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As of b6f7d145, I am trying to get GHC to specialize away all dictionary-passing, but it is failing in a very simple cross-module case.

Given the following two modules:

module Print where

import Prelude (String, IO, putStrLn, Show(..))

print :: (Show a) => a -> IO ()
print x = putStrLn (show x)

module Main1 (main) where

import Print
import Prelude (Show(..), IO)

data T = A | B deriving Show

main :: IO ()
main = print A

I am compiling Main1 with the following optimization flags:

-fspecialise -fenable-rewrite-rules \
-fspecialise-aggressively -fsolve-constant-dicts -fcross-module-specialise \
-fexpose-all-unfoldings

I expected the combination of expose-all-unfoldings and cross-module-specialise to result in a T-specialized print, but alas, the main I get still has dictionary passing:

-- RHS size: {terms: 3, types: 1, coercions: 0, joins: 0/0}
main :: IO ()
[GblId]
main = print @T Main1.$fShowT Main1.A

What is missing here to specialize print?