class SyntaxTree::Parser

def on_massign(target, value)

on_massign: ((MLHS | MLHSParen) target, untyped value) -> MAssign
:call-seq: 
def on_massign(target, value)
  comma_range = target.location.end_char...value.location.start_char
  target.comma = true if source[comma_range].strip.start_with?(",")
  MAssign.new(
    target: target,
    value: value,
    location: target.location.to(value.location)
  )
end