Takes a record of fields and ensures only one instance of a field value type exists.

prismic-custom-type-model-with-singleton-field.ts

// Takes a record of fields and ensures only one instance of a field value type exists.
// See: @prismicio/types

type WithSingletonField<
	Fields extends Record<string, CustomTypeField>,
	FieldType extends CustomTypeField,
	FieldName extends string,
> = {
	[P in keyof Fields as Fields[P] extends FieldType
		? P extends FieldName
			? P
			: never
		: P]: Fields[P] extends FieldType
		? P extends FieldName
			? FieldType
			: never
		: Fields[P];
};