Top level opaque type not transparent inside class in definition scope

[prolativ]

Compiler version

3.4.0-RC1-bin-20230825-2616c8b-NIGHTLY and before

Minimized code

opaque type Foo = String

class Bar:
  val foo: Foo = "abc"

Output

[error] Opaque.scala:4:18
[error] Found:    ("abc" : String)
[error] Required: Foo
[error]   val foo: Foo = "abc"
[error]                  ^^^^^

Expectation

This should compile. Because Bar is defined in the same scope as Foo the definition of Foo should be transparent inside the body of Bar.

[prolativ]

The problem doesn't occur if the snippet from above is moved to an object, e.g.

object Scope:
  opaque type Foo = String

  class Bar:
    val foo: Foo = "abc"

or if the opaque type is referenced from inside a top level method, e.g.

opaque type Foo = String

def bar =
  val foo: Foo = "abc"

so my assumption is that the problem is caused by the fact that the type gets moved to the synthetic package object but the scopes are compared for opaqueness/transparentness at a later point in the compilation pipeline

[prolativ]

Possibly related to #18097

[som-snytt]

#15050 has commentary

[bishabosha]

this is as specified, Foo is in the scope of the wrapping top-level-definition object for the file, and Bar is in its own top level scope. see the docs