From 6e851d63f0e086e58d846818335df57fb872c295 Mon Sep 17 00:00:00 2001
From: George Thomas <georgefsthomas@gmail.com>
Date: Tue, 9 Dec 2025 16:47:12 +0000
Subject: [PATCH] Show diff for golden test failures

---
 haskell/Main.hs         | 2 +-
 haskell/Pre.hs          | 4 ++++
 haskell/Puzzles/Day4.hs | 2 +-
 3 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/haskell/Main.hs b/haskell/Main.hs
index 39af2f4..4aaf91c 100644
--- a/haskell/Main.hs
+++ b/haskell/Main.hs
@@ -43,7 +43,7 @@ main =
                             withResource (parseFile $ "../inputs/" <> t <> "/" <> pt) mempty \input ->
                                 testGroup pt $
                                     ( zip (map show [1 :: Int ..]) parts <&> \(n, pp) ->
-                                        goldenVsString n ("../outputs/" <> t <> "/" <> pt <> "/" <> n) $
+                                        goldenVsStringDiff n diffCommand ("../outputs/" <> t <> "/" <> pt <> "/" <> n) $
                                             TL.encodeUtf8 . pp <$> input
                                     )
                                         <> [testGroup "extra" $ extraTests isRealData ("../outputs/" <> t <> "/" <> pt <> "/extra/") input]
diff --git a/haskell/Pre.hs b/haskell/Pre.hs
index 89157ed..d472881 100644
--- a/haskell/Pre.hs
+++ b/haskell/Pre.hs
@@ -41,6 +41,7 @@ module Pre (
     allUnorderedPairs,
     adjacentPairs,
     sortPair,
+    diffCommand,
 )
 where
 
@@ -122,3 +123,6 @@ adjacentPairs = \case
 
 sortPair :: (Ord a) => (a, a) -> (a, a)
 sortPair (a, b) = if a <= b then (a, b) else (b, a)
+
+diffCommand :: FilePath -> FilePath -> [String]
+diffCommand a b = ["diff", "--color=always", a, b]
diff --git a/haskell/Puzzles/Day4.hs b/haskell/Puzzles/Day4.hs
index 74411dc..1be6346 100644
--- a/haskell/Puzzles/Day4.hs
+++ b/haskell/Puzzles/Day4.hs
@@ -31,7 +31,7 @@ puzzle =
                 let frames = Seq.fromList . takeUntil noneAccessible . fmap snd . generateFrames . mkGrid <$> input
                     nFrames = if isRealData then 58 else 9
                  in ( [0 .. nFrames] <&> \n ->
-                        goldenVsString (show n) (path <> "frames/" <> show n) $
+                        goldenVsStringDiff (show n) diffCommand (path <> "frames/" <> show n) $
                             TL.encodeUtf8 . maybe "frame list too short!" drawGrid . Seq.lookup n <$> frames
                     )
                         <> [ testCase "end" do