Merge #958: Clarify string coercion errors

Author: Anton-Latukha

src/Nix/Convert.hs

@@ -204,7 +204,7 @@ instance ( Convertible e t f m
           (M.lookup "outPath" s)
       _ -> stub
 
-  fromValue = fromMayToValue $ TString mempty
+  fromValue = fromMayToValue $ TString HasContext
 
 instance Convertible e t f m
   => FromValue ByteString m (NValue' t f m (NValue t f m)) where

src/Nix/Eval.hs

@@ -467,14 +467,9 @@ assembleString
    . (MonadEval v m, FromValue NixString m v)
   => NString (m v)
   -> m (Maybe NixString)
-assembleString =
-  fromParts .
-    \case
-      Indented   _ parts -> parts
-      DoubleQuoted parts -> parts
+assembleString = fromParts . stringParts
  where
   fromParts xs = (mconcat <$>) . sequence <$> traverse go xs
-
   go =
     runAntiquoted
       "\n"

src/Nix/Expr/Types.hs

@@ -654,6 +654,10 @@ paramName :: Params r -> Maybe VarName
 paramName (Param n       ) = pure n
 paramName (ParamSet _ _ n) = n
 
+stringParts :: NString r -> [Antiquoted Text r]
+stringParts (DoubleQuoted parts) = parts
+stringParts (Indented _   parts) = parts
+
 stripPositionInfo :: NExpr -> NExpr
 stripPositionInfo = transport phi
  where

src/Nix/Value.hs

@@ -753,8 +753,8 @@ describeValue =
     TFloat             -> "a float"
     TBool              -> "a boolean"
     TNull              -> "a null"
-    TString NoContext  -> "a string"
-    TString HasContext -> "a string with context"
+    TString NoContext  -> "a string with no context"
+    TString HasContext -> "a string"
     TList              -> "a list"
     TSet               -> "an attr set"
     TClosure           -> "a function"