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spurious errors / crashes when pattern matching meets super #8138

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scabug opened this issue Jan 10, 2014 · 9 comments
Closed

spurious errors / crashes when pattern matching meets super #8138

scabug opened this issue Jan 10, 2014 · 9 comments
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@retronym
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patmat
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2.10.4-RC2

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@scabug
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scabug commented Jan 10, 2014 

import scala.language.experimental.macros
import scala.reflect.macros.WhiteboxContext

object Test {
  def impl(c: WhiteboxContext)(tree: c.Tree) = {
    import c.universe._
    object FindMatch extends Transformer {
      tree match {
        case arg: List[List[Tree]] =>
          // doesn't compile:
          // Test.scala:10: error: missing parameter type for expanded function ((x$1) => x$1.foreach(((y) => super.transform(y))))
          arg.foreach{_.foreach{y=>super.transform(y)}}

          // crashes in GenICode:
          // error: Unknown type: <notype>, <notype> [class scala.reflect.internal.Types$NoType$, class scala.reflect.internal.Types$NoType$] TypeRef? false
          // error: scala.reflect.internal.FatalError: Unknown type: <notype>, <notype> [class scala.reflect.internal.Types$NoType$, class scala.reflect.internal.Types$NoType$] TypeRef? false
          //   at scala.reflect.internal.SymbolTable.abort(SymbolTable.scala:56)
          //   at scala.tools.nsc.Global.abort(Global.scala:263)
          //   at scala.tools.nsc.backend.icode.TypeKinds$class.toTypeKind(TypeKinds.scala:401)
          //   at scala.tools.nsc.backend.icode.ICodes.toTypeKind(ICodes.scala:19)
          //   at scala.tools.nsc.backend.icode.GenICode$ICodePhase.genLoadApply1$1(GenICode.scala:607)
          //   at scala.tools.nsc.backend.icode.GenICode$ICodePhase.scala$tools$nsc$backend$icode$GenICode$ICodePhase$$genLoad(GenICode.scala:634)
          //   at scala.tools.nsc.backend.icode.GenICode$ICodePhase.gen(GenICode.scala:119)
          //   at scala.tools.nsc.backend.icode.GenICode$ICodePhase$$anonfun$gen$1.apply(GenICode.scala:67)
          //   at scala.tools.nsc.backend.icode.GenICode$ICodePhase$$anonfun$gen$1.apply(GenICode.scala:67)
          arg.foreach{(x: List[Tree]) => x.foreach{y=>super.transform(y)}}
      }
    }
  }
}
@scabug
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scabug commented Jan 10, 2014

Imported From: https://issues.scala-lang.org/browse/SI-8138?orig=1
Reporter: @xeno-by
Affected Versions: 2.11.0-M7

@scabug
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scabug commented Jan 10, 2014

@DarkDimius said:
Please be so kind to tell if there's a workaround.

@scabug
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scabug commented Jan 12, 2014

@retronym said:
With -Ycheck:all:

[Now checking: typer]
warning: [check: typer]
Out of scope symbol reference {
      tree  ModuleDef            object FindMatch extends c.universe.Transformer {...
  position  OffsetPosition       sandbox/test.scala:11
  with sym  ModuleSymbol         object FindMatch                                         in  method impl -> object Test -> package <empty>
   encl(1)  MethodSymbol         def impl(c: scala.reflect.macros.WhiteboxContext): Unit  in  object Test -> package <empty>
   encl(2)  ModuleSymbol         object Test                                              in  package <empty>
    ref to  ModuleClassSymbol    FindMatch (<module>)                                     in  method impl -> object Test -> package <empty>
}

@scabug
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scabug commented Jan 12, 2014

@retronym said:
Minimized:

class U {
  trait Transformer {
    def transform(a: Tree): Tree = ???
  }  
  trait Tree
}

object Test {
  def m(u: U) = {
    // val u = u0 // works
    class C extends u.Transformer {
      override def transform(t: u.Tree): u.Tree = {
        null match {
          case _ =>
            // crashes in GenICode:
            // error: Unknown type: <notype>, <notype> [class scala.reflect.internal.Types$NoType$, class scala.reflect.internal.Types$NoType$] TypeRef? false
            (y: Any) => super.transform(???)
        }
        ???
      }
    }
  }
}

@scabug
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scabug commented Jan 12, 2014

@xeno-by said:
@jason. The missing parameter type error is also spurious, right?

@scabug
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scabug commented Jan 12, 2014

@retronym said:
This fixes the crasher. https://github.com/retronym/scala/tree/ticket/8138

Not sure about the inference failure yet.

@scabug
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scabug commented Jan 12, 2014

@retronym said:
The inference failure does not appear to be a bug; the type of arg contains a pair of overloaded foreach members; one contributed by Tree, and the second contributed by List[List[Tree]]

This amounts to:

trait A { def foo(f: Int => String)}
sealed abstract class B1
final class B extends B1 { def foo(f: String => Int)}

object Test {
  def foo(a: A) = a match {
    case b: B1 =>
      b.foo(x => x)
  }
}

It is a pity that our static checks don't detect the "fruitless type test" here as they would if B were final.

@scabug
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scabug commented Jan 12, 2014

@retronym said:
scala/scala#3356

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scabug commented Jan 12, 2014

@retronym said:
The logic that would need tweaking in CheckabilityChecker:

    def areIrreconcilableAsParents(sym1: Symbol, sym2: Symbol): Boolean = areUnrelatedClasses(sym1, sym2) && (
         sym1.initialize.isEffectivelyFinal // initialization important
      || sym2.initialize.isEffectivelyFinal
      || !sym1.isTrait && !sym2.isTrait
      || sym1.isSealed && sym2.isSealed && allChildrenAreIrreconcilable(sym1, sym2) && !currentRun.compiles(sym1) && !currentRun.compiles(sym2)

@scabug scabug closed this as completed Jan 21, 2014
@scabug scabug added this to the 2.10.4-RC2 milestone Apr 7, 2017
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