Closed hierarchy

src/Consume/Consume.cs

@@ -109,6 +109,7 @@ class Consume
 #endif
         type = typeof(AsyncMethodBuilderAttribute);
         type = typeof(CompilerLoweringPreserveAttribute);
+        type = typeof(IsClosedTypeAttribute);
 #if !NET6_0 && !NET5_0
         type = typeof(ObsoletedOSPlatformAttribute);
         type = typeof(SupportedOSPlatformGuardAttribute);

src/ConsumeCsPreview/ClosedHierarchy.cs

@@ -0,0 +1,38 @@
+namespace ConsumeCsPreview;
+
+// Compile-only coverage for the C# `closed` modifier. The compiler emits
+// IsClosedTypeAttribute on the closed type and
+// CompilerFeatureRequiredAttribute("ClosedClasses") on its constructors,
+// so this only compiles when both are polyfilled.
+
+#region ClosedHierarchy
+
+// Only types in this file can derive from JobStatus
+closed class JobStatus;
+
+sealed class Queued : JobStatus;
+
+sealed class Running(int percentComplete) : JobStatus
+{
+    public int PercentComplete => percentComplete;
+}
+
+sealed class Failed(string error) : JobStatus
+{
+    public string Error => error;
+}
+
+static class ClosedHierarchy
+{
+    // No default arm: the switch is exhaustive because every direct descendant of
+    // the closed JobStatus is handled. Without exhaustiveness this warns CS8509.
+    public static string Describe(JobStatus status) =>
+        status switch
+        {
+            Queued => "queued",
+            Running running => $"{running.PercentComplete}% complete",
+            Failed failed => $"failed: {failed.Error}"
+        };
+}
+
+#endregion

src/ConsumeCsPreview/ConsumeCsPreview.csproj

@@ -0,0 +1,20 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <NoWarn>$(NoWarn);PolyfillTargetsForNuget</NoWarn>
+    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
+    <LangVersion>preview</LangVersion>
+    <TargetFrameworks Condition=" '$(OS)' == 'Windows_NT'">net461;net462;net47;net471;net472;net48;net481;net6.0-windows</TargetFrameworks>
+    <TargetFrameworks>$(TargetFrameworks);netstandard2.0;netstandard2.1;netcoreapp2.0;netcoreapp2.1;netcoreapp2.2;netcoreapp3.0;netcoreapp3.1;net5.0;net6.0;net7.0;net8.0;net9.0;net10.0;net11.0</TargetFrameworks>
+  </PropertyGroup>
+  <ItemGroup>
+    <PackageReference Include="System.Memory" Condition="$(TargetFrameworkIdentifier) == '.NETStandard' or $(TargetFrameworkIdentifier) == '.NETFramework' or $(TargetFramework.StartsWith('netcoreapp'))" />
+    <PackageReference Include="System.ValueTuple" Condition="$(TargetFramework.StartsWith('net46'))" />
+    <PackageReference Include="System.Runtime.InteropServices.RuntimeInformation" Condition="$(TargetFramework.StartsWith('net4'))" />
+    <PackageReference Include="System.Net.Http" Condition="$(TargetFramework.StartsWith('net4'))" />
+    <PackageReference Include="System.Threading.Tasks.Extensions" Condition="$(TargetFramework) == 'netstandard2.0' or $(TargetFramework) == 'netcoreapp2.0' or $(TargetFrameworkIdentifier) == '.NETFramework'" />
+    <PackageReference Include="System.IO.Compression" Condition="$(TargetFrameworkIdentifier) == '.NETFramework'" />
+    <Compile Include="..\Consume\*.cs" />
+  </ItemGroup>
+  <Import Project="$(SolutionDir)\TestIncludes.targets" />
+  <Import Project="$(SolutionDir)\Polyfill\Polyfill.targets" />
+</Project>

src/Polyfill.slnx

@@ -29,6 +29,7 @@
   <Project Path="ConsumeCsDefault/ConsumeCsDefault.csproj" />
   <Project Path="ConsumeCsLatest/ConsumeCsLatest.csproj" />
   <Project Path="ConsumeCsLatestMajor/ConsumeCsLatestMajor.csproj" />
+  <Project Path="ConsumeCsPreview/ConsumeCsPreview.csproj" />
   <Project Path="ConsumeEmbeddedLib/ConsumeEmbeddedLib.csproj" />
   <Project Path="ConsumeInBoxRuntimeInfo/ConsumeInBoxRuntimeInfo.csproj" />
   <Project Path="ConsumeIncorrectVersions/ConsumeIncorrectVersions.csproj" />

