Use of outer type argument in extension inline unapply(Seq) method causes compiler error

[gorilskij]

Compiler version

#15053

Minimized code

object O

extension [T] (ctx: O.type) inline def unapplySeq(input: T): Option[Seq[T]] = Some(Seq(input)) 

@main
def Main = {
  val O(x) = 3
  println(s"x: $x")
}

Output

Compiler error

Exception in thread "main" java.lang.IndexOutOfBoundsException: 0
        at scala.collection.LinearSeqOps.apply(LinearSeq.scala:117)
        at scala.collection.LinearSeqOps.apply$(LinearSeq.scala:114)
        at scala.collection.immutable.List.apply(List.scala:79)
        at dotty.tools.dotc.core.Substituters$.substParams(Substituters.scala:151)
        at dotty.tools.dotc.core.Substituters$SubstParamsMap.apply(Substituters.scala:197)
        at dotty.tools.dotc.core.Substituters$SubstParamsMap.apply(Substituters.scala:197)
        at scala.collection.immutable.List.mapConserve(List.scala:472)
        at dotty.tools.dotc.core.Types$TypeMap.mapOverLambda(Types.scala:5553)
        at dotty.tools.dotc.core.Types$TypeMap.mapOver(Types.scala:5582)
        at dotty.tools.dotc.core.Substituters$.substParams(Substituters.scala:161)
        at dotty.tools.dotc.core.Substituters$SubstParamsMap.apply(Substituters.scala:197)
        at dotty.tools.dotc.core.Types$TypeMap.mapOverLambda(Types.scala:5555)
        at dotty.tools.dotc.core.Types$TypeMap.mapOver(Types.scala:5582)
        at dotty.tools.dotc.core.Substituters$.substParams(Substituters.scala:161)
        ...

Expectation

x: 3

[prolativ]

The issue does not occur if unapplySeq is non-inline or if it's defined as an ordinary method rather than an extension

[prolativ]

Compiler version: 3.2.0-RC1-bin-20220514-bb29e20-NIGHTLY

[rmgk]

I ran into the same issue, you actually do not need any generics, and just unapply has the same issue.
Example:

class C

extension (ctx: C) inline def unapply(input: String): Option[String] = Some("hi")

@main def run = {
  val O = new C
  val O(x) = "3"
}

[gorilskij]

@rmgk
That's a different side of the same issue, see #8577
Both should eventually be resolved by #15191

[nicolasstucki]

We should check if #16358 fixes this