match type failure to reduce with separate compilation

[soronpo]

It seems that match types behave differently across test dependency and fails to reduce (possibly any kind of different module dependency is affected).

Compiler version

v3.0.1-RC2 (also checked on nightly)

Minimized code

Minimized project at: https://github.com/soronpo/dottybug/tree/match_type_fail
Bar.scala //main file

type ++[L, R] = (L, R) match
  case (Int, Int)       => 2
  case (String, String) => "2"
  case (String, Int)    => "2"
  case (Int, String)    => "2"

type Bar[W <: Int] = W ++ "" ++ W

val works = summon[Bar[2] =:= "2"]

Foo.scala //test file (must be in test/scala)

object Foo:
  val fails = summon[Bar[2] =:= "2"]

Output

[error] -- Error: C:\IdeaProjects\dottybug\src\test\scala\Foo.scala:2:36 ------------------------------------------------------------
[error] 2 |  val fails = summon[Bar[2] =:= "2"]
[error]   |                                    ^
[error]   |                                    Cannot prove that Bar[(2 : Int)] =:= ("2" : String).
[error]   |
[error]   |                                    Note: a match type could not be fully reduced:
[error]   |
[error]   |                                      trying to reduce  Bar[(2 : Int)]
[error]   |                                      trying to reduce  (2 : Int) ++ ("" : String) ++ (2 : Int)
[error]   |                                      failed since selector  ((2 : Int) ++ ("" : String), (2 : Int))
[error]   |                                      does not match  case (Int, Int) => (2 : Int)
[error]   |                                      and cannot be shown to be disjoint from it either.
[error]   |                                      Therefore, reduction cannot advance to the remaining cases
[error]   |
[error]   |                                        case (String, String) => ("2" : String)
[error]   |                                        case (String, Int) => ("2" : String)
[error]   |                                        case (Int, String) => ("2" : String)

Expectation

No error. Notice the same expression works within the main module and fails within the test module.

[griggt]

This looks to be a regression from 3.0.0-M2 (regressed in #7389)