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Blaisorblade opened this issue Apr 25, 2018 · 4 comments
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Applications of abstract higher-kinded types to wildcard arguments aren't rejected #4382

Blaisorblade opened this issue Apr 25, 2018 · 4 comments
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area:typer itype:bug

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@Blaisorblade
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Carved out of #4375. The following code compiles, while I expect all the errors described—they're necessary if we want to ensure people can't write existentials (and otherwise, not sure what the current check is for). Such an error is useful for people who might not realize their types mean something else now.

The check for unreducibility seems simply incomplete:

object App {
  type Id[A] >: A <: A
  def v1: Id[_] = ??? // should give error

  type HkL[A] >: A
  def v2: HkL[_] = ??? // should give error

  type HkU[A] <: A
  def v3: HkU[_] = ???  // should give error

  type HkAbs[A]
  def v4: HkAbs[_] = ??? // should give error
}

contrast with

scala> def v: _ = ???
1 |def v: _ = ???
  |       ^
  |       Unbound wildcard type

To demonstrate this is a problem, let's use a trait instead:

trait Foo {
  type HkP[A] >: (A, A) <: (A, A)
  def v1: HkP[_] = ??? // should give error

  type HkL[A] >: (A, A)
  def v2: HkL[_] = ??? // should give error

  type HkU[A] <: (A, A)
  def v3: HkU[_] = ???  // should give error

  type HkAbs[A]
  def v4: HkAbs[_] = ??? // should give error
}
object Bar extends Foo {
  type HkP[A] = (A, A)
  type HkL[A] = (A, A)
  type HkU[A] = (A, A)
  type HkAbs[A] = (A, A)
}

Then at least the types are approximates without crashes (here):

scala> def foo = Bar.v1
def foo: (_, _)
@smarter smarter mentioned this issue Apr 26, 2018
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@smarter
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smarter commented Apr 26, 2018

See #4376 for an example that crashes the compiler because we assume that hk types do not have wildcard arguments.

@odersky odersky closed this as completed in 1d04427 May 1, 2018
odersky added a commit that referenced this issue May 1, 2018
@odersky
Merge pull request #4423 from dotty-staging/fix-#4382
1c79982 
Fix #4382: Disallow wildcard arguments for higher-kinded types
@Blaisorblade
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We still get the same crash from

trait x0[x0[_]] {
  (??? :x0[_]):x0[Int]
}

which has no syntax errors. If you rename x0's type argument to anything other than x0 everything works.

That's minimized from #4452's and #4389:

// From 09d8cdb2f7be2b81c318d338626268b7ec28ab12.scala <==
trait x0[x0[]] {
(x1:x0[_):x0[

@Blaisorblade Blaisorblade reopened this May 3, 2018
@Blaisorblade
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More precisely, the full stack trace is a bit different later, but still the same idea:

