Use FeatureSwitchDefinition in a few places

src/coreclr/System.Private.CoreLib/System.Private.CoreLib.csproj

@@ -25,7 +25,6 @@
 
   <ItemGroup>
     <ILLinkSubstitutionsXmls Include="$(ILLinkDirectory)ILLink.Substitutions.xml" />
-    <ILLinkSubstitutionsXmls Condition="'$(TargetsWindows)' == 'true'" Include="$(ILLinkDirectory)ILLink.Substitutions.Windows.xml" />
   </ItemGroup>
 
   <!-- Note that various places in SPCL depend on this resource name i.e. TplEventSource -->

src/coreclr/System.Private.CoreLib/src/Internal/Runtime/InteropServices/InMemoryAssemblyLoader.cs

@@ -15,6 +15,7 @@ namespace Internal.Runtime.InteropServices
     [SupportedOSPlatform("windows")]
     internal static class InMemoryAssemblyLoader
     {
+        [FeatureSwitchDefinition("System.Runtime.InteropServices.EnableCppCLIHostActivation")]
         private static bool IsSupported { get; } = InitializeIsSupported();
         private static bool InitializeIsSupported() => AppContext.TryGetSwitch("System.Runtime.InteropServices.EnableCppCLIHostActivation", out bool isSupported) ? isSupported : true;
 

src/coreclr/System.Private.CoreLib/src/System/Reflection/Metadata/MetadataUpdater.cs

@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
 
@@ -59,6 +60,7 @@ public static void ApplyUpdate(Assembly assembly, ReadOnlySpan<byte> metadataDel
         /// <summary>
         /// Returns true if the apply assembly update is enabled and available.
         /// </summary>
+        [FeatureSwitchDefinition("System.Reflection.Metadata.MetadataUpdater.IsSupported")]
         public static bool IsSupported { get; } = IsApplyUpdateSupported();
     }
 }

src/coreclr/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshal.CoreCLR.cs

@@ -330,6 +330,7 @@ internal static unsafe bool IsPinnable(object? obj)
             => (obj == null) || !RuntimeHelpers.GetMethodTable(obj)->ContainsGCPointers;
 
 #if TARGET_WINDOWS
+        [FeatureSwitchDefinition("System.Runtime.InteropServices.BuiltInComInterop.IsSupported")]
         internal static bool IsBuiltInComSupported { get; } = IsBuiltInComSupportedInternal();
 
         [LibraryImport(RuntimeHelpers.QCall, EntryPoint = "MarshalNative_IsBuiltInComSupported")]

src/coreclr/nativeaot/System.Private.CoreLib/src/System.Private.CoreLib.csproj

@@ -8,7 +8,6 @@
   </ItemGroup>
 
   <ItemGroup>
-    <ILLinkSubstitutionsXmls Include="ILLink\ILLink.Substitutions.xml" />
     <ILLinkLinkAttributesXmls Include="ILLink\ILLink.LinkAttributes.xml" />
   </ItemGroup>
   <ItemGroup Condition="'$(TargetsUnix)'=='true'">

src/coreclr/nativeaot/System.Private.CoreLib/src/System/Collections/Generic/Comparer.NativeAot.cs

@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 #nullable enable
+using System.Diagnostics.CodeAnalysis;
 using System.Runtime.CompilerServices;
 using System.Threading;
 
@@ -12,7 +13,7 @@ namespace System.Collections.Generic
 {
     public abstract partial class Comparer<T> : IComparer, IComparer<T>
     {
-        // The AOT compiler can flip this to false under certain circumstances.
+        [FeatureSwitchDefinition("System.Collections.Generic.DefaultComparers")]
         private static bool SupportsGenericIComparableInterfaces => true;
 
         [Intrinsic]

src/coreclr/nativeaot/System.Private.CoreLib/src/System/Collections/Generic/EqualityComparer.NativeAot.cs

@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 #nullable enable
+using System.Diagnostics.CodeAnalysis;
 using System.Runtime.CompilerServices;
 using System.Threading;
 
