Don't suppress all warnings with SuppressTrimAnalysisWarnings

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

@@ -59,7 +59,7 @@ Copyright (c) .NET Foundation. All rights reserved.
 
   <!-- Suppress warnings produced by the linker or by the ILLink Roslyn analyzer. -->
   <PropertyGroup Condition="'$(SuppressTrimAnalysisWarnings)' == 'true'">
-    <ILLinkWarningLevel Condition="'$(ILLinkWarningLevel)' == ''">0</ILLinkWarningLevel>
+    <_ExtraTrimmerArgs>$(_ExtraTrimmerArgs) --notrimwarn</_ExtraTrimmerArgs>
     <EnableTrimAnalyzer Condition="'$(EnableTrimAnalyzer)' == ''">false</EnableTrimAnalyzer>
   </PropertyGroup>
 
@@ -223,6 +223,17 @@ Copyright (c) .NET Foundation. All rights reserved.
       <TrimmerSingleWarn Condition=" '$(TrimmerSingleWarn)' == '' ">true</TrimmerSingleWarn>
     </PropertyGroup>
 
+   <!-- Suppressions to work around issues in previous versions of the framework. See https://github.com/dotnet/runtime/issues/40336 -->
+    <PropertyGroup Condition="'$(SuppressTrimAnalysisWarnings)' == 'true' And $([MSBuild]::VersionLessThan('$(TargetFrameworkVersion)', '6.0'))">
+      <!-- Framework embedded XML descriptors reference windows-only members. -->
+      <NoWarn Condition=" !$(RuntimeIdentifier.StartsWith('win')) ">$(NoWarn);IL2008</NoWarn> <!-- Unresolved type referenced in XML. -->
+      <NoWarn Condition=" !$(RuntimeIdentifier.StartsWith('win')) ">$(NoWarn);IL2009</NoWarn> <!-- Unresolved member on type referenced in XML. -->
+      <!-- Framework has DynamicDependencyAttributes that reference windows-only members. -->
+      <NoWarn Condition=" !$(RuntimeIdentifier.StartsWith('win')) ">$(NoWarn);IL2037</NoWarn> <!-- Unresolved member for DynamicDependencyAttribute -->
+      <!-- Framework embedded XML descriptors reference 32-bit-only members. -->
+      <NoWarn Condition=" '$(PlatformTarget)' != 'x64' AND '$(PlatformTarget)' != 'arm64'">$(NoWarn);IL2009;IL2012</NoWarn> <!-- Unresolved field referenced in XML -->
+    </PropertyGroup>
+
     <!-- Enable serialization discovery for compat in < 7.0 -->
     <PropertyGroup Condition="$([MSBuild]::VersionLessThan('$(TargetFrameworkVersion)', '7.0'))">
       <_ExtraTrimmerArgs>--enable-serialization-discovery $(_ExtraTrimmerArgs)</_ExtraTrimmerArgs>

src/linker/Linker/Driver.cs

@@ -505,6 +505,10 @@ protected int SetupContext (ILogger? customLogger = null)
 						context.WarningSuppressionWriter = new WarningSuppressionWriter (context, fileOutputKind);
 						continue;
 
+					case "--notrimwarn":
+						context.NoTrimWarn = true;
+						continue;
+
 					case "--nowarn":
 						if (!GetStringParam (token, out string? noWarnArgument))
 							return -1;

src/linker/Linker/LinkContext.cs

@@ -163,6 +163,8 @@ internal TypeNameResolver TypeNameResolver {
 
 		public HashSet<int> NoWarn { get; set; }
 
+		public bool NoTrimWarn { get; set; }
+
 		public Dictionary<int, bool> WarnAsError { get; set; }
 
 		public bool GeneralWarnAsError { get; set; }
@@ -700,8 +702,11 @@ public void FlushCachedWarnings ()
 			_cachedWarningMessageContainers.Clear ();
 		}
 
