instead of returning ast and error, why not just returned the transformed ast? errors don't need to be returned, you could just add them to the extractedErrors map.


so the api would be: 

````
@param AST astChunk AST chunk to transform
@param Object.<string> extractedErrors Map to add new errors to
@returns AST transformed AST chunk
function transform(astChunk, extractedErrors) {
 ....
}
````