@@ -12,7 +13,7 @@ namespace System.Collections.Generic
 {
     public abstract partial class EqualityComparer<T> : IEqualityComparer, IEqualityComparer<T>
     {
-        // The AOT compiler can flip this to false under certain circumstances.
+        [FeatureSwitchDefinition("System.Collections.Generic.DefaultComparers")]
         private static bool SupportsGenericIEquatableInterfaces => true;
 
         [Intrinsic]

src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Metadata/MetadataUpdater.cs

@@ -1,6 +1,8 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Diagnostics.CodeAnalysis;
+
 namespace System.Reflection.Metadata
 {
     public static class MetadataUpdater
@@ -10,6 +12,7 @@ public static void ApplyUpdate(Assembly assembly, ReadOnlySpan<byte> metadataDel
             throw new PlatformNotSupportedException();
         }
 
+        [FeatureSwitchDefinition("System.Reflection.Metadata.MetadataUpdater.IsSupported")]
         public static bool IsSupported => false;
     }
 }

src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Runtime/General/TypeUnifier.cs

@@ -4,6 +4,7 @@
 using System;
 using System.Collections.Concurrent;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Reflection;
 using System.Reflection.Runtime.General;
 using System.Reflection.Runtime.MethodInfos;
@@ -36,6 +37,7 @@ namespace System.Reflection.Runtime.General
 {
     internal static partial class TypeUnifier
     {
+        [FeatureSwitchDefinition("System.Reflection.IsTypeConstructionEagerlyValidated")]
         // This can be replaced at native compile time using a feature switch.
         internal static bool IsTypeConstructionEagerlyValidated => true;
 

src/coreclr/nativeaot/System.Private.CoreLib/src/System/RuntimeType.cs

@@ -46,6 +46,7 @@ internal void Free()
             RuntimeImports.RhHandleFree(_runtimeTypeInfoHandle);
         }
 
+        [FeatureSwitchDefinition("System.Reflection")]
         private static bool IsReflectionDisabled => false;
 
         private static bool DoNotThrowForNames => AppContext.TryGetSwitch("Switch.System.Reflection.Disabled.DoNotThrowForNames", out bool doNotThrow) && doNotThrow;

src/libraries/Microsoft.Extensions.DependencyInjection/src/Microsoft.Extensions.DependencyInjection.csproj

@@ -18,10 +18,6 @@
                                '$(ILEmitBackendSaveAssemblies)' == 'true'">$(DefineConstants);SAVE_ASSEMBLIES</DefineConstants>
   </PropertyGroup>
 
-  <ItemGroup>
-    <ILLinkSubstitutionsXmls Include="$(ILLinkDirectory)ILLink.Substitutions.xml" />
-  </ItemGroup>
-
   <ItemGroup>
     <Compile Include="**\*.cs" />
     <Compile Remove="ServiceLookup\ILEmit\**\*.cs" />
@@ -47,6 +43,10 @@
     <Compile Include="$(CoreLibSharedDir)System\Diagnostics\CodeAnalysis\UnconditionalSuppressMessageAttribute.cs" />
   </ItemGroup>
 
+  <ItemGroup Condition="'$(TargetFrameworkIdentifier)' != '.NETCoreApp' or $([MSBuild]::VersionLessThan('$(TargetFrameworkVersion)', '9.0'))">
+    <Compile Include="$(CoreLibSharedDir)System\Diagnostics\CodeAnalysis\FeatureSwitchDefinitionAttribute.cs" />
+  </ItemGroup>
+
   <ItemGroup>
     <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.DependencyInjection.Abstractions\src\Microsoft.Extensions.DependencyInjection.Abstractions.csproj" />
   </ItemGroup>

src/libraries/Microsoft.Extensions.DependencyInjection/src/ServiceProvider.cs

@@ -37,6 +37,7 @@ public sealed class ServiceProvider : IServiceProvider, IKeyedServiceProvider, I
         internal static bool VerifyOpenGenericServiceTrimmability { get; } =
             AppContext.TryGetSwitch("Microsoft.Extensions.DependencyInjection.VerifyOpenGenericServiceTrimmability", out bool verifyOpenGenerics) ? verifyOpenGenerics : false;
 
