Stratego signature generation fails with string literals in context-free syntax

[RvanBaarle]

Using string or character literals in context-free syntax causes the build to fail on signature generation. Such as the following example:

module start

context-free start-symbols

  Start

context-free sorts

  Start
  Word

context-free syntax

  Start.Empty = <>
  Start.Program = Word*
  Word.Hello = "Hello"  // Does not work
  Word.World = <World>  // Templates do work
  
syntax
  Word-CF.DoubleQuotedWord =  "\"" Word-CF "\""  // Does not work
  Word-CF.QuotedWord = QUOTE-CF Word-CF QUOTE-CF // Does work

lexical sorts
  QUOTE

lexical syntax
  QUOTE = "'"

  LAYOUT = [\ \n\v\f\r]

context-free restrictions

  LAYOUT? -/- [\ \n\v\f\r]

This example produces the following error (Note the occurences of nabl2.Var("./src/start.sdf3", "y_1-..."){OfSort(SORT("TYPE"))} in the AST):

ERROR: Could not check Stratego because it could not be configured
  Exception of message: mb.spoofax.lwb.compiler.stratego.StrategoConfigureExceptions$Sdf3SignatureGenerateFail: SDF3 to signature generator failed
  Caused by: mb.stratego.common.StrategoExceptions$StrategyFail: Invoking Stratego strategy 'pp-stratego-string' failed 
Stratego stack trace:
	abox2text_list_1_2
	abox2text_1_2
	abox2text_0_1
	box2text_string_0_1
	pp_stratego_string_0_0
	pp_stratego_string_0_0
Stratego input term:
Module(
  "signatures/start-sig"
, [ Imports([Import("libstratego-lib")])
  , Signature(
      [ Sorts([SortNoArgs("Start"{TermIndex("./src/start.sdf3", 12)}), SortNoArgs("Word"{TermIndex("./src/start.sdf3", 14)})]{TermIndex("./src/start.sdf3", 19)})
      , Sorts([SortNoArgs("QUOTE"{TermIndex("./src/start.sdf3", 154)})]{TermIndex("./src/start.sdf3", 158)})
      , Constructors(
          [ OpDecl("Empty"{TermIndex("./src/start.sdf3", 24)}, ConstType(SortNoArgs("Start"{TermIndex("./src/start.sdf3", 22)})))
          , OpDecl(
              "Program"{TermIndex("./src/start.sdf3", 41)}
            , FunType(
                [ConstType(Sort("List", [ConstType(SortNoArgs("Word"{TermIndex("./src/start.sdf3", 72)}))]))]
              , ConstType(SortNoArgs("Start"{TermIndex("./src/start.sdf3", 39)}))
              )
            )
          , OpDecl(
              "Hello"{TermIndex("./src/start.sdf3", 58)}
            , FunType([nabl2.Var("./src/start.sdf3", "y_1-225"){OfSort(SORT("TYPE"))}], ConstType(SortNoArgs("Word"{TermIndex("./src/start.sdf3", 56)})))
            )
          , OpDecl("World"{TermIndex("./src/start.sdf3", 74)}, ConstType(SortNoArgs("Word"{TermIndex("./src/start.sdf3", 72)})))
          , OpDecl("Start-Plhdr", ConstType(SortNoArgs("Start")))
          , OpDecl("Word-Plhdr", ConstType(SortNoArgs("Word")))
          , OpDecl(
              "Start-Plhdr"
            , FunType([ConstType(SortNoArgs("COMPLETION-INSERTION"))], ConstType(SortNoArgs("Start")))
            )
          , OpDecl(
              "Word-Plhdr"
            , FunType([ConstType(SortNoArgs("COMPLETION-INSERTION"))], ConstType(SortNoArgs("Word")))
            )
          , OpDecl("Start-Opt-Plhdr", ConstType(SortNoArgs("Start")))
          , OpDecl("Word-Opt-Plhdr", ConstType(SortNoArgs("Word")))
          , OpDecl(
              "DoubleQuotedWord"{TermIndex("./src/start.sdf3", 103)}
            , FunType(
                [nabl2.Var("./src/start.sdf3", "y_1-139"){OfSort(SORT("TYPE"))}, ConstType(SortNoArgs("Word"{TermIndex("./src/start.sdf3", 72)})), nabl2.Var("./src/start.sdf3", "y_1-147"){OfSort(SORT("TYPE"))}]
              , ConstType(SortNoArgs("Word"{TermIndex("./src/start.sdf3", 100)}))
              )
            )
          , OpDecl(
              "QuotedWord"{TermIndex("./src/start.sdf3", 126)}
            , FunType(
                [ConstType(SortNoArgs("QUOTE"{TermIndex("./src/start.sdf3", 161)})), ConstType(SortNoArgs("Word"{TermIndex("./src/start.sdf3", 72)})), ConstType(SortNoArgs("QUOTE"{TermIndex("./src/start.sdf3", 161)}))]
              , ConstType(SortNoArgs("Word"{TermIndex("./src/start.sdf3", 123)}))
              )
            )
          , OpDecl("Word-Plhdr", ConstType(SortNoArgs("Word")))
          , OpDecl("QUOTE-Plhdr", ConstType(SortNoArgs("QUOTE")))
          , OpDecl(
              "Word-Plhdr"
            , FunType([ConstType(SortNoArgs("COMPLETION-INSERTION"))], ConstType(SortNoArgs("Word")))
            )
          , OpDecl(
              "QUOTE-Plhdr"
            , FunType([ConstType(SortNoArgs("COMPLETION-INSERTION"))], ConstType(SortNoArgs("QUOTE")))
            )
          , OpDeclInj(FunType([SortVar("string")], ConstType(SortNoArgs("QUOTE"{TermIndex("./src/start.sdf3", 161)}))))
          ]
        )
      ]
    )
  ]
)

[Gohla]

Fixed in metaborg/sdf@eafe4ac