Populate JsonPropertyInfo.AttributeProvider in the source generator.

src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Metadata/DefaultJsonTypeInfoResolver.Helpers.cs

@@ -113,6 +113,33 @@ private static void PopulateProperties(JsonTypeInfo typeInfo)
             }
         }
 
+        private const BindingFlags AllInstanceMembers =
+            BindingFlags.Instance |
+            BindingFlags.Public |
+            BindingFlags.NonPublic |
+            BindingFlags.DeclaredOnly;
+
+        /// <summary>
+        /// Looks up the type for a member matching the given name and member type.
+        /// </summary>
+        [RequiresUnreferencedCode(JsonSerializer.SerializationUnreferencedCodeMessage)]
+        internal static MemberInfo? LookupMemberInfo(Type type, MemberTypes memberType, string name)
+        {
+            Debug.Assert(memberType is MemberTypes.Field or MemberTypes.Property);
+
+            // Walk the type hierarchy starting from the current type up to the base type(s)
+            foreach (Type t in type.GetSortedTypeHierarchy())
+            {
+                MemberInfo[] members = t.GetMember(name, memberType, AllInstanceMembers);
+                if (members.Length > 0)
+                {
+                    return members[0];
+                }
+            }
+
+            return null;
+        }
+
         [RequiresUnreferencedCode(JsonSerializer.SerializationUnreferencedCodeMessage)]
         [RequiresDynamicCode(JsonSerializer.SerializationRequiresDynamicCodeMessage)]
         private static void AddMembersDeclaredBySuperType(
@@ -124,17 +151,11 @@ private static void AddMembersDeclaredBySuperType(
             Debug.Assert(!typeInfo.IsReadOnly);
             Debug.Assert(currentType.IsAssignableFrom(typeInfo.Type));
 
-            const BindingFlags BindingFlags =
-                BindingFlags.Instance |
-                BindingFlags.Public |
-                BindingFlags.NonPublic |
-                BindingFlags.DeclaredOnly;
-
             // Compiler adds RequiredMemberAttribute to type if any of the members are marked with 'required' keyword.
             bool shouldCheckMembersForRequiredMemberAttribute =
                 !constructorHasSetsRequiredMembersAttribute && currentType.HasRequiredMemberAttribute();
 
-            foreach (PropertyInfo propertyInfo in currentType.GetProperties(BindingFlags))
+            foreach (PropertyInfo propertyInfo in currentType.GetProperties(AllInstanceMembers))
             {
                 // Ignore indexers and virtual properties that have overrides that were [JsonIgnore]d.
                 if (propertyInfo.GetIndexParameters().Length > 0 ||
@@ -160,7 +181,7 @@ private static void AddMembersDeclaredBySuperType(
                 }
             }
 
-            foreach (FieldInfo fieldInfo in currentType.GetFields(BindingFlags))
+            foreach (FieldInfo fieldInfo in currentType.GetFields(AllInstanceMembers))
             {
                 bool hasJsonIncludeAtribute = fieldInfo.GetCustomAttribute<JsonIncludeAttribute>(inherit: false) != null;
                 if (hasJsonIncludeAtribute || (fieldInfo.IsPublic && typeInfo.Options.IncludeFields))

src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Metadata/JsonMetadataServices.Helpers.cs

@@ -190,6 +190,7 @@ private static JsonPropertyInfo<T> CreatePropertyInfoCore<T>(JsonPropertyInfoVal
             propertyInfo.IgnoreCondition = propertyInfoValues.IgnoreCondition;
             propertyInfo.JsonTypeInfo = propertyInfoValues.PropertyTypeInfo;
             propertyInfo.NumberHandling = propertyInfoValues.NumberHandling;
+            propertyInfo.IsSourceGenerated = true;
 
             return propertyInfo;
         }

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

@@ -5,6 +5,7 @@
 using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
 using System.Reflection;
+using System.Threading;
 
 namespace System.Text.Json.Serialization.Metadata
 {
@@ -162,17 +163,39 @@ internal JsonIgnoreCondition? IgnoreCondition
         /// </remarks>
         public ICustomAttributeProvider? AttributeProvider
         {
-            get => _attributeProvider;
+            get
+            {
+                ICustomAttributeProvider attributeProvider = _attributeProvider ?? InitializeAttributeProvider();
+                return ReferenceEquals(attributeProvider, s_nullAttributeProvider) ? null : attributeProvider;
+            }
             set
             {
                 VerifyMutable();
 
