Narrowing of types is too shallow

[scabug]

I run into this problem when refactoring the cake:

trait Outer { outer =>
  val other: Other
  // type checks
  val f = (Outer.this.other: outer.other.type)
  // fails to type check:
  // type mismatch;
  // found : Outer.this.other.type (with underlying type Other)
  // required: Outer{val other: Outer.this.other.type}
  val alias: Outer { val other: outer.other.type } = Outer.this 
}

abstract class Other

This looks like should be trivially true but it fails to type check. According to Adriaan it fails because narrowing of types is to shallow and is not being applied to members.

This will be probably closed as Won't Fix but I filed it just for record.

[scabug]

Imported From: https://issues.scala-lang.org/browse/SI-7585?orig=1
Reporter: @gkossakowski
Affected Versions: 2.11.0-M3

[scabug]

@gkossakowski said:
Added Jason to watcher as I'm sure he might enjoy seeing this fun problem.

[scabug]

@paulp said:
It can lose several of the players:

trait Outer {
  val x: Object
  def alias: Outer { val x: Outer.this.x.type } = this
}

[scabug]

@paulp said:
Also, it's a duplicate of #4663.

[scabug]

@paulp said:
See also #6767 and the other tickets linked there. I'm not sure there's any benefit in opening more variations on "the singleton type is not correctly propagated."

[scabug]

@gkossakowski said:
No, there's no benefit apart from documenting that people run into this problem on various occasions.

I was very surprised to discover that "this" doesn't to the that trivial refinement especially when the type ascription works.

[scabug]

@paulp said:
I remember this feeling, surprise. Gave life a certain zest.

[scabug]

@paulp said:
Also, I'm sure you can head off a few dozen duplicates-to-be by reading the issues I have reported which are still open. There are 142 of them. I promise you will encounter enough of these issues in practice to justify the initial investment. I put an awful lot of increasingly pointless-seeming work into them. Here they are.

https://issues.scala-lang.org/secure/IssueNavigator.jspa?mode=hide&requestId=12210