Ycheck that java classes are not used as objects

[DarkDimius]

This passes Ycheck, bu it should not:

import java.lang.Math

val myMath: Math.type = Math
myMath.sqrt(3.0)

[liufengyun]

@DarkDimius when I run the code on my machine, it generates compiling errors. It seems this issue is already fixed.

tests/neg/i972.scala:4: error: object Math is not a value
  val myMath: Math.type = Math
              ^
tests/neg/i972.scala:4: error: object Math is not a value
  val myMath: Math.type = Math
                          ^
two errors found

The code for tests/neg/i972.scala:

import java.lang.Math

object Foo {
  val myMath: Math.type = Math
  myMath.sqrt(3.0)
}

[DarkDimius]

@liufengyun, the errors you are showing are Typer errors.
The issue that I was talking about is that if phases generate such code, it will pass Ycheck and trigger an exception in GenBCode.

[liufengyun]

@DarkDimius thanks for explanation. If I were to work this issue, how can I reproduce the error?

[DarkDimius]

You need to create a phase, that does something similar to:

val JLMath = ctx.requiredModule("java.lang.Math")
SyntheticValDef("myMath".toTermName, ref(JLMath)) // this tree should not pass Ycheck
Apply(ref(idFunction), ref(JLMath)) // this tree should not pass Ycheck

I believe that the best way to check is: if there is an Ident or Select that refers to java module, it needs to be wrapped with a Select around it.

[liufengyun]

Thanks @DarkDimius for the tip.

The thing I'm still unclear is, if the code can't pass the front-end type checking, does it mean it can never happen, thus we can save the check?

[DarkDimius]

if the code can't pass the front-end type checking, does it mean it can never happen, thus we can save the check?

Ycheck exists not to check user. It exists to verify correctness of phases and tress transformed by them.
This could happen if one writes a phases, that treats all modules equally, even those coming from Java. I had a master student fall in this trap.