class SyntaxTree::Parser

def on_mlhs_paren(contents)

on_mlhs_paren: ((MLHS | MLHSParen) contents) -> MLHSParen
:call-seq: 
def on_mlhs_paren(contents)
  lparen = consume_token(LParen)
  rparen = consume_token(RParen)
  comma_range = lparen.location.end_char...rparen.location.start_char
  contents.comma = true if source[comma_range].strip.end_with?(",")
  MLHSParen.new(
    contents: contents,
    location: lparen.location.to(rparen.location)
  )
end