type family consistency checks, interaction with hs-boot files

It's not clear to me how the type family consistency check should interact with hs-boot files.

In particular, what if an hs-boot file has an import that the hs file doesn't have?

This sets up the situation where A.hs and C.hs have conflicting definitions. A.hs and A.hs-boot have different imports, A.hs-boot imports C but A.hs does not. Then when consistency is checked for A.hs we error about inconsistency with C.

-- T.hs
{-# LANGUAGE TypeFamilies #-}
module T where

type family T a

-- C.hs
{-# LANGUAGE TypeFamilies #-}
module C where

import T

type instance T Int = Int

-- A.hs-boot
{-# LANGUAGE TypeFamilies #-}
module A where

import T
import C

-- A.hs
{-# LANGUAGE TypeFamilies #-}
module A where

import T

data A = A

type instance T Int = ()

Now GHC reports:

A.hs:1:1: error: [GHC-34447]
    Conflicting family instance declarations:
      T Int = Int -- Defined in module C
      T Int = () -- Defined at A.hs:8:15
  |
1 | {-# LANGUAGE TypeFamilies #-}
  | ^

But A doesn't import C so it's unclear to me why this is an error.

Any thoughts @simonpj @sheaf @adamgundry ?