[Breaking change]: [JsonNumberHandling] on collection of non-number properties

[layomia]

Description

Minor breaking change introduced in .NET 6 Preview 1:

Applying JsonNumberHandlingAttribute on a collection of non-numbers e.g. List was previously (in 5.0) a no-op. Now, InvalidOperationException is thrown as it is not a valid configuration.

public class ClassWith_AttributeOnComplexListProperty
{
    // Attribute not allowed here, previously ignored.
    [JsonNumberHandling(JsonNumberHandling.AllowReadingFromString | JsonNumberHandling.WriteAsString)]
    public List<MyClass> MyList { get; set; }

    // Attribute allowed here and will be honored.
    [JsonNumberHandling(JsonNumberHandling.AllowReadingFromString | JsonNumberHandling.WriteAsString)]
    public List<int> MyOtherList { get; set; }
}

Version

Other (please put exact version in description textbox)

Previous behavior

Provided in description.

New behavior

Provided in description.

Type of breaking change

• Binary incompatible: Existing binaries may encounter a breaking change in behavior, such as failure to load/execute or different run-time behavior.
• Source incompatible: Source code may encounter a breaking change in behavior when targeting the new runtime/component/SDK, such as compile errors or different run-time behavior.

Reason for change

It was a side effect of a performance optimization for the number handling feature.

Recommended action

Remove the attribute on incompatible collection properties.

Feature area

Core .NET libraries

Affected APIs

All JsonSerializer (de)serialization methods.