+        [FeatureSwitchDefinition("Microsoft.Extensions.DependencyInjection.DisableDynamicEngine")]
         internal static bool DisableDynamicEngine { get; } =
             AppContext.TryGetSwitch("Microsoft.Extensions.DependencyInjection.DisableDynamicEngine", out bool disableDynamicEngine) ? disableDynamicEngine : false;
 

src/libraries/System.ComponentModel.TypeConverter/src/System.ComponentModel.TypeConverter.csproj

@@ -7,10 +7,6 @@
     <UseCompilerGeneratedDocXmlFile>false</UseCompilerGeneratedDocXmlFile>
   </PropertyGroup>
 
-  <ItemGroup>
-    <ILLinkSubstitutionsXmls Include="$(ILLinkDirectory)ILLink.Substitutions.xml" />
-  </ItemGroup>
-
   <ItemGroup>
     <Compile Include="MS\Internal\Xml\Linq\ComponentModel\XComponentModel.cs" />
     <Compile Include="System\ComponentModel\ArrayConverter.cs" />

src/libraries/System.ComponentModel.TypeConverter/src/System/ComponentModel/Design/DesigntimeLicenseContextSerializer.cs

@@ -17,6 +17,7 @@ public class DesigntimeLicenseContextSerializer
     {
         internal const byte BinaryWriterMagic = 255;
 
+        [FeatureSwitchDefinition("System.ComponentModel.TypeConverter.EnableUnsafeBinaryFormatterInDesigntimeLicenseContextSerialization")]
         private static bool EnableUnsafeBinaryFormatterInDesigntimeLicenseContextSerialization { get; } = AppContext.TryGetSwitch("System.ComponentModel.TypeConverter.EnableUnsafeBinaryFormatterInDesigntimeLicenseContextSerialization", out bool isEnabled) ? isEnabled : false;
 
         // Not creatable.

src/libraries/System.Diagnostics.DiagnosticSource/src/ILLink/ILLink.Substitutions.Shared.xml

@@ -1,8 +1,5 @@
 <linker>
   <assembly fullname="System.Diagnostics.DiagnosticSource" feature="System.Diagnostics.Metrics.Meter.IsSupported" featurevalue="false">
-    <type fullname="System.Diagnostics.Metrics.Meter">
-      <method signature="System.Boolean get_IsSupported()" body="stub" value="false" />
-    </type>
     <type fullname="System.Diagnostics.Metrics.Instrument">
       <method signature="System.Boolean get_Enabled()" body="stub" value="false" />
     </type>

src/libraries/System.Diagnostics.DiagnosticSource/src/System.Diagnostics.DiagnosticSource.csproj

@@ -123,6 +123,10 @@ System.Diagnostics.DiagnosticSource</PackageDescription>
     <Compile Include="$(CoreLibSharedDir)System\Runtime\CompilerServices\IsExternalInit.cs" />
   </ItemGroup>
 
+  <ItemGroup Condition="'$(TargetFrameworkIdentifier)' != '.NETCoreApp' or $([MSBuild]::VersionLessThan('$(TargetFrameworkVersion)', '9.0'))">
+    <Compile Include="$(CoreLibSharedDir)System\Diagnostics\CodeAnalysis\FeatureSwitchDefinitionAttribute.cs" />
+  </ItemGroup>
+
   <ItemGroup Condition="'$(TargetFrameworkIdentifier)' == '.NETCoreApp' or
                         '$(TargetFramework)' == 'netstandard2.0'">
     <Compile Include="System\Diagnostics\Activity.DateTime.corefx.cs" />

src/libraries/System.Diagnostics.DiagnosticSource/src/System/Diagnostics/Metrics/Meter.cs

@@ -4,6 +4,7 @@
 using System.Collections.Generic;
 using System.ComponentModel;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Threading;
 
 namespace System.Diagnostics.Metrics
@@ -20,6 +21,7 @@ public class Meter : IDisposable
 
         internal bool Disposed { get; private set; }
 
+        [FeatureSwitchDefinition("System.Diagnostics.Metrics.Meter.IsSupported")]
         internal static bool IsSupported { get; } = InitializeIsSupported();
 
         private static bool InitializeIsSupported() =>

src/libraries/System.Linq.Expressions/src/System.Linq.Expressions.csproj

@@ -12,10 +12,6 @@
     <UseCompilerGeneratedDocXmlFile>false</UseCompilerGeneratedDocXmlFile>
   </PropertyGroup>
 
