SHIFT004: Type has no generated shape

Property	Value
Rule ID	SHIFT004
Category	ShapeShift.Usage
Default severity	Warning
Enabled by default	Yes
Code fix	Apply `[GenerateShape]` to the type

Cause

A call site supplies a type argument to a method whose type parameter is constrained to PolyType's IShapeable<T>, but the supplied type does not provide the required shape.

Rule description

ShapeShift's NativeAOT-ready APIs obtain contracts from PolyType source-generated shapes. The C# compiler already reports the unsatisfied constraint, but its message describes an interface conversion rather than the ShapeShift remedy. This diagnostic names the type that needs a shape and enables a code fix that applies the attribute for you.

Type arguments that are themselves type parameters are not reported, because the final type is unknown at that call site.

How to fix violations

Apply [GenerateShape] to the type and make the declaration partial:

// Violation
public class Person
{
    public string? Name { get; set; }
}

string json = serializer.Serialize(person);

// Fixed
[GenerateShape]
public partial class Person
{
    public string? Name { get; set; }
}

string json = serializer.Serialize(person);

When the type is not yours to edit — a BCL type, or a type from another package — declare a witness class instead and pass it as the provider type argument:

[GenerateShapeFor<Uri>]
internal partial class Witness;

string json = serializer.Serialize<Uri, Witness>(uri);

The same diagnostic is reported when a witness is supplied that provides a shape for some other type.

Code fix

The IDE offers to apply [PolyType.GenerateShape] and add the partial modifier. The fix is offered only when the type has exactly one declaration in the current solution, so there is never a question about which file to edit, and it is never offered for types that come from referenced assemblies.

When to suppress warnings

Do not suppress this diagnostic. The call site does not compile while the violation remains.