SHIFT002: Converter type cannot be activated

Property	Value
Rule ID	SHIFT002
Category	ShapeShift.Usage
Default severity	Error
Enabled by default	Yes
Code fix	Make an existing parameterless constructor public

Cause

A converter named by ShapeShiftConverterAttribute is abstract, or it has no public parameterless constructor.

Rule description

ShapeShift activates an attribute-specified converter through its public parameterless constructor. A converter that is abstract, that declares only parameterized constructors, or whose parameterless constructor is not public cannot be activated, and serialization of the annotated type throws a ShapeShiftSerializationException.

Open generic converter types are not analyzed, because ShapeShift resolves those through PolyType associated type shapes.

How to fix violations

Give the converter a public parameterless constructor.

// Violation
public class PersonConverter : ShapeShiftConverter<Person, JsonEncoder, JsonDecoder>
{
    private PersonConverter() { }
    // ...
}

// Fixed
public class PersonConverter : ShapeShiftConverter<Person, JsonEncoder, JsonDecoder>
{
    public PersonConverter() { }
    // ...
}

If the converter genuinely requires construction arguments, do not use the attribute. Register a fully constructed instance on the serializer instead:

JsonSerializer serializer = new() { Converters = [new PersonConverter(dependency)] };

A converter may also declare a constructor that takes a ConverterContext<TEncoder, TDecoder>; that form is available through the serializer's converter-type collection rather than through the attribute.

Code fix

When the converter already declares a non-public parameterless constructor, the IDE offers to widen it to public. No fix is offered when no parameterless constructor exists, because adding one could skip initialization the author requires.

When to suppress warnings

Do not suppress this diagnostic. The annotated type cannot be serialized while the violation remains.