[WIP] Fix unexpected nullability in get-only properties for JSON schema

src/libraries/System.Text.Json/gen/JsonSourceGenerator.Emitter.cs

@@ -932,7 +932,7 @@ property.DefaultIgnoreCondition is JsonIgnoreCondition.Always &&
                     {
                         writer.WriteLine($"properties[{i}].IsGetNullable = false;");
                     }
-                    if (property.IsSetterNonNullableAnnotation)
+                    if (property.IsSetterNonNullableAnnotation || property.IsReadOnly)
                     {
                         writer.WriteLine($"properties[{i}].IsSetNullable = false;");
                     }

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

@@ -952,19 +952,21 @@ private static void DeterminePropertyNullability(JsonPropertyInfo propertyInfo,
                 return;
             }
 
-            NullabilityInfo nullabilityInfo;
             if (propertyInfo.MemberType is MemberTypes.Property)
             {
-                nullabilityInfo = nullabilityCtx.Create((PropertyInfo)memberInfo);
+                var reflectionPropertyInfo = (PropertyInfo)memberInfo;
+                NullabilityInfo nullabilityInfo = nullabilityCtx.Create(reflectionPropertyInfo);
+                propertyInfo.IsGetNullable = reflectionPropertyInfo.GetMethod is not null && nullabilityInfo.ReadState is not NullabilityState.NotNull;
+                propertyInfo.IsSetNullable = reflectionPropertyInfo.SetMethod is not null && nullabilityInfo.WriteState is not NullabilityState.NotNull;
             }
             else
             {
                 Debug.Assert(propertyInfo.MemberType is MemberTypes.Field);
-                nullabilityInfo = nullabilityCtx.Create((FieldInfo)memberInfo);
+                var fieldInfo = (FieldInfo)memberInfo;
+                NullabilityInfo nullabilityInfo = nullabilityCtx.Create(fieldInfo);
+                propertyInfo.IsGetNullable = nullabilityInfo.ReadState is not NullabilityState.NotNull;
+                propertyInfo.IsSetNullable = !fieldInfo.IsInitOnly && nullabilityInfo.WriteState is not NullabilityState.NotNull;
             }
-
-            propertyInfo.IsGetNullable = nullabilityInfo.ReadState is not NullabilityState.NotNull;
-            propertyInfo.IsSetNullable = nullabilityInfo.WriteState is not NullabilityState.NotNull;
         }
 
         [RequiresUnreferencedCode(JsonSerializer.SerializationUnreferencedCodeMessage)]

src/libraries/System.Text.Json/tests/Common/JsonSchemaExporterTests.cs

@@ -82,6 +82,30 @@ public void TreatNullObliviousAsNonNullable_True_MarksReferenceTypesAsNonNullabl
             Assert.Equal(expectedType, (string)schema["type"]!);
         }
 
+        [Fact]
+        public void GetOnlyProperties_DoNotUseSetterNullabilityInSchema()
+        {
+            JsonNode schema = Serializer.DefaultOptions.GetJsonSchemaAsNode(typeof(PocoWithGetOnlyProperties));
+            const string ExpectedJsonSchema = """
+                {
+                    "type": ["object", "null"],
+                    "properties": {
+                        "Values": {
+                            "type": "array",
+                            "items": { "type": ["string", "null"] }
+                        },
+                        "SingleValueGetOnly": { "type": "string" },
+                        "NullableGetOnly": { "type": ["string", "null"] },
+                        "SingleValueGetSet": { "type": "string" },
+                        "NonNullableReadonlyField": { "type": "string" },
+                        "NullableReadonlyField": { "type": ["string", "null"] }
+                    }
+                }
+                """;
+
+            AssertValidJsonSchema(typeof(PocoWithGetOnlyProperties), ExpectedJsonSchema, schema);
+        }
+
         [Theory]
         [InlineData(typeof(Type))]
         [InlineData(typeof(MethodInfo))]
@@ -262,6 +286,18 @@ public void LegacySchemaExporter_CanAccessReflectedMembers()
 
         record PocoWithProperty(int Value);
 
