Display FFI errors to user

CHANGELOG.md

@@ -13,6 +13,7 @@ Bugfixes:
 Other improvements:
 
 - Use `replaceState` for setting query params (#266 by @ptrfrncsmrph)
+- Display missing FFI dependency error message to user (#268 by @ptrfrncsmrph)
 
 ## [v2021-11-30.1](https://github.com/purescript/trypurescript/releases/tag/v2021-11-11.1)
 

client/public/css/index.css

@@ -221,6 +221,12 @@ pre code {
   background: none;
   border: 0;
   margin: 0;
+  overflow-x: auto;
+  white-space: pre-wrap;
+  white-space: -moz-pre-wrap;
+  white-space: -pre-wrap;
+  white-space: -o-pre-wrap;
+  word-wrap: break-word;
 }
 
 iframe {

client/src/Try/Container.purs

@@ -6,7 +6,7 @@ import Ace (Annotation)
 import Control.Monad.Except (runExceptT)
 import Data.Array (fold)
 import Data.Array as Array
-import Data.Either (Either(..), hush)
+import Data.Either (Either(..))
 import Data.Foldable (for_, oneOf)
 import Data.FoldableWithIndex (foldMapWithIndex)
 import Data.Maybe (Maybe(..), fromMaybe, isNothing)
@@ -189,17 +189,22 @@ component = H.mkComponent
           if settings.showJs then
             H.liftEffect teardownIFrame
           else do
-            mbSources <- H.liftAff $ map hush $ runExceptT $ runLoader loader (JS js)
+            eitherSources <- H.liftAff $ runExceptT $ runLoader loader (JS js)
             for_ warnings \warnings_ -> do
               let anns = Array.mapMaybe (toAnnotation MarkerWarning) warnings_
               _ <- H.query _editor unit $ H.tell $ Editor.SetAnnotations anns
               pure unit
-            for_ mbSources \sources -> do
-              let eventData = Object.insert "<file>" (JS js) sources
-              H.liftAff $ makeAff \f -> do 
-                runEffectFn3 setupIFrame eventData (f (Right unit)) (f (Left $ Aff.error "Could not load iframe"))
-                mempty
-            H.modify_ _ { compiled = Just (Right res) }
+            case eitherSources of
+              Right sources -> do
+                let eventData = Object.insert "<file>" (JS js) sources
+                H.liftAff $ makeAff \f -> do 
+                  runEffectFn3 setupIFrame eventData (f (Right unit)) (f (Left $ Aff.error "Could not load iframe"))
+                  mempty
+                H.modify_ _ { compiled = Just (Right res) }
+              Left err -> do
+                H.liftEffect teardownIFrame
+                H.liftEffect $ error err
+                H.modify_ _ { compiled = Just (Left err) }
 
     HandleEditor (Editor.TextChanged text) -> do
       _ <- H.fork $ handleAction $ Cache text
@@ -383,7 +388,7 @@ component = H.mkComponent
 
     renderCompiled = case _ of
       Left err ->
-        renderPlaintext "Unable to parse the response from the server."
+        renderPlaintext err
       Right res -> case res of
         CompileFailed { error } -> case error of
           OtherError err ->

client/src/Try/Loader.purs

@@ -7,13 +7,14 @@ module Try.Loader
 import Prelude
 
 import Control.Bind (bindFlipped)
-import Control.Monad.Except (ExceptT)
+import Control.Monad.Except (ExceptT, throwError)
 import Control.Parallel (parTraverse)
+import Data.Array (foldMap)
 import Data.Array as Array
 import Data.Array.NonEmpty as NonEmpty
 import Data.Maybe (Maybe(..), fromMaybe)
 import Data.Newtype (unwrap)
-import Data.String (Pattern(..))
+import Data.String (Pattern(..), joinWith)
 import Data.String as String
 import Data.String.Regex (Regex)
 import Data.String.Regex as Regex
@@ -112,10 +113,20 @@ makeLoader rootPath = Loader (go Object.empty <<< parseDeps "<file>")
                   deps = { name: _, path: Nothing } <$> shim.deps
                 pure { name, path, deps, src }
               Nothing ->
-                pure { name, path, deps: [], src: ffiDep name }
+                throwError (missingFFIDep name)
         liftEffect $ putModule name mod
         pure mod
 
+  missingFFIDep :: String -> String
+  missingFFIDep name =
+    joinWith "\n" $
+      [ "Compilation succeeded, but the following FFI dependency is missing:"
+      , " - " <> name
+      , ""
+      , "We don't provide FFI shims for all libraries; for example, Node libraries are not supported on Try PureScript."
+      , "If you would like to suggest a new FFI shim be supported, please open an issue."
+      ]
+
   go :: Object JS -> Array Dependency -> ExceptT String Aff (Object JS)
   go ms []   = pure ms
   go ms deps = do
@@ -130,6 +141,3 @@ makeLoader rootPath = Loader (go Object.empty <<< parseDeps "<file>")
       # bindFlipped _.deps
       # Array.nubBy (comparing _.name)
       # go ms'
-
-ffiDep :: String -> JS
-ffiDep name = JS $ "throw new Error('FFI dependency not provided: " <> name <> "');"