Don't always create a new stack.yaml file

Not my intention originally, but this paves the way quite nicely for
implementing #59

src/Stack/Config.hs

@@ -231,13 +231,20 @@ loadConfig configArgs = do
 loadBuildConfig :: (MonadLogger m,MonadIO m,MonadCatch m,MonadReader env m,HasHttpManager env,MonadBaseControl IO m)
                 => Maybe (Project, Path Abs File, ConfigMonoid)
                 -> Config
+                -> NoBuildConfigStrategy
                 -> m BuildConfig
-loadBuildConfig mproject config = do
+loadBuildConfig mproject config noConfigStrat = do
     env <- ask
     let miniConfig = MiniConfig (getHttpManager env) config
     (project, stackYamlFP) <- case mproject of
-        Just (project, fp, _) -> return (project, fp)
-        Nothing -> do
+      Just (project, fp, _) -> return (project, fp)
+      Nothing -> case noConfigStrat of
+        ThrowException -> do
+            currDir <- getWorkingDir
+            throwM $ NoProjectConfigFound currDir
+        ExecStrategy ->
+            error "You do not have a stack.yaml. This will be handled in the future, see https://github.com/fpco/stack/issues/59"
+        CreateConfig -> do
             currDir <- getWorkingDir
             (r, flags, cabalFileExists) <- runReaderT (getDefaultResolver currDir) miniConfig
             let dest = currDir </> stackDotYaml

src/Stack/Types/Config.hs

@@ -172,13 +172,18 @@ data BuildConfig = BuildConfig
 data LoadConfig m = LoadConfig
     { lcConfig          :: !Config
       -- ^ Top-level Stack configuration.
-    , lcLoadBuildConfig :: !(m BuildConfig)
-        -- ^ Action to load the remaining 'BuildConfig'.  This action will create a project if one
-        -- does not already exist.
+    , lcLoadBuildConfig :: !(NoBuildConfigStrategy -> m BuildConfig)
+        -- ^ Action to load the remaining 'BuildConfig'.
     , lcProjectRoot     :: !(Maybe (Path Abs Dir))
         -- ^ The project root directory, if in a project.
     }
 
+data NoBuildConfigStrategy
+    = ThrowException
+    | CreateConfig
+    | ExecStrategy
+    deriving (Show, Eq, Ord)
+
 -- | A project is a collection of packages. We can have multiple stack.yaml
 -- files, but only one of them may contain project information.
 data Project = Project
@@ -240,10 +245,6 @@ parseResolver t =
   where
     parseGhc = T.stripPrefix "ghc-" t >>= parseMajorVersionFromString . T.unpack
 
-data ParseResolverException = ParseResolverException Text
-    deriving (Show, Typeable)
-instance Exception ParseResolverException
-
 -- | Class for environment values which have access to the stack root
 class HasStackRoot env where
     getStackRoot :: env -> Path Abs Dir
@@ -327,10 +328,20 @@ instance FromJSON ConfigMonoid where
          return ConfigMonoid {..}
 
 data ConfigException
-  = ConfigInvalidYaml String
-  | ConfigNoFile
-  | ConfigNoDockerConfig
-  deriving (Typeable,Show)
+  = ParseResolverException Text
+  | NoProjectConfigFound (Path Abs Dir)
+  deriving Typeable
+instance Show ConfigException where
+    show (ParseResolverException t) = concat
+        [ "Invalid resolver value: "
+        , T.unpack t
+        , ". Possible valid values include lts-2.12, nightly-2015-01-01, and ghc-7.10."
+        ]
+    show (NoProjectConfigFound dir) = concat
+        [ "Unable to find a stack.yaml file in the current directory ("
+        , toFilePath dir
+        , ") or its ancestors"
+        ]
 instance Exception ConfigException
 
 -- | Helper function to ask the environment and apply getConfig

src/main/Main.hs

@@ -169,7 +169,7 @@ main =
 pathCmd :: PathArg -> GlobalOpts -> IO ()
 pathCmd pathArg go@GlobalOpts{..} = do
   (manager,lc) <- loadConfigWithOpts go
-  buildConfig <- runStackLoggingT manager globalLogLevel (lcLoadBuildConfig lc)
+  buildConfig <- runStackLoggingT manager globalLogLevel (lcLoadBuildConfig lc ExecStrategy)
   runStackT manager globalLogLevel buildConfig (pathString pathArg) >>= putStrLn
 
 
@@ -226,7 +226,7 @@ setupCmd SetupCmdOpts{..} go@GlobalOpts{..} = do
             case scoGhcVersion of
                 Just v -> return (v, Nothing)
                 Nothing -> do
-                    bc <- lcLoadBuildConfig lc
+                    bc <- lcLoadBuildConfig lc ThrowException
                     return (bcGhcVersion bc, Just $ bcStackYaml bc)
         mpaths <- ensureGHC manager (lcConfig lc) SetupOpts
             { soptsInstallIfMissing = True
@@ -249,7 +249,7 @@ cleanCmd _ go@GlobalOpts{..} = do
     (lcProjectRoot lc)
     (do config <- runStackLoggingT manager
                                    globalLogLevel
-                                   (lcLoadBuildConfig lc >>= setupEnv globalSystemGhc manager)
+                                   (lcLoadBuildConfig lc ThrowException >>= setupEnv globalSystemGhc manager)
         runStackT manager globalLogLevel config clean)
 
 -- | Install dependencies
@@ -258,7 +258,7 @@ depsCmd (names, dryRun) go@GlobalOpts{..} = do
     (manager,lc) <- loadConfigWithOpts go
     Docker.rerunWithOptionalContainer (lcConfig lc) (lcProjectRoot lc) $ do
         config <- runStackLoggingT manager globalLogLevel
-            (lcLoadBuildConfig lc >>= setupEnv globalSystemGhc manager)
+            (lcLoadBuildConfig lc ExecStrategy >>= setupEnv globalSystemGhc manager)
         runStackT manager globalLogLevel config $ Stack.Build.build BuildOpts
             { boptsTargets = Right names
             , boptsLibProfile = False
@@ -309,7 +309,7 @@ buildCmd finalAction opts go@GlobalOpts{..} =
         (lcProjectRoot lc)
         (do config <- runStackLoggingT manager
                                        globalLogLevel
-                                       (lcLoadBuildConfig lc >>= setupEnv globalSystemGhc manager)
+                                       (lcLoadBuildConfig lc CreateConfig >>= setupEnv globalSystemGhc manager)
             runStackT manager globalLogLevel config $
                       Stack.Build.build opts { boptsFinalAction = finalAction}))
              (error . printBuildException)
@@ -427,7 +427,7 @@ execCmd (cmd, args) go@GlobalOpts{..} = do
       (lcProjectRoot lc)
       (do config <- runStackLoggingT manager
                                      globalLogLevel
-                                     (lcLoadBuildConfig lc >>= setupEnv globalSystemGhc manager)
+                                     (lcLoadBuildConfig lc ExecStrategy >>= setupEnv globalSystemGhc manager)
           menv <- configEnvOverride (bcConfig config)
                           EnvSettings
                               { esIncludeLocals = True