-                _attributeProvider = value;
+                _attributeProvider = value ?? s_nullAttributeProvider;
             }
         }
 
-        private JsonObjectCreationHandling? _objectCreationHandling;
-        internal JsonObjectCreationHandling EffectiveObjectCreationHandling { get; private set; }
+        // Because the getter can initialize its own backing field, we want to avoid races between the getter and setter.
+        // This is done using CAS on the single _attributeProvider field which employs the following encoding:
+        // null: not initialized, s_nullAttributeProvider: null, otherwise: _attributeProvider
+        private ICustomAttributeProvider? _attributeProvider;
+        private static readonly ICustomAttributeProvider s_nullAttributeProvider = typeof(NullAttributeProviderPlaceholder);
+        private sealed class NullAttributeProviderPlaceholder;
+
+        [UnconditionalSuppressMessage("Trimming", "IL2026:RequiresUnreferencedCode",
+            Justification = "Looks up members that are already being referenced by the source generator.")]
+        private ICustomAttributeProvider InitializeAttributeProvider()
+        {
+            // If the property is source generated, perform a reflection lookup of its MemberInfo.
+            // Avoids overhead of reflection at startup and makes this method trimmable if unused.
+            ICustomAttributeProvider? provider = IsSourceGenerated && MemberName != null
+                ? DefaultJsonTypeInfoResolver.LookupMemberInfo(DeclaringType, MemberType, MemberName)
+                : null;
+
+            provider ??= s_nullAttributeProvider;
+            return Interlocked.CompareExchange(ref _attributeProvider, provider, null) ?? provider;
+        }
 
         /// <summary>
         /// Gets or sets a value indicating if the property or field should be replaced or populated during deserialization.
@@ -202,10 +225,13 @@ public JsonObjectCreationHandling? ObjectCreationHandling
             }
         }
 
-        private ICustomAttributeProvider? _attributeProvider;
+        private JsonObjectCreationHandling? _objectCreationHandling;
+        internal JsonObjectCreationHandling EffectiveObjectCreationHandling { get; private set; }
+
         internal string? MemberName { get; set; }
         internal MemberTypes MemberType { get; set; }
         internal bool IsVirtual { get; set; }
+        internal bool IsSourceGenerated { get; set; }
 
         /// <summary>
         /// Specifies whether the current property is a special extension data property.

src/libraries/System.Text.Json/tests/System.Text.Json.SourceGeneration.Tests/ContextClasses.cs

@@ -58,6 +58,7 @@ public interface ITestContext
         public JsonTypeInfo<TypeWithDerivedAttribute> TypeWithDerivedAttribute { get; }
         public JsonTypeInfo<PolymorphicClass> PolymorphicClass { get; }
         public JsonTypeInfo<PocoWithNumberHandlingAttr> PocoWithNumberHandlingAttr { get; }
+        public JsonTypeInfo<PocoWithMixedVisibilityMembers> PocoWithMixedVisibilityMembers { get; }
     }
 
     internal partial class JsonContext : JsonSerializerContext

src/libraries/System.Text.Json/tests/System.Text.Json.SourceGeneration.Tests/MetadataAndSerializationContextTests.cs

@@ -54,6 +54,7 @@ namespace System.Text.Json.SourceGeneration.Tests
     [JsonSerializable(typeof(TypeWithDerivedAttribute))]
     [JsonSerializable(typeof(PolymorphicClass))]
     [JsonSerializable(typeof(PocoWithNumberHandlingAttr))]
+    [JsonSerializable(typeof(PocoWithMixedVisibilityMembers))]
     internal partial class MetadataAndSerializationContext : JsonSerializerContext, ITestContext
     {
         public JsonSourceGenerationMode JsonSourceGenerationMode => JsonSourceGenerationMode.Default;

src/libraries/System.Text.Json/tests/System.Text.Json.SourceGeneration.Tests/MetadataContextTests.cs