Exception in thread "main" java.lang.ClassCastException: dotty.tools.dotc.core.Types$LambdaParam cannot be cast to dotty.tools.dotc.core.Symbols$Symbol
	at dotty.tools.dotc.core.TypeComparer.compareCaptured$1(TypeComparer.scala:891)
	at dotty.tools.dotc.core.TypeComparer.isSubArg$1(TypeComparer.scala:903)
	at dotty.tools.dotc.core.TypeComparer.isSubArgs(TypeComparer.scala:912)
	at dotty.tools.dotc.core.TypeComparer.isMatchingApply$1(TypeComparer.scala:692)
	at dotty.tools.dotc.core.TypeComparer.compareAppliedType2$1(TypeComparer.scala:796)
	at dotty.tools.dotc.core.TypeComparer.thirdTry$1(TypeComparer.scala:405)
	at dotty.tools.dotc.core.TypeComparer.secondTry$1(TypeComparer.scala:363)
	at dotty.tools.dotc.core.TypeComparer.firstTry$1(TypeComparer.scala:285)
	at dotty.tools.dotc.core.TypeComparer.$anonfun$recur$2(TypeComparer.scala:860)
	at scala.runtime.java8.JFunction0$mcZ$sp.apply(JFunction0$mcZ$sp.java:12)
	at dotty.tools.dotc.reporting.trace$.op1$3(trace.scala:32)
	at dotty.tools.dotc.reporting.trace$.apply(trace.scala:33)
	at dotty.tools.dotc.reporting.trace$.apply(trace.scala:39)
	at dotty.tools.dotc.core.TypeComparer.recur(TypeComparer.scala:129)
	at dotty.tools.dotc.core.TypeComparer.isSubType(TypeComparer.scala:124)
	at dotty.tools.dotc.core.TypeComparer.isSubType(TypeComparer.scala:127)
	at dotty.tools.dotc.core.TypeComparer.topLevelSubType(TypeComparer.scala:110)
	at dotty.tools.dotc.core.Types$Type.$anonfun$$less$colon$less$1(Types.scala:778)
	at scala.runtime.java8.JFunction0$mcZ$sp.apply(JFunction0$mcZ$sp.java:12)
	at dotty.tools.dotc.util.Stats$.track(Stats.scala:35)
	at dotty.tools.dotc.core.Types$Type.$less$colon$less(Types.scala:778)
	at dotty.tools.dotc.typer.Typer.adaptNoArgsOther$1(Typer.scala:2326)
	at dotty.tools.dotc.typer.Typer.adaptNoArgs$1(Typer.scala:2394)
	at dotty.tools.dotc.typer.Typer.adapt1(Typer.scala:2526)
	at dotty.tools.dotc.typer.Typer.$anonfun$adapt$1(Typer.scala:2071)
	at dotty.tools.dotc.util.Stats$.track(Stats.scala:35)
	at dotty.tools.dotc.typer.Typer.adapt(Typer.scala:2066)
	at dotty.tools.dotc.typer.Typer.$anonfun$typed$2(Typer.scala:1856)
	at dotty.tools.dotc.reporting.trace$.op1$3(trace.scala:32)
	at dotty.tools.dotc.reporting.trace$.apply(trace.scala:33)
	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:1852)
	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:1864)
	at dotty.tools.dotc.typer.Typer.ascription$1(Typer.scala:560)
	at dotty.tools.dotc.typer.Typer.$anonfun$typedTyped$5(Typer.scala:578)
	at dotty.tools.dotc.typer.Typer.cases$1(Typer.scala:550)
	at dotty.tools.dotc.typer.Typer.$anonfun$typedTyped$1(Typer.scala:576)
	at dotty.tools.dotc.util.Stats$.track(Stats.scala:35)
	at dotty.tools.dotc.typer.Typer.typedTyped(Typer.scala:536)
	at dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:1778)
	at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:1825)
	at dotty.tools.dotc.typer.Typer.$anonfun$typed$2(Typer.scala:1856)
	at dotty.tools.dotc.reporting.trace$.op1$3(trace.scala:32)
	at dotty.tools.dotc.reporting.trace$.apply(trace.scala:33)
	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:1852)
	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:1864)
	at dotty.tools.dotc.typer.Typer.traverse$1(Typer.scala:1900)
	at dotty.tools.dotc.typer.Typer.typedStats(Typer.scala:1912)
	at dotty.tools.dotc.typer.Typer.$anonfun$typedClassDef$1(Typer.scala:1526)
	at dotty.tools.dotc.util.Stats$.track(Stats.scala:35)
	at dotty.tools.dotc.typer.Typer.typedClassDef(Typer.scala:1450)
	at dotty.tools.dotc.typer.Typer.typedNamed$1(Typer.scala:1765)
	at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:1824)
