FBounded Polymorphism and shouldNot compile giving a false positive

[dhinojosa]

Given the following production code:

package com.evolutionnext.fboundedpolymorphism

trait RecursiveSelfTypeEntity[E <: RecursiveSelfTypeEntity[E]]:
  self: E =>
  def create(): E

  def read(id: Long): Option[E]

  def update(f: E => E): E

  def delete(id: Long): Unit

Given the test:

package com.evolutionnext.fboundedpolymorphism

import org.scalatest.funsuite.AnyFunSuite
import org.scalatest.matchers.should.Matchers

class FBoundedPolymorphismSpec extends AnyFunSuite with Matchers:

  test("""We need to then ensure that Orange extends Entity[Orange],
         |  we then use self types""".stripMargin) {

    class Apple extends RecursiveSelfTypeEntity[Apple]:
      override def create(): Apple = ???

      override def read(id: Long): Option[Apple] = ???

      override def update(f: Apple => Apple): Apple = ???

      override def delete(id: Long): Unit = ???

    class Orange extends RecursiveSelfTypeEntity[Orange]:
      override def create(): Orange = ???

      override def read(id: Long): Option[Orange] = ???

      override def update(f: Orange => Orange): Orange = ???

      override def delete(id: Long): Unit = ???

    info("This is great, now this will not work, as expected and should not compile, uncomment it and view the compile error")

   //    class Banana extends RecursiveSelfTypeEntity[Apple]:
   //        override def create(): Apple = ???
   //
   //        override def read(id: Long): Option[Apple] = ???
   //
   //        override def update(f: Apple => Apple): Apple = ???
   //
   //        override def delete(id: Long): Unit = ???
   
    info("The following test succeeds, but it should fail. False positive")
    """class Banana extends RecursiveSelfTypeEntity[Apple] {
      |  override def create(): Apple = ???
      |  override def read(id: Long): Option[Apple] = ???
      |  override def update(f: Apple => Apple): Apple = ???
      |  override def delete(id: Long): Unit = ???
      |}""".stripMargin shouldNot compile
  }

In the above, if you uncomment the class Banana block you will find that the code block will not compile which is correct. But, when the shouldNot compile code is run with the same block it errors with the following error message

Expected a compiler error, but got none for code: class Banana extends RecursiveSelfTypeEntity[Apple] {
  override def create(): Apple = ???
  override def read(id: Long): Option[Apple] = ???
  override def update(f: Apple => Apple): Apple = ???
  override def delete(id: Long): Unit = ???
}  
ScalaTestFailureLocation: com.evolutionnext.fboundedpolymorphism.FBoundedPolymorphismSpec at (FBoundedPolymorphismSpec.scala:112)
org.scalatest.exceptions.TestFailedException: Expected a compiler error, but got none for code: class Banana extends RecursiveSelfTypeEntity[Apple] {
  override def create(): Apple = ???
  override def read(id: Long): Option[Apple] = ???
  override def update(f: Apple => Apple): Apple = ???
  override def delete(id: Long): Unit = ???
}  
	at com.evolutionnext.fboundedpolymorphism.FBoundedPolymorphismSpec.testFun$proxy4$1(FBoundedPolymorphismSpec.scala:112)
	at com.evolutionnext.fboundedpolymorphism.FBoundedPolymorphismSpec.$init$$$anonfun$4(FBoundedPolymorphismSpec.scala:76)
	at org.scalatest.Transformer.apply$$anonfun$1(Transformer.scala:22)
	at org.scalatest.OutcomeOf.outcomeOf(OutcomeOf.scala:85)
	at org.scalatest.OutcomeOf.outcomeOf$(OutcomeOf.scala:31)
	at org.scalatest.OutcomeOf$.outcomeOf(OutcomeOf.scala:104)
	at org.scalatest.Transformer.apply(Transformer.scala:22)
	at org.scalatest.Transformer.apply(Transformer.scala:21)
	at org.scalatest.funsuite.AnyFunSuiteLike$$anon$1.apply(AnyFunSuiteLike.scala:206)
	at org.scalatest.TestSuite.withFixture(TestSuite.scala:196)
	at org.scalatest.TestSuite.withFixture$(TestSuite.scala:138)
	at org.scalatest.funsuite.AnyFunSuite.withFixture(AnyFunSuite.scala:1563)
	at org.scalatest.funsuite.AnyFunSuiteLike.invokeWithFixture$1(AnyFunSuiteLike.scala:212)
	at org.scalatest.funsuite.AnyFunSuiteLike.runTest$$anonfun$1(AnyFunSuiteLike.scala:216)
	at org.scalatest.SuperEngine.runTestImpl(Engine.scala:306)
	at org.scalatest.funsuite.AnyFunSuiteLike.runTest(AnyFunSuiteLike.scala:216)
	at org.scalatest.funsuite.AnyFunSuiteLike.runTest$(AnyFunSuiteLike.scala:47)
	at org.scalatest.funsuite.AnyFunSuite.runTest(AnyFunSuite.scala:1563)
	at org.scalatest.funsuite.AnyFunSuiteLike.runTests$$anonfun$1(AnyFunSuiteLike.scala:249)
	at org.scalatest.SuperEngine.traverseSubNodes$1$$anonfun$1(Engine.scala:413)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
	at scala.collection.immutable.List.foreach(List.scala:333)
	at org.scalatest.SuperEngine.traverseSubNodes$1(Engine.scala:429)
	at org.scalatest.SuperEngine.runTestsInBranch(Engine.scala:396)
	at org.scalatest.SuperEngine.runTestsImpl(Engine.scala:475)
	at org.scalatest.funsuite.AnyFunSuiteLike.runTests(AnyFunSuiteLike.scala:249)
	at org.scalatest.funsuite.AnyFunSuiteLike.runTests$(AnyFunSuiteLike.scala:47)
	at org.scalatest.funsuite.AnyFunSuite.runTests(AnyFunSuite.scala:1563)
	at org.scalatest.Suite.run(Suite.scala:1114)
	at org.scalatest.Suite.run$(Suite.scala:564)
	at org.scalatest.funsuite.AnyFunSuite.org$scalatest$funsuite$AnyFunSuiteLike$$super$run(AnyFunSuite.scala:1563)
	at org.scalatest.funsuite.AnyFunSuiteLike.run$$anonfun$1(AnyFunSuiteLike.scala:253)
	at org.scalatest.SuperEngine.runImpl(Engine.scala:535)
	at org.scalatest.funsuite.AnyFunSuiteLike.run(AnyFunSuiteLike.scala:253)
	at org.scalatest.funsuite.AnyFunSuiteLike.run$(AnyFunSuiteLike.scala:47)
	at org.scalatest.funsuite.AnyFunSuite.run(AnyFunSuite.scala:1563)
	at org.scalatest.tools.SuiteRunner.run(SuiteRunner.scala:47)
	at org.scalatest.tools.Runner$.doRunRunRunDaDoRunRun$$anonfun$1(Runner.scala:1321)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
	at scala.collection.immutable.List.foreach(List.scala:333)
	at org.scalatest.tools.Runner$.doRunRunRunDaDoRunRun(Runner.scala:1323)
	at org.scalatest.tools.Runner$.runOptionallyWithPassFailReporter$$anonfun$2(Runner.scala:992)
	at scala.runtime.function.JProcedure2.apply(JProcedure2.java:15)
	at scala.runtime.function.JProcedure2.apply(JProcedure2.java:10)
	at org.scalatest.tools.Runner$.withClassLoaderAndDispatchReporter(Runner.scala:1481)
	at org.scalatest.tools.Runner$.runOptionallyWithPassFailReporter(Runner.scala:993)
	at org.scalatest.tools.Runner$.run(Runner.scala:798)
	at org.scalatest.tools.Runner.run(Runner.scala)
	at org.jetbrains.plugins.scala.testingSupport.scalaTest.ScalaTestRunner.runScalaTest2or3(ScalaTestRunner.java:43)
	at org.jetbrains.plugins.scala.testingSupport.scalaTest.ScalaTestRunner.main(ScalaTestRunner.java:26)

