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Compiler allows to compile unsound code #1364

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scabug opened this issue Sep 21, 2008 · 4 comments
Closed

Compiler allows to compile unsound code #1364

scabug opened this issue Sep 21, 2008 · 4 comments
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@dubochet

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@scabug
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scabug commented Sep 21, 2008

Source code:

trait A {
  type T <: { type S[-U] }
  val x : T
  def y : x.S[AnyRef]
  def z : x.S[String] = y
}

object B extends A {
 type T = { type S[U] = U }
 val x : T = null
 def y : x.S[AnyRef] = new AnyRef
 def t : String = z
}

println(B.t)

Compiler version: 2.7.2.RC2

Actual result: Code compiles successfully, but throws an exception at run-time:

java.lang.ClassCastException: java.lang.Object cannot be cast to java.lang.String
	at Main$$$$anon$$1$$B$$.t((virtual file):16)
	at Main$$$$anon$$1.<init>((virtual file):19)
	at Main$$.main((virtual file):4)
	at Main.main((virtual file))
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
	at java.lang.reflect.Method.invoke(Unknown Source)
	at scala.tools.nsc.ObjectRunner$$$$anonfun$$run$$1.apply(ObjectRunner.scala:75)
	at scala.tools.nsc.ObjectRunner$$.withContextClassLoader(ObjectRunner.scala:49)
	at scala.tools.nsc.ObjectRunner$$.run(ObjectRunner.scala:74)
	at scala.tools.nsc.ScriptRunner$$.scala$$tools$$nsc$$ScriptRunner$$$$runCompiled(ScriptRunner.scala:382)
	at scala.tools.nsc.ScriptRunner$$$$anonfun$$runScript$$1.apply(ScriptRunner.scala:410)
	at scala.tools.nsc.ScriptRunner$$$$anonfun$$runScript$$1.apply(ScriptRunner.scala:409)
	at scala.tools.nsc.ScriptRunner$$.withCompiledScript(ScriptRunner.scala:354)
	at scala.tools.nsc.ScriptRunner$$.runScript(ScriptRunner.scala:409)
	at scala.tools.nsc.MainGenericRunner$$.main(MainGenericRunner.scala:179)
	at scala.tools.nsc.MainGenericRunner.main(MainGenericRunner.scala)

Expected result: Compiler should not allow to drop variance annotations (in this case, on the type parameter U) when checking conformance of structural types.
@scabug
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scabug commented Sep 21, 2008

Imported From: https://issues.scala-lang.org/browse/SI-1364?orig=1
Reporter: Vladimir Reshetnikov (nikov)

@scabug
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scabug commented Sep 30, 2008

@lrytz said:
related to #1363

@scabug
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scabug commented Feb 24, 2011

@soc said:
The example doesn't compile anymore in 2.9 trunk:

<console>:18: error: overriding type T in trait A with bounds >: Nothing <: AnyRef{type S[-U]};
 type T has incompatible type
        type T = { type S[U] = U }
             ^

Maybe this was fixed?

@scabug
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scabug commented Mar 3, 2011

@paulp said:
(In r24372) Test case closes #1364, no review.

@scabug scabug closed this as completed May 18, 2011
@scabug scabug added the critical label Apr 6, 2017
@scabug scabug mentioned this issue Apr 7, 2017
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