Implement hpack-hash feature.

src/Hpack.hs

@@ -59,15 +59,21 @@ import           Hpack.CabalFile
 programVersion :: Version -> String
 programVersion v = "hpack version " ++ Version.showVersion v
 
-header :: FilePath -> Version -> Hash -> String
-header p v hash = unlines [
+header :: FilePath -> Version -> Maybe Hash -> String
+header p v mHash = unlines ([
     "-- This file has been generated from " ++ takeFileName p ++ " by " ++ programVersion v ++ "."
   , "--"
   , "-- see: https://github.com/sol/hpack"
-  , "--"
-  , "-- hash: " ++ hash
-  , ""
   ]
+  ++ case mHash of
+      Nothing -> []
+      Just hash ->
+        [ "--"
+        , "-- hash: " ++ hash
+        ]
+  ++ [
+    ""
+  ])
 
 data Options = Options {
   optionsDecodeOptions :: DecodeOptions
@@ -176,13 +182,21 @@ hpackResultWithVersion v (Options options force toStdout) = do
     body = renderPackage (maybe [] cabalFileContents oldCabalFile) pkg
     withoutHeader = cabalVersion ++ body
   let
+    useHash = case packageHpackHash pkg of
+      Just False -> False
+      Just True -> True
+      Nothing -> True
     status = case force of
       Force -> Generated
-      NoForce -> maybe Generated (mkStatus (lines withoutHeader) v) oldCabalFile
+      NoForce -> if useHash
+        then maybe Generated (mkStatus (lines withoutHeader) v) oldCabalFile
+        else Generated -- always rebuild cabal file if omitting hash
   case status of
     Generated -> do
-      let hash = sha256 withoutHeader
-          out  = cabalVersion ++ header (decodeOptionsTarget options) v hash ++ body
+      let mHash = if useHash
+            then Just (sha256 withoutHeader)
+            else Nothing
+          out  = cabalVersion ++ header (decodeOptionsTarget options) v mHash ++ body
       if toStdout
         then Utf8.putStr out
         else Utf8.writeFile cabalFile out

src/Hpack/Config.hs

@@ -148,6 +148,7 @@ package name version = Package {
   , packageDataDir = Nothing
   , packageSourceRepository = Nothing
   , packageCustomSetup = Nothing
+  , packageHpackHash = Nothing
   , packageLibrary = Nothing
   , packageInternalLibraries = mempty
   , packageExecutables = mempty
@@ -534,6 +535,7 @@ data PackageConfig_ library executable = PackageConfig {
 , packageConfigGithub :: Maybe Text
 , packageConfigGit :: Maybe String
 , packageConfigCustomSetup :: Maybe CustomSetupSection
+, packageConfigHpackHash :: Maybe Bool
 , packageConfigLibrary :: Maybe library
 , packageConfigInternalLibraries :: Maybe (Map String library)
 , packageConfigExecutable :: Maybe executable
@@ -837,6 +839,7 @@ data Package = Package {
 , packageDataDir :: Maybe FilePath
 , packageSourceRepository :: Maybe SourceRepository
 , packageCustomSetup :: Maybe CustomSetup
+, packageHpackHash :: Maybe Bool
 , packageLibrary :: Maybe (Section Library)
 , packageInternalLibraries :: Map String (Section Library)
 , packageExecutables :: Map String (Section Executable)
@@ -1111,6 +1114,7 @@ toPackage_ dir (Product g PackageConfig{..}) = do
       , packageDataDir = packageConfigDataDir
       , packageSourceRepository = sourceRepository
       , packageCustomSetup = mCustomSetup
+      , packageHpackHash = packageConfigHpackHash
       , packageLibrary = mLibrary
       , packageInternalLibraries = internalLibraries
       , packageExecutables = executables

test/Hpack/CabalFileSpec.hs

@@ -21,12 +21,17 @@ spec = do
 
     it "includes hash" $ do
       inTempDirectory $ do
-        writeFile file $ header "package.yaml" version hash
+        writeFile file $ header "package.yaml" version (Just hash)
         readCabalFile file `shouldReturn` Just (CabalFile (Just version) (Just hash) [])
 
+    it "hpack-hash:false omits hash" $ do
+      inTempDirectory $ do
+        writeFile file $ header "package.yaml" version Nothing
+        readCabalFile file `shouldReturn` Just (CabalFile (Just version) Nothing [])
+
     it "accepts cabal-version at the beginning of the file" $ do
       inTempDirectory $ do
-        writeFile file $ ("cabal-version: 2.2\n" ++ header "package.yaml" version hash)
+        writeFile file $ ("cabal-version: 2.2\n" ++ header "package.yaml" version (Just hash))
         readCabalFile file `shouldReturn` Just (CabalFile (Just version) (Just hash) ["cabal-version: 2.2"])
 
   describe "extractVersion" $ do

test/HpackSpec.hs

@@ -100,3 +100,12 @@ spec = do
               old <- readFile file
               hpack `shouldReturn` outputUnchanged
               readFile file `shouldReturn` old
+
+        context "hpack-hash: false" $ do
+          it "always generates file" $ do
+            writeFile packageConfig $ unlines [
+                "name: foo"
+              , "hpack-hash: false"
+              ]
+            hpack `shouldReturn` generated
+            hpack `shouldReturn` generated