Fix #5833: Refine condition what constitutes an IFT in adapt

[odersky]

No description provided.

[biboudis]

Before LGTMing I was wondering if the following is valid code. I took the first one and introduced Entry. By refining the return type of the context query based on it (once directly and one via tha parameter) I get the following error:

trait Entry { type Key; val key: Key }

class NarrowDependentDT[E <: Entry]{
  def x: given (e: E) => e.Key = ???
  def y: given (e: Entry) => e.Key = x
}

22 |  def y: given (e: Entry) => e.Key = x
   |                                      ^
   |                                 no implicit argument of type E was found for parameter of given (e: E) => e.Key

WDYT @odersky? Otherwise looks good.

[abgruszecki]

@biboudis are you sure the arguments are the right way around? Your example does compile if x = y instead.

[biboudis]

I also checked the inverse and indeed it worked. I am still confused by this however.

[odersky]

The error seems to be legit. x needs an E as argument, but we only have an Entry.