Use SDK ILLink analyzer for OOBs for downlevel TFMs

eng/illink.targets

@@ -1,11 +1,5 @@
 <Project>
 
-  <PropertyGroup>
-    <!-- Custom trimming logic should always use live ILLink, even when none of the
-         trimming-related SDK properties are set. -->
-    <_RequiresLiveILLink>true</_RequiresLiveILLink>
-  </PropertyGroup>
-
   <PropertyGroup>
     <IsTrimmable Condition="'$(IsTrimmable)' == ''">true</IsTrimmable>
     <PrepareResourcesDependsOn>_EmbedILLinkXmls;$(PrepareResourcesDependsOn)</PrepareResourcesDependsOn>
@@ -210,7 +204,8 @@
       <!-- trim the target assembly -->
       <ILLinkArgs>$(ILLinkArgs) --action link $(TargetName)</ILLinkArgs>
       <ILLinkArgs Condition="'$(ILLinkRewritePDBs)' == 'true' and Exists('$(ILLinkTrimAssemblySymbols)')">$(ILLinkArgs) -b true</ILLinkArgs>
-      <ILLinkArgs Condition="'$(ILLinkRewritePDBs)' == 'true' and Exists('$(ILLinkTrimAssemblySymbols)') and '$(DeterministicSourcePaths)' == 'true'">$(ILLinkArgs) --preserve-symbol-paths</ILLinkArgs>
+      <!-- The preserve-symbol-paths option was introduced in .NET 9 -->
+      <ILLinkArgs Condition="'$(ILLinkRewritePDBs)' == 'true' and Exists('$(ILLinkTrimAssemblySymbols)') and '$(DeterministicSourcePaths)' == 'true' and $([MSBuild]::IsTargetFrameworkCompatible('$(TargetFramework)', 'net9.0'))">$(ILLinkArgs) --preserve-symbol-paths</ILLinkArgs>
       <!-- pass the non-embedded descriptors xml file on the command line -->
       <ILLinkArgs Condition="'@(ILLinkDescriptorsLibraryBuildXml)' != ''">$(ILLinkArgs) -x "@(ILLinkDescriptorsLibraryBuildXml->'%(FullPath)', '" -x "')"</ILLinkArgs>
       <ILLinkArgs Condition="'$(ILLinkSubstitutionsLibraryBuildXml)' != ''">$(ILLinkArgs) --substitutions "$(ILLinkSubstitutionsLibraryBuildXml)"</ILLinkArgs>

eng/liveILLink.targets

@@ -1,33 +1,33 @@
 <Project>
 
-  <!-- NOTE: these targets should be a no-op, unless _RequiresLiveILLink, computed below, is true. -->
+  <!-- NOTE: these targets should be a no-op, unless UseLiveILLink, computed below, is true. -->
 
-  <PropertyGroup>
+  <PropertyGroup Condition="$([MSBuild]::IsTargetFrameworkCompatible('$(TargetFramework)', '$(NetCoreAppCurrent)'))">
     <!-- Keep these conditions in sync with _RequiresILLinkPack in
          https://github.com/dotnet/sdk/blob/main/src/Tasks/Microsoft.NET.Build.Tasks/targets/Microsoft.NET.Publish.targets -->
-    <_RequiresLiveILLink Condition="'$(_RequiresLiveILLink)' == '' And (
+    <UseLiveILLink Condition="'$(UseLiveILLink)' == '' And (
         '$(PublishAot)' == 'true' Or
         '$(IsAotCompatible)' == 'true' Or '$(EnableAotAnalyzer)' == 'true' Or
         '$(PublishTrimmed)' == 'true' Or
         '$(IsTrimmable)' == 'true' Or '$(EnableTrimAnalyzer)' == 'true' Or
-        '$(EnableSingleFileAnalyzer)' == 'true')">true</_RequiresLiveILLink>
+        '$(EnableSingleFileAnalyzer)' == 'true')">true</UseLiveILLink>
   </PropertyGroup>
 
-  <PropertyGroup Condition="'$(_RequiresLiveILLink)' == 'true'">
+  <PropertyGroup Condition="'$(UseLiveILLink)' == 'true'">
     <_ILLinkTasksSourceDir>$(ToolsProjectRoot)illink\src\ILLink.Tasks\</_ILLinkTasksSourceDir>
     <ILLinkAnalyzersPropsPath>$(ToolsProjectRoot)illink\src\ILLink.RoslynAnalyzer\build\Microsoft.NET.ILLink.Analyzers.props</ILLinkAnalyzersPropsPath>
   </PropertyGroup>
 
