impossible to write non-strict right-associative operator

[scabug]

Due to the rewrite of right-associative operators as described in 6.12.3 it's effectively impossible to write a nonstrict right-associative operator; anything you pass will get forced.

I'm guessing this has been reported before and can't be fixed because it would change the meaning of a lot of code, but I couldn't find an obvious duplicate.

// Surprising behavior
object WAT extends App {
 
  object Foo {
    def !:(n: => Any) = "foo"
  }
 
  lazy val a = { println("AAA"); 1 }
  lazy val b = { println("BBB"); 1 }
  
  Foo.`!:`(a) // ok
 
  b !: Foo    // rewritten as { val x = b; Foo.`!:`(x) } 
              // per 6.12.3 and thus forces `b`, oops
 
}
 
// output is BBB

[scabug]

Imported From: https://issues.scala-lang.org/browse/SI-7333?orig=1
Reporter: Rob Norris (rnorris)
Duplicates #1980

[scabug]

@paulp said:
You're right on all counts. It's #1980, and it probably can't be fixed.

val x = f() #:: g() #:: Stream.Nil