No way to recognize if using params belong to extension method

[tgodzik]

Compiler version

3.0.1

Minimized code

  class A
  class B
  class C
  object Foo:
      extension [T](using A)(s: T)(using B)
          def double(using C)(times: Int) = (s.toString + s.toString) * times
      end extension
      given A with {}
      given B with {}
      given C with {}
      "".double(1)
  end Foo

Output

I am trying to print the definition for double method, but it seems it's not possible to see that using C belongs to the double method.

My implementation based on https://github.com/lampepfl/dotty/blob/c8894a0168061ddb1369a426e9bde8d9972c893b/compiler/src/dotty/tools/dotc/printing/RefinedPrinter.scala#L851

will print:
extension [T](using A)(s: T)(using B)(using C) def double(times: Int): String

Expectation

There is a flag to recognize if param belongs to an extension method such as:
sym.is(Flags.ExtensionParam)

[tgodzik]

More context: scalameta/metals#2978

[Kordyjan]

I'm curious if this mechanism will be ever used only for displaying the information to the user. Then the worst it can do is to be slightly confusing. On the other hand, if one tries to rely on it to implement some automatic refactorings, it can cause incorrect results. Nevertheless, I don't think anyone will use that for anything more complicated, so it doesn't really matter.

[bishabosha]

I see it seems to be a bug in the RefinedPrinter also, if you compile the snippet with -Xprint:typer you get the following incorrect output:

extension [T >: Nothing <: Any](using x$1: A)(s: T)(using x$3: B)(using 
  x$4: C
) def double(times: Int): String = 
  augmentString(s.toString().+(s.toString())).*(times)

[Sporarum]

I believe there was a similar issue in Scaladoc, which was fixed in this PR:
#14810

The trick is to compare the positions of the different elements, this is done here:
https://github.com/lampepfl/dotty/pull/14810/files#diff-2f8deab4864c4387aab8b7b9f414216a36767d5e23d3f03ece09eab9addd892dR154-R174

I am not sure this is correct on right-associative extension methods however, please refer to the following (as the doc is not up-to-date yet on the release version):
https://github.com/Sporarum/dotty/blob/typeInterweaving/docs/_docs/reference/contextual/right-associative-extension-methods.md

[Sporarum]

Addenum:
I believe it would be best to add a flag for extension parameters
However I do not know if it is feasible, in the meantime, the position trick seems to work