	at dotty.tools.dotc.typer.Typer.$anonfun$typed$2(Typer.scala:1856)
	at dotty.tools.dotc.reporting.trace$.op1$3(trace.scala:32)
	at dotty.tools.dotc.reporting.trace$.apply(trace.scala:33)
	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:1852)
	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:1864)
	at dotty.tools.dotc.typer.Typer.traverse$1(Typer.scala:1883)
	at dotty.tools.dotc.typer.Typer.typedStats(Typer.scala:1912)
	at dotty.tools.dotc.typer.Typer.$anonfun$typedPackageDef$1(Typer.scala:1631)
	at dotty.tools.dotc.util.Stats$.track(Stats.scala:35)
	at dotty.tools.dotc.typer.Typer.typedPackageDef(Typer.scala:1624)
	at dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:1804)
	at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:1825)
	at dotty.tools.dotc.typer.Typer.$anonfun$typed$2(Typer.scala:1856)
	at dotty.tools.dotc.reporting.trace$.op1$3(trace.scala:32)
	at dotty.tools.dotc.reporting.trace$.apply(trace.scala:33)
	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:1852)
	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:1864)
	at dotty.tools.dotc.typer.Typer.typedExpr(Typer.scala:1924)
	at dotty.tools.dotc.typer.FrontEnd.$anonfun$typeCheck$1(FrontEnd.scala:66)
	at dotty.tools.dotc.typer.FrontEnd.monitor(FrontEnd.scala:34)
	at dotty.tools.dotc.typer.FrontEnd.typeCheck(FrontEnd.scala:64)
	at dotty.tools.dotc.typer.FrontEnd.$anonfun$runOn$7(FrontEnd.scala:95)
	at dotty.tools.dotc.typer.FrontEnd.$anonfun$runOn$7$adapted(FrontEnd.scala:95)
	at scala.collection.immutable.List.foreach(List.scala:389)
	at dotty.tools.dotc.typer.FrontEnd.runOn(FrontEnd.scala:95)
	at dotty.tools.dotc.Run.$anonfun$compileUnits$3(Run.scala:174)
	at scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.java:12)
	at dotty.tools.dotc.util.Stats$.trackTime(Stats.scala:47)
	at dotty.tools.dotc.Run.$anonfun$compileUnits$2(Run.scala:171)
	at dotty.tools.dotc.Run.$anonfun$compileUnits$2$adapted(Run.scala:169)
	at scala.collection.IndexedSeqOptimized.foreach(IndexedSeqOptimized.scala:32)
	at scala.collection.IndexedSeqOptimized.foreach$(IndexedSeqOptimized.scala:29)
	at scala.collection.mutable.ArrayOps$ofRef.foreach(ArrayOps.scala:191)
	at dotty.tools.dotc.Run.runPhases$1(Run.scala:169)
	at dotty.tools.dotc.Run.$anonfun$compileUnits$1(Run.scala:194)
	at scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.java:12)
	at dotty.tools.dotc.util.Stats$.maybeMonitored(Stats.scala:88)
	at dotty.tools.dotc.Run.compileUnits(Run.scala:149)
	at dotty.tools.dotc.Run.compileSources(Run.scala:136)
	at dotty.tools.dotc.Run.compile(Run.scala:120)
	at dotty.tools.dotc.Driver.doCompile(Driver.scala:29)
	at dotty.tools.dotc.Driver.process(Driver.scala:127)
	at dotty.tools.dotc.Driver.process(Driver.scala:96)
	at dotty.tools.dotc.Driver.process(Driver.scala:108)
	at dotty.tools.dotc.Driver.main(Driver.scala:135)
	at dotty.tools.dotc.Main.main(Main.scala)

@Blaisorblade Blaisorblade mentioned this issue May 3, 2018
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@Blaisorblade
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Blaisorblade commented May 11, 2018 •
edited
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EDIT: moved comment to #4376.

@kory33 kory33 mentioned this issue Dec 13, 2018
Closed
OlivierBlanvillain added a commit to dotty-staging/dotty that referenced this issue Mar 19, 2019
@OlivierBlanvillain
Fix scala#4382: Add regression test
b8a3216
liufengyun added a commit that referenced this issue Mar 20, 2019
@liufengyun
Merge pull request #6117 from dotty-staging/fix-#4382
87a6ce4 
 Fix #4382: Add regression test
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