inlined match on tuple, and expanding with *: causes class cast exception at runtime

[rmgk]

Compiler version

3.1.3-RC4, 3.2.0-RC1-bin-20220526-1ea177d-NIGHTLY-git-1ea177d

Minimized code

inline def flatConcat2[A, B](a: A, b: B) =
  b match
    case bs: *:[bh, bt]  => a *: bs

val x: (Int, Int, Int) = flatConcat2(1, (2,3))

Output

java.lang.ClassCastException: class scala.Tuple3 cannot be cast to class scala.Tuple1 (scala.Tuple3 and scala.Tuple1 are in unnamed module of loader sbt.internal.ScalaLibraryClassLoader @3401c1d7)
pointing to the end of the flatConcat2 definition

Expectation

This works if the inline is removed
Should not throw a ClassCastException.

Note, the match type of the def is:

type FlatConcat2[A, B] = B match
  case b *: bs => A *: b *: bs

but adding that does not change anything

[rmgk]

Further minimization:

inline def test[B](b: B) =
  b match
    case b: Tuple => 1 *: b


test((1, 2))

[nicolasstucki]

It seems to be a bug with the erasure of the type Int *: ((Int, Int) & bh *: bt) which is erased as Tuple1