NLTK: Uncontrolled recursion in nltk.featstruct.FeatStructReader causes unhandled RecursionError (DoS) via deeply nested feature-structure input

Summary nltk.featstruct.FeatStructReader used by FeatStructstr and by FeatureGrammar.fromstring parses feature-structure strings such as a=1 with a recursive-descent parser that has no nesting-depth limit. A small, trivially-crafted input 700 bytes with deeply nested brackets drives the parser pa...