GHC enters a loop when partial type signatures and advanced type level code mix

GHC loops when compiling this code. Replacing the _ with the actual type fixes the error.

{-# LANGUAGE PolyKinds, DataKinds, TypeOperators, TypeFamilies, TemplateHaskell, GADTs, PartialTypeSignatures #-}
import Data.Vinyl
import Data.Singletons.TH

newtype MyAttr a b = MyAttr { _unMyAttr :: MyFun (a b) }
type MyRec a b = Rec (MyAttr a) b

type family MyFun (a :: k1) :: k2

data GY (a :: k1) (b :: k2) (c :: k1 -> k3) (d :: k1)
data GNone (a :: k1)

type family GYTF a where
    GYTF (GY a b _ a) = b
    GYTF (GY _ _ c d) = MyFun (c d)

type instance MyFun (GY a b c d) = GYTF (GY a b c d)

type family GNoneTF (a :: k1) :: k2 where

type instance MyFun (GNone a) = GNoneTF a 

type (a :: k1) =: (b :: k2) = a `GY` b
type (a :: j1 -> j2) $ (b :: j1) = a b

infixr 0 $
infixr 9 =:

data FConst (a :: *) (b :: Fields)
data FApply (a :: * -> * -> *) b c (d :: Fields)
data FMap (a :: * -> *) b (d :: Fields)

type instance MyFun (FConst a b) = a
type instance MyFun (FApply b c d a) = b (MyFun (c a)) (MyFun (d a))
type instance MyFun (FMap b c a) = b (MyFun (c a))

data Fields = Name | Author | Image | Description | Ingredients | Instructions | CookTime | PrepTime | TotalTime | Yield | Nutrition | Tags | Url
            | Section | Items | Subsections
            | Calories | Carbohydrates | Cholesterol | Fat | Fiber | Protien | SaturatedFat | Sodium | Sugar | TransFat | UnsaturatedFat | ServingSize

genSingletons [ ''Fields ]

(=::) :: sing f -> MyFun (a f) -> MyAttr a f
_ =:: x = MyAttr x

type NutritionT
    = Calories       =: Maybe Int
    $ Carbohydrates  =: Maybe Int
    $ Cholesterol    =: Maybe Int
    $ Fat            =: Maybe Int
    $ Fiber          =: Maybe Int
    $ Protien        =: Maybe Int
    $ SaturatedFat   =: Maybe Int
    $ Sodium         =: Maybe Int
    $ Sugar          =: Maybe Int
    $ TransFat       =: Maybe Int
    $ UnsaturatedFat =: Maybe Int
    $ ServingSize    =: String
    $ GNone

type NutritionRec = MyRec NutritionT ['Calories, 'Carbohydrates, 'Cholesterol, 'Fat, 'Fiber, 'Protien, 'SaturatedFat, 'Sodium, 'Sugar, 'TransFat, 'UnsaturatedFat, 'ServingSize]

type RecipeT
    = Name         =: String
    $ Author       =: String
    $ Image        =: String
    $ Description  =: String
    $ CookTime     =: Maybe Int
    $ PrepTime     =: Maybe Int
    $ TotalTime    =: Maybe Int
    $ Yield        =: String
    $ Nutrition    =: NutritionRec
    $ Tags         =: [String]
    $ Url          =: String
    $ GNone

type RecipeFormatter = FApply (->) (FConst [String]) (FMap IO RecipeT) 

g :: MyRec RecipeFormatter _ --'[ 'Author ] Uncomment to prevent loop
g
     = SAuthor =:: (\a -> return "Hi")
    :& RNil

main = putStrLn "Hi"

Trac metadata

Trac field	Value
Version	8.0.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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