[cheeseng]

@dhinojosa Hmm, fyi ScalaTest macro for Scala 3 just use scala.compiletime.testing.typeChecks to check that the given code does not compile, I wonder if typeChecks does not cover the compiler phase that perform the check for the given expected error above. @liufengyun Do you have any idea if that is the case?

[liufengyun]

I wonder if typeChecks does not cover the compiler phase that perform the check for the given expected error above

Sorry for the late response. I checked the compiler code implementation of typeChecks, it does run PostTyper phase, which checks the type bounds.

I'd suggest create a minimized test without ScalaTest by using scala.compiletime.testing.typeChecks directly. If the error persists, then report a bug to the Scala 3 compiler.

[cheeseng]

@dhinojosa @liufengyun This is an example without scalatest:

package com.example

object Test: 
  def main(args: Array[String]): Unit =
    val result = 
      scala.compiletime.testing.typeChecks(
        "trait RecursiveSelfTypeEntity[E <: RecursiveSelfTypeEntity[E]]: \n" +
        "  self: E => \n" +
        "  def create(): E \n" +
        "  def read(id: Long): Option[E] \n" +
        "  def update(f: E => E): E \n" +
        "  def delete(id: Long): Unit \n" +
        "\n" +
        "class Apple extends RecursiveSelfTypeEntity[Apple]: \n" +
        "  override def create(): Apple = ??? \n" +
        "  override def read(id: Long): Option[Apple] = ??? \n" +
        "  override def update(f: Apple => Apple): Apple = ??? \n" +
        "  override def delete(id: Long): Unit = ??? \n" +
        " \n" +
        "class Orange extends RecursiveSelfTypeEntity[Orange]: \n" +
        "  override def create(): Orange = ??? \n" +
        "  override def read(id: Long): Option[Orange] = ??? \n" +
        "  override def update(f: Orange => Orange): Orange = ??? \n" +
        "  override def delete(id: Long): Unit = ??? \n" + 
        " \n" +
        "class Banana extends RecursiveSelfTypeEntity[Apple]: \n" +
        "  override def create(): Apple = ??? \n" +
        "  override def read(id: Long): Option[Apple] = ??? \n" +
        "  override def update(f: Apple => Apple): Apple = ??? \n" +
        "  override def delete(id: Long): Unit = ???\n"
      )
    assert(false, "Should fail type check, but it didn't.")

@dhinojosa Would you like to report it to dotty issues?

[dhinojosa]

@cheeseng That last line will always fail since it is false, assert(false, "Should fail type check, but it didn't."). When I replaced it with assert(result, "Should fail type check, but it didn't.") it works fine. Let me know if you want to do a follow up test.

[dhinojosa]

Oh, wait, even if I place the result, this should actually fail. Sorry, brain fail on my part.

[dhinojosa]

Filed: scala/scala3#18150