-Ywarn-value-discard incompatible with Matchers

[mjdiloreto]

// example.scala
import org.scalatest.Matchers

class foo extends Matchers {
  def test(): Unit = {
    1 should equal(1)
  }
}

object Main {
  new foo().test()
}

Compiled with
scalac -Ywarn-value-discard -classpath scalatest_2.12-3.0.8.jar:scalactic_2.12-3.0.8.jar example.scala

returns

scalatest_bug.scala:5: warning: discarded non-Unit value
    1 should equal(1)
      ^
one warning found

I saw #764 was fixed a while ago in 3.0.0, but was this case not addressed?
I also noticed https://groups.google.com/forum/#!topic/scalatest-users/mltBJPFiWiQ had a very similar example (I am not using FunSuite though, just Matchers), but that person seems not to have responded, so I can only imagine it didn't work for them either.

[hearnadam]

Though not ideal, this should silence the warnings (2.12/2.13):
"-Wconf:cat=w-flag-value-discard&msg=discarded non-Unit value of type org\\.scalatest\\.Assertion:s"

• https://www.scala-lang.org/2021/01/12/configuring-and-suppressing-warnings.html

[SethTisue]

Note that the canonical form of the flag is -Wvalue-discard.