-		public bool IsWarningSuppressed (int warningCode, MessageOrigin origin)
+		public bool IsWarningSuppressed (int warningCode, string subcategory, MessageOrigin origin)
 		{
+			if (subcategory == MessageSubCategory.TrimAnalysis && NoTrimWarn)
+				return true;
+
 			// This warning was turned off by --nowarn.
 			if (NoWarn.Contains (warningCode))
 				return true;

src/linker/Linker/MessageContainer.cs

@@ -162,7 +162,7 @@ private static MessageContainer CreateWarningMessageContainer (LinkContext conte
 			if (!(version >= WarnVersion.ILLink0 && version <= WarnVersion.Latest))
 				throw new ArgumentException ($"The provided warning version '{version}' is invalid.");
 
-			if (context.IsWarningSuppressed (code, origin))
+			if (context.IsWarningSuppressed (code, subcategory, origin))
 				return Empty;
 
 			if (version > context.WarnVersion)
@@ -182,7 +182,7 @@ private static MessageContainer CreateWarningMessageContainer (LinkContext conte
 			if (!(version >= WarnVersion.ILLink0 && version <= WarnVersion.Latest))
 				throw new ArgumentException ($"The provided warning version '{version}' is invalid.");
 
-			if (context.IsWarningSuppressed ((int) id, origin))
+			if (context.IsWarningSuppressed ((int) id, subcategory, origin))
 				return Empty;
 
 			if (version > context.WarnVersion)

test/Mono.Linker.Tests.Cases/Extensibility/CustomWarningUsage.cs

@@ -0,0 +1,32 @@
+using System.Diagnostics.CodeAnalysis;
+using Mono.Linker.Tests.Cases.Expectations.Assertions;
+using Mono.Linker.Tests.Cases.Expectations.Metadata;
+
+namespace Mono.Linker.Tests.Cases.Extensibility
+{
+	[SetupCompileBefore ("CustomWarning.dll", new[] { "Dependencies/CustomWarning.cs" }, new[] { "illink.dll", "Mono.Cecil.dll", "netstandard.dll" })]
+	[SetupLinkerArgument ("--custom-step", "CustomWarning,CustomWarning.dll")]
+	[SetupLinkerArgument ("--notrimwarn")]
+	[ExpectedNoWarnings]
+	public class CustomWarningUsage
+	{
+		[ExpectedWarning ("IL2026", "--RUCMethod--", ProducedBy = ProducedBy.Analyzer)]
+		public static void Main ()
+		{
+			new KnownTypeThatShouldWarn ();
+			RUCMethod (); // Warning suppressed by --notrimwarn
+		}
+
+		[ExpectedWarning ("IL6200", "custom warning on type")]
+		[Kept]
+		[KeptMember (".ctor()")]
+		public class KnownTypeThatShouldWarn
+		{
+		}
+
+		[Kept]
+		[KeptAttributeAttribute (typeof (RequiresUnreferencedCodeAttribute))]
+		[RequiresUnreferencedCode ("--RUCMethod--")]
+		static void RUCMethod () { }
+	}
+}

test/Mono.Linker.Tests.Cases/Extensibility/Dependencies/CustomWarning.cs

@@ -0,0 +1,22 @@
+using System;
+using System.Collections.Generic;
+using Mono.Cecil;
+using Mono.Linker;
+using Mono.Linker.Steps;
+
+public class CustomWarning : IMarkHandler
+{
+	LinkContext _context;
+
+	public void Initialize (LinkContext context, MarkContext markContext)
+	{
+		_context = context;
+		markContext.RegisterMarkTypeAction (type => WarnOnKnownType (type));
+	}
+
+	void WarnOnKnownType (TypeDefinition type )
+	{
+		if (type.Name == "KnownTypeThatShouldWarn")
+			_context.LogMessage (MessageContainer.CreateCustomWarningMessage (_context, "custom warning on type", 6200, new MessageOrigin (type), WarnVersion.ILLink5));
+	}
+}