src/Polyfill/IsClosedTypeAttribute.cs

@@ -0,0 +1,40 @@
+#if !NET11_0_OR_GREATER
+
+namespace System.Runtime.CompilerServices;
+
+using Diagnostics;
+using Diagnostics.CodeAnalysis;
+
+/// <summary>
+/// Reserved for use by a compiler for tracking metadata.
+/// This attribute should not be used by developers in source code.
+/// </summary>
+[ExcludeFromCodeCoverage]
+[DebuggerNonUserCode]
+[AttributeUsage(AttributeTargets.Class, Inherited = false)]
+#if PolyUseEmbeddedAttribute
+[global::Microsoft.CodeAnalysis.EmbeddedAttribute]
+#endif
+//Link: https://learn.microsoft.com/en-us/dotnet/api/system.runtime.compilerservices.isclosedtypeattribute?view=net-11.0
+#if PolyPublic
+public
+#endif
+sealed class IsClosedTypeAttribute :
+    Attribute
+{
+    Type[] derivedTypes = Type.EmptyTypes;
+
+    /// <summary>
+    /// Gets or sets the derived types of the closed type.
+    /// A <see langword="null"/> value is normalized to an empty array.
+    /// </summary>
+    public Type[] DerivedTypes
+    {
+        get => derivedTypes;
+        set => derivedTypes = value ?? Type.EmptyTypes;
+    }
+}
+
+#else
+[assembly: System.Runtime.CompilerServices.TypeForwardedTo(typeof(System.Runtime.CompilerServices.IsClosedTypeAttribute))]
+#endif

src/Split/net10.0/IsClosedTypeAttribute.cs

@@ -0,0 +1,32 @@
+// <auto-generated />
+#pragma warning disable
+namespace System.Runtime.CompilerServices;
+using Diagnostics;
+using Diagnostics.CodeAnalysis;
+/// <summary>
+/// Reserved for use by a compiler for tracking metadata.
+/// This attribute should not be used by developers in source code.
+/// </summary>
+[ExcludeFromCodeCoverage]
+[DebuggerNonUserCode]
+[AttributeUsage(AttributeTargets.Class, Inherited = false)]
+#if PolyUseEmbeddedAttribute
+[global::Microsoft.CodeAnalysis.EmbeddedAttribute]
+#endif
+#if PolyPublic
+public
+#endif
+sealed class IsClosedTypeAttribute :
+	Attribute
+{
+	Type[] derivedTypes = Type.EmptyTypes;
+	/// <summary>
+	/// Gets or sets the derived types of the closed type.
+	/// A <see langword="null"/> value is normalized to an empty array.
+	/// </summary>
+	public Type[] DerivedTypes
+	{
+		get => derivedTypes;
+		set => derivedTypes = value ?? Type.EmptyTypes;
+	}
+}

src/Split/net11.0/TypeForwardeds.cs

@@ -18,6 +18,7 @@
 [assembly: TypeForwardedTo(typeof(System.Diagnostics.CodeAnalysis.FeatureGuardAttribute))]
 [assembly: TypeForwardedTo(typeof(System.Diagnostics.CodeAnalysis.FeatureSwitchDefinitionAttribute))]
 [assembly: TypeForwardedTo(typeof(System.Collections.Generic.IAlternateEqualityComparer<,>))]
+[assembly: TypeForwardedTo(typeof(System.Runtime.CompilerServices.IsClosedTypeAttribute))]
 [assembly: TypeForwardedTo(typeof(System.Runtime.CompilerServices.IsExternalInit))]
 [assembly: TypeForwardedTo(typeof(System.Collections.Generic.KeyValuePair))]
 [assembly: TypeForwardedTo(typeof(System.Threading.Lock))]

