Extension method with dependent type bounds

[nicolasstucki]

Compiler version

3.3.1

Minimized code

extension (tuple: Tuple)
  def *:[T >: tuple.type <: Tuple, H](x: H): H *: T = ???

Output

2 |  def `*:`[T >: tuple.type <: Tuple, H](x: H): H *: T = ???
  |                ^^^^^
  |                Not found: tuple - did you mean Tuple?

The issue seems to come from how we handle type parameters

[[syntax trees at end of                     typer]]
    extension [T >: tuple.type <: Tuple, H >: Nothing <: Any](tuple: Tuple)
      def *:(x: H): *:[H, T] = ???

It should be the same as in

extension (tuple: Tuple)
  def ok[T >: tuple.type <: Tuple, H](x: H): H *: T = ???

[[syntax trees at end of                     typer]]
    extension (tuple: Tuple) def ok[T >: tuple.type <: Tuple,
      H >: Nothing <: Any](x: H): *:[H, T] = ???

Expectation

Should compile

[bishabosha]

you would have to lift out type parameters when you do the swap

[nicolasstucki]

The swap seems to be fundamentally broken. The scoping while swapping adds too many restrictions.

[nicolasstucki]

It seems that this and other use cases start working if we do not swap the parameters. They are sapped correctly at the call site. I will investigate further.