System.Text.Json SourceGenerator crashes if context is an inner class of a generic type

[canton7]

Description

If the JsonSerializerContext subclass given to the System.Text.Json source generator is a child of a generic class, the source generator crashes with the following exception, and does not generate any output:

Warning CS8785: Generator 'JsonSourceGenerator' failed to generate source. It will not contribute to the output and compilation errors may occur as a result. Exception was of type 'ArgumentOutOfRangeException' with message 'Length cannot be less than zero.

Reproduction Steps

Create a .NET 6 project with the following code, and build:

public class Model
{
}

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

Expected behavior

The source generator either produces a diagnostic saying that this situation isn't supported, or correctly generates source.

Actual behavior

The source generator crashes with the exception:

ArgumentOutOfRangeException with message 'Length cannot be less than zero.'

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 subclass given to the System.Text.Json source generator is a child of a generic class, the source generator crashes with the following exception, and does not generate any output:

Warning CS8785: Generator 'JsonSourceGenerator' failed to generate source. It will not contribute to the output and compilation errors may occur as a result. Exception was of type 'ArgumentOutOfRangeException' with message 'Length cannot be less than zero.

Reproduction Steps

Create a .NET 6 project with the following code, and build:

public class Model
{
}

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

Expected behavior

The source generator either produces a diagnostic saying that this situation isn't supported, or correctly generates source.

Actual behavior

The source generator crashes with the exception:

ArgumentOutOfRangeException with message 'Length cannot be less than zero.'

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:	-

[SteveDunn]

I think the only solution to this is to generate an analysis error if the class is nested. Seems like an odd design, although I can see from the use in this PR that it's test related.

[canton7]

The JsonSourceGenerator has specific logic to handle the context being a nested type, so I think removing that would be a breaking change. It should be a fairly straightforward fix: you don't need to repeat generic type parameters or anything with declaration another part of a partial generic class. You just need to make sure that you repeat the same type parameter names in the same order.

[stephentoub]

Duplicate of #62762?

[canton7]

I'm not sure if it is a duplicate. #62762 is about the model being an inner type of a generic type; this issue is about the context being an inner type of a generic type.

Although, the exception message is the same, so maybe it's the same underlying cause.

[layomia]

Yes I believe this falls under the same general issue of the generator fumbling for open generic types.