Can generate singleton type instances

[kynthus]

Compiler version

3.0.0

Minimized code

val hello: String = "hello"

object MyObj {
  val a: Int = 123
  val b: Double = 456.789
  val c: String = "ABC"
}

scala> val stringFromSingleton: String = new hello.type()    // Generate `<val>.type`
val stringFromSingleton: String = ""

scala> val myObjFromSingleton: MyObj.type = new MyObj.type() // Generate `<object>.type`
val myObjFromSingleton: MyObj.type = MyObj$@2114eb1a

Output

If generate a singleton type of val, the constructor of the type of immutable variable is called.
If generate a singleton type of object, another object is generated.

Since they are separate instances, false will be returned when comparing reference by eq method.

scala> hello eq stringFromSingleton
val res1: Boolean = false

scala> MyObj eq myObjFromSingleton
val res2: Boolean = false

In addition, for non-REPL, creating a object resulted in a java.lang.IllegalAccessError.

// GenSingleton.scala

object MyObj {
  val a: Int = 123
  val b: Double = 456.789
  val c: String = "ABC"
}

object GenSingleton {
  def main(args: Array[String]): Unit = {
    val myObjFromSingleton: MyObj.type = new MyObj.type() // java.lang.IllegalAccessError
    val hello: String = "hello"
    val stringFromSingleton: String = new hello.type()
  }
}

# scalac GenSingleton.scala
# scala GenSingleton
Exception in thread "main" java.lang.IllegalAccessError: class GenSingleton$ tried to access private method 'void MyObj$.<init>()' (GenSingleton$ and MyObj$ are in unnamed module of loader 'app')
        at GenSingleton$.main(GenSingleton.scala:9)
        at GenSingleton.main(GenSingleton.scala)

Expectation

I expect that the singleton type cannot be generated by new.
It seems that generation is allowed from 3.0.0-RC2 and later, and it is a compile error 3.0.0-RC1 and earlier.

# scala -version
Starting scala3 REPL...
Scala compiler version 3.0.0-RC1 -- Copyright 2002-2021, LAMP/EPFL

val hello: String = "hello"

object MyObj {
  val a: Int = 123
  val b: Double = 456.789
  val c: String = "ABC"
}

scala> val stringFromSingleton: String = new hello.type()
1 |val stringFromSingleton: String = new hello.type()
  |                                      ^^^^^^^^^^
  |                                      (hello : String) is not a class type

scala> val myObjFromSingleton: MyObj.type = new MyObj.type()
1 |val myObjFromSingleton: MyObj.type = new MyObj.type()
  |                                         ^^^^^^^^^^
  |                                         MyObj.type is not a class type

[OlivierBlanvillain]

Regression bisected to 25fa24e