Add platform-specific attributes

src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems

@@ -818,10 +818,15 @@
     <Compile Include="$(MSBuildThisFileDirectory)System\Runtime\Versioning\ComponentGuaranteesAttribute.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Runtime\Versioning\ComponentGuaranteesOptions.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Runtime\Versioning\FrameworkName.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\Runtime\Versioning\MinimumOSPlatformAttribute.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\Runtime\Versioning\ObsoletedInOSPlatformAttribute.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\Runtime\Versioning\OSPlatformAttribute.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Runtime\Versioning\ResourceConsumptionAttribute.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Runtime\Versioning\ResourceExposureAttribute.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Runtime\Versioning\ResourceScope.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Runtime\Versioning\TargetFrameworkAttribute.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\Runtime\Versioning\TargetPlatformAttribute.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\Runtime\Versioning\RemovedInOSPlatformAttribute.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Runtime\Versioning\VersioningHelper.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\RuntimeType.cs" Condition="'$(TargetsCoreRT)' != 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\SByte.cs" />

src/libraries/System.Private.CoreLib/src/System/Runtime/Versioning/MinimumOSPlatformAttribute.cs

@@ -0,0 +1,32 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+namespace System.Runtime.Versioning
+{
+    /// <summary>
+    /// Records the operating system (and minimum version) that supports an API. Multiple attributes can be
+    /// applied to indicate support on multiple operating systems.
+    /// </summary>
+    /// <remarks>
+    /// Callers can apply a <see cref="System.Runtime.Versioning.MinimumOSPlatformAttribute" />
+    /// or use guards to prevent calls to APIs on unsupported operating systems.
+    ///
+    /// A given platform should only be specified once.
+    /// </remarks>
+    [AttributeUsage(AttributeTargets.Assembly |
+                    AttributeTargets.Class |
+                    AttributeTargets.Constructor |
+                    AttributeTargets.Event |
+                    AttributeTargets.Method |
+                    AttributeTargets.Module |
+                    AttributeTargets.Property |
+                    AttributeTargets.Struct,
+                    AllowMultiple = true, Inherited = false)]
+    public sealed class MinimumOSPlatformAttribute : OSPlatformAttribute
+    {
+        public MinimumOSPlatformAttribute(string platformName) : base(platformName)
+        {
+        }
+    }
+}

src/libraries/System.Private.CoreLib/src/System/Runtime/Versioning/OSPlatformAttribute.cs

@@ -0,0 +1,20 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+namespace System.Runtime.Versioning
+{
+    /// <summary>
+    /// Base type for all platform-specific API attributes.
+    /// </summary>
+#pragma warning disable CS3015 // Type has no accessible constructors which use only CLS-compliant types
+    public abstract class OSPlatformAttribute : Attribute
+#pragma warning restore CS3015
+    {
+        private protected OSPlatformAttribute(string platformName)
+        {
+            PlatformName = platformName;
+        }
+        public string PlatformName { get; }
+    }
+}

src/libraries/System.Private.CoreLib/src/System/Runtime/Versioning/ObsoletedInOSPlatformAttribute.cs

@@ -0,0 +1,36 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+namespace System.Runtime.Versioning
+{
+    /// <summary>
+    /// Marks APIs that were obsoleted in a given operating system version.
+    ///
+    /// Primarily used by OS bindings to indicate APIs that should only be used in
+    /// earlier versions.
+    /// </summary>
+    [AttributeUsage(AttributeTargets.Assembly |
+                    AttributeTargets.Class |
+                    AttributeTargets.Constructor |
+                    AttributeTargets.Event |
+                    AttributeTargets.Method |
+                    AttributeTargets.Module |
+                    AttributeTargets.Property |
+                    AttributeTargets.Struct,
+                    AllowMultiple = true, Inherited = false)]
+    public sealed class ObsoletedInOSPlatformAttribute : OSPlatformAttribute
+    {
+        public ObsoletedInOSPlatformAttribute(string platformName) : base(platformName)
+        {
+        }
+
+        public ObsoletedInOSPlatformAttribute(string platformName, string message) : base(platformName)
+        {
+            Message = message;
+        }
+
+        public string? Message { get; }
+        public string? Url { get; set; }
+    }
+}

src/libraries/System.Private.CoreLib/src/System/Runtime/Versioning/RemovedInOSPlatformAttribute.cs

