VerifyError when class has var parameter and extends another class

[bishabosha]

Originally posted at https://contributors.scala-lang.org/t/verify-error-when-using-mutable-fields-in-parametric-enumeration/5531

Compiler version

I use Scala 3.1.0 (17.0.1, Java OpenJDK 64-Bit Server VM).

Minimized code

In this setting, I found a Verify Error when using mutable fields in parametric enumeration as follows:

enum A(c: Int):
  case B(var k: Int) extends A(k)

Output

Exception in thread "main" java.lang.VerifyError: Bad type on operand stack
Exception Details:
  Location:
    A$B.<init>(I)V @7: invokevirtual
  Reason:
    Type uninitializedThis (current frame, stack[1]) is not assignable to 'A$B'
  Current Frame:
    bci: @7
    flags: { flagThisUninit }
    locals: { uninitializedThis, integer }
    stack: { uninitializedThis, uninitializedThis }
  Bytecode:
    0000000: 2a1b b500 1f2a 2ab6 0022 b700 24b1

	at java.base/java.lang.Class.getDeclaredMethods0(Native Method)
	at java.base/java.lang.Class.privateGetDeclaredMethods(Class.java:3402)
	at java.base/java.lang.Class.getMethodsRecursive(Class.java:3543)
	at java.base/java.lang.Class.getMethod0(Class.java:3529)
	at java.base/java.lang.Class.getMethod(Class.java:2225)
	at dotty.tools.scripting.ScriptingDriver.collectMainMethods$3(ScriptingDriver.scala:79)
	at dotty.tools.scripting.ScriptingDriver.$anonfun$3(ScriptingDriver.scala:88)
	at scala.collection.immutable.List.flatMap(List.scala:293)
	at dotty.tools.scripting.ScriptingDriver.detectMainClassAndMethod(ScriptingDriver.scala:89)
	at dotty.tools.scripting.ScriptingDriver.compileAndRun(ScriptingDriver.scala:34)
	at dotty.tools.scripting.Main$.main(Main.scala:43)
	at dotty.tools.MainGenericRunner$.run$1(MainGenericRunner.scala:168)
	at dotty.tools.MainGenericRunner$.main(MainGenericRunner.scala:175)
	at dotty.tools.MainGenericRunner.main(MainGenericRunner.scala)

Expectation

However, the following code does not throw any error:

enum A(c: Int):
  case B(k: Int) extends A(k)

I think that it happens because the compiled JVM bytecode tries to use the mutable field k before its initialization in A(k).

[smarter]

Also happens with non-enums (#14422):

class A {
  class B(z: Any) {}
  class C(var y: Any) extends B(y) {}
  val c = new C("bar")
}

@main def test() =
  new A

[smarter]

Actually both of these issues are already fixed in 3.1.1.