GD0301: The generic type argument must be a Variant compatible type

Cause

An unsupported type is specified for a generic type argument when a Variant-compatible type is expected.

Rule description

When a generic type parameter is annotated with the [MustBeVariant] attribute, the generic type is required to be a Variant-compatible type. For example, the generic Godot.Collections.Array<T> type only supports items of a type that can be converted to Variant.

class SomeType { }
// SomeType is not a valid type because it doesn't derive from GodotObject,
// so it's not compatible with Variant.
var invalidArray = new Godot.Collections.Array<SomeType>();
// System.Int32 is a valid type because it's compatible with Variant.
var validArray = new Godot.Collections.Array<int>();

How to fix violations

To fix a violation of this rule, change the generic type argument to be a Variant-compatible type or use a different API that doesn’t require the generic type argument to be a Variant-compatible type.

When to suppress warnings

Do not suppress a warning from this rule. API that contains generic type arguments annotated with the [MustBeVariant] attribute usually has this requirement because the values will be passed to the engine, if the type can’t be marshalled it will result in runtime errors.

User-contributed notes

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