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Type alias in package object causes type checker assertion failure #6084

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scabug opened this issue Jul 14, 2012 · 8 comments
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Type alias in package object causes type checker assertion failure #6084

scabug opened this issue Jul 14, 2012 · 8 comments

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@scabug
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@scabug scabug commented Jul 14, 2012

The program below causes a crash, apparently due to the type alias in the package object. The commented out version compiles without a crash. See the attachment for the stack trace.

Code similar to this has been present in our Kiama library for quite a while and has compiled fine with the 2.9 series compilers.

// This version crashes the compiler:

package object foo {

    type ==>[T,U] = PartialFunction[T,U]

}

package foo {

    abstract class Foo[T,U] (val f : T ==> U) extends (T ==> U) {

        def bar (r : T ==> U) : T ==> U = 
            r match {
                case d : Foo[_, _] => d.f
                case _             => r
            }

    }

}

// This version compiles with no crashes:

// package foo {

//     abstract class Foo[T,U] (val f : PartialFunction[T,U]) extends (PartialFunction[T,U]) {

//         def bar (r : PartialFunction[T,U]) : PartialFunction[T,U] = 
//             r match {
//                 case d : Foo[_, _] => d.f
//                 case _             => r
//             }

//     }

// }
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@scabug scabug commented Jul 14, 2012

Imported From: https://issues.scala-lang.org/browse/SI-6084?orig=1
Reporter: Tony Sloane (asloane)
Affected Versions: 2.10.0-M5
Attachments:

  • trace.txt (created on Jul 14, 2012 4:33:17 PM UTC, 15345 bytes)
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@scabug scabug commented Jul 14, 2012

@paulp said:
Someone elaborated:

package object foo { type X[T, U] = (T => U) }

package foo {
  abstract class Foo[T, U](val d: T => U) extends (T => U) {
    def f1(r: X[T, U])           = r match { case x: Foo[_,_] => x.d }  // inferred ok
    def f2(r: X[T, U]): (T => U) = r match { case x: Foo[_,_] => x.d }  // dealiased ok
    def f3(r: X[T, U]): X[T, U]  = r match { case x: Foo[_,_] => x.d }  // alias not ok

    // x.d : foo.this.package.type.X[?scala.reflect.internal.Types$NoPrefix$?.T, ?scala.reflect.internal.Types$NoPrefix$?.U] ~>scala.this.Function1[?scala.reflect.internal.Types$NoPrefix$?.T, ?scala.reflect.internal.Types$NoPrefix$?.U]
    //  at scala.Predef$.assert(Predef.scala:170)
    //  at scala.tools.nsc.Global.assert(Global.scala:235)
    //  at scala.tools.nsc.ast.TreeGen.mkCast(TreeGen.scala:252)
    //  at scala.tools.nsc.typechecker.Typers$Typer.typedCase(Typers.scala:2263)
  }
}
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@scabug scabug commented Jul 30, 2012

Tony Sloane (asloane) said:
This regression is still present in 2.10.0-M6.

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@scabug scabug commented Jul 30, 2012

@retronym said:
Paul, the umbrella mkCast you added in 214c145 didn't quite fit this spot: scala/scala@214c145#L11L1916

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@scabug scabug commented Jul 30, 2012

@retronym said:
Marking as critical to get it into contention for 2.10: it's a regression and the fix looks trivial.

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@scabug scabug commented Jul 30, 2012

@paulp said:
That's the right spot, although it seems like my real problem was believing the comment ("no need for pt.normalize here")

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@scabug scabug commented Jul 30, 2012

@scabug scabug closed this Aug 4, 2012
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@scabug scabug commented Aug 23, 2012

Tony Sloane (asloane) said:
To close the loop here, I can confirm that this problem does not occur in Kiama when building with 2.10.0-M7.

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