System.Text.Json source generation should accept init-only properties with JsonIgnoreCondition.Always

[brantburnett]

Description

Currently, using JSON source generation with init-only properties is not supported. However, source generation fails if there are any init-only properties present on a class at all, even those marked with JsonIgnoreCondition.Always. Since such properties are not serialized or deserialized, it seems like they could be ignored for this rule as well.

Reproduction Steps

public class Poco
{
    public string Message { get; set; }

    [JsonIgnore(Condition = JsonIgnoreCondition.Always)]
    public object Info { get; init; }
}

[JsonSerializable(typeof(Poco))]
public partial class MySerializerContext : JsonSerializerContext
{
}

Expected behavior

Source is successfully generated and compiles, ignoring the presence of the init-only property.

Actual behavior

SYSLIB1037 The type 'Poco' defines init-only properties, deserialization of which is currently not supported in source generation mode

Regression?

No

Known Workarounds

Do not include any init-only properties at all, even ignored.

Configuration

.NET 6

Other information

No response

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Issue Details

---

Description

Currently, using JSON source generation with init-only properties is not supported. However, source generation fails if there are any init-only properties present on a class at all, even those marked with JsonIgnoreCondition.Always. Since such properties are not serialized or deserialized, it seems like they could be ignored for this rule as well.

Reproduction Steps

public class Poco
{
    public string Message { get; set; }

    [JsonIgnore(Condition = JsonIgnoreCondition.Always)]
    public object Info { get; init; }
}

[JsonSerializable(typeof(Poco))]
public partial class MySerializerContext : JsonSerializerContext
{
}

Expected behavior

Source is successfully generated and compiles, ignoring the presence of the init-only property.

Actual behavior

SYSLIB1037 The type 'Poco' defines init-only properties, deserialization of which is currently not supported in source generation mode

Regression?

No

Known Workarounds

Do not include any init-only properties at all, even ignored.

Configuration

.NET 6

Other information

No response

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

[eiriktsarpalis]

Can reproduce. Likely related to #63443.

[eiriktsarpalis]

We won't have time to work on this for .NET 7, moving to Future.

[brantburnett]

@eiriktsarpalis would you be interested in a community PR to address this, or is testing bandwidth also a concern?

[eiriktsarpalis]

Hi @brantburnett, we're always open to community contributions.

[eiriktsarpalis]

Fixed by #79828.