testsuite: Rework handling of output sanitization

Previously un-cleaned artifacts were kept as reference output, making
it difficult to tell what has changed and causing spurious changes in
the version control history. Here we rework this, cleaning the output
during acceptance. To accomplish this it was necessary to move to strict
I/O to ensure the reference handle was closed before accept attempts to
open the reference file.

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
     }