lib: include source info in txn balance errors

Partially address simonmichael/hledger#904

hledger-lib/Hledger/Data/Transaction.hs

@@ -335,13 +335,13 @@ balanceTransactionUpdate :: MonadError String m
   -> Maybe (Map.Map CommoditySymbol AmountStyle)
   -> Transaction -> m Transaction
 balanceTransactionUpdate update mstyles t =
-  finalize =<< inferBalancingAmount update (fromMaybe Map.empty mstyles) t
+  (finalize =<< inferBalancingAmount update (fromMaybe Map.empty mstyles) t)
+    `catchError` (throwError . annotateErrorWithTxn t)
   where
     finalize t' = let t'' = inferBalancingPrices t'
                   in if isTransactionBalanced mstyles t''
                      then return $ txnTieKnot t''
-                     else throwError $ printerr $ nonzerobalanceerror t''
-    printerr s = intercalate "\n" [s, showTransactionUnelided t]
+                     else throwError $ nonzerobalanceerror t''
     nonzerobalanceerror :: Transaction -> String
     nonzerobalanceerror t = printf "could not balance this transaction (%s%s%s)" rmsg sep bvmsg
         where
@@ -354,6 +354,8 @@ balanceTransactionUpdate update mstyles t =
                   ++ showMixedAmount (costOfMixedAmount bvsum)
           sep = if not (null rmsg) && not (null bvmsg) then "; " else "" :: String
 
+    annotateErrorWithTxn t e = intercalate "\n" [showGenericSourcePos $ tsourcepos t, e, showTransactionUnelided t]
+
 -- | Infer up to one missing amount for this transactions's real postings, and
 -- likewise for its balanced virtual postings, if needed; or return an error
 -- message if we can't.
@@ -368,14 +370,13 @@ inferBalancingAmount :: MonadError String m =>
                      -> m Transaction
 inferBalancingAmount update styles t@Transaction{tpostings=ps}
   | length amountlessrealps > 1
-      = throwError $ printerr "could not balance this transaction - can't have more than one real posting with no amount (remember to put 2 or more spaces before amounts)"
+      = throwError "could not balance this transaction - can't have more than one real posting with no amount (remember to put 2 or more spaces before amounts)"
   | length amountlessbvps > 1
-      = throwError $ printerr "could not balance this transaction - can't have more than one balanced virtual posting with no amount (remember to put 2 or more spaces before amounts)"
+      = throwError "could not balance this transaction - can't have more than one balanced virtual posting with no amount (remember to put 2 or more spaces before amounts)"
   | otherwise
       = do postings <- mapM inferamount ps
            return t{tpostings=postings}
   where
-    printerr s = intercalate "\n" [s, showTransactionUnelided t]
     (amountfulrealps, amountlessrealps) = partition hasAmount (realPostings t)
     realsum = sumStrict $ map pamount amountfulrealps
     (amountfulbvps, amountlessbvps) = partition hasAmount (balancedVirtualPostings t)

tests/journal/parse-errors.test

@@ -34,7 +34,12 @@ $ hledger -f - print
 # 3. So in these tests we must sometimes force the desired format, like so.
 # Now we see the error from the journal reader.
 $ hledger -f journal:- print
->2 /hledger: could not balance this transaction \(real postings are off by 1\)/
+>2 /could not balance this transaction \(real postings are off by 1\)/
+>=1
+
+# 4. We expect to have reference to line number with last posting
+$ hledger -f journal:- print
+>2 /\<2\>/
 >=1
 
 # A posting without two spaces between account and amount.
@@ -42,7 +47,7 @@ $ hledger -f journal:- print
 2018/1/1
   (a) 1
 
-# 4. hledger doesn't detect this as an error directly, it parses account name "(a) 1" and
+# 5. hledger doesn't detect this as an error directly, it parses account name "(a) 1" and
 # amount 0 here.
 $ hledger -f - print -x
 2018/01/01
@@ -50,3 +55,24 @@ $ hledger -f - print -x
 
 >=
 
+# 6. Two (or more) postings with implicit amount cannot be balanced.
+<
+2018/1/1
+  a  1
+  b
+  c
+
+$ hledger -f journal:- print
+>2 /\<4\>/
+>=1
+
+# 7. Two (or more) virtual postings with implicit amount cannot be balanced.
+<
+2018/1/1
+  [a]  1
+  [b]
+  [c]
+
+$ hledger -f journal:- print
+>2 /\<4\>/
+>=1