fix json source generator serialize when writing (#116004)

* fix json source generator serialize when writing

* Update JsonSerializerContextTests.cs

* Update JsonSerializerContextTests.cs

remove required modifier

* test: update JsonIgnoreCondition_WhenWriting test case

removing the serializer options

Author: WeihanLi

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

@@ -846,6 +846,9 @@ private void GenerateFastPathFuncForObject(SourceWriter writer, ContextGeneratio
 
                     switch (defaultCheckType)
                     {
+                        case SerializedValueCheckType.Ignore:
+                            break;
+
                         case SerializedValueCheckType.IgnoreWhenNull:
                             writer.WriteLine($"if ({propValueExpr} is not null)");
                             writer.WriteLine('{');
@@ -1053,12 +1056,14 @@ private enum SerializedValueCheckType
                 IgnoreWhenNull,
                 IgnoreWhenDefault,
                 DisallowNull,
+                Ignore
             }
 
             private static SerializedValueCheckType GetCheckType(ContextGenerationSpec contextSpec, PropertyGenerationSpec propertySpec)
             {
                 return (propertySpec.DefaultIgnoreCondition ?? contextSpec.GeneratedOptionsSpec?.DefaultIgnoreCondition) switch
                 {
+                    JsonIgnoreCondition.WhenWriting => SerializedValueCheckType.Ignore,
                     JsonIgnoreCondition.WhenWritingNull => propertySpec.PropertyType.CanBeNull ? SerializedValueCheckType.IgnoreWhenNull : SerializedValueCheckType.None,
                     JsonIgnoreCondition.WhenWritingDefault => propertySpec.PropertyType.CanBeNull ? SerializedValueCheckType.IgnoreWhenNull : SerializedValueCheckType.IgnoreWhenDefault,
                     _ when propertySpec.IsGetterNonNullableAnnotation && contextSpec.GeneratedOptionsSpec?.RespectNullableAnnotations is true => SerializedValueCheckType.DisallowNull,

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

@@ -2168,11 +2168,9 @@ public async Task IgnoreConditionWhenWritingDefault_WinsOver_IgnoreReadOnlyField
         [Fact]
         public async Task JsonIgnoreCondition_WhenWriting()
         {
-            var options = new JsonSerializerOptions { IgnoreReadOnlyProperties = true };
             var json = await Serializer.SerializeWrapper
                 (
-                    new JsonIgnoreCondition_WhenReadingWritingTestModel { Age = 10, Name = "Mike" },
-                    options
+                    new JsonIgnoreCondition_WhenReadingWritingTestModel { Age = 10, Name = "Mike" }
                 );
             Assert.Equal("""{"Age":10}""", json);
         }

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

@@ -937,5 +937,45 @@ internal class SelfReference
         {
             public SelfReference Me { get; set; }
         }
+
+        [Fact]
+        public static void SerializeIgnoreWhenWritingTest()
+        {
+            var p = new IgnoreWhenReadingWritingPerson
+            {
+                Id = 1,
+                Name = "Alice",
+                Description = "test"
+            };
+            var serializedJson = JsonSerializer.Serialize(p, SerializeIgnoreReadingWritingJsonSerializerContext.Default.IgnoreWhenReadingWritingPerson);
+            Assert.Equal("""{"Name":"Alice","Description":"test"}""", serializedJson);
+        }
+
+        [Fact]
+        public static void SerializeIgnoreWhenReadingTest()
+        {
+            var json = """{"Id":1,"Name":"Alice","Description":"test"}""";
+            var deserialized = JsonSerializer.Deserialize<IgnoreWhenReadingWritingPerson>(json, SerializeIgnoreReadingWritingJsonSerializerContext.Default.IgnoreWhenReadingWritingPerson);
+            Assert.NotNull(deserialized);
+            Assert.Equal(1, deserialized.Id);
+            Assert.Equal("Alice", deserialized.Name);
+            Assert.Null(deserialized.Description);
+        }
+
+        internal sealed class IgnoreWhenReadingWritingPerson
+        {
+            [JsonIgnore(Condition = JsonIgnoreCondition.WhenWriting)]
+            public int Id { get; set; }
+
+            public string Name { get; set; }
+
+            [JsonIgnore(Condition = JsonIgnoreCondition.WhenReading)]
+            public string? Description { get; set; }
+        }
+
+        [JsonSerializable(typeof(IgnoreWhenReadingWritingPerson))]
+        internal partial class SerializeIgnoreReadingWritingJsonSerializerContext : JsonSerializerContext
+        {
+        }
     }
 }