Scala Programming Language
  1. Scala Programming Language
  2. SI-5012

findOrCreateModuleVar picks the wrong symbol

    Details

    • Type: Bug Bug
    • Status: Closed
    • Priority: Major Major
    • Resolution: Fixed
    • Affects Version/s: Scala 2.9.2
    • Fix Version/s: None
    • Component/s: Misc Compiler
    • Labels:
      None

      Description

      I was looking today at refchecks in order to learn how modules are transformed. In so doing I spotted a bug.

      scalac wrongly tells there's an error in the following program (the program is OK, in fact):

      class D { 
        object p // (program point 1) 
      }  
      
      class C { 
        def m: D = { 
          if("abc".length == 0) {
            object p       // (program point 2)
          }
          null 
        } 
      }
      

      Summary: eliminateModuleDefs(tree: Tree) wants to expand the ModuleDef at "program point 2".
      As part of that, it invokes

        def findOrCreateModuleVar() = localTyper.typedPos(tree.pos) {
          lazy val createModuleVar = gen.mkModuleVarDef(sym)
          sym.owner.info.decl(nme.moduleVarName(sym.name.toTermName)) match {
            // In case we are dealing with local symbol then we already have
            // to correct error with forward reference
            case NoSymbol => createModuleVar
            case vsym     => ValDef(vsym)
          }
        }
      

      with tree bound to that ModuleDef. Normal behavior would be to enter the case NoSymbol,
      however it finds a vsym (surprisingly, for the lowering of another module, that in "program point 1").

      The assumptions under which findOrCreateModuleVar are written appear to be:
      (a) for a module owned by class, sym.owner.info is a ClassInfo and thus decl() on it looks up where intended.
      (b) for a module owned by something else, that same lookup will be performed on an EmptyScope.

      Assumption (b) proves wrong when sym.owner.info returns a NullaryMethodType. In that case, NullaryMethodType.decls delegates to resultType.decls. In our case, that resultType ("D") happens to have as member an object with the same name, but not the one we're looking for.

        Activity

        Hide
        Commit Message Bot added a comment -

        (extempore in r25757) Fix bug in ModuleDef elimination.

        Fixes corner case diagnosed by miguel. Closes SI-5012, no review.

        Show
        Commit Message Bot added a comment - (extempore in r25757 ) Fix bug in ModuleDef elimination. Fixes corner case diagnosed by miguel. Closes SI-5012 , no review.

          People

          • Assignee:
            Paul Phillips
            Reporter:
            Miguel Garcia
          • Votes:
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            Watchers:
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            Dates

            • Created:
              Updated:
              Resolved:

              Development