-  <Import Project="$(_ILLinkTasksSourceDir)build\Microsoft.NET.ILLink.Tasks.props" Condition="'$(_RequiresLiveILLink)' == 'true'" />
+  <Import Project="$(_ILLinkTasksSourceDir)build\Microsoft.NET.ILLink.Tasks.props" Condition="'$(UseLiveILLink)' == 'true'" />
 
-  <PropertyGroup Condition="'$(_RequiresLiveILLink)' == 'true'">
+  <PropertyGroup Condition="'$(UseLiveILLink)' == 'true'">
     <!-- Don't use SDK's trimming functionality. -->
     <_RequiresILLinkPack>false</_RequiresILLinkPack>
     <ILLinkTasksAssembly Condition="'$(MSBuildRuntimeType)' == 'Core'">$(ToolsILLinkDir)net\ILLink.Tasks.dll</ILLinkTasksAssembly>
     <ILLinkTasksAssembly Condition="'$(MSBuildRuntimeType)' != 'Core'">$(ToolsILLinkDir)netframework\ILLink.Tasks.dll</ILLinkTasksAssembly>
   </PropertyGroup>
 
-  <ItemGroup Condition="'$(_RequiresLiveILLink)' == 'true'">
+  <ItemGroup Condition="'$(UseLiveILLink)' == 'true'">
     <!-- The assembly shouldn't be referenced, nor promoted to a package dependency, nor copied to the output directory. -->
     <ProjectReference Include="$(_ILLinkTasksSourceDir)ILLink.Tasks.csproj"
                       ReferenceOutputAssembly="false"

src/coreclr/tools/cdac-build-tool/Directory.Build.props

@@ -1,7 +1,7 @@
 <Project>
   <!-- we don't trim cdac-build-tool; we don't need the live trimmer -->
   <PropertyGroup>
-    <_RequiresLiveILLink>false</_RequiresLiveILLink>
+    <UseLiveILLink>false</UseLiveILLink>
   </PropertyGroup>
   <Import Project="..\Directory.Build.props" />
 </Project>

src/libraries/Directory.Build.props

@@ -48,8 +48,6 @@
     <!-- Nullability is enabled by default except for test projects, which instead default to annotations. -->
     <Nullable Condition="'$(Nullable)' == '' and '$(IsTestProject)' != 'true'">enable</Nullable>
     <Nullable Condition="'$(Nullable)' == '' and '$(IsTestProject)' == 'true'">annotations</Nullable>
-    <!-- AOT compatibility is enabled by default for src/ref projects. -->
-    <IsAotCompatible Condition="'$(IsAotCompatible)' == '' and ('$(IsSourceProject)' == 'true' or '$(IsReferenceAssemblyProject)' == 'true')">true</IsAotCompatible>
   </PropertyGroup>
 
   <!-- Set up common paths -->

src/libraries/Directory.Build.targets

@@ -66,6 +66,12 @@
     <DisableImplicitFrameworkReferences Condition="'$(TargetFrameworkIdentifier)' == '.NETCoreApp' and
                                                    '$(TargetFrameworkVersion)' == 'v$(NetCoreAppCurrentVersion)' and
                                                    ('$(IsNETCoreAppRef)' == 'true' or '$(IsNETCoreAppSrc)' == 'true')">true</DisableImplicitFrameworkReferences>
+    <!-- AOT compatibility is enabled by default for src/ref projects. -->
+    <IsAotCompatible Condition="'$(IsAotCompatible)' == '' and ('$(IsSourceProject)' == 'true' or '$(IsReferenceAssemblyProject)' == 'true')">true</IsAotCompatible>
+    <!-- Source-build only builds the current TFM, so there's an intentional "gap" in downlevel TFMs.
+         The SDK warns about this gap (NETSDK1210), but it's expected for source-build since those
+         downlevel TFMs aren't shipped. Silence the warning. -->
+    <_SilenceIsAotCompatibleUnsupportedWarning Condition="'$(DotNetBuildSourceOnly)' == 'true'">true</_SilenceIsAotCompatibleUnsupportedWarning>
     <!-- Enable trimming for any source project that's part of the shared framework.
          Don't attempt to trim PNSE assemblies which are generated from the reference source. -->
     <ILLinkTrimAssembly Condition="'$(ILLinkTrimAssembly)' == '' and
@@ -140,7 +146,12 @@
   <Import Project="$(RepositoryEngineeringDir)testing\runsettings.targets" Condition="'$(EnableRunSettingsSupport)' == 'true'" />
   <Import Project="$(RepositoryEngineeringDir)testing\coverage.targets" Condition="'$(EnableRunSettingsSupport)' == 'true' or '$(EnableCoverageSupport)' == 'true'" />
 
