Resolve ILLink warnings in System.Memory.Data

The current APIs require unreferenced code, since they call into JsonSerializer without providing JsonTypeInfo.

#54979 is logged to add "trim compatible" APIs here.

Author: eerhardt

src/libraries/System.Memory.Data/ref/System.Memory.Data.cs

@@ -9,14 +9,16 @@ namespace System
     public partial class BinaryData
     {
         public BinaryData(byte[] data) { }
+        [System.Diagnostics.CodeAnalysis.RequiresUnreferencedCodeAttribute("JSON serialization and deserialization might require types that cannot be statically analyzed.")]
         public BinaryData(object? jsonSerializable, System.Text.Json.JsonSerializerOptions? options = null, System.Type? type = null) { }
         public BinaryData(System.ReadOnlyMemory<byte> data) { }
         public BinaryData(string data) { }
-        public static BinaryData Empty { get; }
+        public static System.BinaryData Empty { get { throw null; } }
         [System.ComponentModel.EditorBrowsableAttribute(System.ComponentModel.EditorBrowsableState.Never)]
-        public override bool Equals([System.Diagnostics.CodeAnalysis.NotNullWhen(true)] object? obj) { throw null; }
+        public override bool Equals([System.Diagnostics.CodeAnalysis.NotNullWhenAttribute(true)] object? obj) { throw null; }
         public static System.BinaryData FromBytes(byte[] data) { throw null; }
         public static System.BinaryData FromBytes(System.ReadOnlyMemory<byte> data) { throw null; }
+        [System.Diagnostics.CodeAnalysis.RequiresUnreferencedCodeAttribute("JSON serialization and deserialization might require types that cannot be statically analyzed.")]
         public static System.BinaryData FromObjectAsJson<T>(T jsonSerializable, System.Text.Json.JsonSerializerOptions? options = null) { throw null; }
         public static System.BinaryData FromStream(System.IO.Stream stream) { throw null; }
         public static System.Threading.Tasks.Task<System.BinaryData> FromStreamAsync(System.IO.Stream stream, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
@@ -27,6 +29,7 @@ public BinaryData(string data) { }
         public static implicit operator System.ReadOnlySpan<byte> (System.BinaryData? data) { throw null; }
         public byte[] ToArray() { throw null; }
         public System.ReadOnlyMemory<byte> ToMemory() { throw null; }
+        [System.Diagnostics.CodeAnalysis.RequiresUnreferencedCodeAttribute("JSON serialization and deserialization might require types that cannot be statically analyzed.")]
         public T? ToObjectFromJson<T>(System.Text.Json.JsonSerializerOptions? options = null) { throw null; }
         public System.IO.Stream ToStream() { throw null; }
         public override string ToString() { throw null; }

src/libraries/System.Memory.Data/ref/System.Memory.Data.csproj

@@ -6,6 +6,9 @@
   <ItemGroup>
     <Compile Include="System.Memory.Data.cs" />
   </ItemGroup>
+  <ItemGroup Condition="!$([MSBuild]::IsTargetFrameworkCompatible('$(TargetFramework)', 'net5.0'))">
+    <Compile Include="$(CoreLibSharedDir)System\Diagnostics\CodeAnalysis\RequiresUnreferencedCodeAttribute.cs" />
+  </ItemGroup>
   <ItemGroup>
     <ProjectReference Include="$(LibrariesProjectRoot)System.Text.Json\ref\System.Text.Json.csproj" />
   </ItemGroup>

src/libraries/System.Memory.Data/src/ILLink/ILLink.Suppressions.xml

@@ -13,6 +13,10 @@
              Link="Common\System\Threading\Tasks\TaskToApm.cs" />
   </ItemGroup>
 
+  <ItemGroup Condition="!$([MSBuild]::IsTargetFrameworkCompatible('$(TargetFramework)', 'net5.0'))">
+    <Compile Include="$(CoreLibSharedDir)System\Diagnostics\CodeAnalysis\RequiresUnreferencedCodeAttribute.cs" />
+  </ItemGroup>
+
   <ItemGroup>
     <ProjectReference Include="$(LibrariesProjectRoot)System.Text.Json\src\System.Text.Json.csproj" />
   </ItemGroup>

src/libraries/System.Memory.Data/src/System.Memory.Data.csproj

@@ -4,7 +4,6 @@
 using System.ComponentModel;
 using System.Diagnostics.CodeAnalysis;
 using System.IO;
-using System.Runtime.InteropServices;
 using System.Text;
 using System.Text.Json;
 using System.Threading;
@@ -17,6 +16,8 @@ namespace System
     /// </summary>
     public class BinaryData
     {
+        private const string JsonSerializerRequiresUnreferencedCode = "JSON serialization and deserialization might require types that cannot be statically analyzed.";
+
         /// <summary>
         /// The backing store for the <see cref="BinaryData"/> instance.
         /// </summary>
@@ -41,12 +42,12 @@ public BinaryData(byte[] data)
         /// Creates a <see cref="BinaryData"/> instance by serializing the provided object to JSON
         /// using <see cref="JsonSerializer"/>.
         /// </summary>
-        ///
         /// <param name="jsonSerializable">The object that will be serialized to JSON using
         /// <see cref="JsonSerializer"/>.</param>
         /// <param name="options">The options to use when serializing to JSON.</param>
         /// <param name="type">The type to use when serializing the data. If not specified, <see cref="object.GetType"/> will
         /// be used to determine the type.</param>
+        [RequiresUnreferencedCode(JsonSerializerRequiresUnreferencedCode)]
         public BinaryData(object? jsonSerializable, JsonSerializerOptions? options = default, Type? type = default)
         {
             type ??= jsonSerializable?.GetType() ?? typeof(object);
@@ -177,12 +178,11 @@ private static async Task<BinaryData> FromStreamAsync(Stream stream, bool async,
         /// Creates a <see cref="BinaryData"/> instance by serializing the provided object using
         /// the <see cref="JsonSerializer"/>.
         /// </summary>
-        ///
         /// <typeparam name="T">The type to use when serializing the data.</typeparam>
         /// <param name="jsonSerializable">The data to use.</param>
         /// <param name="options">The options to use when serializing to JSON.</param>
-        ///
         /// <returns>A value representing the UTF-8 encoding of the JSON representation of <paramref name="jsonSerializable" />.</returns>
+        [RequiresUnreferencedCode(JsonSerializerRequiresUnreferencedCode)]
         public static BinaryData FromObjectAsJson<T>(T jsonSerializable, JsonSerializerOptions? options = default)
         {
             byte[] buffer = JsonSerializer.SerializeToUtf8Bytes(jsonSerializable, typeof(T), options);
@@ -230,6 +230,7 @@ public override unsafe string ToString()
         /// converted to.</typeparam>
         /// <param name="options">The <see cref="JsonSerializerOptions"/> to use when serializing to JSON.</param>
         /// <returns>The data converted to the specified type.</returns>
+        [RequiresUnreferencedCode(JsonSerializerRequiresUnreferencedCode)]
         public T? ToObjectFromJson<T>(JsonSerializerOptions? options = default)
         {
             return JsonSerializer.Deserialize<T>(_bytes.Span, options);