"VerifyError: Bad type on operand stack" when Class with `var` extends class with lambda

[jlprat]

It seems that when we have a class with a var as a member that extends a class that has a lambda as a member the class is not instantiable at runtime.
I check current reported bugs and this is not like any of the others already reported for "Bad type on operand stack".

Compiler version

3.0.2 and 3.1.0-RC2

Minimized code

This code compiles in Scala 3 and in Scala 2. You can find a reproducer here

class ClassWithLambda(sup: () => Long)
class ClassWithVar(var msg: String) extends ClassWithLambda(() => 1)
val _ = new ClassWithVar("foo")

def main(args: Array[String]): Unit = {
  println("it worked")
}

Output

When we run the previous code in Scala 3.x we get the following output.

[error] (run-main-a) java.lang.VerifyError: Bad type on operand stack
[error] Exception Details:
[error]   Location:
[error]     example/Reproducer$ClassWithVar.<init>(Ljava/lang/String;)V @10: invokevirtual
[error]   Reason:
[error]     Type uninitializedThis (current frame, stack[2]) is not assignable to 'example/Reproducer$ClassWithVar'
[error]   Current Frame:
[error]     bci: @10
[error]     flags: { flagThisUninit }
[error]     locals: { uninitializedThis, 'java/lang/String' }
[error]     stack: { uninitializedThis, 'example/Reproducer$', uninitializedThis }
[error]   Bytecode:
[error]     0x0000000: 2a2b b500 0f2a b200 152a b600 18b6 001c
[error]     0x0000010: b700 1fb1
[error] java.lang.VerifyError: Bad type on operand stack
[error] Exception Details:
[error]   Location:
[error]     example/Reproducer$ClassWithVar.<init>(Ljava/lang/String;)V @10: invokevirtual
[error]   Reason:
[error]     Type uninitializedThis (current frame, stack[2]) is not assignable to 'example/Reproducer$ClassWithVar'
[error]   Current Frame:
[error]     bci: @10
[error]     flags: { flagThisUninit }
[error]     locals: { uninitializedThis, 'java/lang/String' }
[error]     stack: { uninitializedThis, 'example/Reproducer$', uninitializedThis }
[error]   Bytecode:
[error]     0x0000000: 2a2b b500 0f2a b200 152a b600 18b6 001c
[error]     0x0000010: b700 1fb1
[error]
[error] 	at example.Reproducer$.<clinit>(Reproducer.scala:19)
[error] 	at example.main.main(Reproducer.scala:21)
[error] 	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
[error] 	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
[error] 	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
[error] 	at java.lang.reflect.Method.invoke(Method.java:498)

Expectation

Code should run in Scala 3 (3.0.2 and 3.1.0-RC2) as it runs in Scala 2.

it worked

Notes

Please note that the following does compile and run in Scala 3.x and 2.13.

class ClassWithLambda(sup: () => Long)
class ClassWithoutVar(msg: String) extends ClassWithLambda(() => 1)

class ClassWithoutLambda(something: Int)
class ClassWithVarExtendingNotLambda(var msg: String) extends ClassWithoutLambda(1)

val _ = new ClassWithoutVar("foo") // This can be instantiated at runtime
val _ = new ClassWithVarExtendingNotLambda("foo") // This can be instantiated at runtime

def main(args: Array[String]): Unit = {
  println("it worked")
}

[smarter]

Workaround:

class ClassWithLambda(sup: () => Long)
class ClassWithVar(_msg: String) extends ClassWithLambda(() => 1) {
  var msg: String = _msg
}

[jlprat]

Yes true! I forgot to add the workaround. I came up with the same one.