-  <Import Project="$(RepositoryEngineeringDir)illink.targets" Condition="'$(IsSourceProject)' == 'true' or '$(IsReferenceAssemblyProject)' == 'true' or '$(ExplicitlyImportCustomILLinkTargets)' == 'true'" />
+  <PropertyGroup>
+    <ImportCustomILLinkTargets Condition="'$(ImportCustomILLinkTargets)' == '' And
+      ('$(IsSourceProject)' == 'true' Or '$(IsReferenceAssemblyProject)' == 'true') And
+      $([MSBuild]::IsTargetFrameworkCompatible('$(TargetFramework)', 'net6.0'))">true</ImportCustomILLinkTargets>
+  </PropertyGroup>
+  <Import Project="$(RepositoryEngineeringDir)illink.targets" Condition="'$(ImportCustomILLinkTargets)' == 'true'" />
   <Import Project="$(RepositoryEngineeringDir)liveILLink.targets" />
   <Import Project="$(RepositoryEngineeringDir)nativeSanitizers.targets" />
 

src/libraries/Microsoft.Bcl.AsyncInterfaces/src/Microsoft.Bcl.AsyncInterfaces.csproj

@@ -2,6 +2,9 @@
 
   <PropertyGroup>
     <TargetFrameworks>netstandard2.0;$(NetFrameworkMinimum);netstandard2.1</TargetFrameworks>
+    <!-- Use live ILLink so that the shim assembly gets IsAotCompatible and IsTrimmable metadata despite
+         not targeting a TFM supported by the shipping trimming tooling. -->
+    <UseLiveILLink>true</UseLiveILLink>
     <IsPackable>true</IsPackable>
     <!-- This assembly should never be placed inbox as it is only for downlevel compatibility. -->
     <PackageDescription>Provides the IAsyncEnumerable&lt;T&gt; and IAsyncDisposable interfaces and helper types for .NET Standard 2.0. This package is not required starting with .NET Standard 2.1 and .NET Core 3.0.</PackageDescription>

src/libraries/Microsoft.Bcl.Numerics/src/Microsoft.Bcl.Numerics.csproj

@@ -2,6 +2,9 @@
 
   <PropertyGroup>
     <TargetFrameworks>netstandard2.0;$(NetFrameworkMinimum);netstandard2.1</TargetFrameworks>
+    <!-- Use live ILLink so that the shim assembly gets IsAotCompatible and IsTrimmable metadata despite
+         not targeting a TFM supported by the shipping trimming tooling. -->
+    <UseLiveILLink>true</UseLiveILLink>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <IsPackable>true</IsPackable>
     <!-- This assembly should never be placed inbox as it is only for downlevel compatibility. -->

src/libraries/Microsoft.XmlSerializer.Generator/src/Microsoft.XmlSerializer.Generator.csproj

@@ -17,6 +17,7 @@
     <!-- this assembly doesn't need to be binplaced -->
     <EnableBinPlacing>false</EnableBinPlacing>
     <IsTrimmable>false</IsTrimmable>
+    <IsAotCompatible>false</IsAotCompatible>
     <!-- TODO: Add package README file: https://github.com/dotnet/runtime/issues/99358 -->
     <EnableDefaultPackageReadmeFile>false</EnableDefaultPackageReadmeFile>
   </PropertyGroup>

src/libraries/System.ComponentModel.Composition/Directory.Build.props

@@ -4,5 +4,7 @@
     <StrongNameKeyId>ECMA</StrongNameKeyId>
     <IsTrimmable>false</IsTrimmable>
     <IsAotCompatible>false</IsAotCompatible>
+    <!-- Need ILLink task to generate resource substitutions -->
+    <UseLiveILLink>true</UseLiveILLink>
   </PropertyGroup>
 </Project>

