Consider checking `-Wnonunit-statement` after macro expansion

[kyri-petrou]

Compiler version

3.3.5, 3.6.3

Minimized code

//> using scala 3.6.3
//> using options -Wnonunit-statement, -Xfatal-warnings

object Main {
  def foo(): String = "foo"

  def code = scala.compiletime.codeOf {
    foo()
    foo()
  }
}

Output

Compiler warning / error:

unused value of type String
  foo()

Expectation

This code should not emit any warnings as the foo() statement is not discarded. This behaviour (checking for non-unit statements) is causing an issue for zio-test users that have this warning enabled; see zio/zio#9233 and zio/zio#9552.

[som-snytt]

-Wunused has the same open question. It wound up working like -Wmacros:default in Scala 2, where the expansion resolves references but does not introduce new definitions to be checked. Future work would be to offer more control, as
-Wmacros:before,after,either,both.

Open ticket about remaining compiletime behavior for that warning.
#21805

Oh, I created -Winlined as a placeholder or reminder, but nothing set in stone.