Better aeson error messages. addresses #269

This overrides the aeson combinators to have better error messages
Just import Data.Aeson.Extended instead of Data.Aeson

src/Data/Aeson/Extended.hs

@@ -0,0 +1,23 @@
+-- | The purpose of this module is to provide better failure messages
+-- When parsing a key of an object, this makes sure the key itself will show up
+module Data.Aeson.Extended (
+    module Export
+  , (.:)
+  , (.:?)
+  ) where
+
+import Data.Aeson as Export hiding ((.:), (.:?))
+import qualified Data.Aeson as A
+
+import Data.Aeson.Types hiding ((.:), (.:?))
+
+import Data.Text (unpack, Text)
+import Data.Monoid ((<>))
+
+(.:) :: FromJSON a => Object -> Text -> Parser a
+(.:) o p = modifyFailure (("failed to parse field " <> unpack p <> ": ") <>) (o A..: p)
+{-# INLINE (.:) #-}
+
+(.:?) :: FromJSON a => Object -> Text -> Parser (Maybe a)
+(.:?) o p = modifyFailure (("failed to parse field " <> unpack p <> ": ") <>) (o A..:? p)
+{-# INLINE (.:?) #-}

src/Network/HTTP/Download.hs

@@ -26,7 +26,7 @@ import           Control.Monad.Catch         (MonadThrow, throwM)
 import           Control.Monad.IO.Class      (MonadIO, liftIO)
 import           Control.Monad.Reader        (MonadReader, ReaderT, ask,
                                               runReaderT)
-import           Data.Aeson                  (FromJSON, parseJSON)
+import           Data.Aeson.Extended         (FromJSON, parseJSON)
 import           Data.Aeson.Parser           (json')
 import           Data.Aeson.Types            (parseEither)
 import qualified Data.ByteString             as S

src/Stack/Build/Types.hs

@@ -13,7 +13,7 @@ module Stack.Build.Types where
 
 import Control.DeepSeq
 import Control.Exception
-import Data.Aeson
+import Data.Aeson.Extended
 import Data.Binary (Binary(..))
 import qualified Data.ByteString as S
 import Data.Char (isSpace)

src/Stack/BuildPlan.hs

@@ -36,8 +36,7 @@ import           Control.Monad.Reader (asks)
 import           Control.Monad.State.Strict      (State, execState, get, modify,
                                                   put)
 import           Control.Monad.Trans.Control (MonadBaseControl)
-import           Data.Aeson (FromJSON (..))
-import           Data.Aeson (withObject, withText, (.:))
+import           Data.Aeson.Extended (FromJSON (..), withObject, withText, (.:))
 import           Data.Binary.VersionTagged (taggedDecodeOrLoad)
 import           Data.ByteString (ByteString)
 import qualified Data.ByteString.Char8 as S8

src/Stack/Config.hs

@@ -36,7 +36,7 @@ import           Control.Monad.Logger hiding (Loc)
 import           Control.Monad.Reader (MonadReader, ask, runReaderT)
 import           Control.Monad.Trans.Control (MonadBaseControl)
 import qualified Crypto.Hash.SHA256 as SHA256
-import           Data.Aeson
+import           Data.Aeson.Extended
 import qualified Data.ByteString.Base16 as B16
 import qualified Data.ByteString.Lazy as L
 import           Data.Either (partitionEithers)

src/Stack/Docker.hs

@@ -26,7 +26,7 @@ import           Control.Monad.Catch (MonadThrow, throwM)
 import           Control.Monad.IO.Class (MonadIO,liftIO)
 import           Control.Monad.Logger (MonadLogger,logError,logInfo,logWarn)
 import           Control.Monad.Writer (execWriter,runWriter,tell)
-import           Data.Aeson (FromJSON(..),(.:),(.:?),(.!=),eitherDecode)
+import           Data.Aeson.Extended (FromJSON(..),(.:),(.:?),(.!=),eitherDecode)
 import           Data.ByteString.Builder (stringUtf8,charUtf8,toLazyByteString)
 import qualified Data.ByteString.Char8 as BS
 import qualified Data.ByteString.Lazy.Char8 as LBS

src/Stack/PackageIndex.hs

@@ -33,7 +33,7 @@ import           Control.Monad.Logger                  (MonadLogger, logDebug,
                                                         logInfo, logWarn)
 import           Control.Monad.Reader (asks)
 
