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PackratParsers and RegexParsers / JavaTokenParsers don't work well in combination #318

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PackratParsers and RegexParsers / JavaTokenParsers don't work well in combination#318
@scabug

Description

@scabug
scabug
opened on Dec 14, 2013

We have a parser that inherits from both JavaTokenParsers and PackratParsers; and it turns out that the .parse() method that the former provides (via RegexParsers) is incompatible with the latter. And, to make matters worse, that incompatibility only shows up very rarely; I'm filing this bug so that at least there will be some google hit out there if somebody else runs into this error.

Basically, the situation is this: I'm calling

parser.parse(parser.definitionOfSomeTerm, "input string")

And, depending on the details of what I'm trying to parse and what the input is, I'll occasionally get this:

scala.util.parsing.input.CharSequenceReader cannot be cast to scala.util.parsing.combinator.PackratParsers$PackratReader
java.lang.ClassCastException: scala.util.parsing.input.CharSequenceReader cannot be cast to scala.util.parsing.combinator.PackratParsers$PackratReader
	at scala.util.parsing.combinator.PackratParsers$$anon$2.apply(PackratParsers.scala:239)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$flatMap$1.apply(Parsers.scala:239)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$flatMap$1.apply(Parsers.scala:239)
	at scala.util.parsing.combinator.Parsers$$anon$3.apply(Parsers.scala:222)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$flatMap$1.apply(Parsers.scala:239)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$flatMap$1.apply(Parsers.scala:239)
	at scala.util.parsing.combinator.Parsers$$anon$3.apply(Parsers.scala:222)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$map$1.apply(Parsers.scala:242)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$map$1.apply(Parsers.scala:242)
	at scala.util.parsing.combinator.Parsers$$anon$3.apply(Parsers.scala:222)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$$anon$3.apply(Parsers.scala:222)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$$anon$3.apply(Parsers.scala:222)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$flatMap$1.apply(Parsers.scala:239)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$flatMap$1.apply(Parsers.scala:239)
	at scala.util.parsing.combinator.Parsers$$anon$3.apply(Parsers.scala:222)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$flatMap$1.apply(Parsers.scala:239)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$flatMap$1.apply(Parsers.scala:239)
	at scala.util.parsing.combinator.Parsers$$anon$3.apply(Parsers.scala:222)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$map$1.apply(Parsers.scala:242)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$map$1.apply(Parsers.scala:242)
	at scala.util.parsing.combinator.Parsers$$anon$3.apply(Parsers.scala:222)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$$anon$3.apply(Parsers.scala:222)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$flatMap$1.apply(Parsers.scala:239)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$flatMap$1.apply(Parsers.scala:239)
	at scala.util.parsing.combinator.Parsers$$anon$3.apply(Parsers.scala:222)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$flatMap$1.apply(Parsers.scala:239)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$flatMap$1.apply(Parsers.scala:239)
	at scala.util.parsing.combinator.Parsers$$anon$3.apply(Parsers.scala:222)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$map$1.apply(Parsers.scala:242)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$map$1.apply(Parsers.scala:242)
	at scala.util.parsing.combinator.Parsers$$anon$3.apply(Parsers.scala:222)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$$anon$3.apply(Parsers.scala:222)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$map$1.apply(Parsers.scala:242)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$map$1.apply(Parsers.scala:242)
	at scala.util.parsing.combinator.Parsers$$anon$3.apply(Parsers.scala:222)
	at scala.util.parsing.combinator.Parsers$$anon$3.apply(Parsers.scala:222)
	at scala.util.parsing.combinator.Parsers$Success.flatMapWithNext(Parsers.scala:142)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$flatMap$1.apply(Parsers.scala:239)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$flatMap$1.apply(Parsers.scala:239)
	at scala.util.parsing.combinator.Parsers$$anon$3.apply(Parsers.scala:222)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$map$1.apply(Parsers.scala:242)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$map$1.apply(Parsers.scala:242)
	at scala.util.parsing.combinator.Parsers$$anon$3.apply(Parsers.scala:222)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1$$anonfun$apply$2.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1$$anonfun$apply$2.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$Failure.append(Parsers.scala:202)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$$anon$3.apply(Parsers.scala:222)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$$anon$3.apply(Parsers.scala:222)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$$anon$3.apply(Parsers.scala:222)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$$anon$3.apply(Parsers.scala:222)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$$anon$3.apply(Parsers.scala:222)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$$anon$3.apply(Parsers.scala:222)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$$anon$3.apply(Parsers.scala:222)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$$anon$3.apply(Parsers.scala:222)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$$anon$3.apply(Parsers.scala:222)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$$anon$3.apply(Parsers.scala:222)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$$anon$3.apply(Parsers.scala:222)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$$anon$3.apply(Parsers.scala:222)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$$anon$3.apply(Parsers.scala:222)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$$anon$3.apply(Parsers.scala:222)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$$anon$3.apply(Parsers.scala:222)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$$anon$3.apply(Parsers.scala:222)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$$anon$3.apply(Parsers.scala:222)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$$anon$3.apply(Parsers.scala:222)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$$anon$3.apply(Parsers.scala:222)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$$anon$3.apply(Parsers.scala:222)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$$anon$3.apply(Parsers.scala:222)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$$anon$3.apply(Parsers.scala:222)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$$anon$3.apply(Parsers.scala:222)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$$anon$3.apply(Parsers.scala:222)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$$anon$3.apply(Parsers.scala:222)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$$anon$3.apply(Parsers.scala:222)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$$anon$3.apply(Parsers.scala:222)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$$anon$3.apply(Parsers.scala:222)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$$anon$3.apply(Parsers.scala:222)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$$anon$3.apply(Parsers.scala:222)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$$anon$3.apply(Parsers.scala:222)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$$anon$3.apply(Parsers.scala:222)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$$anon$3.apply(Parsers.scala:222)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$$anon$3.apply(Parsers.scala:222)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$$anon$3.apply(Parsers.scala:222)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$$anon$3.apply(Parsers.scala:222)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$$anon$3.apply(Parsers.scala:222)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$$anon$3.apply(Parsers.scala:222)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$$anon$3.apply(Parsers.scala:222)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$Parser$$anonfun$append$1.apply(Parsers.scala:254)
	at scala.util.parsing.combinator.Parsers$$anon$3.apply(Parsers.scala:222)
	at scala.util.parsing.combinator.RegexParsers$class.parse(RegexParsers.scala:148)
	at com.sumologic.stream_language.language.SearchQueryParserV2.parse(SearchQueryParserV2.scala:12)

The problem is that RegexParsersers.parse(Parser, CharSequence) constructs a CharSequenceReader, while PackratParsers assumes that it's passed a PackratReader. (But it doesn't actually use that assumption much of the time.)

It's easy to work around once you know the problem: wrap it like this:

  def parseSubstring[T](parser: Parser[T], input: String): ParseResult[T] = {
    parse(parser, new PackratReader(new CharSequenceReader(input)))
  }

And quite possibly it's the case that we shouldn't inherit from PackratParsers at all, I'm honestly not sure why we are. Still, it seems a little unfortunate that PackratParsers has a type restriction that is documented in the Scaladoc but not enforced in the underlying code.

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