`export` to consider imported prefixes

[japgolly]

Compiler version

• 3.0.0-RC1
• 3.0.1-RC1-bin-20210411-b44cafa-NIGHTLY

Minimized code

object A:
  object B:
    object C

object X {
  import A.B

  B.C        // ok
  export B.C // error
}

Output

[error] 9 |  export B.C // error
[error]   |         ^
[error]   |         Not found: B
[error] one error found

Expectation

Compilation.

[bishabosha]

I believe that this is as specified: http://dotty.epfl.ch/docs/reference/other-new-features/export.html#elaboration-of-export-clauses

Export clauses are processed when the type information of the enclosing object or class is completed. Completion so far consisted of the following steps:
...
6. Compute the types of all paths in export clauses in a context logically inside the class but not considering any imports or exports in that class.