System.Text.Json source generator doesn't work with native AOT IlcDisableReflection

[cfbao]

Description

System.Text.Json source generator generates code (that calls code) that uses reflection, hence incompatible with the IlcDisableReflection native AOT option.

Was expecting that source generator can eliminate reflection and work with IlcDisableReflection.

offending line seems to be this:

runtime/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonConverterOfT.cs

Line 22 in 7368836

IsInternalConverter = GetType().Assembly == typeof(JsonConverter).Assembly;

Reproduction Steps

• Follow native AOT sample app's readme to create the project
• replace Program.cs with the following

using System.Text.Json;
using System.Text.Json.Serialization;

MyClass stuff = new() { Prop = "value" };
string json = JsonSerializer.Serialize( stuff, MyJsonContext.Default.MyClass );
Console.WriteLine( json );

internal record MyClass {
	public string? Prop { get; set; }
}

[JsonSerializable( typeof( MyClass ) )]
internal partial class MyJsonContext : JsonSerializerContext { }

• add <IlcDisableReflection>true</IlcDisableReflection> to csproj file
• run dotnet publish -r <RID>
• run the produced exe

Expected behavior

program prints {"Prop":"value"} on the console

Actual behavior

the following error shows up

Unhandled Exception: EETypeRva:0x002EFD88: Reflection_Disabled
   at Internal.Reflection.RuntimeTypeInfo.get_Assembly() + 0x59
   at System.Text.Json.Serialization.JsonConverter`1..ctor() + 0xc8
   at System.Text.Json.Serialization.JsonResumableConverter`1..ctor() + 0x18
   at System.Text.Json.Serialization.Converters.JsonMetadataServicesConverter`1..ctor(Func`1, ConverterStrategy) + 0x30
   at System.Text.Json.Serialization.Metadata.SourceGenJsonTypeInfo`1.GetConverter(JsonObjectInfoValues`1) + 0x194
   at System.Text.Json.Serialization.Metadata.SourceGenJsonTypeInfo`1..ctor(JsonSerializerOptions, JsonObjectInfoValues`1) + 0x78
   at System.Text.Json.Serialization.Metadata.JsonMetadataServices.CreateObjectInfo[T](JsonSerializerOptions, JsonObjectInfoValues`1) + 0x67
   at MyJsonContext.get_Stuff() + 0x2cd
   at Program.<Main>$(String[]) + 0x73

Regression?

No response

Known Workarounds

No response

Configuration

.NET SDK 7.0.100-preview.3.22179.4, commit c48f2c30ee
Windows 10.0.18363, RID: win10-x64
Host version: 7.0.0-preview.3.22175.4, commit 162f836

Other information

No response

[ghost]

Tagging subscribers to this area: @dotnet/area-system-text-json, @gregsdennis
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Issue Details

---

Description

System.Text.Json source generator generates code (that calls code) that uses reflection, hence incompatible with the IlcDisableReflection native AOT option.

Was expecting that source generator can eliminate reflection and work with IlcDisableReflection.

offending line seems to be this:

runtime/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonConverterOfT.cs

Line 22 in 7368836

IsInternalConverter = GetType().Assembly == typeof(JsonConverter).Assembly;

Reproduction Steps

• Follow native AOT sample app's readme to create the project
• replace Program.cs with the following

using System.Text.Json;
using System.Text.Json.Serialization;

MyClass stuff = new() { Prop = "value" };
string json = JsonSerializer.Serialize( stuff, MyJsonContext.Default.MyClass );
Console.WriteLine( json );

internal record MyClass {
	public string? Prop { get; set; }
}

[JsonSerializable( typeof( MyClass ) )]
internal partial class MyJsonContext : JsonSerializerContext { }

• add <IlcDisableReflection>true</IlcDisableReflection> to csproj file
• run dotnet publish -r <RID>
• run the produced exe

Expected behavior

program prints {"Prop":"value"} on the console

Actual behavior

the following error shows up

Unhandled Exception: EETypeRva:0x002EFD88: Reflection_Disabled
   at Internal.Reflection.RuntimeTypeInfo.get_Assembly() + 0x59
   at System.Text.Json.Serialization.JsonConverter`1..ctor() + 0xc8
   at System.Text.Json.Serialization.JsonResumableConverter`1..ctor() + 0x18
   at System.Text.Json.Serialization.Converters.JsonMetadataServicesConverter`1..ctor(Func`1, ConverterStrategy) + 0x30
   at System.Text.Json.Serialization.Metadata.SourceGenJsonTypeInfo`1.GetConverter(JsonObjectInfoValues`1) + 0x194
   at System.Text.Json.Serialization.Metadata.SourceGenJsonTypeInfo`1..ctor(JsonSerializerOptions, JsonObjectInfoValues`1) + 0x78
   at System.Text.Json.Serialization.Metadata.JsonMetadataServices.CreateObjectInfo[T](JsonSerializerOptions, JsonObjectInfoValues`1) + 0x67
   at MyJsonContext.get_Stuff() + 0x2cd
   at Program.<Main>$(String[]) + 0x73

Regression?

No response

Known Workarounds

No response

Configuration

.NET SDK 7.0.100-preview.3.22179.4, commit c48f2c30ee
Windows 10.0.18363, RID: win10-x64
Host version: 7.0.0-preview.3.22175.4, commit 162f836

Other information

No response

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

[jkotas]

IlcDisableReflection mode is very restrictive. It disables majority of the reflection APIs, even the ones that are generally ok with AOT. We do not plan support it in its current form.

#67193
dotnet/runtimelab#635 (comment)

[layomia]

Current work to support JsonSerialzier's conformance with AOT analysis: #68464, #68878.

[eiriktsarpalis]

I think we can close this as wontfix. Most of the System.Text.Json.Serialization infrastructure depends on some degree of reflection, even in source generated scenaria. We likely won't be able to change this in the future.

That being said, fast-path serialization in source gen should not require any reflection in principle, however fast-path deserialization is not yet implemented (#55043) and it is still missing features compared to the metadata-based serializer.