How to disable "unset private variable" warning

Question
#1

After switching compiler from 3.3.0 to 3.3.1 I started getting a lot of “unset private variable” warnings (hundreds in a single project). This is typically related to code that is using JavaFX and @FXML annotations, like here:

  @javafx.fxml.FXML
  private var button : javafx.scene.control.Button = _

I short, @FXML will cause assignment of proper value to button based on declaration in related .fxml file, but Scala compiler is not aware of that and is issuing a warning.

Is there a proper way to disable those new warnings?

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#2

scalac -W says scalac -Wunused:privates, so -Wunused:-privates to disable.

Alternatively, -Wconf:msg=unset private var:s to silence the warning.

Scala 3 doesn’t have the fine-grained category support for messages in Scala 2.

3 Likes
#3

This problem also arises when you do give the variable a value:

class Test(x: Int) : 
  private var y = x
  def show(): Unit = println(y)

(new Test(42)).show()

gives unset private variable on the second line.

#4

Isn’t that a bug, as in false positive warning (“here comes the wolf”) that should be reported?
It is after all not unset…

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#5

Yes, i think so, have made a report.

Btw, it does not always produce such a warning, I have other private variables where this does not happen. I was not able to find a pattern yet.

2 Likes
#6

I commented on the ticket that Scala 2 says to make it a val.

At issue is not whether the var is initialized with underscore or an explicit value; underscore just means the default value.

It’s warning that button_= is never called.

If the field is set only reflectively, then warnings are – what’s the word for when you subvert the type system and everything the language puts in place to help you write sound code?

It feels natural for a UI framework to be unsafe and written in javascript, such that one is destined for the eternal flames of the underworld.

The word “subvert” is too tame.

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#7

Thank you for pointing this out. I should have waited for more opinions before submitting the issue. My apologies.