Unexpected compilation warnings: Auto-application to () is deprecated.

[LuciferYang]

The test code is as follows and the test file named IsEmptySuite.scala

import org.scalatest.funsuite.AnyFunSuite // scalastyle:ignore funsuite
class IsEmptySuite extends AnyFunSuite { // scalastyle:ignore funsuite
  class Foo {
    def isEmpty(): Boolean = true
    def isTrue(x: Boolean): Boolean = x
  }
  test("test Foo#isEmpty") {
    val foo = new Foo
    Predef.assert(foo.isEmpty()) // no compilation warnings.
    assert(foo.isEmpty() === true) // no compilation warnings.
    assert(foo.isTrue(foo.isEmpty())) // no compilation warnings.
    assert(foo.isEmpty()) // an unexpected compilation warning.
  }
}

Then we I compile the code with Scala 2.13+

bin/scalac -deprecation  -classpath scalatest-funsuite_2.13-3.2.17.jar:scalatest-core_2.13-3.2.17.jar:scalactic_2.13-3.2.17.jar:scalatest-compatible-3.2.17.jar IsEmptySuite.scala

There will be compilation warning as follows:

IsEmptySuite.scala:12: warning: Auto-application to `()` is deprecated. Supply the empty argument list `()` explicitly to invoke method isEmpty,
or remove the empty argument list from its definition (Java-defined methods are exempt).
In Scala 3, an unapplied method like this will be eta-expanded into a function.
    assert(foo.isEmpty()) // an unexpected compilation warning.
          ^
1 warning

I want to know why this compile warning occurs on the last assertion line but not on the others. Other than renaming isEmpty() to isEmpty, are there any other methods to eliminate this compile warning?

[LuciferYang]

friendly ping @cheeseng , I'm not sure whether this question should be directed to you and the scalatest community. I would be very happy if I could receive your help. Thanks ~

[cheeseng]

@LuciferYang I think that's probably coming from code generated by our Scala 2 macro, I'll take a look at this today.

[LuciferYang]

@LuciferYang I think that's probably coming from code generated by our Scala 2 macro, I'll take a look at this today.

Thanks very much for your help ~

[cheeseng]

@LuciferYang Fyi I submitted the following PR for this:

#2298

[som-snytt]

@cheeseng this issue was not auto-closed when the PR was merged.