Bad error message when compacting a Compact#

When I run this:

main :: IO ()
main = do
  cpt@(Compact cpt# _ _) <- compact (55 :: Int)
  _ <- compactAdd cpt (MyCompact cpt#)
  return ()

data MyCompact = MyCompact Compact#

I get this error message:

compaction failed: cannot compact mutable objects

This error message is misleading. I don't really know if it makes sense to allow a Compact# to be stored in a compact region, but if someone tries to do it, I would rather the error say:

cannot compact Compact# values

Or something like that.

Trac metadata

Trac field	Value
Version	8.2.1-rc2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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