No "Reference to uninitialized value" warning

[Bersier]

Compiler version

3.1.3

Minimized code

val a = b
val b = 1

@main def main(): Unit =
  println(a)

Output

0

Expectation

Expected output: 1. The natural expected behavior is that initialization would follow the dependency graph, and it would be a compiler error if it contains a cycle.

At the very least, the compiler should issue an uninitialized value warning, as in Scala 2, a fortiori when -Ysafe-init is enabled.

As it stands, referential transparency and val immutability are violated without so much as a warning.

[SethTisue]

https://docs.scala-lang.org/scala3/reference/other-new-features/safe-initialization.html exists, but requires a -Y flag

there's some older history on this (in Scala 2) at https://docs.scala-lang.org/tutorials/FAQ/initialization-order.html, linked from https://docs.scala-lang.org/tutorials/FAQ/index.html#why-is-my-abstract-or-overridden-val-null

[keynmol]

-Ysafe-init doesn't catch it in the presented by the author, but in a modified scenario it does:

object test:
  val a = b
  val b = 1

@main def hello =
  println(test.a)

-- Warning: test.scala:3:6 -----------------------------------------------------
3 |  val b = 1
  |      ^
  |      Access non-initialized value b. Calling trace:
  |      -> val a = b	[ test.scala:2 ]
  |                 ^
1 warning found

[odersky]

Maybe -Ysafe-init can be changed so that it also works for toplevel code?

[liufengyun]

Maybe -Ysafe-init can be changed so that it also works for toplevel code?

I'll have a look, it should behave the same as top-level objects.