@@ -53,6 +53,7 @@ namespace System.Text.Json.SourceGeneration.Tests
     [JsonSerializable(typeof(TypeWithDerivedAttribute), GenerationMode = JsonSourceGenerationMode.Metadata)]
     [JsonSerializable(typeof(PolymorphicClass), GenerationMode = JsonSourceGenerationMode.Metadata)]
     [JsonSerializable(typeof(PocoWithNumberHandlingAttr), GenerationMode = JsonSourceGenerationMode.Metadata)]
+    [JsonSerializable(typeof(PocoWithMixedVisibilityMembers), GenerationMode = JsonSourceGenerationMode.Metadata)]
     internal partial class MetadataWithPerTypeAttributeContext : JsonSerializerContext, ITestContext
     {
         public JsonSourceGenerationMode JsonSourceGenerationMode => JsonSourceGenerationMode.Metadata;
@@ -156,6 +157,7 @@ public override void EnsureFastPathGeneratedAsExpected()
     [JsonSerializable(typeof(TypeWithDerivedAttribute))]
     [JsonSerializable(typeof(PolymorphicClass))]
     [JsonSerializable(typeof(PocoWithNumberHandlingAttr))]
+    [JsonSerializable(typeof(PocoWithMixedVisibilityMembers))]
     internal partial class MetadataContext : JsonSerializerContext, ITestContext
     {
         public JsonSourceGenerationMode JsonSourceGenerationMode => JsonSourceGenerationMode.Metadata;

src/libraries/System.Text.Json/tests/System.Text.Json.SourceGeneration.Tests/MixedModeContextTests.cs

@@ -54,6 +54,7 @@ namespace System.Text.Json.SourceGeneration.Tests
     [JsonSerializable(typeof(TypeWithDerivedAttribute), GenerationMode = JsonSourceGenerationMode.Metadata | JsonSourceGenerationMode.Serialization)]
     [JsonSerializable(typeof(PolymorphicClass), GenerationMode = JsonSourceGenerationMode.Metadata | JsonSourceGenerationMode.Serialization)]
     [JsonSerializable(typeof(PocoWithNumberHandlingAttr), GenerationMode = JsonSourceGenerationMode.Metadata | JsonSourceGenerationMode.Serialization)]
+    [JsonSerializable(typeof(PocoWithMixedVisibilityMembers), GenerationMode = JsonSourceGenerationMode.Metadata | JsonSourceGenerationMode.Serialization)]
     internal partial class MixedModeContext : JsonSerializerContext, ITestContext
     {
         public JsonSourceGenerationMode JsonSourceGenerationMode => JsonSourceGenerationMode.Metadata | JsonSourceGenerationMode.Serialization;

src/libraries/System.Text.Json/tests/System.Text.Json.SourceGeneration.Tests/RealWorldContextTests.cs

@@ -4,6 +4,7 @@
 using System.Collections.Generic;
 using System.IO;
 using System.Linq;
+using System.Reflection;
 using System.Text.Json.Serialization;
 using System.Text.Json.Serialization.Metadata;
 using Xunit;
@@ -1111,5 +1112,36 @@ public void NumberHandlingHonoredOnPoco()
                 JsonTestHelper.AssertJsonEqual(@"{""Id"":""0""}", JsonSerializer.Serialize(new PocoWithNumberHandlingAttr(), DefaultContext.PocoWithNumberHandlingAttr));
             }
         }
+
+        [Theory]
+        [InlineData(MemberTypes.Property, nameof(PocoWithMixedVisibilityMembers.PublicProperty))]
+        [InlineData(MemberTypes.Field, nameof(PocoWithMixedVisibilityMembers.PublicField))]
+        [InlineData(MemberTypes.Property, nameof(PocoWithMixedVisibilityMembers.InternalProperty))]
+        [InlineData(MemberTypes.Field, nameof(PocoWithMixedVisibilityMembers.InternalField))]
+        [InlineData(MemberTypes.Property, nameof(PocoWithMixedVisibilityMembers.PropertyWithCustomName), "customProp")]
+        [InlineData(MemberTypes.Field, nameof(PocoWithMixedVisibilityMembers.FieldWithCustomName), "customField")]
+        [InlineData(MemberTypes.Property, nameof(PocoWithMixedVisibilityMembers.BaseProperty))]
+        [InlineData(MemberTypes.Property, nameof(PocoWithMixedVisibilityMembers.ShadowProperty))]
+        public void JsonPropertyInfo_PopulatesAttributeProvider(MemberTypes memberType, string propertyName, string? jsonPropertyName = null)
+        {
+            if (DefaultContext.JsonSourceGenerationMode is JsonSourceGenerationMode.Serialization)
+            {
+                return; // No metadata generated
+            }
+
+            JsonTypeInfo typeInfo = DefaultContext.PocoWithMixedVisibilityMembers;
+            string name = jsonPropertyName ?? propertyName;
+            JsonPropertyInfo prop = typeInfo.Properties.FirstOrDefault(prop => prop.Name == name);
+            Assert.NotNull(prop);
+
+            MemberInfo memberInfo = Assert.IsAssignableFrom<MemberInfo>(prop.AttributeProvider);
+            string? actualJsonPropertyName = memberInfo.GetCustomAttribute<JsonPropertyNameAttribute>()?.Name;
+
+            Assert.True(memberInfo.DeclaringType.IsAssignableFrom(typeInfo.Type));
+            Assert.Equal(memberType, memberInfo.MemberType);
+            Assert.Equal(prop.PropertyType, memberInfo is PropertyInfo p ? p.PropertyType : ((FieldInfo)memberInfo).FieldType);
+            Assert.Equal(propertyName, memberInfo.Name);
+            Assert.Equal(jsonPropertyName, actualJsonPropertyName);
+        }
     }
 }

