Make Stack.IDE exceptions prettier

Author: mpilgrem

doc/maintainers/stack_errors.md

@@ -156,6 +156,12 @@ to take stock of the errors that Stack itself can raise, by reference to the
         [S-3025] | HoogleDatabaseNotFound
         ~~~
 
+    -   `Stack.IDE.IdePrettyException`
+
+        ~~~haskell
+        [S-9208] = FileTargetIsInvalidAbsFile
+        ~~~
+
     -   `Stack.Init.InitException`
 
         ~~~haskell

src/Stack/IDE.hs

@@ -58,16 +58,22 @@ import           Stack.Types.SourceMap
                    ( ProjectPackage (..), SMWanted (..), ppComponentsMaybe )
 import           System.IO ( putStrLn )
 
--- | Type representing exceptions thrown by functions exported by the
+-- | Type representing \'pretty\' exceptions thrown by functions exported by the
 -- "Stack.IDE" module.
-newtype IdeException
-  = MissingFileTarget String
+newtype IdePrettyException
+  = FileTargetIsInvalidAbsFile String
   deriving (Show, Typeable)
 
-instance Exception IdeException where
-  displayException (MissingFileTarget name) =
-    "Error: [S-9208]\n"
-    ++ "Cannot find file target " ++ name ++ "."
+instance Pretty IdePrettyException where
+  pretty (FileTargetIsInvalidAbsFile name) =
+       "[S-9208]"
+    <> line
+    <> fillSep
+         [ flow "Cannot work out a valid path for file target"
+         , style File (fromString name) <> "."
+         ]
+
+instance Exception IdePrettyException
 
 -- | Function underlying the @stack ide packages@ command. List packages in the
 -- project.
@@ -196,7 +202,7 @@ preprocessTarget rawTarget =
         let fp = T.unpack rawTarget
         mpath <- forgivingResolveFile' fp
         case mpath of
-          Nothing -> throwM (MissingFileTarget fp)
+          Nothing -> prettyThrowM (FileTargetIsInvalidAbsFile fp)
           Just path -> pure path
       pure (Just fileTarget)
     else pure Nothing