Data.Functor.Classes: fix Ord1 instance for Down

libraries/base/Data/Functor/Classes.hs

@@ -834,7 +834,10 @@ instance Eq1 Down where
 
 -- | @since 4.12.0.0
 instance Ord1 Down where
-    liftCompare comp (Down x) (Down y) = comp x y
+    liftCompare comp (Down x) (Down y) = case comp x y of
+        LT -> GT
+        EQ -> EQ
+        GT -> LT
 
 -- | @since 4.12.0.0
 instance Read1 Down where

libraries/base/changelog.md

@@ -33,6 +33,8 @@
     have an HasCallStack constraint. Hopefully providing better error messages in case
     they are used in unexpected ways.
 
+  * Fix the `Ord1` instance for `Data.Ord.Down` to reverse sort order.
+
 ## 4.16.0.0 *Nov 2021*
 
   * The unary tuple type, `Solo`, is now exported by `Data.Tuple`.

testsuite/tests/lib/base/T17472.hs

+module Main where
+
+import Data.Ord
+import Data.Functor.Classes
+
+-- Should print GT
+main :: IO ()
+main = print $ compare1 (Down 1) (Down 2)

testsuite/tests/lib/base/T17472.stdout

+GT

testsuite/tests/lib/base/all.T

@@ -5,3 +5,4 @@ test('T16916', when(opsys('mingw32'), skip), compile_and_run, ['-O2 -threaded -w
 test('T17310', normal, compile, [''])
 test('T19691', normal, compile, [''])
 test('executablePath', extra_run_opts(config.os), compile_and_run, [''])
+test('T17472', normal, compile_and_run, [''])