Can't apply a [JsonConstructor] attribute on a record class with more than one constructor

[zxopink]

Description

my record:

public record class TargetScreen(PointF[] Locations) : Attack
{
    public TargetScreen(Point[] locations, Size size) 
    : this(locations.Select(p => new PointF(p.X / size.Width, p.Y / size.Height)).ToArray())
    { /*Empty*/ }

    public bool IsEmpty => Locations.Length == 0;
    public static readonly TargetScreen Empty = new TargetScreen(Array.Empty<PointF>());
}

I want to serialize the record using JsonSerializer but it throws an exception:
Deserialization of types without a parameterless constructor, a singular parameterized constructor, or a parameterized constructor annotated with 'JsonConstructorAttribute' is not supported

I want to add a [JsonConstructor] attribute to the TargetScreen(PointF[] Locations) but it won't allow me to put an attribute on it

Reproduction Steps

Copy the class and deserialize it:

using System.Drawing;
using System.Text.Json;

TargetScreen target = new(new PointF[] { new(1f, 2f), new(3f, 4f) });
string json = JsonSerializer.Serialize(target);
Console.WriteLine(json);

TargetScreen back = JsonSerializer.Deserialize<TargetScreen>(json);
Console.WriteLine(back);

Expected behavior

I expected to put a [JsonConstructor] attribute on the record and make the record's main constructor the json constructor.

Actual behavior

Gives an error:
Attribute 'JsonConstructor' is not valid on this declaration type. It is only valid on 'constructor' declarations.

Regression?

No response

Known Workarounds

switch to a normal class or play around with the constructors

Configuration

Visual Studio 2022, .NET 6, C# 9

Other information

No response

[ghost]

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

---

Description

my record:

public record class TargetScreen(PointF[] Locations) : Attack
{
    public TargetScreen(Point[] locations, Size size) 
    : this(locations.Select(p => new PointF(p.X / size.Width, p.Y / size.Height)).ToArray())
    { /*Empty*/ }

    public bool IsEmpty => Locations.Length == 0;
    public static readonly TargetScreen Empty = new TargetScreen(Array.Empty<PointF>());
}

I want to serialize the record using JsonSerializer but it throws an exception:
Deserialization of types without a parameterless constructor, a singular parameterized constructor, or a parameterized constructor annotated with 'JsonConstructorAttribute' is not supported

I want to add a [JsonConstructor] attribute to the TargetScreen(PointF[] Locations) but it won't allow me to put an attribute on it

Reproduction Steps

Copy the class and deserialize it:

using System.Drawing;
using System.Text.Json;

TargetScreen target = new(new PointF[] { new(1f, 2f), new(3f, 4f) });
string json = JsonSerializer.Serialize(target);
Console.WriteLine(json);

TargetScreen back = JsonSerializer.Deserialize<TargetScreen>(json);
Console.WriteLine(back);

Expected behavior

I expected to put a [JsonConstructor] attribute on the record and make the record's main constructor the json constructor.

Actual behavior

Gives an error:
Attribute 'JsonConstructor' is not valid on this declaration type. It is only valid on 'constructor' declarations.

Regression?

No response

Known Workarounds

switch to a normal class or play around with the constructors

Configuration

Visual Studio 2022, .NET 6, C# 9

Other information

No response

Author:	zxopink
Assignees:	-
Labels:	area-System.Text.Json
Milestone:	-

[eiriktsarpalis]

This is a constraint of C# language itself, and is tracked by the following issue: dotnet/csharplang#7047