JsonSerializer.Serialize overloads accepting JsonSerializerContext don't support unspeakable types.

[DamianEdwards]

Description

When using the System.Text.Json source generator, attempting to serialize a compiler-generated instance of IAsyncEnumerable<T> throws an exception saying a TypeInfo could not be found.

Reproduction Steps

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

var stream = new MemoryStream();
var todos = GetTodosAsync(10);
await JsonSerializer.SerializeAsync(stream, todos, todos.GetType(), AppJsonSerializerContext.Default);

async IAsyncEnumerable<Todo> GetTodosAsync(int count)
{
    for (int i = 0; i < count; i++)
    {
        await Task.Delay(10);
        yield return new Todo { Id = i, Name = $"Todo {i}" };
    }
}

class Todo
{
    public int Id { get; set; }
    public string? Name { get; set; }
}

[JsonSerializable(typeof(IAsyncEnumerable<Todo>))]
internal partial class AppJsonSerializerContext : JsonSerializerContext
{

}

Expected behavior

The result gets serialized.

Actual behavior

An exception is thrown:

System.InvalidOperationException
  HResult=0x80131509
  Message=JsonTypeInfo metadata for type 'Program+<<<Main>$>g__GetTodosAsync|0_0>d' was not provided by TypeInfoResolver of type 'AppJsonSerializerContext'. If using source generation, ensure that all root types passed to the serializer have been annotated with 'JsonSerializableAttribute', along with any types that might be serialized polymorphically.
  Source=System.Text.Json
  StackTrace:
   at System.Text.Json.ThrowHelper.ThrowInvalidOperationException_NoMetadataForType(Type type, IJsonTypeInfoResolver resolver) in /_/src/libraries/System.Text.Json/src/System/Text/Json/ThrowHelper.Serialization.cs:line 743
   at System.Text.Json.JsonSerializer.GetTypeInfo(JsonSerializerContext context, Type inputType) in /_/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializer.Helpers.cs:line 50
   at System.Text.Json.JsonSerializer.Serialize(Object value, Type inputType, JsonSerializerContext context) in /_/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializer.Write.String.cs:line 152
   at Program.<Main>$(String[] args) in C:\Users\damia\source\repos\JsonAsyncEnumerable\JsonAsyncEnumerable\Program.cs:line 5

Regression?

No, but this was expected to work after the recent changes to support unspeakable types in the JSON source generator.

Known Workarounds

None.

Configuration

SDK version: 8.0.100-preview.3.23178.7
Runtime version: 8.0.0-preview.3.23174.8
OS: Windows 11 x64 22H2

Other information

No response

[ghost]

Tagging subscribers to this area: @dotnet/area-system-text-json, @gregsdennis
See info in area-owners.md if you want to be subscribed.

Issue Details

---

Description

When using the System.Text.Json source generator, attempting to serialize a compiler-generated instance of IAsyncEnumerable<T> throws an exception saying a TypeInfo could not be found.

Reproduction Steps

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

var todos = GetTodosAsync(10);
var json = JsonSerializer.Serialize(GetTodosAsync(10), todos.GetType(), AppJsonSerializerContext.Default);

async IAsyncEnumerable<Todo> GetTodosAsync(int count)
{
    for (int i = 0; i < count; i++)
    {
        await Task.Delay(10);
        yield return new Todo { Id = i, Name = $"Todo {i}" };
    }
}

class Todo
{
    public int Id { get; set; }
    public string? Name { get; set; }
}

[JsonSerializable(typeof(IAsyncEnumerable<Todo>))]
internal partial class AppJsonSerializerContext : JsonSerializerContext
{

}

Expected behavior

The result gets serialized.

Actual behavior

An exception is thrown:

System.InvalidOperationException
  HResult=0x80131509
  Message=JsonTypeInfo metadata for type 'Program+<<<Main>$>g__GetTodosAsync|0_0>d' was not provided by TypeInfoResolver of type 'AppJsonSerializerContext'. If using source generation, ensure that all root types passed to the serializer have been annotated with 'JsonSerializableAttribute', along with any types that might be serialized polymorphically.
  Source=System.Text.Json
  StackTrace:
   at System.Text.Json.ThrowHelper.ThrowInvalidOperationException_NoMetadataForType(Type type, IJsonTypeInfoResolver resolver) in /_/src/libraries/System.Text.Json/src/System/Text/Json/ThrowHelper.Serialization.cs:line 743
   at System.Text.Json.JsonSerializer.GetTypeInfo(JsonSerializerContext context, Type inputType) in /_/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializer.Helpers.cs:line 50
   at System.Text.Json.JsonSerializer.Serialize(Object value, Type inputType, JsonSerializerContext context) in /_/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializer.Write.String.cs:line 152
   at Program.<Main>$(String[] args) in C:\Users\damia\source\repos\JsonAsyncEnumerable\JsonAsyncEnumerable\Program.cs:line 5

Regression?

No, but this was expected to work after the recent changes to support unspeakable types in the JSON source generator.

Known Workarounds

None.

Configuration

SDK version: 8.0.100-preview.3.23178.7
Runtime version: 8.0.0-preview.3.23174.8
OS: Windows 11 x64 22H2

Other information

No response

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

[eerhardt]

We think this should be fixed by dotnet/aspnetcore#47548. Is that right @eiriktsarpalis?

[eiriktsarpalis]

@eerhardt That's correct when it comes to using GetTypeInfo, since it cannot be made to work with unspeakable types.

When it comes to the particular repro, the reason why JsonSerializerContext fails to work with unspeakable types is because it uses its own metadata resolution logic:

runtime/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializer.Helpers.cs

Lines 42 to 55 in 50c8895

	private static JsonTypeInfo GetTypeInfo(JsonSerializerContext context, Type inputType)
	{
	Debug.Assert(context != null);
	Debug.Assert(inputType != null);
	JsonTypeInfo? info = context.GetTypeInfo(inputType);
	if (info is null)
	{
	ThrowHelper.ThrowInvalidOperationException_NoMetadataForType(inputType, context);
	}
	info.EnsureConfigured();
	return info;
	}

I had wanted to shim these methods over their JsonSerializerOptions counterparts, but annoyingly they throw InvalidOperationException instead of NotSupportedException -- so it would force a breaking change. This should be fixed in conjunction with #81269 and we might want to consider taking that breaking change.

cc @krwq @layomia

[eiriktsarpalis]

The changes in #84768 reverted support for unspeakable types in overloads that accept explicit Type parameters, it now only kicks in when serializing values of declared type object. Given @eerhardt's plan in dotnet/aspnetcore#47548 (comment) I'm going to close this as out of scope for Goldilocks.