Usages of experimentals are not always checked in types

[prolativ]

Compiler version

3.1.1-RC1

Minimized code

import annotation.experimental

@experimental trait Exp
@experimental val exp = 1

type Foo = Option[Exp]
type Bar = Option[exp.type]
type Baz = Exp | Int
type Quux = [X] = X match
  case Exp => Int
type Quuz[A <: Exp] = Int

Output

Compiles successfully

Expectation

The compilation should fail and all the usages of the experimentals should be reported as errors

[odersky]

What happens with @deprecated? The two should work exactly the same.

[nicolasstucki]

We also miss all these cases with @deprecated.

Only one error is emitted for the following example. Scala 2 emits all of them except the exp.type.

@deprecated trait Exp
@deprecated val exp = 1

def test1 = exp // error
def test2(a: Exp) = ()

type Foo0 = Exp
type Foo = Option[Exp]
type Bar = Option[exp.type]
type Baz = Exp | Int // error
type Quux = [X] =>> X match
  case Exp => Int
type Quuz[A <: Exp] = Int

See https://scastie.scala-lang.org/U0JDQtjQTBK64CRf7PqPTA for Scala 2 example

[odersky]

I think the right fix is to check deprecation and experimental before RefChecks, when we still have the full types.