-import           Data.Aeson
+import           Data.Aeson.Extended
 import qualified Data.Binary as Binary
 import           Data.Binary.VersionTagged (taggedDecodeOrLoad)
 import           Data.ByteString (ByteString)

src/Stack/Setup.hs

@@ -24,7 +24,7 @@ import           Control.Monad.Reader (MonadReader, ReaderT (..), asks)
 import           Control.Monad.State (get, put, modify)
 import           Control.Monad.Trans.Control
 
-import           Data.Aeson
+import           Data.Aeson.Extended
 import qualified Data.ByteString as S
 import qualified Data.ByteString.Char8 as S8
 import           Data.Conduit (Conduit, ($$), (=$), await, yield, awaitForever)

src/Stack/Types/Config.hs

@@ -14,7 +14,7 @@ import           Control.Exception
 import           Control.Monad (liftM, mzero)
 import           Control.Monad.Catch (MonadThrow, throwM)
 import           Control.Monad.Reader (MonadReader, ask, asks, MonadIO, liftIO)
-import           Data.Aeson (ToJSON, toJSON, FromJSON, parseJSON, withText, withObject, object
+import           Data.Aeson.Extended (ToJSON, toJSON, FromJSON, parseJSON, withText, withObject, object
                             ,(.=), (.:?), (.!=), (.:), Value (String))
 import           Data.Binary (Binary)
 import           Data.ByteString (ByteString)

src/Stack/Types/Docker.hs

@@ -5,7 +5,7 @@
 module Stack.Types.Docker where
 
 import Control.Applicative
-import Data.Aeson
+import Data.Aeson.Extended
 import Data.Monoid
 import Data.Text (Text)
 import Path

src/Stack/Types/FlagName.hs

@@ -23,7 +23,7 @@ module Stack.Types.FlagName
 
 import           Control.Applicative
 import           Control.Monad.Catch
-import           Data.Aeson
+import           Data.Aeson.Extended
 import           Data.Attoparsec.ByteString.Char8
 import           Data.Attoparsec.Combinators
 import           Data.Binary (Binary)

src/Stack/Types/GhcPkgId.hs

@@ -14,7 +14,7 @@ module Stack.Types.GhcPkgId
 
 import           Control.Applicative
 import           Control.Monad.Catch
-import           Data.Aeson
+import           Data.Aeson.Extended
 import           Data.Attoparsec.ByteString.Char8
 import           Data.Binary (Binary)
 import           Data.ByteString.Char8 (ByteString)

src/Stack/Types/PackageIdentifier.hs

@@ -23,7 +23,7 @@ import           Control.Applicative
 import           Control.DeepSeq
 import           Control.Exception (Exception)
 import           Control.Monad.Catch (MonadThrow, throwM)
-import           Data.Aeson
+import           Data.Aeson.Extended
 import           Data.Attoparsec.ByteString.Char8
 import           Data.Binary (Binary)
 import           Data.ByteString (ByteString)

src/Stack/Types/PackageName.hs

@@ -27,7 +27,7 @@ import           Control.Applicative
 import           Control.DeepSeq
 import           Control.Monad
 import           Control.Monad.Catch
-import           Data.Aeson
+import           Data.Aeson.Extended
 import           Data.Attoparsec.ByteString.Char8
 import           Data.Attoparsec.Combinators
 import           Data.Binary (Binary)

src/Stack/Types/Version.hs

@@ -30,7 +30,7 @@ module Stack.Types.Version
 import           Control.Applicative
 import           Control.DeepSeq
 import           Control.Monad.Catch
-import           Data.Aeson
+import           Data.Aeson.Extended
 import           Data.Attoparsec.ByteString.Char8
 import           Data.Binary (Binary)
 import           Data.ByteString (ByteString)

stack.cabal

@@ -65,6 +65,7 @@ library
                      Path.IO
                      System.Process.PagerEditor
                      Paths_stack
+                     Data.Aeson.Extended
                      Data.Attoparsec.Combinators
                      Data.Binary.VersionTagged
                      Data.Set.Monad