Add an ExplicitProject constructor, which reads options from a file

Language/Haskell/GhcMod/Cradle.hs

@@ -37,6 +37,7 @@ findCradle' dir = run $
     msum [ stackCradle dir
          , cabalCradle dir
          , sandboxCradle dir
+         , explicitCradle dir
          , plainCradle dir
          ]
  where run a = fillTempDir =<< (fromJust <$> runMaybeT a)
@@ -122,3 +123,15 @@ plainCradle wdir = do
       , cradleCabalFile  = Nothing
       , cradleDistDir    = "dist"
       }
+
+explicitCradle :: IOish m => FilePath -> MaybeT m Cradle
+explicitCradle wdir = do
+    optionsFile <- MaybeT $ liftIO $ findExplicitOptionsFile wdir
+    return $ Cradle {
+        cradleProjectType = ExplicitProject
+      , cradleCurrentDir = wdir
+      , cradleRootDir    = takeDirectory optionsFile
+      , cradleTempDir    = error "tmpDir"
+      , cradleCabalFile  = Just optionsFile
+      , cradleDistDir    = ""
+      }

Language/Haskell/GhcMod/GhcPkg.hs

@@ -87,6 +87,7 @@ getPackageDbStack = do
         getCabalPackageDbStack
     StackProject ->
         getStackPackageDbStack
+    ExplicitProject -> return []
   return $ fromMaybe stack mCusPkgStack
 
 getPackageCachePaths :: IOish m => FilePath -> GhcModT m [FilePath]

Language/Haskell/GhcMod/PathsAndFiles.hs

@@ -85,6 +85,15 @@ findStackConfigFile dir = do
       Just (d, Just a)  -> return $ Just $ d </> a
       Just (_, Nothing) -> error "findStackConfigFile"
 
+findExplicitOptionsFile :: FilePath -> IO (Maybe FilePath)
+findExplicitOptionsFile dir = do
+    dss <- findFileInParentsP (==explicitOptionsFile) dir
+    return $ case find (not . null . snd) $ dss of
+               Just (expDir, _:_) -> Just (expDir </> explicitOptionsFile)
+               _ -> Nothing
+  where
+    explicitOptionsFile = "ghc-mod.options"
+
 getStackDistDir :: (IOish m, GmOut m) => FilePath -> m (Maybe FilePath)
 getStackDistDir projdir = U.withDirectory_ projdir $ runMaybeT $ do
     takeWhile (/='\n') <$> readStack ["path", "--dist-dir"]

Language/Haskell/GhcMod/Target.hs

@@ -151,10 +151,18 @@ targetGhcOptions crdl sefnmn = do
     case cradleProjectType crdl of
       CabalProject -> cabalOpts crdl
       StackProject -> cabalOpts crdl
+      ExplicitProject -> explicitOpts crdl
       _ -> sandboxOpts crdl
  where
    zipMap f l = l `zip` (f `map` l)
 
+   explicitOpts :: Cradle -> GhcModT m [String]
+   explicitOpts Cradle {..} = case cradleCabalFile of
+       Nothing -> return []
+       Just optionsFile -> do
+           contents <- liftIO $ readFile optionsFile
+           return $ lines contents
+
    cabalOpts :: Cradle -> GhcModT m [String]
    cabalOpts Cradle{..} = do
        mcs <- cabalResolvedComponents

Language/Haskell/GhcMod/Types.hs

@@ -139,7 +139,7 @@ defaultOptions = Options {
 
 ----------------------------------------------------------------
 
-data ProjectType = CabalProject | SandboxProject | PlainProject | StackProject
+data ProjectType = CabalProject | SandboxProject | PlainProject | StackProject | ExplicitProject
                  deriving (Eq, Show)
 
 -- | The environment where this library is used.