Fix casting of generic tuple selection

[dwijnand]

Obviously, in hindsight, we can't use the types of the unapply arguments
as the type for selecting the components of a (generic) tuple...

Fixes #14587

[test_non_bootstrapped]

[michelou]

@dwijnand 👍

[oscar-broman]

Perhaps not directly related to this, but the type inferred for bar below is Some[(Some[Int], String) | (None.type, String)]. Should it not be Some[(Option[Int], String)]?

  def foo: String
  val bar = {
    if (foo.isEmpty) Some((Some(1), ""))
    else Some((None, ""))
  }

[dwijnand]

Perhaps not directly related to this, but the type inferred for bar below is Some[(Some[Int], String) | (None.type, String)]. Should it not be Some[(Option[Int], String)]?

The former reduces to the latter but that only happens when and if it needs to. What difference does it make to you? (Which sounds miles more aggressive than I mean it... 😅 )

[oscar-broman]

Nothing at all, only thing I can think of is some obscure cases where it might make things harder for type class derivation.

I just noticed it when trying this out in Scala 2 and just wanted to be sure nothing was overlooked.

[dwijnand]

[error] ## Exception when compiling 56 sources to /__w/dotty/dotty/community-build/community-projects/scodec/unitTests/target/scala-3.1.3-RC1-bin-SNAPSHOT/test-classes
[error] java.lang.AssertionError: assertion failed: Failed to find type at index 1 in (Option[Int], Option[Int], Option[Int])
[error] scala.Predef$Ensuring$.ensuring$extension(Predef.scala:279)
[error] dotty.tools.dotc.transform.PatternMatcher$Translator.tupleApp$1(PatternMatcher.scala:335)

[nicolasstucki]

Otherwise LGTM

[nicolasstucki]

Doc tests failed due to a time out. I restarted the tests.