stack+ghcjs.diff

diff --git a/src/Stack/Build.hs b/src/Stack/Build.hs
index 9b00447..50b8d61 100644
--- a/src/Stack/Build.hs
+++ b/src/Stack/Build.hs
@@ -53,7 +53,7 @@ build :: M env m
       => (Set (Path Abs File) -> IO ()) -- ^ callback after discovering all local files
       -> BuildOpts
       -> m ()
-build setLocalFiles bopts = do
+build setLocalFiles bopts = errorWhenUnsupported bopts $ do
     menv <- getMinimalEnvOverride
 
     (mbp, locals, extraToBuild, sourceMap) <- loadSourceMap bopts
@@ -136,3 +136,13 @@ clean = do
     forM_
         (Map.keys (bcPackages bconfig))
         (distDirFromDir >=> removeTreeIfExists)
+
+errorWhenUnsupported :: M env m => BuildOpts -> m () -> m ()
+errorWhenUnsupported bopts inner = do
+    useGHCJS <- asks (configUseGHCJS . getConfig)
+    if useGHCJS
+        then case boptsFinalAction bopts of
+            DoTests _ -> $logError "GHCJS doesn't support running tests (yet!)"
+            DoBenchmarks -> $logError "GHCJS doesn't support running benchmarks (yet!)"
+            DoNothing -> inner
+        else inner
diff --git a/src/Stack/Build/Execute.hs b/src/Stack/Build/Execute.hs
index 63136fe..dab1f21 100644
--- a/src/Stack/Build/Execute.hs
+++ b/src/Stack/Build/Execute.hs
@@ -45