-  <ItemGroup>
-    <ILLinkSubstitutionsXmls Include="$(ILLinkDirectory)ILLink.Substitutions.xml" />
-  </ItemGroup>
-
   <ItemGroup>
     <Compile Include="$(CommonPath)System\Obsoletions.cs"
              Link="Common\System\Obsoletions.cs" />

src/libraries/System.Linq.Expressions/src/System/Dynamic/Utils/DelegateHelpers.cs

@@ -13,7 +13,7 @@ namespace System.Dynamic.Utils
 {
     internal static class DelegateHelpers
     {
-        // This can be flipped to false using feature switches at publishing time
+        [FeatureSwitchDefinition("System.Linq.Expressions.CanEmitObjectArrayDelegate")]
         internal static bool CanEmitObjectArrayDelegate => true;
 
         // Separate class so that the it can be trimmed away and doesn't get conflated

src/libraries/System.Net.Http/src/System.Net.Http.csproj

@@ -28,10 +28,6 @@
     <ILLinkSubstitutionsXmls Include="$(ILLinkDirectory)ILLink.Substitutions.xml" />
   </ItemGroup>
 
-  <ItemGroup Condition="'$(TargetPlatformIdentifier)' == 'android' or '$(TargetPlatformIdentifier)' == 'ios' or '$(TargetPlatformIdentifier)' == 'maccatalyst' or '$(TargetPlatformIdentifier)' == 'tvos' or '$(TargetPlatformIdentifier)' == 'browser' or '$(TargetPlatformIdentifier)' == 'wasi'">
-    <ILLinkSubstitutionsXmls Include="$(ILLinkDirectory)ILLink.Substitutions.mobile.xml" Condition="'$(TargetPlatformIdentifier)' != 'browser' and '$(TargetPlatformIdentifier)' != 'wasi'" />
-  </ItemGroup>
-
   <ItemGroup Condition="'$(TargetPlatformIdentifier)' != ''">
     <Compile Include="System\Net\Http\ByteArrayContent.cs" />
     <Compile Include="System\Net\Http\CancellationHelper.cs" />

src/libraries/System.Net.Http/src/System/Net/Http/HttpClientHandler.AnyMobile.cs

@@ -789,6 +789,7 @@ private void ThrowForModifiedManagedSslOptionsIfStarted()
             _socketHandler!.SslOptions = _socketHandler!.SslOptions;
         }
 
+        [FeatureSwitchDefinition("System.Net.Http.UseNativeHttpHandler")]
         private static bool IsNativeHandlerEnabled => RuntimeSettingParser.QueryRuntimeSettingSwitch(
                 "System.Net.Http.UseNativeHttpHandler",
                 false);

src/libraries/System.Net.Security/src/System.Net.Security.csproj

@@ -295,7 +295,6 @@
   </ItemGroup>
 
   <ItemGroup Condition="'$(TargetPlatformIdentifier)' != '' and '$(TargetPlatformIdentifier)' != 'windows' and '$(UseManagedNtlm)' != 'true'">
-    <ILLinkSubstitutionsXmls Include="$(ILLinkDirectory)ILLink.Substitutions.xml" />
     <Compile Include="System\Net\NegotiateAuthenticationPal.Unix.cs" />
     <Compile Include="$(CommonPath)Microsoft\Win32\SafeHandles\GssSafeHandles.cs"
              Link="Common\Microsoft\Win32\SafeHandles\GssSafeHandles.cs" />

src/libraries/System.Net.Security/src/System/Net/NegotiateAuthenticationPal.Unix.cs

@@ -21,6 +21,8 @@ internal partial class NegotiateAuthenticationPal
     {
         private static readonly Lazy<bool> _hasSystemNetSecurityNative = new Lazy<bool>(CheckHasSystemNetSecurityNative);
         internal static bool HasSystemNetSecurityNative => _hasSystemNetSecurityNative.Value;
+
+        [FeatureSwitchDefinition("System.Net.Security.UseManagedNtlm")]
         private static bool UseManagedNtlm { get; } =
             AppContext.TryGetSwitch("System.Net.Security.UseManagedNtlm", out bool useManagedNtlm) ?
             useManagedNtlm :