Tactics plugin fails to solve program involving two different instantiations for fmap

[siraben]

Consider

data Fix f a = Fix (f (Fix f a))

instance Functor f => Functor (Fix f) where
  fmap f (Fix x) = _

The tactics plugin fails to fill the hole. One potential solution would be

instance Functor f => Functor (Fix f) where
  fmap f (Fix x) = Fix (fmap (fmap f) x)

Where the first fmap is on the functor f and the second fmap is on the functor Fix f (i.e. recursive call for this instance of fmap). According to @isovector the two different types for fmap combined with the way recursive calls are handled result in the tactic plugin failing to find a solution.

This has been tested as of commit 6c14163.

[isovector]

This is (half) fixed in #1347, but also broken due to #1346.

[isovector]

Closing this in favor of #1346 which better describes the problem.