Summary:
`advance()` is intended to be called with a grammarContext after
we lazy parse a function. Not doing so can lead to the next token being
scanned incorrectly and erroring when it should not.
Reviewed By: dulinriley
Differential Revision: D25347491
fbshipit-source-id: 9a8d865227d247e64cd8706c3f263631356af408