[API Proposal]: System.Text.JsonSerializerContext should support deserialization to private members.

[voroninp]

Background and motivation

Reflection-based deserialization has no problems with accessing properties with private setters when [JsonInclude] is applied.
Yet JsonSerializerContext throws an exception in this case.

Why cannot source generator [UnsafeAccessor] to write to the property?

public sealed record Foo
{
    public int Bar { get; private set; }
}

public static class BreakIntoFoo
{
    [UnsafeAccessor(UnsafeAccessorKind.Method, Name = $"set_{nameof(Foo.Bar)}")]
    public static extern void SetProp(Foo foo, int value);
}

var foo = new Foo();
BreakIntoFoo.SetProp(foo, 5);
Console.WriteLine(foo.Bar); // You see 5 here.

API Proposal

Api won't not change at all, the internals should.

API Usage

As usual.

Alternative Designs

No response

Risks

I assume that UnsafeAccessorAttribute is taken into account by the linker when trimming the app. If it's not the case, then this feature won't be trimming firendly.

[ghost]

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Issue Details

---

Background and motivation

Reflection-based deserialization has no problems with accessing properties with private setters when [JsonInclude] is applied.
Yet JsonSerializerContext throws an exception in this case.

Why cannot source generator [UnsafeAccessor] to write to the property?

public sealed record Foo
{
    public int Bar { get; private set; }
}

public static class BreakIntoFoo
{
    [UnsafeAccessor(UnsafeAccessorKind.Method, Name = $"set_{nameof(Foo.Bar)}")]
    public static extern void SetProp(Foo foo, int value);
}

var foo = new Foo();
BreakIntoFoo.SetProp(foo, 5);
Console.WriteLine(foo.Bar); // You see 5 here.

API Proposal

Api won't not change at all, the internals should.

API Usage

As usual.

Alternative Designs

No response

Risks

I assume that UnsafeAccessorAttribute is taken into account by the linker when trimming the app. If it's not the case, then this feature won't be trimming firendly.

Author:	voroninp
Assignees:	-
Labels:	api-suggestion, area-System.Text.Json
Milestone:	-

[eiriktsarpalis]

Duplicate of #88519.

Note that we wouldn't be supporting private members by default, only those annotated with the JsonInclude attribute. Also, UnsafeAccessorAttribute is only available in .NET 8 and newer versions, so this would be challenging to support in multi-targeted projects.