+        public sealed class PocoWithGetOnlyProperties
+        {
+            public IEnumerable<string> Values => [];
+            public string SingleValueGetOnly { get; } = "value";
+            public string? NullableGetOnly { get; }
+            public string SingleValueGetSet { get; set; } = "value";
+            [JsonInclude]
+            public readonly string NonNullableReadonlyField = "value";
+            [JsonInclude]
+            public readonly string? NullableReadonlyField;
+        }
+
         [JsonSerializable(typeof(PocoWithProperty))]
         partial class PocoWithPropertyContext : JsonSerializerContext;
 

src/libraries/System.Text.Json/tests/Common/NullableAnnotationsTests.cs

@@ -356,6 +356,44 @@ public async Task WriteNotNullPropertiesWithNullIgnoreConditions_Succeeds()
             Assert.Equal("{}", json);
         }
 
+        [Theory]
+        [MemberData(nameof(GetReadonlyMembers))]
+        public void IsSetNullable_ReadonlyMember_IsFalse(Type type, string propertyName)
+        {
+            JsonTypeInfo typeInfo = Serializer.GetTypeInfo(type, s_optionsWithIgnoredNullability);
+            JsonPropertyInfo propertyInfo = typeInfo.Properties.Single(p => p.Name == propertyName);
+            Assert.False(propertyInfo.IsSetNullable);
+        }
+
+        [Theory]
+        [MemberData(nameof(GetReadonlyMembersWithExpectedGetNullability))]
+        public void IsGetNullable_ReadonlyMember_MatchesAnnotation(Type type, string propertyName, bool expectedIsGetNullable)
+        {
+            JsonTypeInfo typeInfo = Serializer.GetTypeInfo(type, s_optionsWithIgnoredNullability);
+            JsonPropertyInfo propertyInfo = typeInfo.Properties.Single(p => p.Name == propertyName);
+            Assert.Equal(expectedIsGetNullable, propertyInfo.IsGetNullable);
+        }
+
+        public static IEnumerable<object[]> GetReadonlyMembers()
+        {
+            yield return Wrap(typeof(ClassWithReadonlyMembers), nameof(ClassWithReadonlyMembers.NonNullableGetOnly));
+            yield return Wrap(typeof(ClassWithReadonlyMembers), nameof(ClassWithReadonlyMembers.NullableGetOnly));
+            yield return Wrap(typeof(ClassWithReadonlyMembers), nameof(ClassWithReadonlyMembers.NonNullableReadonlyField));
+            yield return Wrap(typeof(ClassWithReadonlyMembers), nameof(ClassWithReadonlyMembers.NullableReadonlyField));
+
+            static object[] Wrap(Type type, string propertyName) => [type, propertyName];
+        }
+
+        public static IEnumerable<object[]> GetReadonlyMembersWithExpectedGetNullability()
+        {
+            yield return Wrap(typeof(ClassWithReadonlyMembers), nameof(ClassWithReadonlyMembers.NonNullableGetOnly), false);
+            yield return Wrap(typeof(ClassWithReadonlyMembers), nameof(ClassWithReadonlyMembers.NullableGetOnly), true);
+            yield return Wrap(typeof(ClassWithReadonlyMembers), nameof(ClassWithReadonlyMembers.NonNullableReadonlyField), false);
+            yield return Wrap(typeof(ClassWithReadonlyMembers), nameof(ClassWithReadonlyMembers.NullableReadonlyField), true);
+
+            static object[] Wrap(Type type, string propertyName, bool isGetNullable) => [type, propertyName, isGetNullable];
+        }
+
         public class NotNullablePropertyClass
         {
             public string Property { get; set; }
@@ -793,5 +831,15 @@ public class ClassWithNonNullableRequiredProperty
         {
             public required string Property { get; set; }
         }
+
+        public class ClassWithReadonlyMembers
+        {
+            public string NonNullableGetOnly { get; }
+            public string? NullableGetOnly { get; }
+            [JsonInclude]
+            public readonly string NonNullableReadonlyField = "value";
+            [JsonInclude]
+            public readonly string? NullableReadonlyField;
+        }
     }
 }

src/libraries/System.Text.Json/tests/System.Text.Json.SourceGeneration.Tests/Serialization/JsonSchemaExporterTests.cs

