Add unsafe evolution attributes

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

@@ -896,6 +896,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)System\Runtime\CompilerServices\IteratorStateMachineAttribute.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Runtime\CompilerServices\ITuple.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Runtime\CompilerServices\LoadHint.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\Runtime\CompilerServices\MemorySafetyRulesAttribute.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Runtime\CompilerServices\MethodCodeType.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Runtime\CompilerServices\MethodImplAttribute.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Runtime\CompilerServices\MethodImplOptions.cs" />

src/libraries/System.Private.CoreLib/src/System/Diagnostics/CodeAnalysis/RequiresUnsafeAttribute.cs

@@ -4,16 +4,17 @@
 namespace System.Diagnostics.CodeAnalysis
 {
     /// <summary>
-    /// Indicates that the specified method requires unsafe code that may not be available
-    /// in all execution environments.
+    /// Indicates that the specified member requires the caller to be in an unsafe context.
     /// </summary>
-    /// <remarks>
-    /// This allows tools to understand which methods are unsafe to call when targeting
-    /// environments that do not support unsafe code.
-    /// </remarks>
-    [AttributeUsage(AttributeTargets.Method | AttributeTargets.Constructor, Inherited = false)]
-    [Conditional("DEBUG")]
-    internal sealed class RequiresUnsafeAttribute : Attribute
+    [AttributeUsage(
+        AttributeTargets.Constructor | AttributeTargets.Event | AttributeTargets.Method | AttributeTargets.Property,
+        Inherited = false,
+        AllowMultiple = false)]
+    public sealed class RequiresUnsafeAttribute : Attribute
     {
+        /// <summary>
+        /// Initializes a new instance of the <see cref="RequiresUnsafeAttribute"/> class.
+        /// </summary>
+        public RequiresUnsafeAttribute() { }
     }
 }

src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/MemorySafetyRulesAttribute.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.
+
+using System.ComponentModel;
+
+namespace System.Runtime.CompilerServices
+{
+    /// <summary>Indicates the version of the memory safety rules used when the module was compiled.</summary>
+    [EditorBrowsable(EditorBrowsableState.Never)]
+    [AttributeUsage(AttributeTargets.Module, Inherited = false, AllowMultiple = false)]
+    public sealed class MemorySafetyRulesAttribute : Attribute
+    {
+        /// <summary>Initializes a new instance of the <see cref="MemorySafetyRulesAttribute"/> class.</summary>
+        /// <param name="version">The version of the memory safety rules used when the module was compiled.</param>
+        public MemorySafetyRulesAttribute(int version) => Version = version;
+
+        /// <summary>Gets the version of the memory safety rules used when the module was compiled.</summary>
+        public int Version { get; }
+    }
+}

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

@@ -9110,6 +9110,11 @@ public RequiresUnreferencedCodeAttribute(string message) { }
         public string Message { get { throw null; } }
         public string? Url { get { throw null; } set { } }
     }
+    [System.AttributeUsageAttribute(System.AttributeTargets.Constructor | System.AttributeTargets.Event | System.AttributeTargets.Method | System.AttributeTargets.Property, Inherited=false, AllowMultiple=false)]
+    public sealed partial class RequiresUnsafeAttribute : System.Attribute
+    {
+        public RequiresUnsafeAttribute() { }
+    }
     [System.AttributeUsageAttribute(System.AttributeTargets.Constructor, AllowMultiple=false, Inherited=false)]
     public sealed partial class SetsRequiredMembersAttribute : System.Attribute
     {
@@ -14028,6 +14033,13 @@ public enum LoadHint
         Always = 1,
         Sometimes = 2,
     }
+    [System.AttributeUsageAttribute(System.AttributeTargets.Module, Inherited=false, AllowMultiple=false)]
+    [System.ComponentModel.EditorBrowsableAttribute(System.ComponentModel.EditorBrowsableState.Never)]
+    public sealed partial class MemorySafetyRulesAttribute : System.Attribute
+    {
+        public MemorySafetyRulesAttribute(int version) { }
+        public int Version { get { throw null; } }
+    }
     public enum MethodCodeType
     {
         IL = 0,

src/libraries/System.Runtime/tests/System.Runtime.Tests/System/Diagnostics/CodeAnalysis/RequiresUnsafeAttributeTests.cs

@@ -0,0 +1,15 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using Xunit;
+
+namespace System.Diagnostics.CodeAnalysis.Tests;
+
+public class RequiresUnsafeAttributeTests
+{
+    [Fact]
+    public static void TestConstructor()
+    {
+        new RequiresUnsafeAttribute();
+    }
+}

src/libraries/System.Runtime/tests/System.Runtime.Tests/System/Runtime/CompilerServices/AttributesTests.cs

@@ -235,6 +235,17 @@ public static void RefSafetyRulesAttributeTests(int version)
             Assert.Equal(version, attr.Version);
         }
 
+        [Theory]
+        [InlineData(-1)]
+        [InlineData(0)]
+        [InlineData(2)]
+        [InlineData(42)]
+        public static void MemorySafetyRulesAttributeTests(int version)
+        {
+            var attr = new MemorySafetyRulesAttribute(version);
+            Assert.Equal(version, attr.Version);
+        }
+
         [Theory]
         [InlineData("1")]
         [InlineData("2")]