CsvReader: simplify '-' signs if there exist more than one (#548)

It prevents hledger to crash later, as it fails to read
amount strings containing more than one '-'

Fix #524

hledger-lib/Hledger/Read/CsvReader.hs

@@ -35,6 +35,7 @@ import Control.Monad.Except
 import Control.Monad.State.Strict (StateT, get, modify', evalStateT)
 -- import Test.HUnit
 import Data.Char (toLower, isDigit, isSpace)
+import Data.List (findIndices)
 import Data.List.Compat
 import Data.Maybe
 import Data.Ord
@@ -641,7 +642,7 @@ transactionFromCsvRecord sourcepos rules record = t
     comment     = maybe "" render $ mfieldtemplate "comment"
     precomment  = maybe "" render $ mfieldtemplate "precomment"
     currency    = maybe (fromMaybe "" mdefaultcurrency) render $ mfieldtemplate "currency"
-    amountstr   = (currency++) $ negateIfParenthesised $ getAmountStr rules record
+    amountstr   = (currency++) $ simplifySign $ negateIfParenthesised $ getAmountStr rules record
     amount      = either amounterror (Mixed . (:[])) $ runParser (evalStateT (amountp <* eof) mempty) "" $ T.pack amountstr
     amounterror err = error' $ unlines
       ["error: could not parse \""++amountstr++"\" as an amount"
@@ -711,6 +712,18 @@ getAmountStr rules record =
     (Nothing, Just _,  Just _)  -> error' $ "both amount-in and amount-out have a value\n"++showRecord record
     _                           -> error' $ "found values for amount and for amount-in/amount-out - please use either amount or amount-in/amount-out\n"++showRecord record
 
+-- From a String representing an Amount, simplify the sign by
+-- removing '-' by pair from the left. It happens that some amount
+-- strings contain 2 '-' because of CSV reading rules
+simplifySign :: String -> String
+simplifySign amount
+  | length indices < 2 = amount
+  | otherwise = simplifySign $ simplify2 amount
+  where
+    indices = findIndices (== '-') amount
+    simplify = delete '-'
+    simplify2 = simplify . simplify
+
 negateIfParenthesised :: String -> String
 negateIfParenthesised ('(':s) | lastMay s == Just ')' = negateStr $ init s
 negateIfParenthesised s                               = s

tests/csv/read.test

@@ -93,3 +93,16 @@
 
 >>>2 /using conversion rules file.*t.rules/
 >>>=0
+# 9. read CSV with rule double-negating column
+ rm -rf t.rules$$; printf 'skip 1\n\ncurrency $\n\nfields date, payee, payment\n\namount -%%payment\naccount1 liabilities:bank\naccount2 expense:other' >t.rules$$; echo 'date,payee,amount\n2009/10/9,Flubber Co,50\n2009/11/09,Merchant Credit,-60' | hledger -f- print --rules-file t.rules$$; rm -rf t.rules$$
+>>>
+2009/10/09
+    expense:other              $50
+    liabilities:bank          $-50
+
+2009/11/09
+    expense:other             $-60
+    liabilities:bank           $60
+
+>>>2 /using conversion rules file.*t.rules/
+>>>=0