JsonExtensionDataAttribute not working with custom overflow converters in source gen

[eiriktsarpalis]

The following unit test:

runtime/src/libraries/System.Text.Json/tests/Common/ExtensionDataTests.cs

Lines 518 to 529 in 534d1df

	[Theory]
	[InlineData(typeof(Dictionary<string, object>), typeof(DictionaryOverflowConverter), typeof(object))]
	[InlineData(typeof(Dictionary<string, JsonElement>), typeof(JsonElementOverflowConverter), typeof(JsonElement))]
	[InlineData(typeof(CustomOverflowDictionary<object>), typeof(CustomObjectDictionaryOverflowConverter), typeof(object))]
	[InlineData(typeof(CustomOverflowDictionary<JsonElement>), typeof(CustomJsonElementDictionaryOverflowConverter), typeof(JsonElement))]
	public void ExtensionProperty_IgnoresCustomSerializerWithOptions(Type overflowType, Type converterType, Type elementType)
	{
	typeof(ExtensionDataTests)
	.GetMethod(nameof(ExtensionProperty_IgnoresCustomSerializerWithOptionsInternal), BindingFlags.Static | BindingFlags.NonPublic)
	.MakeGenericMethod(overflowType, elementType, converterType)
	.Invoke(null, null);
	}

hardcodes testing to the reflection serializer. Switching the test to use source gen causes it to fail.

Discovered while investigating #86975.

[ghost]

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Issue Details

---

The following unit test:

runtime/src/libraries/System.Text.Json/tests/Common/ExtensionDataTests.cs

Lines 518 to 529 in 534d1df

	[Theory]
	[InlineData(typeof(Dictionary<string, object>), typeof(DictionaryOverflowConverter), typeof(object))]
	[InlineData(typeof(Dictionary<string, JsonElement>), typeof(JsonElementOverflowConverter), typeof(JsonElement))]
	[InlineData(typeof(CustomOverflowDictionary<object>), typeof(CustomObjectDictionaryOverflowConverter), typeof(object))]
	[InlineData(typeof(CustomOverflowDictionary<JsonElement>), typeof(CustomJsonElementDictionaryOverflowConverter), typeof(JsonElement))]
	public void ExtensionProperty_IgnoresCustomSerializerWithOptions(Type overflowType, Type converterType, Type elementType)
	{
	typeof(ExtensionDataTests)
	.GetMethod(nameof(ExtensionProperty_IgnoresCustomSerializerWithOptionsInternal), BindingFlags.Static | BindingFlags.NonPublic)
	.MakeGenericMethod(overflowType, elementType, converterType)
	.Invoke(null, null);
	}

hardcodes testing to the reflection serializer. Switching the test to use source gen causes it to fail.

Discovered while investigating #86975.

Author:	eiriktsarpalis
Assignees:	-
Labels:	area-System.Text.Json, untriaged
Milestone:	-