testsuite: Make closureSize less sensitive to optimisationwip/robustify-closuresize

1 files changed, 8 insertions, 2 deletions

diff --git a/libraries/ghc-heap/tests/closure_size.hs b/libraries/ghc-heap/tests/closure_size.hs
index d77060779e..b04e7a77f9 100644
--- a/libraries/ghc-heap/tests/closure_size.hs
+++ b/libraries/ghc-heap/tests/closure_size.hs
@@ -1,6 +1,7 @@
 {-# LANGUAGE BangPatterns #-}
 {-# LANGUAGE TypeApplications #-}
 {-# LANGUAGE ScopedTypeVariables #-}
+{-# LANGUAGE MagicHash #-}
 
 import Control.Monad
 import Type.Reflection
@@ -17,12 +18,17 @@ assertSize !x expected = do
     putStrLn $ prettyCallStack callStack
 {-# NOINLINE assertSize #-}
 
-pap :: Int -> Char -> Int
+pap :: Int -> Maybe Char -> Int
 pap x _ = x
 {-# NOINLINE pap #-}
 
 main :: IO ()
 main = do
+  -- Ensure that GHC can't turn PAP into a FUN (see #16531)
+  let x :: Int
+      x = 42
+      {-# NOINLINE x #-}
+
   assertSize 'a' 2
   assertSize (Just ()) 2
   assertSize (Nothing :: Maybe ()) 2
@@ -30,5 +36,5 @@ main = do
   assertSize ((1,2,3) :: (Int,Int,Int)) 4
   assertSize (id :: Int -> Int) 1
   assertSize (fst :: (Int,Int) -> Int) 1
-  assertSize (pap 1) 2
+  assertSize (pap x) 2