@@ -0,0 +1,29 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+namespace System.Runtime.Versioning
+{
+    /// <summary>
+    /// Marks APIs that were removed in a given operating system version.
+    /// </summary>
+    /// <remarks>
+    /// Primarily used by OS bindings to indicate APIs that are only available in
+    /// earlier versions.
+    /// </remarks>
+    [AttributeUsage(AttributeTargets.Assembly |
+                    AttributeTargets.Class |
+                    AttributeTargets.Constructor |
+                    AttributeTargets.Event |
+                    AttributeTargets.Method |
+                    AttributeTargets.Module |
+                    AttributeTargets.Property |
+                    AttributeTargets.Struct,
+                    AllowMultiple = true, Inherited = false)]
+    public sealed class RemovedInOSPlatformAttribute : OSPlatformAttribute
+    {
+        public RemovedInOSPlatformAttribute(string platformName) : base(platformName)
+        {
+        }
+    }
+}

src/libraries/System.Private.CoreLib/src/System/Runtime/Versioning/TargetPlatformAttribute.cs

@@ -0,0 +1,18 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+namespace System.Runtime.Versioning
+{
+    /// <summary>
+    /// Records the platform that the project targeted.
+    /// </summary>
+    [AttributeUsage(AttributeTargets.Assembly,
+                    AllowMultiple = false, Inherited = false)]
+    public sealed class TargetPlatformAttribute : OSPlatformAttribute
+    {
+        public TargetPlatformAttribute(string platformName) : base(platformName)
+        {
+        }
+    }
+}

src/libraries/System.Runtime/ref/System.Runtime.cs

@@ -9913,6 +9913,31 @@ public FrameworkName(string identifier, System.Version version, string? profile)
         public static bool operator !=(System.Runtime.Versioning.FrameworkName? left, System.Runtime.Versioning.FrameworkName? right) { throw null; }
         public override string ToString() { throw null; }
     }
+    [System.AttributeUsageAttribute(System.AttributeTargets.Assembly | System.AttributeTargets.Class | System.AttributeTargets.Constructor | System.AttributeTargets.Event | System.AttributeTargets.Method | System.AttributeTargets.Module | System.AttributeTargets.Property | System.AttributeTargets.Struct, AllowMultiple = true, Inherited = false)]
+    public sealed class MinimumOSPlatformAttribute : System.Runtime.Versioning.OSPlatformAttribute
+    {
+        public MinimumOSPlatformAttribute(string platformName) : base(platformName) { }
+    }
+    [System.AttributeUsageAttribute(System.AttributeTargets.Assembly | System.AttributeTargets.Class | System.AttributeTargets.Constructor | System.AttributeTargets.Event | System.AttributeTargets.Method | System.AttributeTargets.Module | System.AttributeTargets.Property | System.AttributeTargets.Struct, AllowMultiple = true, Inherited = false)]
+    public sealed class ObsoletedInOSPlatformAttribute : System.Runtime.Versioning.OSPlatformAttribute
+    {
+        public ObsoletedInOSPlatformAttribute(string platformName) : base(platformName) { }
+        public ObsoletedInOSPlatformAttribute(string platformName, string message) : base(platformName) { }
+        public string? Message { get; }
+        public string? Url { get; set; }
+    }
+#pragma warning disable CS3015 // Type has no accessible constructors which use only CLS-compliant types
+    public abstract class OSPlatformAttribute : System.Attribute
+#pragma warning restore CS3015 // Type has no accessible constructors which use only CLS-compliant types
+    {
+        private protected OSPlatformAttribute(string platformName) { }
+        public string PlatformName { get; }
+    }
+    [System.AttributeUsageAttribute(System.AttributeTargets.Assembly | System.AttributeTargets.Class | System.AttributeTargets.Constructor | System.AttributeTargets.Event | System.AttributeTargets.Method | System.AttributeTargets.Module | System.AttributeTargets.Property | System.AttributeTargets.Struct, AllowMultiple = true, Inherited = false)]
+    public sealed class RemovedInOSPlatformAttribute : System.Runtime.Versioning.OSPlatformAttribute
+    {
+        public RemovedInOSPlatformAttribute(string platformName) : base(platformName) { }
+    }
     [System.AttributeUsageAttribute(System.AttributeTargets.Constructor | System.AttributeTargets.Method | System.AttributeTargets.Property, Inherited=false)]
     [System.Diagnostics.ConditionalAttribute("RESOURCE_ANNOTATION_WORK")]
     public sealed partial class ResourceConsumptionAttribute : System.Attribute
@@ -9947,6 +9972,11 @@ public TargetFrameworkAttribute(string frameworkName) { }
         public string? FrameworkDisplayName { get { throw null; } set { } }
         public string FrameworkName { get { throw null; } }
     }
+    [System.AttributeUsageAttribute(System.AttributeTargets.Assembly, AllowMultiple = false, Inherited = false)]
+    public sealed class TargetPlatformAttribute : System.Runtime.Versioning.OSPlatformAttribute
+    {
+        public TargetPlatformAttribute(string platformName) : base(platformName) { }
+    }
     public static partial class VersioningHelper
     {
         public static string MakeVersionSafeName(string? name, System.Runtime.Versioning.ResourceScope from, System.Runtime.Versioning.ResourceScope to) { throw null; }

