hs-boot file handling is not quite correct

Looking at GHC.Unit.Types.hs-boot you see:

data UnitId
data GenModule unit
data GenUnit uid
data Indefinite unit

What is the kind of GenModule? The inferred kind is k -> * with -XGHC2021 so the hs-boot file decides that's the kind of GenModule.

Looking in GHC.Unit.Types.hs, the definition is

 data GenModule unit = Module                                                    
    { moduleUnit :: !unit       -- ^ Unit the module belongs to                  
    , moduleName :: !ModuleName -- ^ Module name (e.g. A.B.C)                    
    }                                                                            
    deriving (Eq,Ord,Data,Functor)

do the inferred kind of GenModule is * -> *. Which is not the same as the kind declared in the hs-boot file, so there should be an error.

The root cause of this issue is the same as #12035 (closed) I think, but the fix there was not general enough.

The reason I found this, is that I have a patch which fixed this bug and it failed to compile this module when testing my patch building GHC.