Add RequiresDynamicCodeAttribute to runtime

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

@@ -252,6 +252,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)System\DefaultBinder.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Delegate.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Diagnostics\CodeAnalysis\RequiresAssemblyFilesAttribute.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\Diagnostics\CodeAnalysis\RequiresDynamicCodeAttribute.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Diagnostics\CodeAnalysis\RequiresUnreferencedCodeAttribute.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Diagnostics\CodeAnalysis\DynamicallyAccessedMemberTypes.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Diagnostics\CodeAnalysis\DynamicallyAccessedMembersAttribute.cs" />

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

@@ -0,0 +1,39 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+namespace System.Diagnostics.CodeAnalysis
+{
+    /// <summary>
+    /// Indicates that the specified method requires the ability to generate new code at runtime,
+    /// for example through <see cref="System.Reflection"/>.
+    /// </summary>
+    /// <remarks>
+    /// This allows tools to understand which methods are unsafe to call when compiling ahead of time.
+    /// </remarks>
+    [AttributeUsage(AttributeTargets.Method | AttributeTargets.Constructor, Inherited = false)]
+    public sealed class RequiresDynamicCodeAttribute : Attribute
+    {
+        /// <summary>
+        /// Initializes a new instance of the <see cref="RequiresDynamicCodeAttribute"/> class
+        /// with the specified message.
+        /// </summary>
+        /// <param name="message">
+        /// A message that contains information about the usage of dynamic code.
+        /// </param>
+        public RequiresDynamicCodeAttribute(string message)
+        {
+            Message = message;
+        }
+
+        /// <summary>
+        /// Gets a message that contains information about the usage of dynamic code.
+        /// </summary>
+        public string Message { get; }
+
+        /// <summary>
+        /// Gets or sets an optional URL that contains more information about the method,
+        /// why it requires dynamic code, and what options a consumer has to deal with it.
+        /// </summary>
+        public string? Url { get; set; }
+    }
+}

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

@@ -9084,6 +9084,13 @@ public sealed partial class RequiresAssemblyFilesAttribute : System.Attribute
         public string? Message { get { throw null; } }
         public string? Url { get { throw null; } set { } }
     }
+    [System.AttributeUsageAttribute(System.AttributeTargets.Constructor | System.AttributeTargets.Method, Inherited = false)]
+    public sealed partial class RequiresDynamicCodeAttribute : System.Attribute
+    {
+        public RequiresDynamicCodeAttribute(string message) { }
+        public string Message { get { throw null; } }
+        public string? Url { get { throw null; } set { } }
+    }
     [System.AttributeUsageAttribute(System.AttributeTargets.Class | System.AttributeTargets.Constructor | System.AttributeTargets.Method, Inherited=false)]
     public sealed partial class RequiresUnreferencedCodeAttribute : System.Attribute
     {

src/libraries/System.Runtime/tests/System/Diagnostics/CodeAnalysis/RequiresDynamicCodeAttributeTests.cs

@@ -0,0 +1,34 @@
+// 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 RequiresDynamicCodeAttributeTests
+    {
+        [Fact]
+        public void TestConstructor()
+        {
+            var attr = new RequiresDynamicCodeAttribute("User Message");
+
+            Assert.Equal("User Message", attr.Message);
+            Assert.Null(attr.Url);
+        }
+
+        [Theory]
+        [InlineData("https://dot.net")]
+        [InlineData("")]
+        [InlineData(null)]
+        public void TestSetUrl(string url)
+        {
+            var attr = new RequiresDynamicCodeAttribute("User Message")
+            {
+                Url = url
+            };
+
+            Assert.Equal("User Message", attr.Message);
+            Assert.Equal(url, attr.Url);
+        }
+    }
+}