@@ -128,6 +128,7 @@ public sealed partial class JsonSchemaExporterTests_SourceGen()
         [JsonSerializable(typeof(ClassWithPropertyNameRequiringFragmentEncoding))]
         [JsonSerializable(typeof(ClassWithOptionalObjectParameter))]
         [JsonSerializable(typeof(ClassWithPropertiesUsingCustomConverters))]
+        [JsonSerializable(typeof(JsonSchemaExporterTests.PocoWithGetOnlyProperties))]
 #pragma warning disable CS0612 // Type or member is obsolete
         [JsonSerializable(typeof(MyObsoleteType))]
 #pragma warning restore CS0612 // Type or member is obsolete

src/libraries/System.Text.Json/tests/System.Text.Json.SourceGeneration.Tests/Serialization/NullableAnnotationsTests.cs

@@ -69,6 +69,7 @@ protected NullableAnnotationsTests_Metadata(JsonSerializerWrapper serializer)
         [JsonSerializable(typeof(ClassWithNonNullableInitProperty))]
         [JsonSerializable(typeof(ClassWithNullableRequiredProperty))]
         [JsonSerializable(typeof(ClassWithNonNullableRequiredProperty))]
+        [JsonSerializable(typeof(ClassWithReadonlyMembers))]
         internal sealed partial class NullableAnnotationsTestsContext_Metadata
             : JsonSerializerContext { }
     }
@@ -136,6 +137,7 @@ protected NullableAnnotationsTests_Default(JsonSerializerWrapper serializer)
         [JsonSerializable(typeof(ClassWithNonNullableInitProperty))]
         [JsonSerializable(typeof(ClassWithNullableRequiredProperty))]
         [JsonSerializable(typeof(ClassWithNonNullableRequiredProperty))]
+        [JsonSerializable(typeof(ClassWithReadonlyMembers))]
         internal sealed partial class NullableAnnotationsTestsContext_Default
             : JsonSerializerContext
         { }

src/libraries/System.Text.Json/tests/System.Text.Json.SourceGeneration.Unit.Tests/Baselines/ConstructorWithDefaultValues/net462/MyContext.Config.g.cs.txt

@@ -69,6 +69,7 @@ namespace TestApp
             };
 
             properties[0] = global::System.Text.Json.Serialization.Metadata.JsonMetadataServices.CreatePropertyInfo<string>(options, info0);
+            properties[0].IsSetNullable = false;
 
             var info1 = new global::System.Text.Json.Serialization.Metadata.JsonPropertyInfoValues<int>
             {
@@ -89,6 +90,7 @@ namespace TestApp
             };
 
             properties[1] = global::System.Text.Json.Serialization.Metadata.JsonMetadataServices.CreatePropertyInfo<int>(options, info1);
+            properties[1].IsSetNullable = false;
 
             var info2 = new global::System.Text.Json.Serialization.Metadata.JsonPropertyInfoValues<bool>
             {
@@ -109,6 +111,7 @@ namespace TestApp
             };
 
             properties[2] = global::System.Text.Json.Serialization.Metadata.JsonMetadataServices.CreatePropertyInfo<bool>(options, info2);
+            properties[2].IsSetNullable = false;
 
             return properties;
         }

src/libraries/System.Text.Json/tests/System.Text.Json.SourceGeneration.Unit.Tests/Baselines/ConstructorWithDefaultValues/netcoreapp/MyContext.Config.g.cs.txt

