import { HasTag, SomeSpec, Spec, SpecSuccess, SpecTag, SpectypesError } from './types.js';
/**
 * Spec that tells babel plugin to generate a wrapper for an external transformer spec.
 *
 * @param spec An external transformer spec
 */
export declare const transformer: <ItemSpec extends Spec = SomeSpec>(spec: HasTag<ItemSpec, 'filter'> extends true ? SpectypesError<'filter', 'transformer'> : ItemSpec extends Spec<readonly string[], 'validator', unknown> ? {
    readonly "spectypes error: validator can't be wrapped with 'transformer'": never;
} : ItemSpec) => Spec<SpecTag<ItemSpec>, 'transformer', SpecSuccess<ItemSpec>>;