From 11684843a09893f09bf80be84086d7040b8e79ad Mon Sep 17 00:00:00 2001
From: Sam Jeeves <sam.jeeves@live.com>
Date: Sat, 14 Oct 2017 22:10:57 +0200
Subject: [PATCH] Balance assertion errors now show line of failed assertion
 posting. Fixes #481.

---
 hledger-lib/Hledger/Data/Journal.hs     | 4 +++-
 hledger-lib/Hledger/Data/Transaction.hs | 5 +++++
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/hledger-lib/Hledger/Data/Journal.hs b/hledger-lib/Hledger/Data/Journal.hs
index dcd7bbb34..6a115c9ef 100644
--- a/hledger-lib/Hledger/Data/Journal.hs
+++ b/hledger-lib/Hledger/Data/Journal.hs
@@ -535,7 +535,9 @@ checkBalanceAssertion p@Posting{ pbalanceassertion = Just ass} amt
             (case ptransaction p of
                Nothing -> ":" -- shouldn't happen
                Just t ->  printf " in %s:\nin transaction:\n%s"
-                          (showGenericSourcePos $ tsourcepos t) (chomp $ show t) :: String)
+                          (showGenericSourcePos postingPos) (chomp $ show t) :: String
+                            where postingLine = fromJust $ elemIndex p $ tpostings t -- assume postings are in order
+                                  postingPos = increaseSourceLine (1+postingLine) (tsourcepos t))
             (showPostingLine p)
             (showDate $ postingDate p)
             (T.unpack $ paccount p) -- XXX pack
diff --git a/hledger-lib/Hledger/Data/Transaction.hs b/hledger-lib/Hledger/Data/Transaction.hs
index 7c75a1dac..acd6454dd 100644
--- a/hledger-lib/Hledger/Data/Transaction.hs
+++ b/hledger-lib/Hledger/Data/Transaction.hs
@@ -42,6 +42,7 @@ module Hledger.Data.Transaction (
   sourceFilePath,
   sourceFirstLine,
   showGenericSourcePos,
+  increaseSourceLine,
   -- * misc.
   tests_Hledger_Data_Transaction
 )
@@ -81,6 +82,10 @@ sourceFirstLine = \case
     GenericSourcePos _ line _ -> line
     JournalSourcePos _ (line, _) -> line
 
+increaseSourceLine :: Int -> GenericSourcePos -> GenericSourcePos
+increaseSourceLine val (GenericSourcePos fp line col) = GenericSourcePos fp (line+val) col
+increaseSourceLine val (JournalSourcePos fp (first, _)) = GenericSourcePos fp (first+val) 0
+
 showGenericSourcePos :: GenericSourcePos -> String
 showGenericSourcePos = \case
     GenericSourcePos fp line column -> show fp ++ " (line " ++ show line ++ ", column " ++ show column ++ ")"