src/Split/net461/IsClosedTypeAttribute.cs

@@ -0,0 +1,32 @@
+// <auto-generated />
+#pragma warning disable
+namespace System.Runtime.CompilerServices;
+using Diagnostics;
+using Diagnostics.CodeAnalysis;
+/// <summary>
+/// Reserved for use by a compiler for tracking metadata.
+/// This attribute should not be used by developers in source code.
+/// </summary>
+[ExcludeFromCodeCoverage]
+[DebuggerNonUserCode]
+[AttributeUsage(AttributeTargets.Class, Inherited = false)]
+#if PolyUseEmbeddedAttribute
+[global::Microsoft.CodeAnalysis.EmbeddedAttribute]
+#endif
+#if PolyPublic
+public
+#endif
+sealed class IsClosedTypeAttribute :
+	Attribute
+{
+	Type[] derivedTypes = Type.EmptyTypes;
+	/// <summary>
+	/// Gets or sets the derived types of the closed type.
+	/// A <see langword="null"/> value is normalized to an empty array.
+	/// </summary>
+	public Type[] DerivedTypes
+	{
+		get => derivedTypes;
+		set => derivedTypes = value ?? Type.EmptyTypes;
+	}
+}

src/Split/net462/IsClosedTypeAttribute.cs

@@ -0,0 +1,32 @@
+// <auto-generated />
+#pragma warning disable
+namespace System.Runtime.CompilerServices;
+using Diagnostics;
+using Diagnostics.CodeAnalysis;
+/// <summary>
+/// Reserved for use by a compiler for tracking metadata.
+/// This attribute should not be used by developers in source code.
+/// </summary>
+[ExcludeFromCodeCoverage]
+[DebuggerNonUserCode]
+[AttributeUsage(AttributeTargets.Class, Inherited = false)]
+#if PolyUseEmbeddedAttribute
+[global::Microsoft.CodeAnalysis.EmbeddedAttribute]
+#endif
+#if PolyPublic
+public
+#endif
+sealed class IsClosedTypeAttribute :
+	Attribute
+{
+	Type[] derivedTypes = Type.EmptyTypes;
+	/// <summary>
+	/// Gets or sets the derived types of the closed type.
+	/// A <see langword="null"/> value is normalized to an empty array.
+	/// </summary>
+	public Type[] DerivedTypes
+	{
+		get => derivedTypes;
+		set => derivedTypes = value ?? Type.EmptyTypes;
+	}
+}

src/Split/net47/IsClosedTypeAttribute.cs

@@ -0,0 +1,32 @@
+// <auto-generated />
+#pragma warning disable
+namespace System.Runtime.CompilerServices;
+using Diagnostics;
+using Diagnostics.CodeAnalysis;
+/// <summary>
+/// Reserved for use by a compiler for tracking metadata.
+/// This attribute should not be used by developers in source code.
+/// </summary>
+[ExcludeFromCodeCoverage]
+[DebuggerNonUserCode]
+[AttributeUsage(AttributeTargets.Class, Inherited = false)]
+#if PolyUseEmbeddedAttribute
+[global::Microsoft.CodeAnalysis.EmbeddedAttribute]
+#endif
+#if PolyPublic
+public
+#endif
+sealed class IsClosedTypeAttribute :
+	Attribute
+{
+	Type[] derivedTypes = Type.EmptyTypes;
+	/// <summary>
+	/// Gets or sets the derived types of the closed type.
+	/// A <see langword="null"/> value is normalized to an empty array.
+	/// </summary>
+	public Type[] DerivedTypes
+	{
+		get => derivedTypes;
+		set => derivedTypes = value ?? Type.EmptyTypes;
+	}
+}

src/Split/net471/IsClosedTypeAttribute.cs

@@ -0,0 +1,32 @@
+// <auto-generated />
+#pragma warning disable
+namespace System.Runtime.CompilerServices;
+using Diagnostics;
+using Diagnostics.CodeAnalysis;
+/// <summary>
+/// Reserved for use by a compiler for tracking metadata.
+/// This attribute should not be used by developers in source code.
+/// </summary>
+[ExcludeFromCodeCoverage]
+[DebuggerNonUserCode]
+[AttributeUsage(AttributeTargets.Class, Inherited = false)]
+#if PolyUseEmbeddedAttribute
+[global::Microsoft.CodeAnalysis.EmbeddedAttribute]
+#endif
+#if PolyPublic
+public
+#endif
+sealed class IsClosedTypeAttribute :
+	Attribute
+{
+	Type[] derivedTypes = Type.EmptyTypes;
+	/// <summary>
+	/// Gets or sets the derived types of the closed type.
+	/// A <see langword="null"/> value is normalized to an empty array.
+	/// </summary>
+	public Type[] DerivedTypes
+	{
+		get => derivedTypes;
+		set => derivedTypes = value ?? Type.EmptyTypes;
+	}
+}