src/libraries/System.Runtime/tests/System.Runtime.Tests.csproj

@@ -221,6 +221,7 @@
     <Compile Include="System\Runtime\Serialization\OptionalFieldAttributeTests.cs" />
     <Compile Include="System\Runtime\Serialization\SerializationExceptionTests.cs" />
     <Compile Include="System\Runtime\Serialization\StreamingContextTests.cs" />
+    <Compile Include="System\Runtime\Versioning\OSPlatformAttributeTests.cs" />
     <Compile Include="System\Security\SecurityAttributeTests.cs" />
     <Compile Include="System\Security\SecurityExceptionTests.cs" />
     <Compile Include="System\Text\StringBuilderTests.cs" />
@@ -278,4 +279,4 @@
   <ItemGroup>
     <PackageReference Include="Moq" Version="$(MoqVersion)" />
   </ItemGroup>
-</Project>
+</Project>

src/libraries/System.Runtime/tests/System/Runtime/Versioning/OSPlatformAttributeTests.cs

@@ -0,0 +1,55 @@
+using System.Diagnostics.CodeAnalysis;
+using Xunit;
+
+namespace System.Runtime.Versioning.Tests
+{
+    public class OSPlatformAttributeTests
+    {
+        [Theory]
+        [InlineData("Windows10.0")]
+        [InlineData("iOS")]
+        [InlineData("")]
+        public void TestTargetPlatformAttribute(string platformName)
+        {
+            var tpa = new TargetPlatformAttribute(platformName);
+
+            Assert.Equal(platformName, tpa.PlatformName);
+        }
+
+        [Theory]
+        [InlineData("Windows8.0", "Obsolete", "http://test.com/obsoletedInOSPlatform")]
+        [InlineData("Linux", "Message", null)]
+        [InlineData("iOS13", null, null)]
+        [InlineData("", null, "http://test.com/obsoletedInOSPlatform")]
+        public void TestObsoletedInOSPlatformAttribute(string platformName, string message, string url)
+        {
+            var opa = message == null ? new ObsoletedInOSPlatformAttribute(platformName) { Url = url} : new ObsoletedInOSPlatformAttribute(platformName, message) { Url = url };
+
+            Assert.Equal(platformName, opa.PlatformName);
+            Assert.Equal(message, opa.Message);
+            Assert.Equal(url, opa.Url);
+        }
+
+        [Theory]
+        [InlineData("Windows8.0")]
+        [InlineData("Android4.1")]
+        [InlineData("")]
+        public void TestRemovedInOSPlatformAttribute(string platformName)
+        {
+            var tpa = new RemovedInOSPlatformAttribute(platformName);
+
+            Assert.Equal(platformName, tpa.PlatformName);
+        }
+
+        [Theory]
+        [InlineData("Windows10.0")]
+        [InlineData("OSX")]
+        [InlineData("")]
+        public void TestMinimumOSPlatformAttribute(string platformName)
+        {
+            var tpa = new MinimumOSPlatformAttribute(platformName);
+
+            Assert.Equal(platformName, tpa.PlatformName);
+        }
+    }
+}