths Condition=" '$(_TrimmerPreserveSymbolPaths)' == '' ">false</_TrimmerPreserveSymbolPaths>