Language feature flag doesn't export

[Adam-Vandervorst]

Compiler version

3.1.2

Minimized code

object Content:
  implicit lazy val answer: Int = 42

object DSL:
  export scala.language.postfixOps
  export Content.answer

  extension (n: Int)
    def test : Boolean = n == 1

object Test:
  import DSL.{*, given}

  val a = answer // works
  val b = 2 test // fails

Output

postfix operator `test` needs to be enabled
by making the implicit value scala.language.postfixOps visible.

Expectation

Compile.

Requiring the feature flag imports everywhere (some logic using these is used) is cumbersome.
Moreover, it is often desireable to encapsulate these in (optional) objects, avoiding compiler options making them avaiable to the whole project.

[som-snytt]

It exports, but feature lookup only examines imports. It would be a useful feat to follow export statements somehow.

[odersky]

I am against. The point with language feature imports is that we want to make it obvious for the reader what goes on. So they are intentionally restricted.

[Adam-Vandervorst]

In that case, making the implicit value scala.language.postfixOps visible is misleading.

I definitely see the need to restrict its use, though what happens in my experience is that the project gets a language-feature compiler option, which is much less safe or restricted than the missing export behavior.

[som-snytt]

The feature flag is like deprecation, but instead of annoying you with deprecation messages until you stop using it, it annoys you with imports.

The flip side of the expression problem is that it's now possible (and indeed usual) to have subprojects of small granularity, on which the compiler option can be enabled.