JSON support required properties

src/libraries/System.Text.Json/ref/System.Text.Json.cs

@@ -944,6 +944,11 @@ public sealed partial class JsonPropertyOrderAttribute : System.Text.Json.Serial
         public JsonPropertyOrderAttribute(int order) { }
         public int Order { get { throw null; } }
     }
+    [System.AttributeUsageAttribute(System.AttributeTargets.Field | System.AttributeTargets.Property, AllowMultiple = false)]
+    public sealed partial class JsonRequiredAttribute : System.Text.Json.Serialization.JsonAttribute
+    {
+        public JsonRequiredAttribute() { }
+    }
     [System.AttributeUsageAttribute(System.AttributeTargets.Class, AllowMultiple=true)]
     public sealed partial class JsonSerializableAttribute : System.Text.Json.Serialization.JsonAttribute
     {
@@ -1152,6 +1157,7 @@ internal JsonPropertyInfo() { }
         public System.Text.Json.Serialization.JsonConverter? CustomConverter { get { throw null; } set { } }
         public System.Func<object, object?>? Get { get { throw null; } set { } }
         public bool IsExtensionData { get { throw null; } set { } }
+        public bool IsRequired { get { throw null; } set { } }
         public string Name { get { throw null; } set { } }
         public System.Text.Json.Serialization.JsonNumberHandling? NumberHandling { get { throw null; } set { } }
         public System.Text.Json.JsonSerializerOptions Options { get { throw null; } }

src/libraries/System.Text.Json/src/System.Text.Json.csproj

@@ -100,6 +100,7 @@ The System.Text.Json library is built-in as part of the shared framework in .NET
     <Compile Include="System\Text\Json\Serialization\Attributes\JsonNumberHandlingAttribute.cs" />
     <Compile Include="System\Text\Json\Serialization\Attributes\JsonPolymorphicAttribute.cs" />
     <Compile Include="System\Text\Json\Serialization\Attributes\JsonPropertyNameAttribute.cs" />
+    <Compile Include="System\Text\Json\Serialization\Attributes\JsonRequiredAttribute.cs" />
     <Compile Include="System\Text\Json\Serialization\Attributes\JsonPropertyOrderAttribute.cs" />
     <Compile Include="System\Text\Json\Serialization\Converters\CastingConverter.cs" />
     <Compile Include="System\Text\Json\Serialization\Converters\Collection\ImmutableDictionaryOfTKeyTValueConverterWithReflection.cs" />

src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Attributes/JsonRequiredAttribute.cs

@@ -0,0 +1,19 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+namespace System.Text.Json.Serialization
+{
+    /// <summary>
+    /// Specifies the property is required when deserializing.
+    /// </summary>
+    [AttributeUsage(AttributeTargets.Property | AttributeTargets.Field, AllowMultiple = false)]
+    public sealed class JsonRequiredAttribute : JsonAttribute
+    {
+        /// <summary>
+        /// Initializes a new instance of <see cref="JsonRequiredAttribute"/>.
+        /// </summary>
+        public JsonRequiredAttribute()
+        {
+        }
+    }
+}

src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Metadata/JsonPropertyInfo.cs

@@ -203,7 +203,18 @@ public bool IsExtensionData
 
         private bool _isExtensionDataProperty;
 
-        internal bool IsRequired
+        /// <summary>
+        /// Specifies whether the current property is required during deserialization.
+        /// </summary>
+        /// <exception cref="InvalidOperationException">
+        /// The <see cref="JsonPropertyInfo"/> instance has been locked for further modification.
+        /// </exception>
+        /// <remarks>
+        /// For contracts originating from <see cref="DefaultJsonTypeInfoResolver"/> or <see cref="JsonSerializerContext"/>,
+        /// the value of this property will be mapped from based on presence of <see cref="JsonRequiredAttribute"/> annotation or presence of <see langword="required"/> keyword.
+        /// If SetsRequiredMembersAttribute is specified on the constructor the <see langword="required"/> keyword will not influence value of this property.
+        /// </remarks>
+        public bool IsRequired
         {
             get => _isRequired;
             set
@@ -506,10 +517,8 @@ private bool NumberHandingIsApplicable()
 
         private void DetermineIsRequired(MemberInfo memberInfo, bool shouldCheckForRequiredKeyword)
         {
-            if (shouldCheckForRequiredKeyword && memberInfo.HasRequiredMemberAttribute())
-            {
-                IsRequired = true;
-            }
+            IsRequired = memberInfo.GetCustomAttribute<JsonRequiredAttribute>(inherit: false) != null
+                || (shouldCheckForRequiredKeyword && memberInfo.HasRequiredMemberAttribute());
         }
 
         internal abstract bool GetMemberAndWriteJson(object obj, ref WriteStack state, Utf8JsonWriter writer);

src/libraries/System.Text.Json/tests/System.Text.Json.Tests/Serialization/JsonSerializerWrapper.Reflection.cs

@@ -646,10 +646,9 @@ public static JsonSerializerOptions ResolveOptionsInstanceWithSmallBuffer(JsonSe
 
                 JsonSerializerOptions smallBufferCopy = new JsonSerializerOptions(options)
                 {
-                    // Copy the resolver explicitly until https://github.com/dotnet/aspnetcore/issues/38720 is resolved.
-                    TypeInfoResolver = options.TypeInfoResolver,
                     DefaultBufferSize = 1,
                 };
+
                 s_smallBufferMap.Add(options, smallBufferCopy);
                 return smallBufferCopy;
             }