src/Split/net472/IsClosedTypeAttribute.cs

@@ -0,0 +1,32 @@
+// <auto-generated />
+#pragma warning disable
+namespace System.Runtime.CompilerServices;
+using Diagnostics;
+using Diagnostics.CodeAnalysis;
+/// <summary>
+/// Reserved for use by a compiler for tracking metadata.
+/// This attribute should not be used by developers in source code.
+/// </summary>
+[ExcludeFromCodeCoverage]
+[DebuggerNonUserCode]
+[AttributeUsage(AttributeTargets.Class, Inherited = false)]
+#if PolyUseEmbeddedAttribute
+[global::Microsoft.CodeAnalysis.EmbeddedAttribute]
+#endif
+#if PolyPublic
+public
+#endif
+sealed class IsClosedTypeAttribute :
+	Attribute
+{
+	Type[] derivedTypes = Type.EmptyTypes;
+	/// <summary>
+	/// Gets or sets the derived types of the closed type.
+	/// A <see langword="null"/> value is normalized to an empty array.
+	/// </summary>
+	public Type[] DerivedTypes
+	{
+		get => derivedTypes;
+		set => derivedTypes = value ?? Type.EmptyTypes;
+	}
+}

src/Split/net48/IsClosedTypeAttribute.cs

@@ -0,0 +1,32 @@
+// <auto-generated />
+#pragma warning disable
+namespace System.Runtime.CompilerServices;
+using Diagnostics;
+using Diagnostics.CodeAnalysis;
+/// <summary>
+/// Reserved for use by a compiler for tracking metadata.
+/// This attribute should not be used by developers in source code.
+/// </summary>
+[ExcludeFromCodeCoverage]
+[DebuggerNonUserCode]
+[AttributeUsage(AttributeTargets.Class, Inherited = false)]
+#if PolyUseEmbeddedAttribute
+[global::Microsoft.CodeAnalysis.EmbeddedAttribute]
+#endif
+#if PolyPublic
+public
+#endif
+sealed class IsClosedTypeAttribute :
+	Attribute
+{
+	Type[] derivedTypes = Type.EmptyTypes;
+	/// <summary>
+	/// Gets or sets the derived types of the closed type.
+	/// A <see langword="null"/> value is normalized to an empty array.
+	/// </summary>
+	public Type[] DerivedTypes
+	{
+		get => derivedTypes;
+		set => derivedTypes = value ?? Type.EmptyTypes;
+	}
+}

src/Split/net481/IsClosedTypeAttribute.cs

@@ -0,0 +1,32 @@
+// <auto-generated />
+#pragma warning disable
+namespace System.Runtime.CompilerServices;
+using Diagnostics;
+using Diagnostics.CodeAnalysis;
+/// <summary>
+/// Reserved for use by a compiler for tracking metadata.
+/// This attribute should not be used by developers in source code.
+/// </summary>
+[ExcludeFromCodeCoverage]
+[DebuggerNonUserCode]
+[AttributeUsage(AttributeTargets.Class, Inherited = false)]
+#if PolyUseEmbeddedAttribute
+[global::Microsoft.CodeAnalysis.EmbeddedAttribute]
+#endif
+#if PolyPublic
+public
+#endif
+sealed class IsClosedTypeAttribute :
+	Attribute
+{
+	Type[] derivedTypes = Type.EmptyTypes;
+	/// <summary>
+	/// Gets or sets the derived types of the closed type.
+	/// A <see langword="null"/> value is normalized to an empty array.
+	/// </summary>
+	public Type[] DerivedTypes
+	{
+		get => derivedTypes;
+		set => derivedTypes = value ?? Type.EmptyTypes;
+	}
+}