Missing class op rules when using API

[Erdi, Gergo]

PUBLIC

Hi,

I'm trying to compile the following two modules:

```
{-# LANGUAGE NoImplicitPrelude #-}
module MiniMonad where

class Functor f where
    fmap :: (a -> b) -> f a -> f b

class (Functor f) => Applicative f where
    pure :: a -> f a

class (Applicative m) => Monad m where
    return :: a -> m a
    return = pure

    (>>=)  :: m a -> (a -> m b) -> m b
    infixl 1 >>=
```

```
{-# LANGUAGE NoImplicitPrelude #-}
module SpecMain where

import MiniMonad

data Identity a = MkIdentity a

instance Functor Identity where
    fmap f (MkIdentity x) = MkIdentity (f x)

instance Applicative Identity where
    pure x = MkIdentity x

instance Monad Identity where

run :: Identity a -> a
run (MkIdentity x) = x

foo :: ()
foo = run (return ())
```

If I compile these from the CLI, I see three rules firing:

```
./_build/stage1/bin/ghc -debug -fforce-recomp -dno-typeable-binds input/SpecMain.hs -iinput -O0  -ddump-rule-rewrites -dsuppress-all
```

```
[1 of 2] Compiling MiniMonad        ( input/MiniMonad.hs, input/MiniMonad.o )
[2 of 2] Compiling SpecMain         ( input/SpecMain.hs, input/SpecMain.o )
tc_iface_decl/2 Monad

input/SpecMain.hs:14:10: warning: [-Wmissing-methods]
    * No explicit implementation for
        '>>='
    * In the instance declaration for 'Monad Identity'
   |
14 | instance Monad Identity where
   |          ^^^^^^^^^^^^^^
Rule fired
    Rule: Class op $p1Monad
    Module: (BUILTIN)
    Before: MiniMonad.$p1Monad
              TyArg SpecMain.Identity ValArg SpecMain.$fMonadIdentity
    After:  SpecMain.$fApplicativeIdentity
    Cont:   StrictArg MiniMonad.pure
            ApplyToTy a_avS
            Stop[RhsCtxt(Recursive)] a_avS -> SpecMain.Identity a_avS
Rule fired
    Rule: Class op pure
    Module: (BUILTIN)
    Before: MiniMonad.pure
              TyArg SpecMain.Identity ValArg SpecMain.$fApplicativeIdentity
    After:  $cpure_aw8
    Cont:   ApplyToTy a_avS
            Stop[RhsCtxt(Recursive)] a_avS -> SpecMain.Identity a_avS
Rule fired
    Rule: Class op return
    Module: (BUILTIN)
    Before: MiniMonad.return
              TyArg SpecMain.Identity ValArg SpecMain.$fMonadIdentity
    After:  $creturn_avP
    Cont:   ApplyToTy ()
            ApplyToVal nodup hole () -> SpecMain.Identity () GHC.Tuple.Prim.()
            Select nodup wild_X1
            Stop[RhsCtxt(NonRecursive)] ()
```

However, if I try this via the API (see attached `main.hs`), then only `Class op return` fires:


```
Processing module MiniMonad
Processing module SpecMain

input/SpecMain.hs:14:10: warning: [-Wmissing-methods]
    * No explicit implementation for
        '>>='
    * In the instance declaration for 'Monad Identity'
   |
14 | instance Monad Identity where
   |          ^^^^^^^^^^^^^^
Rule fired
    Rule: Class op return
    Module: (BUILTIN)
    Before: MiniMonad.return
              TyArg SpecMain.Identity ValArg SpecMain.$fMonadIdentity
    After:  $creturn_aqm
    Cont:   ApplyToTy ()
            ApplyToVal nodup hole () -> SpecMain.Identity () GHC.Tuple.Prim.()
            Select nodup wild_X1
            Stop[RhsCtxt(NonRecursive)] ()
All done.
```

This of course leads to much worse code further downstream (and is catastrophic for my use case where I rely on extensive specialisation).

Why is that? What is missing from my `main.hs` that only one of the three method rules is correctly used when compiling the second module?

Thanks,
Gergo

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