System.Text.Json SourceGenerator behaves oddly if context is generic

[canton7]

Description

If the JsonSerializerContext given to the System.Text.Json source generator is generic, the source generator generates some very odd code.

Reproduction Steps

Create a .NET 6 project containing the following, and look at the source generated by the System.Text.Json source generator:

public class Model
{
}

[JsonSerializable(typeof(Model))]
internal partial class MyJsonContext<T> : JsonSerializerContext
{
}

Expected behavior

The source generator either produces a diagnostic saying that generic contexts aren't supported (and does not attempt to generate source), or the source generated is valid C#.

Actual behavior

It's a mix of things.

The class declaration itself is non-generic:

internal partial class MyJsonContext

The default context is sort-of generic, but is confused about what a generic type parameter is:

        private static global::MyJsonContext<global::MyJsonContext.T>? s_defaultContext;
        public static global::MyJsonContext<global::MyJsonContext.T> Default => s_defaultContext ??= new global::MyJsonContext<global::MyJsonContext.T>(new global::System.Text.Json.JsonSerializerOptions(s_defaultOptions));

The constructors are invalid C#:

        public MyJsonContext`1() : base(null)
        {
        }
        
        public MyJsonContext`1(global::System.Text.Json.JsonSerializerOptions options) : base(options)
        {
        }

Regression?

No

Known Workarounds

None

Configuration

.NET 6, Visual Studio 17.2.0 Preview 1.0.

Other information

No response

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Issue Details

---

Description

If the JsonSerializerContext given to the System.Text.Json source generator is generic, the source generator generates some very odd code.

Reproduction Steps

Create a .NET 6 project containing the following, and look at the source generated by the System.Text.Json source generator:

public class Model
{
}

[JsonSerializable(typeof(Model))]
internal partial class MyJsonContext<T> : JsonSerializerContext
{
}

Expected behavior

The source generator either produces a diagnostic saying that generic contexts aren't supported (and does not attempt to generate source), or the source generated is valid C#.

Actual behavior

It's a mix of things.

The class declaration itself is non-generic:

internal partial class MyJsonContext

The default context is sort-of generic, but is confused about what a generic type parameter is:

        private static global::MyJsonContext<global::MyJsonContext.T>? s_defaultContext;
        public static global::MyJsonContext<global::MyJsonContext.T> Default => s_defaultContext ??= new global::MyJsonContext<global::MyJsonContext.T>(new global::System.Text.Json.JsonSerializerOptions(s_defaultOptions));

The constructors are invalid C#:

        public MyJsonContext`1() : base(null)
        {
        }
        
        public MyJsonContext`1(global::System.Text.Json.JsonSerializerOptions options) : base(options)
        {
        }

Regression?

No

Known Workarounds

None

Configuration

.NET 6, Visual Studio 17.2.0 Preview 1.0.

Other information

No response

Author:	canton7
Assignees:	-
Labels:	area-System.Text.Json, untriaged
Milestone:	-

[layomia]

This is a bug since the generator is produced invalid syntax. Do you have any scenario/reason for making your context type generic?

[layomia]

Same underlying issue as #62762.