src/libraries/System.Composition.Hosting/src/System.Composition.Hosting.csproj

@@ -4,6 +4,8 @@
     <TargetFrameworks>$(NetCoreAppCurrent);$(NetCoreAppPrevious);$(NetCoreAppMinimum);netstandard2.0;$(NetFrameworkMinimum)</TargetFrameworks>
     <IsTrimmable>false</IsTrimmable>
     <IsAotCompatible>false</IsAotCompatible>
+    <!-- Need ILLink task to generate resource substitutions -->
+    <UseLiveILLink>true</UseLiveILLink>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
     <UseCompilerGeneratedDocXmlFile>false</UseCompilerGeneratedDocXmlFile>
     <IsPackable>true</IsPackable>

src/libraries/System.Composition.TypedParts/src/System.Composition.TypedParts.csproj

@@ -5,6 +5,8 @@
     <RootNamespace>System.Composition</RootNamespace>
     <IsTrimmable>false</IsTrimmable>
     <IsAotCompatible>false</IsAotCompatible>
+    <!-- Need ILLink task to generate resource substitutions -->
+    <UseLiveILLink>true</UseLiveILLink>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
     <UseCompilerGeneratedDocXmlFile>false</UseCompilerGeneratedDocXmlFile>
     <IsPackable>true</IsPackable>

src/libraries/System.Configuration.ConfigurationManager/Directory.Build.props

@@ -6,5 +6,7 @@
     <!-- opt-out of trimming until it works https://github.com/dotnet/runtime/issues/49062 -->
     <IsTrimmable>false</IsTrimmable>
     <IsAotCompatible>false</IsAotCompatible>
+    <!-- Need ILLink task to generate resource substitutions -->
+    <UseLiveILLink>true</UseLiveILLink>
   </PropertyGroup>
 </Project>

src/libraries/System.Diagnostics.EventLog/src/Messages/System.Diagnostics.EventLog.Messages.csproj

@@ -1,6 +1,9 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <TargetFramework>netstandard2.0</TargetFramework>
+    <!-- This assembly doesn't contain any code and does not participate in trim analysis. -->
+    <IsAotCompatible>false</IsAotCompatible>
+    <IsTrimmable>false</IsTrimmable>
     <Nullable>disable</Nullable>
     <Win32Resource>EventLogMessages.res</Win32Resource>
     <!-- Override the parent Directory.Build.props -->

src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Value/EnumConverter.cs

@@ -5,6 +5,7 @@
 using System.Collections.Concurrent;
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Reflection;
 using System.Runtime.CompilerServices;
 using System.Text.Encodings.Web;
@@ -523,7 +524,7 @@ private static EnumFieldInfo[] ResolveEnumFields(JsonNamingPolicy? namingPolicy)
             Debug.Assert(names.Length == values.Length);
 
             Dictionary<string, string>? enumMemberAttributes = null;
-            foreach (FieldInfo field in typeof(T).GetFields(BindingFlags.Public | BindingFlags.Static))
+            foreach (FieldInfo field in GetFields())
             {
                 if (field.GetCustomAttribute<JsonStringEnumMemberNameAttribute>() is { } attribute)
                 {
@@ -561,6 +562,12 @@ private static EnumFieldInfo[] ResolveEnumFields(JsonNamingPolicy? namingPolicy)
             }
 
             return enumFields;
+
+#if !NET9_0_OR_GREATER
+            [UnconditionalSuppressMessage("ReflectionAnalysis", "IL2090:UnrecognizedReflectionPattern",
+                Justification = "Enum fields are always preserved by trimming.")]
+#endif
+            static IEnumerable<FieldInfo> GetFields() => typeof(T).GetFields(BindingFlags.Public | BindingFlags.Static);
         }
 
         private static string ResolveAndValidateJsonName(string name, JsonNamingPolicy? namingPolicy, EnumFieldNameKind kind)

src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Value/EnumConverterFactory.cs

@@ -25,7 +25,13 @@ public override JsonConverter CreateConverter(Type type, JsonSerializerOptions o
             return Create(type, EnumConverterOptions.AllowNumbers, namingPolicy: null, options);
         }
 
