3 files changed, 40 insertions, 8 deletions
diff --git a/haddock-test/haddock-test.cabal b/haddock-test/haddock-test.cabal
index 0394da8f..2b75ea81 100644
--- a/haddock-test/haddock-test.cabal
+++ b/haddock-test/haddock-test.cabal
@@ -16,7 +16,7 @@ library
   default-language: Haskell2010
   ghc-options: -Wall
   hs-source-dirs:   src
-  build-depends:    base, directory, process, filepath, Cabal, xml, xhtml, syb
+  build-depends:    base, bytestring, directory, process, filepath, Cabal, xml, xhtml, syb
 
   exposed-modules:
     Test.Haddock
diff --git a/haddock-test/src/Test/Haddock.hs b/haddock-test/src/Test/Haddock.hs
index e8a0ac8e..6041c77c 100644
--- a/haddock-test/src/Test/Haddock.hs
+++ b/haddock-test/src/Test/Haddock.hs
@@ -16,6 +16,7 @@ import System.Exit
 import System.FilePath
 import System.IO
 import System.Process
+import qualified Data.ByteString.Char8 as BS
 
 import Test.Haddock.Config
 import Test.Haddock.Process
@@ -95,8 +96,8 @@ checkFile cfg file = do
     hasRef <- doesFileExist $ refFile dcfg file
     if hasRef
         then do
-            mout <- ccfgRead ccfg file <$> readFile (outFile dcfg file)
-            mref <- ccfgRead ccfg file <$> readFile (refFile dcfg file)
+            mout <- readOut cfg file
+            mref <- readRef cfg file
             return $ case (mout, mref) of
                 (Just out, Just ref)
                     | ccfgEqual ccfg out ref -> Pass
@@ -107,11 +108,34 @@ checkFile cfg file = do
     ccfg = cfgCheckConfig cfg
     dcfg = cfgDirConfig cfg
 
+-- We use ByteString here to ensure that no lazy I/O is performed.
+-- This way to ensure that the reference file isn't held open in
+-- case after `diffFile` (which is problematic if we need to rewrite
+-- the reference file in `maybeAcceptFile`)
+
+-- | Read the reference artifact for a test
+readRef :: Config c -> FilePath -> IO (Maybe c)
+readRef cfg file =
+    ccfgRead ccfg . BS.unpack
+    <$> BS.readFile (refFile dcfg file)
+  where
+    ccfg = cfgCheckConfig cfg
+    dcfg = cfgDirConfig cfg
+
+-- | Read (and clean) the test output artifact for a test
+readOut :: Config c -> FilePath -> IO (Maybe c)
+readOut cfg file =
+    fmap (ccfgClean ccfg file) . ccfgRead ccfg . BS.unpack
+    <$> BS.readFile (outFile dcfg file)
+  where
+    ccfg = cfgCheckConfig cfg
+    dcfg = cfgDirConfig cfg
+
 
 diffFile :: Config c -> FilePath -> FilePath -> IO ()
 diffFile cfg diff file = do
-    Just out <- ccfgRead ccfg file <$> readFile (outFile dcfg file)
-    Just ref <- ccfgRead ccfg file <$> readFile (refFile dcfg file)
+    Just out <- readOut cfg file
+    Just ref <- readRef cfg file
     writeFile outFile' $ ccfgDump ccfg out
     writeFile refFile' $ ccfgDump ccfg ref
 
@@ -130,10 +154,14 @@ diffFile cfg diff file = do
 
 
 maybeAcceptFile :: Config c -> FilePath -> CheckResult -> IO CheckResult
-maybeAcceptFile cfg@(Config { cfgDirConfig = dcfg }) file result
+maybeAcceptFile cfg file result
     | cfgAccept cfg && result `elem` [NoRef, Fail] = do
-        copyFile' (outFile dcfg file) (refFile dcfg file)
+        Just out <- readOut cfg file
+        writeFile (refFile dcfg file) $ ccfgDump ccfg out
         pure Accepted
+  where
+    dcfg = cfgDirConfig cfg
+    ccfg = cfgCheckConfig cfg
 maybeAcceptFile _ _ result = pure result
 
 
diff --git a/haddock-test/src/Test/Haddock/Config.hs b/haddock-test/src/Test/Haddock/Config.hs
index cd878178..dea101d8 100644
--- a/haddock-test/src/Test/Haddock/Config.hs
+++ b/haddock-test/src/Test/Haddock/Config.hs
@@ -42,7 +42,11 @@ data TestPackage = TestPackage
 
 
 data CheckConfig c = CheckConfig
-    { ccfgRead :: String -> String -> Maybe c
+    { ccfgRead :: String -> Maybe c
+      -- ^ @f contents@ parses file contents @contents@ to
+      -- produce a thing to be compared.
+    , ccfgClean :: String -> c -> c
+      -- ^ @f fname x@ cleans @x@ to such that it can be compared
     , ccfgDump :: c -> String
     , ccfgEqual :: c -> c -> Bool
     }