System.Text.Json Source Generator not working with classes in global namespace

[Vake93]

Description

If a class is defined in the global namespace, the JsonSerializerContext class code generation does not work.
Installed .NET SDK Version is: 6.0.100-preview.6.21355.2

Steps to re-create this is as follows:

1. Create a new .NET 6 console application
2. Add a reference to the latest preview of System.Text.Json NuGet (I tested with 6.0.0-rc.1.21405.12)
3. Replace the contents of Program.cs with the following

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

string SerializeSourceGen() => JsonSerializer.Serialize(new Person("Vishvaka", "Ranasinghe", 28));

SerializeSourceGen();

public class Person
{
    public Person(string firstName, string lastName, uint age)
    {
        FirstName = firstName;
        LastName = lastName;
        Age = age;
    }

    public string FirstName { get; set; }

    public string LastName { get; set; }

    public uint Age { get; set; }
}

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

4. Run with dotnet run command. Notice the build fails.
5. Now replace the contents of Program.cs with the following

using Experiments;
using System.Text.Json;

string SerializeSourceGen() => JsonSerializer.Serialize(new Person("Vishvaka", "Ranasinghe", 28));
SerializeSourceGen();

6. Create new Models.cs file with the contents as:

using System.Text.Json.Serialization;

namespace Experiments
{
    public class Person
    {
        public Person(string firstName, string lastName, uint age)
        {
            FirstName = firstName;
            LastName = lastName;
            Age = age;
        }

        public string FirstName { get; set; }

        public string LastName { get; set; }

        public uint Age { get; set; }
    }

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

7. Project build and run as expected.

Not having support for classes cause the need to create additional files with namespaces when trying to create a simple application using top-level statements.

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Issue Details

---

Description

If a class is defined in the global namespace, the JsonSerializerContext class code generation does not work.
Installed .NET SDK Version is: 6.0.100-preview.6.21355.2

Steps to re-create this is as follows:

1. Create a new .NET 6 console application
2. Add a reference to the latest preview of System.Text.Json NuGet (I tested with 6.0.0-rc.1.21405.12)
3. Replace the contents of Program.cs with the following

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

string SerializeSourceGen() => JsonSerializer.Serialize(new Person("Vishvaka", "Ranasinghe", 28));

SerializeSourceGen();

public class Person
{
    public Person(string firstName, string lastName, uint age)
    {
        FirstName = firstName;
        LastName = lastName;
        Age = age;
    }

    public string FirstName { get; set; }

    public string LastName { get; set; }

    public uint Age { get; set; }
}

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

4. Run with dotnet run command. Notice the build fails.
5. Now replace the contents of Program.cs with the following

using Experiments;
using System.Text.Json;

string SerializeSourceGen() => JsonSerializer.Serialize(new Person("Vishvaka", "Ranasinghe", 28));
SerializeSourceGen();

6. Create new Models.cs file with the contents as:

using System.Text.Json.Serialization;

namespace Experiments
{
    public class Person
    {
        public Person(string firstName, string lastName, uint age)
        {
            FirstName = firstName;
            LastName = lastName;
            Age = age;
        }

        public string FirstName { get; set; }

        public string LastName { get; set; }

        public uint Age { get; set; }
    }

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

7. Project build and run as expected.

Not having support for classes cause the need to create additional files with namespaces when trying to create a simple application using top-level statements.

Author:	Vake93
Assignees:	-
Labels:	area-System.Text.Json, untriaged
Milestone:	-

[stephentoub]

Thanks. Dup of #56920.