-        [UnconditionalSuppressMessage("ReflectionAnalysis", "IL2071:UnrecognizedReflectionPattern",
+        [UnconditionalSuppressMessage(
+            "ReflectionAnalysis",
+#if NET9_0_OR_GREATER
+            "IL2071:UnrecognizedReflectionPattern",
+#else
+            "IL2070:UnrecognizedReflectionPattern",
+#endif
             Justification = "'EnumConverter<T> where T : struct' implies 'T : new()', so the trimmer is warning calling MakeGenericType here because enumType's constructors are not annotated. " +
             "But EnumConverter doesn't call new T(), so this is safe.")]
         public static JsonConverter Create(Type enumType, EnumConverterOptions converterOptions, JsonNamingPolicy? namingPolicy, JsonSerializerOptions options)

src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Value/NullableConverterFactory.cs

@@ -43,7 +43,13 @@ public static JsonConverter CreateValueConverter(Type valueTypeToConvert, JsonCo
                 culture: null)!;
         }
 
-        [UnconditionalSuppressMessage("ReflectionAnalysis", "IL2071:UnrecognizedReflectionPattern",
+        [UnconditionalSuppressMessage(
+            "ReflectionAnalysis",
+#if NET9_0_OR_GREATER
+            "IL2071:UnrecognizedReflectionPattern",
+#else
+            "IL2070:UnrecognizedReflectionPattern",
+#endif
             Justification = "'NullableConverter<T> where T : struct' implies 'T : new()', so the trimmer is warning calling MakeGenericType here because valueTypeToConvert's constructors are not annotated. " +
             "But NullableConverter doesn't call new T(), so this is safe.")]
         [return: DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)]

src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Metadata/ReflectionEmitMemberAccessor.cs

@@ -153,6 +153,10 @@ public override JsonTypeInfo.ParameterizedConstructorDelegate<T, TArg0, TArg1, T
             return dynamicMethod;
         }
 
+#if !NET9_0_OR_GREATER
+        [UnconditionalSuppressMessage("ReflectionAnalysis", "IL2046",
+            Justification = "The type is annotated with RequiresUnreferencedCode, so the trimmer will warn at construction time.")]
+#endif
         public override Action<TCollection, object?> CreateAddMethodDelegate<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicMethods)] TCollection>() =>
             CreateDelegate<Action<TCollection, object?>>(CreateAddMethodDelegate(typeof(TCollection)));
 

src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Metadata/ReflectionMemberAccessor.cs

@@ -112,6 +112,10 @@ public override JsonTypeInfo.ParameterizedConstructorDelegate<T, TArg0, TArg1, T
             };
         }
 
+#if !NET9_0_OR_GREATER
+        [UnconditionalSuppressMessage("ReflectionAnalysis", "IL2046",
+            Justification = "The type is annotated with RequiresUnreferencedCode, so the trimmer will warn at construction time.")]
+#endif
         public override Action<TCollection, object?> CreateAddMethodDelegate<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicMethods)] TCollection>()
         {
             Type collectionType = typeof(TCollection);

src/libraries/oob-trim.proj

@@ -3,7 +3,7 @@
   <PropertyGroup>
     <TargetFramework>$(NetCoreAppCurrent)-$(TargetOS)</TargetFramework>
      <!-- Import the illink file which contains some of the logic required to illink the out-of-band assemblies. -->
-    <ExplicitlyImportCustomILLinkTargets>true</ExplicitlyImportCustomILLinkTargets>
+    <ImportCustomILLinkTargets>true</ImportCustomILLinkTargets>
   </PropertyGroup>
 
   <ItemGroup>

src/libraries/sfx-finish.proj

@@ -7,7 +7,7 @@
     <NoDefaultSlnGenSolutionFolder>true</NoDefaultSlnGenSolutionFolder>
     <FrameworkListOutputPath>$(MicrosoftNetCoreAppRefPackDataDir)FrameworkList.xml</FrameworkListOutputPath>
     <!-- Import the illink file which contains some of the logic required to illink the shared framework assemblies. -->
-    <ExplicitlyImportCustomILLinkTargets>true</ExplicitlyImportCustomILLinkTargets>
+    <ImportCustomILLinkTargets>true</ImportCustomILLinkTargets>
 
     <PackageOverridesInputPath>$(InstallerProjectRoot)pkg\sfx\Microsoft.NETCore.App\PackageOverrides.txt</PackageOverridesInputPath>
     <PackageOverridesOutputPath>$(MicrosoftNetCoreAppRefPackDataDir)PackageOverrides.txt</PackageOverridesOutputPath>