Add error position

library/Hasql/Private/Decoders/Result.hs

@@ -80,7 +80,16 @@ serverError =
         LibPQ.resultErrorField result LibPQ.DiagMessageDetail
       hint <-
         LibPQ.resultErrorField result LibPQ.DiagMessageHint
-      pure $ Left $ ServerError code message detail hint
+      position <-
+        parsePosition <$> LibPQ.resultErrorField result LibPQ.DiagStatementPosition
+      pure $ Left $ ServerError code message detail hint position
+  where
+    parsePosition = \case
+      Nothing -> Nothing
+      Just pos ->
+        case Attoparsec.parseOnly (Attoparsec.decimal <* Attoparsec.endOfInput) pos of
+          Right pos -> Just pos
+          _ -> Nothing
 
 {-# INLINE maybe #-}
 maybe :: Row.Row a -> Result (Maybe a)

library/Hasql/Private/Errors.hs

@@ -54,6 +54,9 @@ data ResultError
       -- This is intended to differ from detail in that it offers advice
       -- (potentially inappropriate) rather than hard facts. Might run to
       -- multiple lines.
+      (Maybe Int)
+      -- ^ __Position__. Error cursor position as an index into the original
+      -- statement string. Positions are measured in characters not bytes.
   | -- |
     -- The database returned an unexpected result.
     -- Indicates an improper statement or a schema mismatch.

tasty/Main.hs

@@ -153,7 +153,7 @@ tree =
                 where
                   resultTest =
                     \case
-                      Right (Left (Session.QueryError _ _ (Session.ResultError (Session.ServerError "26000" _ _ _)))) -> False
+                      Right (Left (Session.QueryError _ _ (Session.ResultError (Session.ServerError "26000" _ _ _ _)))) -> False
                       _ -> True
                   session =
                     catchError session (const (pure ())) *> session