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assertion failure in superaccessors #5969

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scabug opened this issue Jun 23, 2012 · 6 comments
Closed

assertion failure in superaccessors #5969

scabug opened this issue Jun 23, 2012 · 6 comments
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@scabug scabug commented Jun 23, 2012

This was a difficult minimization. g must be overloaded; the expression must be typed as an argument; and both legs of the if as well as the call to map appear to be necessary. Remove any of the above, and one sees the appropriate error message - List(g(x)) is attempting to call g with a String rather than one of the types upon which it is overloaded.

class C1
class C2
class A {
  def f(x: Any) = x
  def g(x: C1): String = "A"
  def g(x: C2): String = "B"
  
  def crash() = f(List[String]() flatMap { x =>
    if (false) List(g(x)) else List[C1]() map g
  })
}
// at scala.Predef$.assert(Predef.scala:162)
// at scala.tools.nsc.Global.assert(Global.scala:235)
// at scala.tools.nsc.typechecker.SuperAccessors$SuperAccTransformer.transform(SuperAccessors.scala:291)
// at scala.tools.nsc.typechecker.SuperAccessors$SuperAccTransformer$$anonfun$transformArgs$1.apply(SuperAccessors.scala:74)
// at scala.tools.nsc.typechecker.SuperAccessors$SuperAccTransformer$$anonfun$transformArgs$1.apply(SuperAccessors.scala:71)
// at scala.reflect.internal.TreeInfo$$anonfun$mapMethodParamsAndArgs$1.apply(TreeInfo.scala:115)
// at scala.reflect.internal.TreeInfo$$anonfun$mapMethodParamsAndArgs$1.apply(TreeInfo.scala:115)
// at scala.reflect.internal.util.Collections$class.foreach2(Collections.scala:150)
// at scala.reflect.internal.SymbolTable.foreach2(SymbolTable.scala:12)
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@scabug scabug commented Jun 23, 2012

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@scabug scabug commented Jun 23, 2012

@paulp said:
It's a regression since 2.9.

% scalac29 -d /tmp bug.scala 
bug.scala:9: error: overloaded method value g with alternatives:
  (x: C2)String <and>
  (x: C1)String
 cannot be applied to (String)
    if (false) List(g(x)) else List[C1]() map g
                    ^
one error found
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@scabug scabug commented Jun 24, 2012

@retronym said:
That's slippery. Observing it from a safe distance:

class C1
class C2
class A {
  def f(x: Any) = x
  def g(x: C1): String = "A"
  def g(x: C2): String = "B"

  def hof(x: String => Any) {}

  class X[A]() {
    def this(a: A) = this()
    def map[B](f: A => Any): Any = ??? // remove type parameter => avoid crash
  }

  def crash() = hof { x =>
    if (false) new X(g("")) else new X[C1]().map(g)

    // Other lubby situations crash:
    //
    // (true: Boolean) match {
    //   case false => new X(g("")); case true => new X[C1]().map(g)
    // }

    // try new X(g("")) catch { case _ => new X[C1]().map(g) }

    // List(new X(g("")), new X[C1]().map(g))
  }

  // No crash if the argument isn't a function
  // def nocrash1() = identity {
  //   if (false) new X(g("")) else new X[C1]().map(g)
  // }
}

The error is buffered into a Context deep down in type checking, but it doesn't get reported later on. It's pretty hard to see through the thicket of silent(...) / tryTwice(...) etc.

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@scabug scabug commented Jun 24, 2012

@som-snytt said:
In #5687, the assert fails on an expr of the form new C().f().g() where C is "erroneous or inaccessible type" because of a bad type member. Only the top Apply gets error type.

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@scabug scabug commented Jun 27, 2012

@hubertp said:
#5687 is not related to this one at all.

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@scabug scabug commented Jul 7, 2012

@scabug scabug closed this Jul 7, 2012
@scabug scabug added this to the 2.10.0-M4 milestone Apr 7, 2017
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