Adapted multiarg infix is just a tuple

[som-snytt]

Don't warn about this common idiom.

(42, 27) :: Nil     // nowarn

It will warn after tweaking how right-associative applications are type-checked.

Currently, parser pulls the arg into a temp val, so there is no adaptation.

After the tweak, the rewrite happens after typecheck of desugared application, so there is normal adaptation.

[som-snytt]

Extracted from the other PR, where the test looked like

// don't bug me about adapting a tuple when I wrote a tuple arg to infix
class `lukas warned me about this and I brushed him off but that was last year before pandemic` {
  def `tuple in infix expression must not warn` = (42, 27) :: Nil
}

[dwijnand]

from the other PR

Which one?

[som-snytt]

#7741 about to get refreshed

[som-snytt]

/rebuild