@@ -69,6 +69,7 @@ namespace TestApp
             };
 
             properties[0] = global::System.Text.Json.Serialization.Metadata.JsonMetadataServices.CreatePropertyInfo<string>(options, info0);
+            properties[0].IsSetNullable = false;
 
             var info1 = new global::System.Text.Json.Serialization.Metadata.JsonPropertyInfoValues<int>
             {
@@ -89,6 +90,7 @@ namespace TestApp
             };
 
             properties[1] = global::System.Text.Json.Serialization.Metadata.JsonMetadataServices.CreatePropertyInfo<int>(options, info1);
+            properties[1].IsSetNullable = false;
 
             var info2 = new global::System.Text.Json.Serialization.Metadata.JsonPropertyInfoValues<bool>
             {
@@ -109,6 +111,7 @@ namespace TestApp
             };
 
             properties[2] = global::System.Text.Json.Serialization.Metadata.JsonMetadataServices.CreatePropertyInfo<bool>(options, info2);
+            properties[2].IsSetNullable = false;
 
             return properties;
         }

src/libraries/System.Text.Json/tests/System.Text.Json.SourceGeneration.Unit.Tests/Baselines/ParameterizedConstructor/net462/MyContext.Point.g.cs.txt

@@ -69,6 +69,7 @@ namespace TestApp
             };
 
             properties[0] = global::System.Text.Json.Serialization.Metadata.JsonMetadataServices.CreatePropertyInfo<int>(options, info0);
+            properties[0].IsSetNullable = false;
 
             var info1 = new global::System.Text.Json.Serialization.Metadata.JsonPropertyInfoValues<int>
             {
@@ -89,6 +90,7 @@ namespace TestApp
             };
 
             properties[1] = global::System.Text.Json.Serialization.Metadata.JsonMetadataServices.CreatePropertyInfo<int>(options, info1);
+            properties[1].IsSetNullable = false;
 
             return properties;
         }

src/libraries/System.Text.Json/tests/System.Text.Json.SourceGeneration.Unit.Tests/Baselines/ParameterizedConstructor/netcoreapp/MyContext.Point.g.cs.txt

@@ -69,6 +69,7 @@ namespace TestApp
             };
 
             properties[0] = global::System.Text.Json.Serialization.Metadata.JsonMetadataServices.CreatePropertyInfo<int>(options, info0);
+            properties[0].IsSetNullable = false;
 
             var info1 = new global::System.Text.Json.Serialization.Metadata.JsonPropertyInfoValues<int>
             {
@@ -89,6 +90,7 @@ namespace TestApp
             };
 
             properties[1] = global::System.Text.Json.Serialization.Metadata.JsonMetadataServices.CreatePropertyInfo<int>(options, info1);
+            properties[1].IsSetNullable = false;
 
             return properties;
         }

src/libraries/System.Text.Json/tests/System.Text.Json.SourceGeneration.Unit.Tests/Baselines/UnsafeAccessors_InaccessibleConstructor/net462/MyContext.InaccessibleCtor.g.cs.txt

@@ -69,6 +69,7 @@ namespace TestApp
             };
 
             properties[0] = global::System.Text.Json.Serialization.Metadata.JsonMetadataServices.CreatePropertyInfo<string>(options, info0);
+            properties[0].IsSetNullable = false;
 
             var info1 = new global::System.Text.Json.Serialization.Metadata.JsonPropertyInfoValues<int>
             {
@@ -89,6 +90,7 @@ namespace TestApp
             };
 
             properties[1] = global::System.Text.Json.Serialization.Metadata.JsonMetadataServices.CreatePropertyInfo<int>(options, info1);
+            properties[1].IsSetNullable = false;
 
             return properties;
         }

src/libraries/System.Text.Json/tests/System.Text.Json.SourceGeneration.Unit.Tests/Baselines/UnsafeAccessors_InaccessibleConstructor/netcoreapp/MyContext.InaccessibleCtor.g.cs.txt

@@ -69,6 +69,7 @@ namespace TestApp
             };
 
             properties[0] = global::System.Text.Json.Serialization.Metadata.JsonMetadataServices.CreatePropertyInfo<string>(options, info0);
+            properties[0].IsSetNullable = false;
 
             var info1 = new global::System.Text.Json.Serialization.Metadata.JsonPropertyInfoValues<int>
             {
@@ -89,6 +90,7 @@ namespace TestApp
             };
 
             properties[1] = global::System.Text.Json.Serialization.Metadata.JsonMetadataServices.CreatePropertyInfo<int>(options, info1);
+            properties[1].IsSetNullable = false;
 
             return properties;
         }