Don't require an existing GHC installation for stack config set

Fixes #2692.

Author: sjakobi

src/Stack/Config.hs

@@ -29,6 +29,7 @@ module Stack.Config
   ,packagesParser
   ,resolvePackageEntry
   ,getImplicitGlobalProjectDir
+  ,getStackYaml
   ,getSnapshots
   ,makeConcreteResolver
   ,checkOwnership
@@ -141,6 +142,17 @@ getImplicitGlobalProjectDir config =
   where
     stackRoot = configStackRoot config
 
+-- | This is slightly more expensive than @'asks' ('bcStackYaml' '.' 'getBuildConfig')@
+-- and should only be used when no 'BuildConfig' is at hand.
+getStackYaml
+    :: (MonadIO m, MonadLogger m, MonadReader env m, HasConfig env)
+    => m (Path Abs File)
+getStackYaml = do
+    config <- asks getConfig
+    case configMaybeProject config of
+        Just (_project, stackYaml) -> return stackYaml
+        Nothing -> liftM (</> stackDotYaml) (getImplicitGlobalProjectDir config)
+
 -- | Download the 'Snapshots' value from stackage.org.
 getSnapshots :: (MonadThrow m, MonadMask m, MonadIO m, MonadReader env m, HasHttpManager env, HasConfig env, MonadLogger m)
              => m Snapshots

src/Stack/ConfigCmd.hs

@@ -12,6 +12,7 @@ module Stack.ConfigCmd
        ,cfgCmdName) where
 
 import           Control.Applicative
+import           Control.Monad
 import           Control.Monad.Catch (MonadMask, throwM)
 import           Control.Monad.IO.Class
 import           Control.Monad.Logger
@@ -29,7 +30,7 @@ import qualified Options.Applicative.Types as OA
 import           Path
 import           Prelude -- Silence redundant import warnings
 import           Stack.BuildPlan
-import           Stack.Config (makeConcreteResolver)
+import           Stack.Config (makeConcreteResolver, getStackYaml)
 import           Stack.Types.BuildPlan
 import           Stack.Types.Config
 
@@ -56,18 +57,18 @@ cfgCmdSet :: ( MonadIO m
              , MonadBaseControl IO m
              , MonadMask m
              , MonadReader env m
-             , HasBuildConfig env
+             , HasConfig env
              , HasHttpManager env
              , HasGHCVariant env
              , MonadLogger m)
              => ConfigCmdSet -> m ()
 cfgCmdSet cmd = do
     configFilePath <-
-        asks
-            (toFilePath .
-             case configCmdSetScope cmd of
-                 CommandScopeProject -> bcStackYaml . getBuildConfig
-                 CommandScopeGlobal -> configUserConfigPath . getConfig)
+        liftM
+            toFilePath
+            (case configCmdSetScope cmd of
+                 CommandScopeProject -> getStackYaml
+                 CommandScopeGlobal -> asks (configUserConfigPath . getConfig))
     -- We don't need to worry about checking for a valid yaml here
     (config :: Yaml.Object) <-
         liftIO (Yaml.decodeFileEither configFilePath) >>= either throwM return
@@ -87,7 +88,7 @@ cfgCmdSetValue
        , MonadBaseControl IO m
        , MonadMask m
        , MonadReader env m
-       , HasBuildConfig env
+       , HasConfig env
        , HasHttpManager env
        , HasGHCVariant env
        , MonadLogger m)

src/Stack/Types/Config.hs

@@ -345,6 +345,8 @@ data Config =
          ,configDumpLogs            :: !DumpLogs
          -- ^ Dump logs of local non-dependencies when doing a build.
          ,configMaybeProject        :: !(Maybe (Project, Path Abs File))
+         -- ^ 'Just' when a local project can be found, 'Nothing' when stack must
+         -- fall back on the implicit global project.
          }
 
 -- | Which packages do ghc-options on the command line apply to?

src/main/Main.hs

@@ -843,13 +843,10 @@ dockerCleanupCmd cleanupOpts go@GlobalOpts{..} = do
             Docker.cleanup cleanupOpts
 
 cfgSetCmd :: ConfigCmd.ConfigCmdSet -> GlobalOpts -> IO ()
-cfgSetCmd co go@GlobalOpts{..} =
-    withBuildConfigAndLock
-        go
-        (\_ -> do env <- ask
-                  runReaderT
-                      (cfgCmdSet co)
-                      env)
+cfgSetCmd co go@GlobalOpts {..} =
+    withMiniConfigAndLock go $
+    do env <- ask
+       runReaderT (cfgCmdSet co) env
 
 imgDockerCmd :: (Bool, [Text]) -> GlobalOpts -> IO ()
 imgDockerCmd (rebuild,images) go@GlobalOpts{..} = do