Refinement hole fits don't include suggestions from other (prerequisite) typeclasses.

Summary

Hole fits don't include suggestions from other (prerequisite) typeclasses.

Steps to reproduce

module Typeclasses where

data Tree a = Leaf a | Node (Tree a) (Tree a)
    deriving (Eq,Show)

instance Functor Tree where
    fmap f (Leaf a)   = Leaf $ f a
    fmap f (Node a b) = Node (fmap f a) (fmap f b)

instance Applicative Tree where
    pure = Leaf
    (Leaf f)   <*> x = _ --fmap f x
    (Node f g) <*> x = Node (f <*> x) (g <*> x)

Compiled with ghc tests/Typeclasses.hs -frefinement-level-hole-fits=3 -fno-max-refinement-hole-fits

Suggests Leaf, (<*>), Node, pure, id, head, last, asTypeOf, (!!)

Expected behavior

Since fmap f x or f <$> x is typecorrect, I would expect it to show up. Both because fmap for Tree is defined above, and because Functor is a prerequisite of Applicative.

Environment

• GHC version used: Glasgow Haskell Compiler, Version 8.9.0.20190705, stage 2 booted by GHC version 8.6.5