-Wsafe-init doesn't detect initialization order problems

[kubukoz]

Compiler version

3.6.1, 3.6.4-RC1-bin-20241204-a67dbb0-NIGHTLY

Minimized code

case class Record(region: String, env: String)

object foo {

  val record = Record(region, env)

  val region = "oops"
  val env = "hello"

}

object Demo extends App { println(foo.record) }

compiled with -Wsafe-init

Output

Record(null,null)

Expectation

something similar to 2.13's behavior under -Xcheckinit:

scala-cli run . --scala 2.13 -Xcheckinit                                                                                                                                                   
Compiling project (Scala 2.13.15, JVM (21))
[warn] ./demo.scala:5:23
[warn] Reference to uninitialized value region
[warn]   val record = Record(region, env)
[warn]                       ^^^^^^
[warn] ./demo.scala:5:31
[warn] Reference to uninitialized value env
[warn]   val record = Record(region, env)
[warn]                               ^^^
Compiled project (Scala 2.13.15, JVM (21))
Exception in thread "main" java.lang.ExceptionInInitializerError
        at Demo$.delayedEndpoint$Demo$1(demo.scala:12)
        at Demo$delayedInit$body.apply(demo.scala:12)
        at scala.Function0.apply$mcV$sp(Function0.scala:42)
        at scala.Function0.apply$mcV$sp$(Function0.scala:42)
        at scala.runtime.AbstractFunction0.apply$mcV$sp(AbstractFunction0.scala:17)
        at scala.App.$anonfun$main$1(App.scala:98)
        at scala.App.$anonfun$main$1$adapted(App.scala:98)
        at scala.collection.IterableOnceOps.foreach(IterableOnce.scala:619)
        at scala.collection.IterableOnceOps.foreach$(IterableOnce.scala:617)
        at scala.collection.AbstractIterable.foreach(Iterable.scala:935)
        at scala.App.main(App.scala:98)
        at scala.App.main$(App.scala:96)
        at Demo$.main(demo.scala:12)
        at Demo.main(demo.scala)
Caused by: scala.UninitializedFieldError: Uninitialized field: demo.scala: 7
        at foo$.region(demo.scala:7)
        at foo$.<clinit>(demo.scala:5)
        ... 14 more

[kubukoz]

apparently, even without -Xcheckinit you get a warning during compilation - I suppose that's more in line with what -Wsafe-init should do

[som-snytt]

They keep the good stuff in the back.

➜  snips scalac -d ~/sandbox -Ysafe-init-global init-order.scala
-- Warning: init-order.scala:6:22 ----------------------------------------------
6 |  val record = Record(region, env)
  |                      ^^^^^^
  |               Access uninitialized field value region. Calling trace:
  |               ├── object foo {      [ init-order.scala:4 ]
  |               │   ^
  |               └── val record = Record(region, env)  [ init-order.scala:6 ]
  |                                       ^^^^^^
-- Warning: init-order.scala:6:30 ----------------------------------------------
6 |  val record = Record(region, env)
  |                              ^^^
  |               Access uninitialized field value env. Calling trace:
  |               ├── object foo {      [ init-order.scala:4 ]
  |               │   ^
  |               └── val record = Record(region, env)  [ init-order.scala:6 ]
  |                                               ^^^
2 warnings found

I don't actually know what the difference is, or what difference is intended, although I tried to follow the threads.

[olhotak]

-Wsafe-init works only for classes, not global objects.

-Ysafe-init-global is for global objects, but it is still experimental and under development.

[kubukoz]

Good to know! I like the rendering of the trace, very cool :)

Shall we keep this open or is there another ticket that covers -Ysafe-init-global?

[Gedochao]

Shall we keep this open or is there another ticket that covers -Ysafe-init-global?

@kubukoz let's keep it, I don't think we track this anywhere else at this point.
I guess it's more of a feature request than a bug per se, too.