src/libraries/System.Text.Json/tests/System.Text.Json.SourceGeneration.Tests/SerializationContextTests.cs

@@ -55,6 +55,7 @@ namespace System.Text.Json.SourceGeneration.Tests
     [JsonSerializable(typeof(TypeWithDerivedAttribute))]
     [JsonSerializable(typeof(PolymorphicClass))]
     [JsonSerializable(typeof(PocoWithNumberHandlingAttr))]
+    [JsonSerializable(typeof(PocoWithMixedVisibilityMembers))]
     internal partial class SerializationContext : JsonSerializerContext, ITestContext
     {
         public JsonSourceGenerationMode JsonSourceGenerationMode => JsonSourceGenerationMode.Serialization;
@@ -109,6 +110,7 @@ internal partial class SerializationContext : JsonSerializerContext, ITestContex
     [JsonSerializable(typeof(TypeWithDerivedAttribute), GenerationMode = JsonSourceGenerationMode.Serialization)]
     [JsonSerializable(typeof(PolymorphicClass), GenerationMode = JsonSourceGenerationMode.Serialization)]
     [JsonSerializable(typeof(PocoWithNumberHandlingAttr), GenerationMode = JsonSourceGenerationMode.Serialization)]
+    [JsonSerializable(typeof(PocoWithMixedVisibilityMembers), GenerationMode = JsonSourceGenerationMode.Serialization)]
     internal partial class SerializationWithPerTypeAttributeContext : JsonSerializerContext, ITestContext
     {
         public JsonSourceGenerationMode JsonSourceGenerationMode => JsonSourceGenerationMode.Serialization;
@@ -162,6 +164,7 @@ internal partial class SerializationWithPerTypeAttributeContext : JsonSerializer
     [JsonSerializable(typeof(TypeWithDerivedAttribute), GenerationMode = JsonSourceGenerationMode.Serialization)]
     [JsonSerializable(typeof(PolymorphicClass), GenerationMode = JsonSourceGenerationMode.Serialization)]
     [JsonSerializable(typeof(PocoWithNumberHandlingAttr), GenerationMode = JsonSourceGenerationMode.Serialization)]
+    [JsonSerializable(typeof(PocoWithMixedVisibilityMembers), GenerationMode = JsonSourceGenerationMode.Serialization)]
     internal partial class SerializationContextWithCamelCase : JsonSerializerContext, ITestContext
     {
         public JsonSourceGenerationMode JsonSourceGenerationMode => JsonSourceGenerationMode.Serialization;

src/libraries/System.Text.Json/tests/System.Text.Json.SourceGeneration.Tests/TestClasses.cs

@@ -305,4 +305,32 @@ public class PocoWithNumberHandlingAttr
     {
         public int Id { get; set; }
     }
+
+    public class PocoWithMixedVisibilityMembersBase
+    {
+        public string BaseProperty { get; set; }
+        public string ShadowProperty { get; set; }
+    }
+
+    public class PocoWithMixedVisibilityMembers : PocoWithMixedVisibilityMembersBase
+    {
+        public string PublicProperty { get; set; }
+
+        [JsonInclude]
+        public string PublicField;
+
+        [JsonInclude]
+        internal int InternalProperty { get; set; }
+
+        [JsonInclude]
+        internal int InternalField;
+
+        [JsonPropertyName("customProp")]
+        public string PropertyWithCustomName { get; set; }
+
+        [JsonInclude, JsonPropertyName("customField")]
+        public string FieldWithCustomName;
+
+        public new int ShadowProperty { get; set; }
+    }
 }